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GEOTECHNICAL POLICIES AND PROCEDURES MANUAL 2005

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NDOT Geotechnical Policies and Procedures Manual

NEVADA DEPARTMENT OF TRANSPORTATION GEOTECHNICAL POLICIES AND PROCEDURES MANUAL

Geotechnical Policies and Procedures Manual Published by: Nevada Department of Transportation Materials Division Geotechnical Section 1263 South Stewart Street Carson City, Nevada 89712 (775) 888-7520 phone (775) 888-7501 fax Contributors: NDOT: Parviz Noori P.E., Assistant Chief Materials Engineer Jeffrey A. Palmer, Ph.D., P.E., Principal Geotechnical Engineer Dana A. Boomhower, P.E., Senior Geotechnical Engineer Consultants: Donald L. Woods, J.D., C.P.M., Project Manager Earl Hawkes, Jr., Senior Consultant International Consulting & Contracting 1501 Frandosa Lane Las Vegas, Nevada 89117-1191 (702) 254-6606 phone (702) 254-7067 fax [email protected] email [email protected] email [Chapters 1-4] and Lawrence A. Pierson, C.E.G., Senior Associate George Machan, P.E., Senior Associate Landslide Technology 10250 S.W. Greenburg Road, Suite 111 Portland, Oregon 97223 (503) 452-1200 phone (503) 452-1528 fax [email protected] email [email protected] email [Chapters 5-14] 02/14/2005


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FOREWORD This Geotechnical Section Manual is primarily designed to provide appropriate policies, procedures and practices to be used by Geotechnical Engineering staff in the successful accomplishment of their duties. Also, an important function of this Manual is to provide Consultants with valuable information about working with the Nevada Department of Transportation Geotechnical Section. Materials contained in the Manual are meant to be useful for both the training of new employees and as a reference to be utilized as needed throughout the course of work. This is a resource document. It is not intended to override or replace the necessary use of good judgment, common sense and research of current best practices. This Manual is organized by chapters and general subjects. Pages and attachments are numbered according to chapter location. Page numbers are located in the upper righthand corner of the page and the date of issue is located in the lower left-hand corner. The preparation of the Manual was accomplished under the direction of Parviz Noori, P.E., Assistant Chief Materials Engineer, Geotechnical Section. Mr. Noori generously gave his time, knowledge and suggestions to successfully complete this Manual . Mr .Noor i ’ s st af fwas al so r esponsi bl ef orpr ov i di ng needed mat er i al s and information. Recognition is given to Jeffrey A. Palmer, Ph.D., P.E., Principal Geotechnical Engineer, and Dana A. Boomhower, P.E., Senior Geotechnical Engineer, for their contributions. The consulting firm of International Consulting & Contracting, Donald L. Woods, J.D., C.P.M., Project Manager, and their subcontractors, Landslide Technology, and Earl Hawkes, Jr., Senior Consultant, developed this Manual.

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MASTER TABLE OF CONTENTS CREDITS...........................................................................................................................................i FORWARD ....................................................................................................................................... ii TABLE OF CONTENTS................................................................................................................... iii INTRODUCTION ............................................................................................................CHAPTER 1 ORIENTATION ...............................................................................................................CHAPTER 2 ROLES AND RESPONSIBILITIES..................................................................................CHAPTER 3 WORK BY CONSULTANTS AND LOCAL GOVERNMENTS..........................................CHAPTER 4 GEOTECHNICAL INVESTIGATION PLANNING GUIDELINES......................................CHAPTER 5 GEOTECHNICAL INVESTIGATION PROCEDURES .....................................................CHAPTER 6 IN SITU TESTING ..........................................................................................................CHAPTER 7 LABORATORY TESTS...................................................................................................CHAPTER 8 MATERIALS DESCRIPTION ..........................................................................................CHAPTER 9 FIELD INSTRUMENTATION ........................................................................................CHAPTER 10 ANALYSIS AND DESIGN .............................................................................................CHAPTER 11 PRESENTATION OF GEOTECHNICAL INFORMATION .............................................CHAPTER 12 CONSTRUCTION PHASE ............................................................................................CHAPTER 13 MAINTENANCE PHASE...............................................................................................CHAPTER 14 DEFINITIONS................................................................................................................. GLOSSARY

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GEOTECHNICAL POLICIES AND PROCEDURES MANUAL

CHAPTER 1 INTRODUCTION

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INTRODUCTION

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TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. 8. 9.

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PURPOSE............................................................................................................ 1 INTRODUCTION.................................................................................................. 1 HISTORY ............................................................................................................. 2 PHILOSOPHY, MISSIONS AND GOALS ............................................................ 2 OVERVIEW.......................................................................................................... 2 EXCEPTIONS AND INTERPRETATIONS........................................................... 3 MANUAL UPDATES ............................................................................................ 3 RESPONSIBILITY OF GEOTECHNICAL ENGINEERS ...................................... 3 TERMS, DEFINITIONS AND ABBREVIATIONS ................................................. 3


INTRODUCTION

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PURPOSE

This Manual provides direction for the accomplishment of work in the Geotechnical Section of the Nevada Department of Transportation (NDOT). Specific tasks are described which relate to the geotechnical aspects of investigation, design and construction of roadways and roadway structures. General direction and policies are also included in this Manual. It is intended that areas covered herein will offer the new employee, particularly Geotechnical Engineers in the Geotechnical Section, a basic understanding of the Department, Division and Section, and most importantly, the general requirements to accomplish the assigned tasks. This Manual can be useful for parties external to the Geotechnical Section. These parties may include other Divisions, other State employees, Consultants, contractors, and the public. General requirements and directions are given to provide a framework of minimum expectations of Engineers in the Geotechnical Section. No attempt is made to provide comprehensive procedures and practices, a design handbook, or the scope of services for individual projects. This Manual is not intended in any way to limit the individual employee from exercising their valuable professional judgment and common sense, and should not be considered a standard to be met regardless of impacts. This Manual was developed to help serve the very necessary function of facilitating accurate, timely and appropriate communication. This is important when considering the complexities of the many tasks in the Geotechnical Section. This Manual should be utilized to improve communication by providing an understanding of basic task components, functional relationships and Division requirements. Thet i t l e“ Geot echni cal Engi neer s”i susedt hr oughoutt hi sManual .Fort hepur poseof clarification, Geotechnical Engineers refers to Staff III Registered Professional Engineers, and anyposi t i onunderf i l l i ngSt af fI I I ’ si nt heGeot echnical Section. Other titles commonly used in this Manual are Principal Geotechnical Engineer that refers to the Manager I, and Assistant Materials Engineer that refers to the Administrator I, both of the Geotechnical Section. Any questions about the content of this Manual are to be referred to the Principal Geotechnical Engineer. 2.

INTRODUCTION

This Manual is organized into chapters, which discuss various subjects of importance in the accomplishment of work for the Geotechnical Section. A Table of Contents, Appendices, and various Figures, are found in the chapters. Each chapter also includes descriptions of the sections of the chapter. Each page contains the issue date in the lower left-hand corner and a page number in the upper right hand corner. Pages, figures and tables are numbered according to the chapter sections in the Manual. 02/14/2005


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Various materials and publications are noted as references, and often included as figures in the individual chapters. When publication dates are given, they are for reference purposes only, as revisions may have been made at a later date. The reader is responsible to verify the most recent material or publication is used. 3.

HISTORY

The Department was created as the Nevada Department of Highways in 1917. Prior to this time, the State did not have a role in road improvements. However, in 1917 the Legislature mandated that the State Engineer would have general supervision of roadwork. This work was performed by convict labor when funds were made available. Currently, the Department is a large department of the State government, having l egi sl at i v eaut hor i t yandf undi ngt omai nt ai nandi mpr ov eNev ada’ sHi ghway s.I nf or mat i on about the Department may be found on the Department website at http://www.nevadadot.com. 4.

PHILOSOPHY, MISSIONS AND GOALS

The Department and Divisions have philosophies, missions, and goals; new hires and Consultants should contact the Administrative Assistant of the Materials Division to obtain the most current verbiage. 5.

OVERVIEW

The Department has the responsibility for construction, operation and maintenance of the highways and bridges, which are part of the State highway system. The Department also oversees various allied projects. Included are projects ranging from the Adopt-A-Highway program to the maintenance of State Historical Markers. TheDepar t ment ’ sheadquar t er s,i ncl udi ngmostdesi gndi v i si ons,i sl ocat edi nCar s onCi t y . The Department is organized into three districts for administrative purposes, as follows: 

District 1 covers southern Nevada, with main offices in Las Vegas.

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District 2 covers northwest Nevada, with main offices in Reno.

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District 3 covers northeast Nevada, with main offices in Elko.

These districts supervise all State transportation activities within their local areas. Major maintenance stations are located in Ely, Tonopah and Winnemucca. The Materials Division is a major organizational unit of the Department. Headquarters for the Materials Division is located at the Carson City Laboratory Facility. The Division also operates an auxiliary testing facility in Las Vegas. The Geotechnical Section is located within the Materials Division, Carson City.

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INTRODUCTION 6.

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EXCEPTIONS AND INTERPRETATIONS

This Manual is written to offer clear direction to the reader. However, it is recognized that policies and procedures may be subject to differing interpretations and that the Manual would be too lengthy for practical use if all areas were covered definitively. It is also understood that occasions will arise, which may warrant the consideration of exceptions to items described in this Manual. Any properly authorized exceptions to this Manual are to be consi der edas“ onet i meonl y ”changes,unl essot her wi sedi r ect ed. 7.

MANUAL UPDATES

Policies, procedures and practices will change from time to time. This Manual is updated as necessary and all users should assure themselves that they are using the latest version. 8.

RESPONSIBILITY OF GEOTECHNICAL ENGINEERS

It is the responsibility of all Geotechnical Engineers to become familiar with the materials presented in this Manual and apply them appropriately while performing work for the Geotechnical Section. 9.

TERMS, DEFINITIONS AND ABBREVIATIONS Commonly used terms, definitions and abbreviations may be found in the Glossary.

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CHAPTER 2 ORIENTATION

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ORIENTATION

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TABLE OF CONTENTS 1. 2. 3. 3.1 3.2 3.3 3.4 3.5 3.6 4. 5. 5.1 5.2 5.3 5.4 6. 7. 8. 8.1 8.2 8.3 9.

10.

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PURPOSE ............................................................................................................ 1 ORGANIZATIONAL RELATIONSHIPS ................................................................ 1 MATERIALS DIVISION ........................................................................................ 1 Administration Section.......................................................................................... 1 Las Vegas Facility ................................................................................................ 1 Structural And Chemical Section .......................................................................... 2 Roadbed And Pavement Design Section ............................................................. 2 Bituminous Section............................................................................................... 2 Geotechnical Section............................................................................................ 2 WORK REQUIREMENTS OF GEOTECHNICAL ENGINEERS ........................... 2 WORK BY GEOTECHNICAL ENGINEERS ......................................................... 2 Geotechnical Reports ........................................................................................... 3 Geotechnical Project Files .................................................................................... 3 TEMPORARY STAFF ASSIGNMENTS ............................................................... 4 Other Tasks.......................................................................................................... 4 PROJECT DEVELOPMENT PROCESS .............................................................. 5 OUTSIDE SERVICES .......................................................................................... 5 NEW HIRE PROCESSING................................................................................... 6 Safety in the Workplace........................................................................................ 6 Hazardous Materials............................................................................................. 6 Emergency Procedures ........................................................................................ 6 FIGURES ............................................................................................................. 7 2-1: Organizational Chart - NDOT ........................................................................ 7 2-2: Organizational Chart –Materials Division ..................................................... 8 2-3: Entry Permit................................................................................................... 9 2-4: New Hire Processing Documents Checklist ................................................ 10 REFERENCES ................................................................................................... 11


ORIENTATION 1.

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PURPOSE

This Chapter summarizes the organization of the Department and function of the Geotechnical Section. It also discusses responsibilities and processing of newly hired employees and includes information regarding policies and documents that new employees should be aware of and could use to understand and verify that all in-processing procedures have been followed. Information in this Chapter is helpful as a reference to all Geotechnical Section employees and outside parties seeking knowledge of current responsibilities and organizational relationship of the Geotechnical Section. 2.

ORGANIZATIONAL RELATIONSHIPS

The Department is divided into divisions which are further divided into sections. The chief executive of the Department is the Director. The major organizational areas of the Department include the Divisions of Administration, Operations, Planning and Program Development, and Engineering. Support offices include Human Resources and Equal Employment Opportunity (EEO), Internal Audit, Programs and Budget, Legal Services, and Special Assistant to the Director. District offices are located in Las Vegas, Reno and Elko, Nevada. The Director of the Department reports to the Transportation Board. The Transportation Board is composed of the Governor (Chair), Lt. Governor (Vice Chair), Comptroller, Attorney General, and three individuals appointed by the Governor. The functions of the Transportation Board include such items as approval of right of way actions, condemnations and selling of properties, budget review, and the naming of highways. A typical organization chart of the Department is included as Figure 2-1. For a current chart, see the Administrative Assistant of the Materials Division. 3.

MATERIALS DIVISION

The Materials Division reports to the Assistant Director, Operations, of the Department. This Division is composed of six sections, consisting of Administration, Las Vegas Facility, Structural and Chemical, Roadbed and Pavement Design, Bituminous, and Geotechnical. A typical organization chart of the Materials Division is included as Figure 22. For a current chart, see the Administrative Assistant of the Materials Division. 3.1

Administration Section

This Section is responsible for the administrative matters of the Division, such as payroll, new employee processing, records management, etc. 3.2

Las Vegas Facility

The Las Vegas Facility is organized into three labs. These labs consist of Concrete and Steel, Asphalt, and Bituminous.

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ORIENTATION 3.3

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Structural And Chemical Section

The offices of this Section consist of the Concrete and Steel Lab, Concrete Specialist, and Chemical. 3.4

Roadbed And Pavement Design Section

This Section is organized into the two offices of Pavement Analysis and Roadbed Design. 3.5

Bituminous Section

Offices of this Section are organized into Bituminous Operations, Roadbed Aggregates, Asphalt Lab, and Bituminous Lab. 3.6

Geotechnical Section

This Section is organized into the offices of Field Exploration and Geotechnical Engineering (which includes the Geotechnical Lab). 4.

WORK REQUIREMENTS OF GEOTECHNICAL ENGINEERS

The job performed by Geotechnical Engineers requires a high level of skill, knowledge, competency, and judgment. Geotechnical Engineers are expected to successfully interpret and apply Federal and State regulations, as well as existing policies and procedures. They are also required to apply their skills to solve difficult problems, involving the analysis of complex data. Geotechnical Engineers conduct investigations and collect soil samples for submission to the laboratory for testing. They review plans and specifications, and work with individuals at all levels, both within and outside of State government. Typical duties of Geotechnical Engineers include exploring, sampling and testing soils underlying new and existing roadbeds and structures, special studies, geotechnical analyses and design, reviewing and writing documents, composing reports, and attending meetings. The official job requirements for Geotechnical Engineers may be found in the State of Nevada, Department of Personnel Class Specifications. The Administrative Assistant of the Materials Division has a copy of the appropriate job requirements. The job requirements included in this document are meant to provide a general framework. Specific details of all duties required of the position are not included. 5.

WORK BY GEOTECHNICAL ENGINEERS

Following is a discussion of typical work produced by Geotechnical Engineers. It is noted that the items described do not represent an all-inclusive list. This discussion is not intended to provide comprehensive detail, but rather to offer a general discussion, which provides an orientation.

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ORIENTATION 5.1

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Geotechnical Reports

Geotechnical Reports are probably the most important and significant work produced by Geotechnical Engineers. This is especially true considering the potential for construction disputes, claims and litigation over varying site condition issues. Disputes, claims and litigation occur commonly in spite of contract language, which attempts to assign responsibility to the contractor for site condition verification. The information contained in Geotechnical Reports is typically utilized during project design, construction, and in the resolution of claims and litigation. Careful and comprehensive documentation of the site investigation findings of the Geotechnical Engineer is essential for projects that involve complex geotechnical issues. Geot echni calEngi neer sshoul d not et hataccor di ng t ot heFHWA,“ Chec kl i stand Guidelines for Review of Geotechnical Reports and Preliminary Plans and Specifications,” FHWA-PD-97-002, 1985, all Geotechnical Reports should contain at least the following information: 

Summary of all subsurface exploration data, including subsurface soil profile, exploration logs, laboratory and/or in situ test results and ground water information

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Interpretation and analysis of the subsurface data

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Specific engineering recommendations for design

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Discussion of conditions which may be encountered during construction, including recommendations for solution of anticipated problems

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Recommended geotechnical special provisions

The recommendations for solution of anticipated construction problems are an area which needs to be treated with caution due to the potential of claims and litigation, which can result from such recommendations. Geotechnical Engineers should discuss recommendations with the Principal Geotechnical Engineer prior to including them in the Geotechnical Report. 5.2

Geotechnical Project Files

Geotechnical Engineers are required to maintain Geotechnical Section project files. These files may contain such items as calculations, laboratory results, fieldwork notes, site investigation results, correspondence, minutes of meetings. It is necessary that the project files be complete and well organized. Materials are organized in these files by category/subject of material, in chronological order. A project file is complete when: 

It contains documentation of all geotechnical efforts

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It is organized in a logical manner (this means other persons can easily and quickly find information they are seeking)

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The project is constructed and closed

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Geotechnical Engineers must provide pertinent information regarding completed projects to the Principal Geotechnical Engineer prior to placing the project files in the appropriate location of the Geotechnical Section file storage area. The Principal Geotechnical Engineer enters this information into a Project Files Database. 5.3

TEMPORARY STAFF ASSIGNMENTS

Geotechnical Engineers may occasionally have other individuals temporarily assigned to them for guidance and training. The most common positions assigned are: 

Rotational Engineers

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Student Interns

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Highway Construction Aides

The Geotechnical Engineer needs to maintain a positive and professional relationship with temporarily assigned individuals. Geotechnical Engineers must also provide necessary direction, encouragement and training to the temporarily assigned individuals. The Geotechnical Engineer needs to provide input to these temporary staff regarding the following items: 

Policies and regulations

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Proper conduct

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Objectives of the job

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Duties to be performed

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Accepted methods of performing duties

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Work performance standards

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How improvements can be made and capabilities are developed

The successful training and development of temporarily assigned individuals have positive, long-term impacts on the entire organization. 5.4

Other Tasks

The services provided by the Geotechnical Section vary, depending on such things as project size, complexity and environmental conditions. Following is a list of general tasks required of Geotechnical Engineers. It is noted that tasks other than those listed are also assigned. 

Attending meetings to discuss the nature and scope of the project (these meetings may include Department employees, Consultants and other outside parties such as cities staff, counties staff , State staff, elected officials, and interested citizens)

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Conducting exploration

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Conducting laboratory testing

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Performing analysis and design

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Providing notes for Special Provisions

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Providing notes and details for, and reviewing Construction Plans

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Performing calculations

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Responding to comments

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Reviewing documents pertaining to geotechnical issues

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Providing technical support to the Resident Engineer (RE) during construction

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Writing Right of Entry memorandums to obtain a right of entry permit to a property

When it is necessary to obtain a right of entry permit to a property, a memorandum to the Right of Way Division must be prepared. This memorandum must indicate the specifics of the request, including the following: 

Project Identification

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Specific property location –attach plan sheets, with boundaries and drill locations marked

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Why access is needed (example –to drill boreholes)

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When access is needed –(provide sufficient lead time)

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Method and detailed description of exploration

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Your name and phone number

An example of an Entry Permit form, developed by Right-of-Way Division, is included as Figure 2-3. 6.

PROJECT DEVELOPMENT PROCESS

Geotechnical Engineers must be familiar with the development process of projects. They are required to keep track of deadlines so that schedules are maintained. 7.

OUTSIDE SERVICES

The duties of Geotechnical Engineers, with respect to Consultants, are mainly concerned with the review of the work performed by these firms. Geotechnical Engineer duties may include tasks such as reviewing Geotechnical Reports, Construction Plans, specifications, calculations, and review comments regarding shop drawings to verify completeness and accuracy. Some reviews are comprehensive,whi l eot her sr equi r e“ spot checks”ofConsul t antwor k. When it is determined that further work is needed, or errors or omissions need to be corrected in work performed by a Consult, the Geotechnical Engineer shall not make any changes in the work product of the Consultant. Applicable comments are to be forwarded to the Consultant, and the Geotechnical Engineer is to verify that necessary actions are taken by the Consultant, and that the Consultant meets required time frames. Consultants are

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responsible for their work product, and must, therefore, perform all tasks using their own staff. 8.

NEW HIRE PROCESSING

It is incumbent upon the new hire to read and understand all of the documents provided and to insure completion of all necessary paperwork. Figure 2-4 is a checklist including some of the items that each new employee should have received. This checklist is useful as a quick reference to the various documents. All employees should review the items in this list periodically for the purpose of insuring a comprehensive understanding of policies and procedures. Employees should note that many documents described herein require a signature, indicating understanding and acceptance of the materials, and that the documents will become a permanent part of their personnel file. 8.1

Safety in the Workplace

Workplace safety is the responsibility of everyone in the workplace. It is the duty of all employees to insure their workplace is safe. This means everything from wearing approved safety equipment to reporting an unsafe work condition or practice. When a workrelated injury does occur, the employee must report it promptly to their immediate supervi sor .Thedocument ,“ Empl oy eeResponsi bi l i t i es, ”descr i best heneedt oi mmedi at el y report all accidents, where to go for medical treatment, and what procedures are in effect during the recovery and rehabilitation periods. Safe work habits and practices are required of all employees. Geotechnical Engineers must maintain safe work habits and practices at all times, especially in the potentially more hazardous areas, such as drilling sites or other field-related work. Any potential safety issues or safety training needs are to be brought to the attention of the Principal Geotechnical Engineer. 8.2

Hazardous Materials

It is common to work with and around potentially dangerous materials. Knowledge about these materials, including their proper use and characteristics, assists employees to remain unharmed. The Department has developed an extensive program to help protect empl oy ees.Thi spr ogr am i sdescr i bedi nt hemanual ,“ Haz ar dCommuni cat i onPr ogr am. ” Areas covered in this manual include the health and physical hazards of chemicals, product labeling, Material Safety Data Sheets (MSDS), and protective equipment. 8.3

Emergency Procedures

Det ai l ed emer gency pr ocedur es ar e pr ov i ded i nt he “ Emer gency Pr ocedur es ” booklet distributed to each new employee, and all employees when revised. These procedures cover situations such as fires, medical and first aid, bomb threats, earthquakes, and explosions. Evacuation maps are on the walls in each area of the Division.

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ORIENTATION 9.

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FIGURES

2-1: Organizational Chart - NDOT

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ORIENTATION

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2-2: Organizational Chart –Materials Division

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ORIENTATION

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2-3: Entry Permit Project E.A. Owner Date ENTRY PERMIT Permission is hereby granted to the STATE OF NEVADA, acting by and through its Department of Transportation, and its employees, authorized agents and contractors to enter upon OWNER'S land, described as for the purposes checked: [ ] Appraisal [ ] Soil Sampling [ ] Materials [ ] Surveying [ ] Other [ ] Environmental Survey - The property owner is advised that if hazardous wastes are found to exist on the property the Nevada Department of Transportation is required to notify the Nevada Department of Environmental Protection. This permission is granted with the understanding that travel will, when practicable, be made on existing trails or roads; upon completion of said entry, the STATE will leave this tract of land in as neat and presentable condition as existed prior to said entry; all fences, structures and other property belonging to the OWNER which the STATE may find necessary to remove or relocate in order to conduct said entry, will be replaced in as nearly their original condition and position as is reasonably possible. It is further understood that the STATE, as provided in Nevada Revised Statutes Section 408.493, will be responsible for the actual damages, if any, caused by the actions or nonactions of its officers, employees or agents in the entry of OWNERS land for the purposes set forth in this permit. This permission is effective from through . Vehicles will not enter into agricultural fields except on existing roads. Care will be exercised by employees or agents of the STATE to not disturb or damage crops, ditches, landscaping or other property of OWNER. Property Owner

Date

Property Owner

Date

Phone number and best time to call [ ] This property is not leased/rented [ ] This property is leased/rented to: Tenant's name Address

Phone

DOT 030-523 rev. 01/01

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Prepared by:


ORIENTATION

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2-4: New Hire Processing Documents Checklist DOCUMENT DESCRIPTION “ Messagef r om t heDi r ect or , ”Memor andum,NDOT “ Super v i sor ’ sRepor tonEmpl oy eeOr i ent at i on, ”NDOT( updat ed2/ 4/ 99) “ Empl oy mentEl i gi bi l i t yVer i f i cat i on, ”U. S.Depar t mentofJus t i ce,I mmi gr at i onand Naturalization Service, OMB No. 1115-0316, Form I-9 (Rev. 11/21/91) W-4 Form (2002) “ Gr oupI nsur anc eBenef i t s”Memor andum,NDOT,Account i ngDi v i si on “ Requestf orEmpl oy eeBenef i t sOr i ent at i on, ”St at eofNev ada( 7/ 02) “ Phot oI DBadge,St at ePer sonalPr oper t yandEqui pmentRequest , ”NDOT,076052 (6/02) Commercial Driver –“ Al cohol andDr ugTes t i ngPol i cy , ”TP1-6-21, NDOT (September 29, 1998) “ Empl oy eeAck nowl edgementofVal i dDr i v er ’ sLi cens eRequi r ement , ”NDOT, 0076-001 (Rev. 4/96) “ Dr i v i ngRecor dCar d, ”NDOT,078-003 (Rev. 8/99) “ Mot orVehi cl eOper at i ngPol i cy , ”Memor andum,dat edOct ober1,1996,NDOT, At t achment ,“ Empl oy eeResponsi bi l i t i esf orOper at i ngaVehi cl e, ”TP1-6-22, NDOT (Rev. 4/2/01). “ Acknowl edgement , ”f orAl cohol / Dr ugFr eeWor kpl ace,TS-58 (7/98) “ Dr ugFr eeWor k pl ace, ”Memor andum dat edMay15,1996,NDOT. “ AboutSubst anceAbuseatWor k, ”Channi ngL.Bet eCo.( 1987) “ Nev adaWor kpl ac eSaf et y , ”Di v i si onofI ndust r i alRel at i ons, Department of Business and Industry. “ Empl oy eeRes ponsi bi l i t i es, ”St at eofNev ada. “ Wor kPl aceVi ol ence, ”TP1-6-30, NDOT (August 16, 2002). “ Haz ar dCommuni cat i onPr ogr am –Empl oy ee’ sChemi cal Gui de, ”NDOT “ Comput erAccessFor m”–SeeChapt er3oft hi sManual“ Comput erSof t war e Tool s”

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ORIENTATION 10.

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REFERENCES

FHWA,“ Checkl i stand Gui del i nesf orRev i ew ofGeot ec hni calRepor t sand Pr el i mi nar y Pl ans and Speci f i cat i ons, ” Publ i cat i on No. FHWA-PD-97-002, October 1985, Reprinted 1988 NDOT,“ Br i dgeDesi gnandPr ocedur esManual , ”Publ i shedAugust1991 NDOT,“ Mat er i al sDi v i si onTest i ngManual , ”Rev i sedDecember28,2000 NDOT,“ Mat er i al sDi v i si on Pav ement ,St r uc t ur alDesi gn and Pol i cyManual , ”Publ i shed January 1996 NDOT,“ St andar dSpeci f i cat i onsf orRoadandBr i dgeConst r uct i on, ”Publ i shed2001 NDOT,“ Tr ans por t at i onPol i ci es”

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CHAPTER 3 ROLES AND RESPONSIBILITIES

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ROLES AND RESPONSIBILITES

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TABLE OF CONTENTS 1. 2. 3. 4. 4.1 4.2 5. 6. 7. 7.1 7.2 7.3 7.4 8. 9. 10. 10.1 10.2 10.3 10.4 10.5 10.6 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

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PURPOSE............................................................................................................ 1 WORK AUTHORIZATIONS ................................................................................. 1 APPROVAL PROCESSES .................................................................................. 1 PERFORMANCE EXPECTATIONS..................................................................... 2 Technical Expectations......................................................................................... 2 Nontechnical Expectations ................................................................................... 2 GENERAL RESPONSIBILITIES .......................................................................... 3 EMERGENCY WORK.......................................................................................... 3 TIME USAGE ....................................................................................................... 4 Time Sheets ......................................................................................................... 4 Breaks and Lunch Periods ................................................................................... 4 Overtime ............................................................................................................... 4 Requests for Leave .............................................................................................. 5 CLIENT SERVICE................................................................................................ 5 CARE AND INVENTORY OF EQUIPMENT......................................................... 5 WRITTEN CORRESPONDENCE ........................................................................ 6 LETTERS ............................................................................................................. 7 MEMORANDUMS ................................................................................................ 7 MEMORANDUM AND LETTER DISTRIBUTION ................................................. 7 TRANSMITTAL FORMS....................................................................................... 7 Facsimiles ............................................................................................................ 8 Email .................................................................................................................... 8 PRINTING REQUESTS ....................................................................................... 8 SUPPLIES AND EQUIPMENT REQUESTS ........................................................ 8 BUDGET REQUESTS ......................................................................................... 9 TRAVEL ............................................................................................................... 9 TRAINING .......................................................................................................... 10 EMPLOYEE APPRAISALS ................................................................................ 10 ETHICAL GUIDELINES ..................................................................................... 10 JOB SITE SAFETY ............................................................................................ 11 JOB SITE HAZARDOUS MATERIALS .............................................................. 11 JOB-RELATED INJURIES ................................................................................. 12 VEHICLE ACCIDENTS ...................................................................................... 12 LOSS REPORTING ........................................................................................... 12 COMPUTER SOFTWARE TOOLS .................................................................... 13 REFERENCE MATERIALS................................................................................ 13 GEOTECHNICAL LABORATORY ..................................................................... 13


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FIGURES ........................................................................................................... 14 3-1: Memorandum ............................................................................................. 14 3-2: Memorandum ............................................................................................. 15 3-3: Transmittal Log .......................................................................................... 16 3-4:Wr i t eI t … Don’ tSayI t ! ................................................................................ 17 3-5: Computer Software Tools........................................................................... 18



1.

3-1

PURPOSE

General job requirements and processes are provided in this Chapter. Areas discussed include such items as financial processes and approvals, general duties and expectations of Geotechnical Engineers, safety, accidents, travel, and various commonly utilized forms and procedures. This Chapter does not provide information concerning the technical requirements and processes encountered by Geotechnical Engineers, which are discussed in Chapters 5 through 14 of this Manual. 2.

WORK AUTHORIZATIONS

Work performed by NDOT is the result of a fairly lengthy and complex budget process, which involves planning for future transportation system needs. Additionally, projects in construction may be assigned a contract charge number. This process includes the prioritization of needs, cost estimates for the various projects and, finally, budgetary approvals, culminating in final legislative approval. Consequently, fiscal year monies are earmarked for specific projects. Work which is not included in the budget is not authorized and should not be performed unless a specific exception is granted by the Principal Geotechnical Engineer, or higher level within the organization. It is important for Geotechnical Engineers to always be cognizant of the need to have proper authorization prior to commencing substantial work efforts. 3.

APPROVAL PROCESSES

As a general rule, Geotechnical Engineers need to follow the normal chain of command for items requiring approval at a higher level. The chain of command for Geotechnical Engineers begins with the Principal Geotechnical Engineer, and then follows with the Assistant Chief Materials Engineer, the Chief Materials Engineer, the Assistant Director of Operations, the Deputy Director and finally, the Director. While Geotechnical Engineers must get initial approval for most matters from the Principal Geotechnical Engineer, some items require specific ultimate approval by the Chief Materials Engineer. A partial list of these items follows:  Training  Permanent specification changes  Research –must include a work plan  Policy changes  Change in duties  NDOTDi r ect or ’ sOf f i cer equest s  Nonrental equipment  Budget augmentations  Computer and software  Contract change orders

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ROLES AND RESPONSIBILITES     

3-2

Out-of-state travel Written correspondence to FHWA and front office staff Proprietary products and specifications Money handling procedures Overtime

Approval processes and proper use of the chain of command are put in place to facilitate the uniform application of policies and procedures, and to insure proper communication and appropriate responsibility and accountability. Geotechnical Engineers are advised to adhere strictly to these policies. 4.

PERFORMANCE EXPECTATIONS

Performance expectations, for Geotechnical Engineers to be successful and productive, fall into the two categories of technical and nontechnical performance. This Section provides some direction for the expectations in those areas. 4.1

Technical Expectations

Technical expectations can be described broadly as: Being responsible for providing accurate and timely geotechnical work. This includes verifying that the final contract documents are correct, that applicable Department approved materials are included, and that the job is constructible from a geotechnical point of view. Other technical expectations include plan review, on site design and support as needed and any necessary construction and postconstruction support. The majority of material in this Manual provides assistance in various technical areas typically encountered, and should be used as a resource whenever necessary. 4.2

Nontechnical Expectations

Complete success on the job cannot occur unless both the technical and nontechnical aspects of the work are performed well. Probably the most important nontechnical area is professional and effective communication. Poor communication can ruin relationships and jeopardize projects. Geotechnical Engineers must exert the efforts needed to make sure communication, verbal and written, is handled appropriately. Other important nontechnical areas, which need to be consistently demonstrated in the behavior of Geotechnical Engineers include:  Reliability  Courtesy  Honesty  Self-Motivation and Discipline  Team Building/Support  Decisiveness  Professionalism

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GENERAL RESPONSIBILITIES

Geotechnical Engineers are responsible for a number of work products, as described in other chapters of this Manual. This Section outlines some of their general responsibilities: 1.

Obtaining all background information from designers, including plan sheets showing bridge abutment and pier locations.

2.

Coordinating and performing field investigation, including: a.

Obtaining Entry Permits.

b.

Marking borehole locations in the presence of the Field Crew Supervisor. If the Field Crew Supervisor cannot be present, then he/she is to be consulted regarding the borehole location.

c.

Obtaining utility clearance.

d.

Verifying that appropriate traffic control arrangements are made.

e.

Insuring needed sampling tools and equipment are available for drilling work.

f.

Coordinating activities with Field Crew staff.

g.

Participating in drilling and/or test pit excavation activities including field testing, soil sampling, logging, and surveying. Insuring drilled holes are properly backfilled after completion.

h.

Making individual travel arrangements.

3.

Requesting tests to be conducted in the laboratory.

4.

Analyzing the data from field and laboratory tests.

5.

Preparing the Geotechnical Report.

6.

Attending meetings.

7.

Reviewing Construction Plans and Special Provisions. Making appropriate comments and recommendations by memorandum to necessary parties.

8.

Providing construction support to Resident Engineers.

9.

Assisting District Engineers in maintenance issues, such as rockfall, slope stability, and soft subgrade problems.

6.

EMERGENCY WORK

Emergencies can generally be described as those occasions which threaten the life, health, safety or welfare of the public, or State employees. The resolution of the legitimate emergency may involve the Department staff, outside contractors, or a combination thereof. From the perspective of the Geotechnical Engineer, emergency situations are extremely rare, and any expenditure of monies or significant effort in an emergency situation will require the prior approval of the Assistant Chief Materials Engineer.

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TIME USAGE

The contract between the Department and its employees for time usage can generally be described as the requirement for employees to make productive and sensible use of their time, and the Department pays the contracted amount of the monies and benefits to the employee for that time. This contract requires employees to hold all nonproductive time to a minimum. Cost tracking cannot occur unless time is accounted for correctly. Cost tracking is necessary and important to measure project performance to account for expenditure of monies. Budgeted and authorized projects are assigned an Engineering Authorization (EA) number. Geotechnical Engineers may only perform project work which has one of these numbers, or authorized overhead. It is also necessary for Geotechnical Engineers to carefully and accurately account for all project work performed by the appropriate EA number. If Geotechnical Engineers are asked to perform work on a project which does not have an approved EA number, they are to refer the matter to the Principal Geotechnical Engineer. If work comes in, the Geotechnical Engineer needs to refer it to the Manager for proper assignment. 7.1

Time Sheets

Biweekly time sheets must be completed by all Geotechnical Engineers. Timesheets, and Application and Authorization for Leav ecar dsar ecov er edi nt heEmpl oy ee’ sPay r ol l Manual. Time sheets are to be completed in a manner, as directed, which accounts for time primarily associated with EA numbers. The need for accurate accounting on projects is twofold. First, it provides the means of determining project costs. Second, it facilitates proper reimbursement to the Geotechnical Section. These are important for documentation, budget preparation, and personnel allocation decisions. NOTE: Each employee is assigned an internal identification number to be used on time sheets. 7.2

Breaks and Lunch Periods

All Geotechnical Engineers are required to take a one-half to one hour break for lunch when they are working in the field. However, when working in the office, the lunch break will be one hour. This lunch break, depending on the needs of the job is to be taken between the hours of 11:00 a.m. and 1:00 p.m. Breaks are to be taken twice during each shift, and consist of two fifteen-minute periods. 7.3

Overtime

The use of overtime is not at the discretion of the Geotechnical Engineer. Overtime must be approved prior to its use. When overtime is needed, the reason for the need, and the estimated amount of time needed, are to be submitted to the supervisor. When overtime needs are encountered in the field, approval is also to be requested of the supervisor. If the

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supervisor cannot be reached and the use of overtime is absolutely necessary, it should be held to a maximum of two hours per day, or eight hours per week. 7.4

Requests for Leave

Al l r equest sf orl eav e( annual , si ck, et c. )ar et obemadebycompl et i ngt he“ Appl i cat i on andAut hor i z at i onf orLeav e”car d,andsubmi t t i ngt hecar dt ot hePrincipal Geotechnical Engineer for approval. Leave will be granted at the convenience of the Geotechnical Section, and requests must be submitted as far in advance of the time requested as is practicable. 8.

CLIENT SERVICE

Geotechnical Engineers must always keep in mind that meeting client needs, and providing a high level of client service, are key factors in successful job performance. Satisfied clients are the main element in achieving usefulness to the organization and personal job security.              

A listing of clients with the typical requests/needs follows: Resident Engineers –During construction, assistance with construction and inspection problems Construction –Assistance with claims from contractors Bridge –Provide foundation recommendations Attorney General –Right-of-way issues, claims resolution Traffic –Provide signal, sign and light foundations recommendations Roadway –Provide cut and fill slope inclinations recommendations Hydraulics –Revetment, rip rap, and geotextile Maintenance –Recommendations for slope and rockfall, roadway/subgrade problems Right-of-Way –Permits, analysis of land use Field Crews (including contracted crews) –Drilling Laboratories –Material analysis issues Surveyor –Mapping areas, including aerial photographs and topographical maps Environmental –Groundwater Other State Organizations/General Public/Consultants – Provide information as requested

Helping customers will require formal and informal methods of correspondence, depending on the nature of the assistance provided. Service of a high level should always be the goal of the Geotechnical Engineer, but this service should also be tempered with the need to account for productive time, as outlined in Sections 2 and 7 of this Chapter. 9.

CARE AND INVENTORY OF EQUIPMENT

Geotechnical Engineers will have some equipment assigned to them on a full time basis. Examples could include such items as a personal computer, camera, or cellular telephone. Other equipment items, such as State vehicles, may be utilized as required, when

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available. All equipment is to be cared for and maintained appropriately. The drilling support truck will be used in this Section as an example of the proper care and inventory of equipment. However, all equipment, whether assigned permanently or on a temporary basis, will be given the proper care described here. The drilling support truck will be operated in a safe, courteous manner, in accordance with the policies described in Chapter 2,“ Oper at i onofNDOTMot orVehi cl es. ”Thet r uckand its included equipment are to be returned clean and ready for the next assignment. If the fuel tank is less than three-quarter full, the truck is to be fueled. Any maintenance or safety issues with the truck are to be reported immediately to Motor Pool. Likewise, any items of equipment stolen or broken are to be reported immediately. If the truck is dirty, it is to be washed. Of particular importance is the requirement to order inventory items for the truck, when such items are consumed or damaged in the course of work. Notes should be taken as such items need replacement, and these items are to be ordered immediately upon returning the truck. Thef or mt obeusedt okeept r ackofi nv ent or yi t emsi st he“ I nv ent or yLi st ”form. 10.

WRITTEN CORRESPONDENCE

The various forms of written correspondence, along with policies governing their use, are discussed in this Section. Different types of correspondence and their appropriate use for given situations are also covered. As a general rule, written correspondence should be as brief as possible, but also needs to deal comprehensively with the subject matter. This means beginning the writing by explaining the purpose of the correspondence. An example would be to indicate that certain information was requested, and that the information is given in the correspondence. Also included should be the necessary facts, such as a description of the problem and the solution, if requested. The solution or recommendation should normally also include the various other options, when possible, along with their respective advantages and disadvantages, and how effective each option would be. Not all correspondence requires a specific recommendation. However, sometimes a recommendation is necessary. An example of where a recommendation must be provided would be when one is specifically requested by a Resident Engineer on a problem encountered on a project which has a contract number. Written correspondence falls into the categories of formal and informal. Letters, memorandums, some emails, and reports are formal correspondence. Transmittal forms, some facsimiles and most emails are informal correspondence. Formal correspondence must be placed in a computer file, backed up on an intranet server, and placed as a hardcopy in the Project file. Color copying, and all other copy work done by the Section in large quantities, or if charged to an EA or Contract number, is to be facilitated by the author of the correspondence t hr oughRepr oduct i on( seet hi sChapt er ,Sect i on11,“ Pr i nt i ngRequest s” ) .

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Finally, all correspondence should be processed in a timely manner. With the exception of reports, which are dealt with in other sections of this Manual, policies regarding the various types of written correspondence are detailed below. 10.1

LETTERS

Letters are used as formal, written correspondence to parties outside of the Department. All letters are to be composed utilizing official letterhead under the name of the Principal Geotechnical Engineer or Assistant Chief Materials Engineer. 10.2

MEMORANDUMS

Memorandums are the most common form of formal, written correspondence utilized when the correspondence is internal to the Department. All memorandums will be formatted using the standard memorandum template, as approved by the Chief Materials Engineer, Materials Division. See Figures 3-1 and 3-2 at the end of this Chapter. 10.3

MEMORANDUM AND LETTER DISTRIBUTION

All memorandums are to be prepared for signature by the Assistant Chief Materials Engineer or Principal Geotechnical Engineer. All project managers are to receive a copy of these memorandums. After signature by the Assistant Chief Materials Engineer or Principal Geotechnical Engineer, the original of the memorandum or letter is to be sent to the Administration Section of the Materials Division for filing and distribution. Typically, this is satisfied by placing the original copy in the Administrative Professional Secr et ar y ’ si n-basket. The Professional Secretary will make four copies and send the original to the addressee. The copies will go to the Department central file, the Materials Division file, the Carson City docket and the Las Vegas docket. The author of the correspondence is then to make and distribute five copies of the letter or memorandum as follows: 

Assistant Chief Materials Engineer



Principal Geotechnical Engineer, two copies



Geotechnical Section Project file



Personal file of the Geotechnical Engineer

The proper distribution of letters and memorandums is critical in achieving necessary documentation, getting information to the appropriate parties, and for ease of research at a later date. 10.4

TRANSMITTAL FORMS

The Transmittal log, Figure 3-3, is a copy of a transmittal form that can be used for sendi ngdocument st ot heot herdi v i si ons.TheWr i t eI tDon’ tSayI tf or m,Fi gur e3-4, can be

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used for internal or Department information communications, but must not contain any geotechnical recommendations. These two types of forms are available for use when very little information needs to be stated. Formal communications and those containing geotechnical recommendations are discussed in Section 10.1 above. 10.5

Facsimiles

Facsimiles (faxes) are an informal method of written correspondence which are appropriate to use when the number of documents being sent is small, and speed of submittal is of benefit. It should be remembered that facsimiles do not provide a record of receipt and action other than a confirmation of delivery. However, if needed, the Geotechnical Engineer can request that the recipient return the cover sheet acknowledging receipt and noting the number of pages received. A printout of the first page showing successful delivery is printed by the fax and needs to be kept in the Project file. All memorandums, recommendations and approvals need to be followed up with a hard copy through the mail. 10.6

Email

Email is another common form of written correspondence. Examples of appropriate use of email for written correspondence are setting up meetings and answering simple requests, where a recorded recommendation is not necessary. When email is used as a type of formal correspondence, the same rules apply as for other forms of written correspondence. Emails with formal correspondence need to be followed up with a hard copy through the mail. 11.

PRINTING REQUESTS

Pr i nt i ngr equest sar ehandl edwi t ht heuseoft he“ Repr oduct i onJobRequestFor m.” This form must be completed in detail, including a full job description, to make sure the request is fulfilled accurately and in a timely manner. The most significant printing requested by Geotechnical Engineers will be Geotechnical Reports. Prior to submitting these reports for printing, they must be approved by the Principal Geotechnical Engineer. The Geotechnical Engineer is required to make certain these reports are formatted properly and that necessary items are included, such as the State seal. 12.

SUPPLIES AND EQUIPMENT REQUESTS

All new and replacement supplies and equipment provided by the Department are for business use only, and may not be utilized for personal use. Before ordering any supplies or equipment, a thorough check of the stockroom and the office supplies cabinet is necessary to make sure the item is not in stock. If the item is not in stock, but is needed in the performance of the job, the first step is to communicate with the Principal Geotechnical Engineer to receive approval to request the item. After Principal Geotechnical Engineer appr ov al , t he“ Combi nat i onReques t f orSuppl i es , Equi pmentandShi ppi ngRecor d”f or mi st obecompl et ed. This form must contain specific

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information, to include accounting information, quantity, stock or model number, detailed description, proposed supplier information (if known), etc. The form is then given to the Administrative Professional Secretary for completion. Sufficient time must be given for the request to be ordered and delivery accomplished. If equipment is needed, and the price exceeds $1000, it must be approved in the budget prior to completing this form. Such requests are first to be discussed with the Principal Geotechnical Engineer. 13.

BUDGET REQUESTS

It has been emphasized in various places in this Chapter that monies can only be expended when they are specifically authorized in the budget. Therefore, the budget process is a very important tool which is utilized to plan programs, activities, and specific supplies and equipment needs. Budget requests are normally due to be finalized in the Geotechnical Section very early in the calendar year. Consequently, planning for requests needs to occur by the end of the preceding calendar year. Each year, specific due dates will be given for budget requests. Typical budget request categories include computer equipment and software, training, equipment, highway construction aids, summer intern students, and Consultants. When Geotechnical Engineers identify potential budget requests, they should discuss them with the Principal Geotechnical Engineer. 14.

TRAVEL

The Department provides travel for employees to facilitate the accomplishment of their work, and to allow training to improve productivity which cannot be obtained in another manner. With few exceptions, travel must have prior authorization. There are two primary written policies to follow concerning travel. The first is NRS 281.160. This Statute provides various policies, reimbursement rates and details on travel advances. The second is TP 1-5-12. This TP establishes detailed procedures for travel. The TP also discusses the various authorizations required for in-state and out-of-state procedures, travel advances, reimbursement rates (note: these rates will be modified on occasion), various forms required, use of private vehicle, air transportation, motor pool and rental vehicles. In addition to complying with the above, the Geotechnical Engineer, when requesting travel, must provide the following to the Administrative Assistant:  A justification for the request  The account to charge, such as EA number  The schedule  Any vehicle arrangements  Travel Advance Form, if desired.

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ROLES AND RESPONSIBILITES 

3-10

Travel Claim Form (including applicable receipts)

When local travel is required, a vehicle may be checked out from the Motor Pool. All Motor Pool procedures must be carefully followed. Since there are a limited number of vehicles, availability is not guaranteed. In some instances, the use of a personal vehicle will be allowed. Mileage reimbursement will be provided when a personal vehicle is utilized for necessary Geotechnical Section travel. Use of a personal vehicle, under these circumstances, must have prior approval of the Principal Geotechnical Engineer, and comply with all applicable policies and procedures. Reimbursement for personal vehicle mileage is processed after the travel. 15.

TRAINING

The Geotechnical Section management supports the continued training of Geotechnical Engineers to provide for professional growth and to keep pace with technical and technological changes. Geotechnical Engineers are responsible for helping management identify needed resources for training opportunities, and to take full advantage of any training attended. 16.

EMPLOYEE APPRAISALS

Employee appraisals, or employee development reports, are an important method of formalized communication between the supervisor and employee. The appraisals process provides for necessary evaluation and feedback. Geotechnical Engineers may be called upon to mentor junior engineers, and provide assistance in preparing employee appraisals. The appr ai salf or m,usedf oral lr egul arempl oy eesofNDOT,i st he“ Depar t mentof Personnel Employee Appraisal & Dev el opmentRepor t . ”Thi sf or m pr ov i desf ort heappr ai sal to be modified for individual job duties, and is formatted to describe the principal assignments of the employee, and rate them, to provide a summary rating of related factors, to provide comments related to the ratings, and for the supervisor to provide a developmental plan and any other suggestions. The form is also used to provide for merit increases and to accomplish the completion of probationary periods. Appraisals of employees are required at three, seven, and eleven months, during probationary periods, and once per year thereafter. All appraisals are to be discussed between the supervisor and employee, and become part of the empl oy ee’ sper sonnelr ecor d. The policies and procedures relating to appraisals can be found in TP 1-6-17. As noted, Geotechnical Engineers may be a mentor to three categories of employees. The first of these is the Rotational Engineer. The second category is that of Highway Construction Aide. The last category is that of Student Intern. 17.

ETHICAL GUIDELINES

NDOT currently has no formal policy covering the matter of ethical considerations. Also, no ethics policy could be written to deal with all possible situations. Nor does this Section 02/14/2005



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attempt a comprehensive discussion of ethics matters. Rather, the purpose is to make the Geotechnical Engineer aware that decisions regarding ethics have to occasionally be made in the work environment. Such decisions must be made with an understanding of, and appreciation for, the need to always demonstrate the very highest ethical behavior.   

While there is no detailed ethics policy, a few common sense rules will always apply: Accept no gifts from anyone doing business with, or seeking to do business with NDOT Avoid any real or potential conflicts of interest Always be professional and honest in personal contacts, and written reports and recommendations

Finally, if any situation occurs where the decision on what to do is not clear, in terms of ethical considerations, always make the decision based on the assumption that there is a possible ethics breach. 18.

JOB SITE SAFETY

Policies and procedures relating to the general aspects of safety are discussed in Chapter 5. However, particular attention should be given to the various job sites, where unsafe conditions tend to more commonly occur. These conditions may relate to the job site conditions, or the practices of individuals working at the job site. When unsafe job site conditions are encountered, the Principal Geotechnical Engineer and the appropriate on site individual are to be notified immediately. If the unsafe conditions relate to maintenance issues, such as a large rock in the roadway, the Maintenance Division is to be immediately notified. The reporting of unsafe job site conditions does not end upon proper notification. The Geotechnical Engineer should also document these incidents. This documentation should be placed in the Project file, depending on the nature of the incident. Geotechnical Engineers should also be vigilant in following appropriate safety practices, and wearing necessary protective gear, particularly during drilling operations. More information on drilling safety is pr ov i dedi nChapt er5,“ Saf et yGui del i nes. ” 19.

JOB SITE HAZARDOUS MATERIALS

The procedures, policies and training for the general aspects of hazardous materials maybef oundi nChapt er2, “ Haz ar dousMat er i al s, ”andal soChapt er5, “ Cont ami nat edSi t es . ” It is the policy of the NDOT Geotechnical Section to not perform hazardous materials drilling, testing or evaluation. When contaminated conditions are encountered, the normal practice is to employ a Consultant to provide the needed services. When Geotechnical Engineers know of, or suspect, hazardous materials contamination at the job site, they are to inform the Principal Geotechnical Engineer immediately and cease any further drilling, testing or evaluation.

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3-12

JOB-RELATED INJURIES

If an injury occurs while on the job, it must be reported as soon as possible to the Principal Geotechnical Engineer, or a higher level. There are also specific procedures and forms required concerning job-related injuries. These are discussed in Chapter 2, “ Safety in t heWor kpl ace. ”It is the responsibility of Geotechnical Engineers to comply with all policies and procedures regarding job-related injuries, including required reporting time frames. Failure to do so can have significant impacts, including the possibility of being ineligi bl ef orwor ker ’ s compensation, or other job benefits. Current telephone numbers are available at the Materials Division office to call for approved occupational medicine providers and pharmacies, should a job-related injury occur. However, in the event of a medical emergency, help should be sought at the nearest medical facility. 21.

VEHICLE ACCIDENTS

This Section deals with the procedures to follow in the event of an accident while driving an NDOT vehicle. Additional discussion regarding NDOT vehicle operation may be found in Chapt er2,“ Oper at i onofNDOTMot orVehi cl es. ” If an accident occurs, while operating an NDOT vehicle, the first responsibility is to provide for assistance to any injured parties, and to seek immediate help for yourself, in the event of injury. The second responsibility is to notify the Principal Geotechnical Engineer, or a higher level, about the specifics oft heacci dent , andcompl et ea“ Vehi cl eAcci dent Repor t ”f or m. This form requires information about you, your vehicle, other persons and vehicles involved in the accident, witnesses, and persons injured. The glove compartment of NDOT vehicles should contain copies of this form. Anot herf or m ut i l i z edi nc onj unc t i onwi t hanNDOTv ehi c ul arac c i dent i st he“ Super v i s or s Vehicle Accident I nv est i gat i on. ”Thi sf or mi scompl et edbyt heempl oy ee’ ssuper v i sor ,andi s an investigation and listing of action taken. Comments and recommendations are made by the District Operations Instructor. Any actions taken are noted by the District Engineer or Division Head, with the requirement that the employee sign the form. There is also a review and findings made by the General Safety Committee. 22.

LOSS REPORTING

In the event of loss or damage of NDOT materials or equipment by theft, pilferage or vandalism, it is the responsibility of the Geotechnical Engineer to notify the Principal Geotechnical Engineer, or higher level immediately. When appropriate, local police authorities will also be notified by the Geotechnical Engineer, and full and complete details given of the items missing or damaged, along with any other pertinent facts concerning the incident.

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3-13

COMPUTER SOFTWARE TOOLS

Various forms of computer software tools are made available in the Geotechnical Section. It is the responsibility of the Geotechnical Engineers to become familiar with the different types of software provided, and to utilize the software to increase productivity and communicate effectively. The software tools currently available are included as Figure 3-5. All new employees must have a processed “ NDOT Request for Computer Access”form. 24.

REFERENCE MATERIALS

Various reference materials are available in the Geotechnical office. These materials are valuable to the Geotechnical Engineer when seeking additional information. Some reference material is provided to the Geotechnical Engineers when they first start the job. The Geotechnical Section has a library with many reference books and literature. 25.

GEOTECHNICAL LABORATORY

Laboratory testing is performed by the Geotechnical Laboratory. The Geotechnical Engineer is responsible for requesting appropriate laboratory tests, while being mindful that unnecessary testing is a waste of assets, resources, and personnel time, and could delay projects. Requests for laboratory work are accomplished through the use of a two-part form, “ Nev ada Depar t mentofTr anspor t at i on Geot echni calLab Task Sheet , ”whi ch i st o be completed for each project. More information on laboratory tests, and samples of the form, maybef oundi nChapt er8,“ Labor at or yTest s. ”

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26.

3-14

FIGURES

3-1: Memorandum STATE OF NEVADA DEPARTMENT OF TRANSPORTATION MEMORANDUM December 27, 2002

To:

Tim Ruguleiski, Resident Engineer _____________________________________

From:

Jeff Palmer, Principal Geotechnical Engineer Subject: Contract 3110, US 95 Widening at Valley View in Las Vegas, Review of CSL, Reports No. 3 and 4

The Geotechnical section has reviewed the Crosshole Sonic Logging (CSL) Reports No. 3 & 4, for the Valley View Bridge over US 95. Report No. 3 presented CSL, test information for five drilled shaft foundations (piers): Piers 1, 2, 4, and 7 in Abutment 1; and Pier 4 in Abutment 2. Of these five piers, all showed test results indicative of good quality concrete, except for Pier 2. This pier showed a velocity reduction of 18% in two spots of one tube pair (between 33.5 and 34.0 meters; and between 27.0 and 37.5 meters). Report No. 4 presented CSL, test information for six drilled shaft foundations (piers): Piers 1, 2, 3, 5, 6, and 7 in Abutment 2. Of these six piers, only three piers showed test results indicative of good quality concrete throughout the shaft. Pier 1 showed velocity reduction of between 12% and 29% in five pairs of tubes between 34.5 and 36.5 meters. Pier 3 showed velocity reductions of between 23% and 30% in two pairs of tubes between 36.0 and 37.0 meters. Pier 5 showed a velocity reduction of 16% in one tube pair between 34.5 and 37.0 meters. These zones of reduced velocity are indicative of anomalous zones within the concrete shaft. Because of these anomalous zones, both the skin resistance and the end bearing capacity of these shafts have been reduced. It is difficult to determine the actual amount of capacity reduction such anomalies produce and the resulting reduction in the design safety factors. Based on previous experience and conversation with the Consultant designer, Walter Vanderpool of Terracon, Inc., the reduction in capacity and factors of safety are determined to be acceptable. We recommend accepting the shafts. It is our strong recommendation to notify the contractor(s) responsible for the shaft construction of the existence of these anomalies and further, to examine and improve their technique for ensuring the cleanliness of the excavations. This step is needed to ensure compliance with the specifications as set for the in the NDOT Standard Specifications for Road and Bridge Construction. If you have any questions or require further information, please call Dana Boomhower at 888-7870, or me at 888-7873. JP:DB:db c:

John Terry, Project Manager

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3-2: Memorandum STATE OF NEVADA DEPARTMENT OF TRANSPORTATION MEMORANDUM February 12, 2002

To:

Nancy Kennedy, Principal Bridge Engineer _____________________________________________

From: Jeff Palmer, Principal Materials Engineer - Geotechnical Subject:

Geotechnical Report –Preliminary Recommendations

Pembroke Drive Bridge (B-1691) over Steamboat Creek –Washoe County EA 72648

The following design recommendations are provided for the Pembroke Drive Bridge Project prior to the completion of the Geotechnical Report. Analysis of the subsurface site conditions and laboratory test results enabled us to calculate bearing capacities for the 460 mm steel pipe piles shown in the 60% plans. These capacities are shown on the following chart. Construction control methods shall include dynamic testing with wave equation analysis, which provides a recommended factor of safety of 2.25. The required pile capacity of 468 kN, provided by the bridge division, is met by using pile 10 meters in length. Pile uplift capacity is 105 kN per pile, and 735 kN per pile group.

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3-3: Transmittal Log Date: To

From

Telephone Number:

For Your

Action Comments

Approval Signature

Information Review

FYI

As We Discussed Per Your Request Please Return Attached Material Please Prepare a Reply to be signed by Please See Me

Remarks:

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3-4: Wr i t eI t … Don’ tSayI t !

STATE OF NEVADA DEPARTMENT OF TRANSPORTATION

WRI TEI T… DON’ TSAYI T! INTERDIVISION COMMUNICATION To: From: Subject:

Date: Reply Wanted: No Reply Wanted:

Message, without recommendations:

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3-5: Computer Software Tools Microsoft Word Microsoft Excel Microsoft Binder Microsoft Outlook Microsoft PowerPoint Microsoft Access Mathcad Xstabl Comp 624P GRL WEAP gINT GEOSYSTEM for Windows Grapher ProShake Rock Database Management Program Goldnail Driven CBEAR Microstation LPILE Plus Group Apile TZPile Shaft MSEW Civil Tech Suite (Epres, Heave, Lpres, Shoring) Rockpack: Rock Slope Stability Analysis 3DTOPOQUADA: Quads for Nevada FOSSA

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CHAPTER 4 WORK BY CONSULTANTS & LOCAL GOVERNMENTS

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WORK BY CONSULTANTS & LOCAL GOVERNMENTS

1. 2. 3. 4. 5. 5.1 5.2 5.3 5.4 6. 7.

8.

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TABLE OF CONTENTS PURPOSE ............................................................................................................ 1 INTRODUCTION .................................................................................................. 1 GEOTECHNICAL INVOLVEMENT PHASES ....................................................... 2 INFORMATION PROVIDED BY DEPARTMENT .................................................. 2 SCOPE/OVERSIGHT OF GEOTECHNICAL SERVICES ..................................... 2 Checklists of Geotechnical Work ......................................................................... 3 Department Review of Consultant Investigations................................................. 3 Department Review of Consultant Reports .......................................................... 4 Construction Phase.............................................................................................. 4 REVIEW OF CONSULTANT PERFORMANCE.................................................... 6 FIGURES ............................................................................................................. 7 4-1: Geotechnical Activity Chart ........................................................................... 7 4-2: Checklist of Geotechnical Work .................................................................... 8 REFERENCES ................................................................................................... 13


WORK BY CONSULTANTS & LOCAL GOVERNMENTS 1.

4-1

PURPOSE

This Chapter defines the engineering process responsibilities of any Consultants performing geotechnical services that affect Department projects, as these individuals become an extension of the Department and therefore must comply with the guidelines and responsibilities as set forth in this Manual. However, this Chapter only describes the pr ocessest obeused,anddoesnotdel v ei nt ot het echni cal“ how t o”t oaccompl i sht he geotechnical engineering technical tasks and procedures. This Chapter also describes the responsibilities of the Geotechnical Engineers, as they relate to Consultants, as well as their interrelationships and roles with those hired to provide services on behalf of the Department. It is not the intent of this Chapter or the Manual to discuss the procedures on how Consultants are selected or enter into a contract with the Department. Employment of Consultants is ty pi cal l yi ncl udedi nt heAdmi ni st r at i v eSer v i cesDi v i si on’ sresponsibilities and covered by TP 1-2-3. That procedure also covers amendments to existing Consultant agreements, and the issuance of Task Orders for On-Call agreements. I nt hi sManual ,t het er m“ Consultant”r ef er s to local governments, developers, and Contractors that perform their own geotechnical work, and/or their Consultants. Construction Plans, specifications, and Special Provisions are r ef er r edt ogener al l yas“ Pl ans” . 2.

INTRODUCTION

All geotechnical related issues for transportation work must be reviewed and approved by the Geotechnical Section. The nature and extent of the involvement by the Geotechnical Section depends upon the nature of the project. Geotechnical services provided by Consultants for the design and construction of roadway projects that affect any of the Department right-of-way are subject to the same geotechnical engineering requirements as for engineering services performed by the Department. Consultants might be retained where the Department does not have necessary equipment, expertise, or manpower. In a few instances, geotechnical services may also be performed by local governments, Consultants or Contractors. Most geotechnical work is conducted before and during the design phase of a roadway project, but services are also provided during the construction phase of the project. In rare instances, services are provided for non-roadway projects. The Department may utilize an On-Call Consultant, for specific tasks. Each Consultant will execute an agreement with a list of services they are to perform. If any of these services are needed, the appropriate Consultant will be issued a Task Order, typically approved by the Assistant Chief Materials Engineer who supervises the Geotechnical Section. Geotechnical Engineers do not select or assign tasks to Consultants under contract to the Department; rather, they contact the Principal Geotechnical Engineer, and request Consultant-provided services. 02/14/2005



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The Geotechnical Section is responsible for evaluating the geotechnical investigation and geotechnical design submitted by Consultants for compliance with Department and FHWA policies and standards. Consultants are responsible for coordinating all activities related to accomplishing the geotechnical investigation, which may involve obtaining permits and/or having an approved traffic control plan. Fieldwork, laboratory testing, analyses, and design recommendations must be in accordance with the procedures and guidelines listed in this Manual. 3.

GEOTECHNICAL INVOLVEMENT PHASES

Any person or firm providing geotechnical services for the Department must be aware of the design and construction phases a project passes through and the involvement periods for those services. Figure 4-1i sa“ Geot echni cal Act i v i t yChar t ”des c r i bi ngt hos ephas es .The30, 60, and 90 percent events correspond to the amount of progress completed on the design. 4.

INFORMATION PROVIDED BY DEPARTMENT

The Geotechnical Section can provide information upon request, which may be useful in the design of a project. The information could include items such as previous Geotechnical Reports, boring logs, laboratory test results, geologic mapping, and as-built plans and construction notes. As-built information should be sought on all rehabilitation projects to obtain knowledge of the existing construction prior to commencing fieldwork. For rehabilitation projects, pavement test data and related information may also be available. 5.

SCOPE/OVERSIGHT OF GEOTECHNICAL SERVICES

All geotechnical services provided for Department projects are reviewed by the Geotechnical Section for comments and approval. Therefore, the procedures and methods described in this Manual are important in standardizing and expediting the information, reports, and techniques utilized by all involved in geotechnical services. Consultants are expected to work independently and keep all parties informed the same as if they were Department Geotechnical Engineers. At all times, Geotechnical Engineers should act in an advisory role as compared to a management role. The Geotechnical Section, and more specifically Geotechnical Engineers, do not manage or supervise Consultants retained by other Divisions. Consultants most likely report to and are responsible to the Project Manager (PM), when working for the Department. During construction, the Resident Engineer (RE) is the coordinator of all communications, including those to and from any Consultants and Department staff. The Geotechnical Section must be contacted prior to commencement of the geotechnical investigation. A Geotechnical Engineer is assigned as the primary contact. Communications between Consultants and Geotechnical Section personnel should be maintained to ensure that investigations meet the requirements of the Department. This will reduce unnecessary delays during the review process, which could affect scheduled 02/14/2005



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construction dates. Geotechnical requirements of the project shall be agreed to by all parties prior to the start of the work. Roadway and/or Bridge Divisions typically have the initial responsibility to provide the Geotechnical Section and other Department Divisions all information concerning a particular project. The Roadway and/or Bridge Divisions are responsible for preparing contract documents after being provided the information described in this Manual. Typically, bids and/or contracts include the following items: 

Geotechnical Report



The latest version of Standard Specifications for Road and Bridge Construction



The latest version of Standard Plans for Road and Bridge Construction



Special Provisions (this includes recommendations made in the Geotechnical Report)



Construction Plans

The Department currently maintains Construction Plans and Special Provisions in several locations. Three of these are the Materials Division, Central Records, and Administrative Services during the time of project advertising. 5.1

Checklists of Geotechnical Work

Consultants must prepare and submit a list of all services they are expected to perform prior to providing those services. These items are covered in the Scope of Services of their agreement. Basic services are included in Figure 4-2 as a simplified nonexclusive Checklist. Al so,r ef ert ot heFHWApubl i cat i on“ Checkl i standGui del i nesf orRev i ew ofGeot echni cal Repor t sand Pr el i mi nar yPl ansand Speci f i cat i ons”( 1985) . Whi l et hesear eusef uland convenient references, other requirements must be met and guidelines must be followed. 5.2

Department Review of Consultant Investigations

On Department projects, Geotechnical Engineers and/or Consultants must adhere to the work described in the Scope of Services, and not exceed those requirements without documented instructions from the Principal Geotechnical Engineer and/or Assistant Chief Materials Engineer. Geotechnical Engineers are expected to respond to formal and informal requests for information submitted directly to the Geotechnical Engineer or passed down from upper management on projects the Geotechnical Engineer has been assigned. All requests should be responded to expeditiously, even if the response is only a promise to locate the information, or to refer the requestor to the proper party for a reply, or to let the requestor know t her equest i sout si det heGeot echni cal Engi neer ’ sr es pons i bi l i t y .I f f ol l owupi spr omi s ed, t hen the Geotechnical Engineer is expected to act in a timely manner. Consultants must submit a quarterly status report on each project. In addition, during the design phase they must provide submittals as outlined in Figure 4-1. Geotechnical Engineers and Consultants are expected to attend status meetings on each of their projects, 02/14/2005



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respond verbally to appropriate questions, and then follow up these conversations with written document at i on.I t i st heGeot echni c al Engi neer ’ sr es pons i bi l i t yt omoni t orandadmi ni s t ereac h of these pieces of correspondence to make sure Consultants respond to those communications and take the appropriate action. Noncompliance will be reported to the Principal Geotechnical Engineer, and the appropriate Project Manager in writing. In-house correspondence between Geotechnical Engineers and their supervisor can be informal, but written records must be maintained. Conversations and meetings must also be documented. 5.3

Department Review of Consultant Reports

Consultants should utilize internal QA/QC procedures that are appropriate for the work performed. Analyses and computations should be checked by an independent geotechnical engineer working for the Consultant. Original analysis computations should be documented and filed. I ti st heGeot echni cal Engi neer ’ sr esponsi bi l i t yt omoni t orandf ol l owupt oseet hat recommendations are acknowledged, acted upon, and documented. In cases where there may be disagreements, the Chief Materials Engineer or Assistant Chief Materials Engineer is responsible for ensuring that disagreements are resolved to the satisfaction of the Department, and that such decisions are accurately documented. All geotechnical documents such as calculations, reports, memorandums, and logs of borings prepared by the Consultant must be provided to the Department in digital format on compact data disks in addition to copies on paper. Report text must be submitted in Microsoft Word, and logs of borings in the gINT program format. When errors, omissions, or questions are encountered, formal correspondence is made to maintain a permanent record for the files. The Geotechnical Report prepared by the Consultant shall be signed, dated, and stamped by a Nevada Registered Professional Engineer. 5.4

Construction Phase

Once the Consultant’ sser v i ceshav ebeenprovided and their recommendations have been accepted by the Geotechnical Section and incorporated into the Department documents, Geotechnical Engineers are expected to understand the documents, and be able to explain and justify them in later meetings and correspondence. Geotechnical information included as part of Construction Plans generally consist of items such as project boring logs, foundation notes, excavation and drilling notes, special embankment details, and drawings. Consultants are responsible for reviewing Contractor’ s (such as wall suppliers) submittals for accuracy and completeness. Communications with Contractors and suppliers follow formal processes routed through the Resident Engineer, unless the Resident Engineer has provided authorization allowing direct contact with the

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supplier. Normally, the Resident Engineer would communicate directly with the construction Contractor who contacts the supplier. Shop drawings and calculations are typically submitted by Contractors prior to commencing portions of the affected work in order to define how they intend to construct the project. Occasionally, additional shop drawings and calculations may be required during the construction phase. Consultants are responsible for checking and approving the geotechnical items in submittals, such as: 

Calculations



Shop Drawings and Plan Details



Applied bearing pressures shown on the drawings



Materials specifications



Construction methods and procedures regarding geotechnical issues



Compliance with specification requirements and Special Provisions

The Geotechnical Section performs a cursory review after Consultants have completed their review. For Consultant-Designed Projects that Consultants have not been retained for construction support, the Geotechnical Engineer performs the above review. Consultants might be requested to review the following: 

Change of site conditions



Change order request



Construction recommendations

The following is a condensed summary representing the process a Contractor’ st y pi c al submittal follows. (The Bridge Division is used as an example for clarity only.) 

The Resident Engineer sends seven copies of the Contractor’ ssubmi t t al t ot heBr i dge Division



The Bridge Division sends one copy of the submittal to the Geotechnical Section



Submittals must to be stamped by a Nevada Registered Professional Engineer



If it is necessary, the Geotechnical Engineer may contact the Resident Engineer to verify if he/she is authorized to contact the Contractor or subcontractors directly



The Geotechnical Section reviews the submittal within time frames specified in Special Provisions or the Standard Specifications (but not stamp the submittals)



The Geotechnical Section sends Bridge Division documentation that the submittals were reviewed and approval or rejection is recommended



Consultants review work must be stamped by a Nevada Registered Professional Engineer.

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WORK BY CONSULTANTS & LOCAL GOVERNMENTS 

4-6

The Geotechnical Section evaluates the Consultant’ sr ev i ew wor kandappr ov esor rejects the Consultant’ sr ev i ewwor k.

Prior to approving the shop drawings and/or calculations, the Geotechnical Section coordinates with the Bridge Division on a joint review. If the shop drawings and/or calculations need to be returned for corrections, one memorandum is written to the Resident Engineer by the Bridge Division incorporating all needed corrections. 6.

REVIEW OF CONSULTANT PERFORMANCE

While Geotechnical Engineers have no supervisory role with Consultants, they are the primary contact and have close relationships with these parties, especially Geotechnical Consultants. Geotechnical Engineers may be requested to provide comments about Consultant’ sper f or mancedur i ngpr oj ect s.Ther ef or e,t heyshoul dbecomef ami l i arwi t ht he forms and procedures utilized in these processes. More details can be obtained from other Department manuals. Geotechnical Engineers providing material or comments for any evaluation processes should use the formal correspondence methods and route the information through the Assistant Chief Materials Engineer.

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FIGURES

4-1: Geotechnical Activity Chart Event Start

Activities The project development process begins. The project coordinator will coordinate the mapping and right-of-entry needs of the project team members and submit all-inclusive requests to Location and Right-of-Way. The right-of-entry at this time is for project personnel to perform noninvasive appraisals of the site conditions, including roadway, hydraulics, structural, geotechnical, and environmental.

ADFS

During the ADFS the team will determine the needs and locations for invasive explorations. A supplemental request by the project coordinator will be issued to Right-of-Way to obtain the rights to perform these investigations. The request must address the exploration methods and the means to access the locations for both environmental and geotechnical personnel. During development of the project alternatives geotechnical information will be obtained and provided to Roadway, Bridge and Hydraulics at the appropriate time to assist in the selection process.

ROD

The FHWA renders a decision on whether the project can proceed to final design. The design team prepares the plans and supporting information for the selected alternative for conducting the PDFS.

PDFS

During the PDFS the team will determine the needs and locations for the explorations necessary to complete the design of the selected alternative. A supplemental request by the project coordinator will be issued to Right-of-Way to obtain the rights to perform these investigations. The request must address the exploration methods and the means to access the locations. Geotechnical exploration will commence when the necessary rights have been secured. The Geotechnical Engineer will provide approximate completion dates of the initial investigation results to the project coordinator in order to adjust the project schedule.

30%

The Geotechnical Engineer will issue a memorandum regarding geologic hazards and preliminary design recommendations as part of the submittal. Geotechnical information will be obtained based on the 30-percent plan set and estimated loads. Additional field investigation will be conducted, if applicable, based on the 30-percent plan set and estimated loads. The Geotechnical Engineer will issue data and recommendations to the Road, Bridge and Hydraulic engineers as needed for achieving their 60-percent design requirements. The Geotechnical Engineer will provide approximate completion dates to the project coordinator in order to adjust the project schedule. The Road, Bridge and Hydraulic engineers will provide updated design information (calculated loads and revised geometry) to the Geotechnical Engineer as it becomes available. Additional field investigation will be conducted, if applicable, based on the updated design information.

60%

The Geotechnical Engineer will issue a draft Geotechnical Report as part of the submittal, based on the updated design information. This information must be sufficient to the purpose of developing designs used for establishing the final right-of-way requirements. The project design is developed sufficiently to establish the final right-of-way requirements.

SET R/W

The final right-of-way requirements are established and forwarded to the chief Right-of-Way agent for acquisition. The Road, Bridge and Hydraulic engineers will provide updated design information, if applicable. Additional field investigation will be conducted, if applicable, based on the updated design information.

90%

The Structural Design and Right-of-Way Divisions perform 90-percent plan reviews. The Geotechnical Engineer issues the final Geotechnical Report, based on the updated design information.

QA/QC

TheDepar t ment ’ squal i t yassur ancepr ocessi scompl et edont he100-percent plans and estimate. The Geotechnical Report is included as a part of this submittal.

PS&E Advertise 02/14/2005

The final specifications are issued and reviewed in conjunction with the plans and estimate. The plans, specifications and estimate are forwarded to administrative services for bid and award. NDOT Geotechnical Policies and Procedures Manual


4-8

4-2: Checklist of Geotechnical Work This is a simplified checklist for easy reference. Additional requirements apply as described in this Manual. Geotechnical services may include, but are not limited to the following: A.

Preliminary Meeting 1. Meeting with Principal Geotechnical Engineer before the geotechnical investigation begins. This will allow the Department to provide information for the field investigation, and provide any special criteria to the Consultant in advance. Discuss boring locations, field sampling, laboratory testing, and design methodology. 2. Meet i ng wi t h Depar t ment ’ sRoadbed Design Section before the pavement analysis and design begin. This will allow the Roadbed Design Section to give the Geotechnical Engineer or the Consultant special design criteria required by the Department.

B.

Exploration 1. Research available information 2. Conduct field reconnaissance 3. Mark boreholes and request utility clearance 4. Request Entry Permits 5. Provide traffic control in accordance with Department policies and procedures 6. Conduct subsurface/rock investigation a. Obtain soil samples for testing b. Log the profile 7. Conduct geophysical investigation 8. Survey the explored area (boreholes) for location and elevation

C.

Laboratory Testing. (laboratory tests and technician duties, must be certified by AASHTO). Tests could include: 1. Gradation 2. Atterberg limits 3. Moisture content 4. Direct shear 5. Unit weight 6. Consolidation 7. Swell 8. Triaxial 9. R-value 10. Compaction 11. Specific gravity 12. Chemical (sulfates, chlorides, pH, resistivity)

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WORK BY CONSULTANTS & LOCAL GOVERNMENTS 13. 14. 15. 16. 17. D.

4-9

Permeability Organic content Unconfined compression LA abrasion Sulfate soundness

Analysis and Design. Common designs include, but are not limited to: 1. Geosynthetic specifications and installation procedures 2. Slope stability for temporary and permanent conditions, static and seismic loading 3. Shallow foundation designs a. Allowable and ultimate bearing pressures for varying cases of embedment depth, footing width, and eccentricities b. Total and differential settlement and expected time to occur 4. Retaining Walls a. Cantilever Walls 1) Footing design: overturning, bearing capacity, sliding, and settlement 2) Soil strength parameters 3) Eccentric loading b. Soil Nail Walls 1) Spacing 2) Hole diameter 3) Nail length 4) Proof test and verification, sequence and procedure of tests c. Tie Back Walls 1) Spacing 2) Hole diameter 3) Bonded and unbonded lengths 4) Prestressing load d. Mechanically Stabilized Earth Walls 1) External stability 2) Global stability 3) Strap length and location 4) Settlement 5) Allowable and ultimate bearing capacities e. Soldier Piles and Lagging 1) Pile spacing 2) Pile diameter 3) Embedment depth 4) Lateral capacity

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5.

E.

Deep Foundations a. Driven Piles 1) Axial capacity versus depth 2) Uplift capacity 3) Pile size and type 4) Pile spacing 5) Settlement 6) Drivability analysis: Wave equation using GRL Weap 7) Lateral loading analysis: L-Pile, Strain Wedge Model b. Drilled Shafts 1) Axial capacity versus depth 2) Uplift capacity 3) Shaft diameter and depth 4) Shaft spacing 5) Settlement 6) Lateral loading analysis: L-Pile, Strain Wedge Model 6. Structural Section a. ACC or PCC thickness b. Type and thickness of Base c. Thickness of Borrow Geotechnical Report 1. General Report Content a. Geologic hazards including seismic evaluation using AASHTO response spectra curves b. Analysis and design material (including structural section, if requested) c. Design recommendations (including structural section, if requested) d. Material specifications e. Construction recommendations (include anticipated construction difficulties) f. Project location sketch or map (include location of borings, existing and proposed structures) g. Boring logs, similar to Department (gINT) form, including the following information:  Start and end dates  Job description  Location (of project)  Boring number  EA number  Ground elevation (of borehole)  Hammer drop system

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             

h. 2.

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Station (of borehole) Offset (of borehole) Engineer (present during drilling) Equipment (drill rig used) Operator (of drill rig) Drilling method Backfilled (of borehole, yes or no, and date) Groundwater level (date measured, depth and elevation) Incremental elevations Depths at incremental elevations Sample number Blowcounts (three SPT values) at 6-inch increments Blowcounts (one SPT value) for last foot Percent recovery (percent length of soil sample recovered per total driven sampler distance)  Lab tests performed  USCS group (Unified Soil Classification System) designation can be based on test results or visual method, if no tests were conducted. It must be stated on the boring logs if the visual method and ASTM D2488 Description of Soils (Visual Manual Procedure) was used  Material description (soil sample and subsurface descriptions)  Remarks (drilling rates, downward pressure, rotational pressure, drilling difficulties, etc.)  Bottom of hole depth or elevation  Names for both the persons responsible for supervising the field study and certifying the boring log Soil test results (triaxial, direct shear, consolidation, gradation, etc.)

Report Format [above sections E.1.a through E.1.h typically should be no more than 2 pages each]. The typical outline is as follows: a. Title page b. Table of contents c. Executive summary (when necessary) d. Report introduction (scope of project) e. Project description (including general site conditions) f. Geologic conditions and seismicity g. Field investigations h. Laboratory analyses i. Discussion of subsurface conditions j. Engineering analyses(including structural section, if requested) NDOT Geotechnical Policies and Procedures Manual

WORK BY CONSULTANTS & LOCAL GOVERNMENTS k. l. m. n.

3.

F.

4-12

Design and construction recommendations (including structural section, if requested) References Figures (topographic site plan, geologic mapping, photographs, geologic cross-sections, typical sections, and recommended design details) Appendices 1) Subsurface explorations data (boring logs with boring log key) 2) Laboratory test results 3) In situ test results 4) Instrumentation results

General requirements for reports: a.

The Geotechnical Report shall include only material in addition to, and/or modi f i cat i ont ot heDepar t ment ’ s“ St andar dSpeci f i cat i onsf orRoadand Br i dge Const r uct i on”f orr ecommended mat er i al s speci f i cation and construction procedures

b.

Recommendations shall be brief, concise, and definite. These should include recommendations for solving anticipated design and construction problems

c.

The Geotechnical Report shall be considered as a bidding document supplementing the Construction Plans and Special Provisions

Plans and Specifications 1.

2.

Special Provisions a.

Required materials specifications

b.

Required construction procedures

Construction Plans a. Project location sketch or map (include location of borings, existing and proposed structures) b. Boring logs

G.

Calculations 1. Submit all reports and calculations to the Department for review and comment 2. These items should be separated from the Geotechnical Report

H.

Reviews and Comments 1.

Respondt oal lDepar t ment ’ scomment s

2.

Review the Construction Plans and Special Provisions

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REFERENCES

FHWA,“ Checkl i standGui del i nesf orRev i ewofGeot echni cal Repor t sandPr el i mi nar yPl ans andSpeci f i cat i ons, ”FHWA-PD-97-002, 1985 FHWA, “ Geot echni cal Di f f er i ngSi t eCondi t i ons, ”Engineering Notebook Issuance GT-15, May 1996. Nevada Department of Transportation, Various documents on Policies and Procedures. Nevada Department of Transportation, Standard Specifications for Road and Bridge Construction. Nevada Department of Transportation, Standard Plans for Road and Bridge Construction.

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CHAPTER 5 GEOTECHNICAL INVESTIGATION PLANNING GUIDELINES

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GEOTECHNICAL INVESTIGATION PLANNING GUIDELINES

5-i

TABLE OF CONTENTS 1. 2. 3. 4. 5. 5.1 5.2 5.3 6. 7. 8. 8.1 8.2 8.3 8.4 8.5 8.6 8.7 9.

10.

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PURPOSE ........................................................................................................... 1 INTRODUCTION ................................................................................................. 1 GENERAL GUIDELINES FOR GEOTECHNICAL INVESTIGATIONS ................ 1 ROADWAY ALIGNMENT INVESTIGATIONS...................................................... 2 ROADWAY CENTERLINE CUT AND EMBANKMENT INVESTIGATIONS......... 3 Embankments Over Soft Ground ......................................................................... 4 Bridge Approach Embankments........................................................................... 5 Rock Slopes ......................................................................................................... 5 LANDSLIDE INVESTIGATIONS .......................................................................... 6 BORROW AREA INVESTIGATIONS................................................................... 7 STRUCTURE INVESTIGATIONS........................................................................ 8 Bridges ................................................................................................................. 8 Earth Retaining Walls........................................................................................... 9 Buildings............................................................................................................... 9 Drainage Structures (Culverts)............................................................................. 9 Large Load Light and Sign Structures ................................................................ 10 Tunnels .............................................................................................................. 10 Detention Basins ................................................................................................ 10 FIGURES ........................................................................................................... 11 5-1: Guidelines for Boring Layout....................................................................... 11 5-2: Minimum Requirements for Boring Depth ................................................... 12 5-3: Guideline Sampling and Testing Criteria..................................................... 13 REFERENCES .................................................................................................. 14


GEOTECHNICAL INVESTIGATION PLANNING GUIDELINES 1.

5-1

PURPOSE

A subsurface investigation may need to be performed at the site of all roadway construction projects, including: widening, extension, modification and rehabilitation. This Chapter presents guidelines to plan the scope of a geotechnical investigation, including a subsurface exploration and testing program. However, as the requirements and conditions vary with each project, engineering judgment is essential in tailoring the investigation to the specific project. The Manual for FHWA,“ Subsur f ace I nv est i gat i ons, ”NHI Course No. 132031, (module 1 1997) and the AASHTO Manual on Subsurface Investigations (1988) provide extensive information on planning and conducting a geotechnical investigation. 2.

INTRODUCTION

A comprehensive investigation program starts with a series of preliminary office studies, such as; a study of project objectives and preliminary plans, review of existing information, identification of geotechnical design issues, formulation of a preliminary exploration and testing plan, and a list of anticipated analyses. Following the office studies, a field reconnaissance should be performed and modifications made, if necessary, to the exploration plan to provide the most useful information. The subsurface exploration program might include both conventional borings and other specialized investigative or in situ testing methods. Subsurface exploration programs should be conducted using a phased approach. This allows the results from critical design areas, or with the most uncertainty, to be performed early in the project. If subsurface information shows materials to be significantly different from those assumed in the planning stages, modifications could be made to the scope of the investigation. Modification to the scope may include boring depths, number of samples, and type of samples. The planning of a geotechnical investigation also includes identification of appropriate laboratory testing and engineering analyses to support geotechnical design needs for the specific project. The results of the investigation are commonly documented in a Geotechnical Report. The amounts and types of data obtained during a geotechnical investigation are often constrained by limitations of time, manpower, equipment, access, or funds. One goal of the investigation program should be to provide sufficient data for the Geotechnical Engineer to recommend the most appropriate and efficient design. Otherwise, more conservative designs with higher factors of safety would be required, which may cost considerably more than a properly conceived exploration program. Another goal should be providing sufficient information for the contractor to bid appropriately and reduce change orders and claims. 3.

GENERAL GUIDELINES FOR GEOTECHNICAL INVESTIGATIONS

An important step in geotechnical analysis and design is to have an adequate subsurface exploration program. The number, depth, spacing, and type of borings, 02/14/2005



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sampling, and testing in an exploration program are so dependent on site conditions and the project, that no uniform rule can be established. The Geotechnical Engineer should develop an overall program that addresses the geotechnical issues to the extent justified by the significance of the project elements. The required investigative effort is also dependent on the type and complexity of the design. Therefore, investigation programs are commonly modified as additional information become available. A phased investigation approach may be most beneficial for large projects and/or projects with difficult geotechnical problems. The planning guidelines presented in Tables 6-1 through 6-3 are considered reasonable for obtaining the minimum subsurface data needed for a cost-effective geotechnical design. Table 6-1, Guidelines for Boring Layout, lists the number and location of borings recommended for various types of facilities. Changes in geological stratigraphy could necessitate additional borings. Table 6-2, Minimum Requirements for Boring Depths, details recommendations for planning the depths of exploration holes. Actual geologic conditions could change exploration depths (such as the actual depth to bedrock or hard strata). In some cases, the presence of unsuitable materials such as highly compressible soils or peat deposits could necessitate additional number and depth of borings, possibly in a grid pattern to identify the lateral extent and depth of these deposits. Planning of exploration programs should take into account the data required for the anticipated engineering analyses. The guidelines contained in Tables 6-1 and 6-2 consider only the use of conventional borings. The Geotechnical Engineer may include cone penetration tests, plate load bearing capacity tests, trench excavation tests, geophysical tests, and/or any other appropriate tests as supplementary to or as substitutes for some, but not all, of the conventional boring exploration tests. Table 6-3, Guideline Sampling and Testing Criteria, describes the types and frequency of samples and tests recommended for various applications and subsurface conditions. The following sections provide additional guidelines for specific project phases and design elements. 4.

ROADWAY ALIGNMENT INVESTIGATIONS

In the early stages of a project, the Geotechnical Engineer may be requested to perform an evaluation of several possible roadway alignments or structure locations. The purpose of this effort is to identify geologic conditions or constraints that could affect the selection decision. This project phase generally does not require extensive subsurface explorations. It is typically limited to preliminary office studies and field reconnaissance where anticipated surface materials are identified and some sampling is performed. General observations should be recorded, including areas of soft soils, organic materials, exposed rock, unstable areas, and other important details. The person performing the field reconnaissance work should be experienced in geological mapping and evaluations. Where time is available, some geotechnical issues may benefit from an extended period of instrumentation and monitoring to measure critical geotechnical parameters, such 02/14/2005



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as fluctuations of groundwater levels and, in the case of slope stability, the location and shape of the failure surface. A properly conducted study of alignment options can potentially result in significant cost savings, especially if there is flexibility given to the designers to locate the new roadway and structures in the most geotechnically favorable locations. 5.

ROADWAY CENTERLINE CUT AND EMBANKMENT INVESTIGATIONS

Soil explorations are conducted along the proposed roadway alignment for the purpose of defining the geotechnical properties of foundation materials. This information is used to define the limits of potential Borrow materials or unsuitable foundation materials that could contribute to settlement or slope stability problems. If poor materials are encountered, the subsurface data can assist designers in developing remedial measures and designing stable cut or fill slopes. This information also aides the designer of the pavement section. Roadbed Design Engineers should be consulted to determine locations where soil samples are needed for design of structural section. Criteria for centerline investigations vary substantially, depending on the location of the proposed roadway, the anticipated subsurface materials, and the type of roadway. It is important that the Geotechnical Engineer visit the site to make sure that all portions of the investigation are planned thoughtfully and are accomplishable so duplication of effort does not occur. The overall investigation costs can be reduced significantly if, for example, the information for a structure and the centerline can be obtained from a single boring. In general, borings should be placed at 200- to 500-foot intervals along the alignment, depending on whether the subsurface conditions are variable or uniform, respectively. Borings could be located along centerline or staggered left and right of the centerline, depending on the locations of maximum cuts and fills as well as the interpreted geology. Borings may be spaced further apart if the project does not have significant earthwork or structures and available information indicates the presence of uniform subsurface conditions. Additional borings may be required to define the limits of any undesirable materials or changes in soil stratification that could affect design and construction. In areas of highly variable soil conditions, additional borings should be included in the transverse direction to determine the three-dimensional variability of subsurface materials. For roadway widening projects that provide additional lanes, borings should be placed at the outer edge of the new lane alignment, which may require difficult mobilization on existing slopes. In areas of significant cut or fill, where stability analysis is anticipated, a minimum of two borings should be placed at critical cross-sections to identify the stratigraphy within and above the crest of cuts and beneath and beyond the toe of embankments. In situ testing and instrumentation may be necessary to determine shear strength and groundwater levels over time. Where slope stability is a concern, inclinometer instruments could be installed 02/14/2005



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during the design phase and used later as a baseline for monitoring slope stability during construction. In all cases, a minimum of three samples per mile, or three per project, whichever is greater, should be obtained for each stratum encountered. Each of the samples representing a particular stratum should be obtained from a different location, with sampling locations spread out over each mile. Samples should be of adequate size to permit classification, moisture content testing, gradation testing, R-Value testing, and Atterberg limits tests. Undisturbed samples should be obtained for any anticipated strength, consolidation, or other specialized testing needs. Borings in areas of little or no grade change should extend to 5 to 10 feet below grade, or drainage pipe or culvert invert level, whichever is deeper. In some cases, including an occasional boring that extends 20 feet below grade is helpful. These deeper borings assist to better define overall geology that could potentially affect design and construction. Deeper borings also apply to projects with deep construction items, such as proposed buried storm sewer systems. Borings typically should include Standard Penetration Tests (SPT). In areas of cuts, borings should extend 5 to 10 feet below the proposed ditch grade. If potentially unstable conditions or materials are encountered at this depth, borings should be extended an additional 10 feet. SPT samples, cuttings samples, undisturbed samples and core samples should be obtained as appropriate for testing and analyses. Strength testing (triaxial tests with pore pressure measurements), consolidation testing, and groundwater instrumentation should be considered to develop parameters for stability and settlement analysis. Some borings for cut slopes in residual soils and slide debris may be drilled to obtain a continuous soil profile for detailed examination of potential weak zones. Materials to be excavated should be evaluated for shrink/swell and for use (R-Value testing) on either the project or disposal. Suitable disposal sites may need to be identified. In areas of fill, borings should extend until all unsuitable materials have been penetrated and the predicted stress from the foundation loading is less than 10 percent of the original overburden pressure. Additional borings may be included to investigate the conditions at the toe of the proposed fill or for in situ tests or speed-drilled instruments installations. A speed-drilled instruments installation boring is a hole that is drilled solely for installing a geotechnical instrument such as vibrating wire piezometer. Although most borings are sampled while being drilled, a speed drilled boring is an unsampled boring used where the stratigraphy is already defined. Because no sampling occurs, the boring is completed much quicker. Probe holes for tests, such as the cone penetrometer, may also be included as needed. 5.1

Embankments Over Soft Ground

Investigations for embankments that will be constructed over soft ground comprised of muck, peat, or other very weak deposits, should include deeper and/or additional borings to determine the limits of the deposit, as necessary, in order to properly analyze and 02/14/2005



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mitigate their effects on embankment settlement and stability. SPT, cuttings, and undisturbed samples should be retrieved in order to classify materials and determine strength and consolidation properties. Some very soft and highly organic materials should be tested in situ with vane shear equipment because retrieving undisturbed samples could be very difficult, and testing disturbed samples typically produces unreliable results. If time allows, groundwater instruments should be installed and monitored to determine how groundwater levels fluctuate throughout the year. 5.2

Bridge Approach Embankments

At least one boring should be taken at the point of highest fill. Usually borings taken for bridge abutments are adequate as long as appropriate samples are obtained for both structure and embankment applications. If settlement or stability problems are anticipated, as may occur due to the height of the proposed embankment and/or the presence of poor foundation soils, additional borings should be taken in the longitudinal and transverse directions. The first of these borings should be no more than 15 feet from the abutment. The remaining borings should be placed at 100-foot intervals until the height of the fill is considered insignificant. Borings should be completed at the toe of the proposed embankment slopes and at the embankment centerline. Borings should be continued to a depth at which the proposed stress increase due to the new embankment load is less than 10 percent of the original overburden pressure and unsuitable founding materials have been penetrated. 5.3

Rock Slopes

Some road alignments may require cut slopes in rock. The geotechnical investigation should be planned to provide the data and geologic interpretations for the analysis and design of stable rock cuts and an evaluation of the constructability of the proposed cuts. A geologic reconnaissance is essential to map geologic conditions and rock structure, which includes office studies of the geology and aerial photographs, quadrangle maps, etc., as well as the field work. The Rockfall Hazard Rating (RHRS) database should be researched for information concerning past and potential rockfall hazards. If rock slopes currently exist on the project, they should be examined for rockfall evidence and unstable rock structure features. Discontinuities and, to a lesser extent, the intact rock strength control rock slope stability at various cut slope angles. Stereonet projections of structural discontinuities (including rock fractures, joints, bedding planes, faults, foliations, etc.) are an extremely useful technique for evaluating the potential for various types of rock slope instabilities. Subsurface investigations should utilize rock-coring methods where appropriate, using double or triple core barrels to obtain a high percentage of core recovery. The core should be carefully logged, noting all discontinuities and unique features and determining the Rock Quality Designations (RQD). Consider whether to obtain oriented core or utilize in-borehole photography to determine the alignment of rock structure. Borings should 02/14/2005



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extend a minimum of 15 feet below the planned excavation depths. Deeper borings may be required if potentially unstable strata are encountered near the base of the proposed cuts. Geotechnical parameters for rock include the orientation of discontinuities, the spatial relationship between proposed cut slopes and mapped discontinuities and the resistance to movement (shear strength) along the discontinuities, as well as the overall rock strength and hardness. The strength along discontinuities can be estimated, or specialized tests could be performed. Discontinuity strength is rarely the same in all directions, since even small variations along the joint surface (steps or undulations), known as asperities, strongly influence the potential for sliding along that surface. This affect is most pronounced when the asperities are oriented perpendicularly to the direction of sliding. Since it is difficult to reproduce field conditions in the laboratory for some applications, in situ direct shear tests may be needed. Intact rock strength/hardness can be estimated by point load tests, or determined by performing unconfined compression tests. Groundwater conditions could affect slope design and stability, and therefore should be measured in boreholes. Critical applications may require observation wells or piezometers. Springs and perched water zones should also be mapped. 6.

LANDSLIDE INVESTIGATIONS

Landslide areas should have been detected in the early stages of the project by means of research and reconnaissance. It is important to conduct a thorough geologic reconnaissance in terrain that might include landslides; otherwise, a landslide may go undetected and not investigated during the field exploration and drilling phases. One landslide reference is the TRB publication on Landslides: Investigation and Mitigation, Special Report 247. To design a landslide remediation, the size and depth of the slide must be known. Inclinometers and piezometers should be installed to accurately define the depth of movement and existing piezometric levels. When monitored over several months or years, this instrumentation can be very valuable in determining the behavior of the landslide and the relationship between periods of active slide movement and seasonal groundwater levels. As a minimum, two instrumented borings should be drilled along the cross-section (axis of movement) of the slide. Larger slides will usually require four or more borings to adequately define the failure shear zone. Borings should extend through the full depth of landslide material, terminating at least 15 feet into underlying stable material. Generally, the boring depths for at least one or two borings should be made even deeper to ensure that an accurate interpretation of the depth of the failure was made and to identify any underlying zones of weakness that could affect the mitigation design. Shallow slides (approximately less than 20 feet deep) can sometimes be effectively evaluated using test pits or trenches, which can expose and allow positive identification of the failure shear zone, its shape and inclination. 02/14/2005



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Monitoring slide movement can be augmented with a line of survey hubs, referred to as a tagline. The hubs should be placed along the axis of the slide and extend beyond the interpreted limits of movement. A cross line, perpendicular to the slide axis, can also be used. The hubs should be surveyed on a regular basis. Movements should be recorded in the X, Y and Z directions. The results can help define the type of slide, the rate of movement, changes in the slide limits, and areas of greatest activity. The vector sums of the X, Y, and Z movements can be plotted and used to help model the actual shape of the failure surface. Piezometer instrumentation should be designed to accurately record specific groundwater heads that act on the failure shear zone and within the slide mass. It is preferable that several piezometers be installed at different depths to accurately model the groundwater conditions. It is common for the crushing and grinding of materials along the failure zone to create a less permeable zone (aquitard), which can lead to the buildup of artesian water pressure acting on the failure surface. This can dramatically decrease stability. A piezometer should be installed in that zone to determine if this condition is present. Placement of piezometers at specific target areas demands an understanding of the slide geometry, which may require a second mobilization once the inclinometers have shown the actual depth of movement. Simply increasing the depth range covered by the slotted portion of an observation well will not provide good results. In fact, the water level readings will tend to be ambiguous and unusable. This can be avoided if the slotted zone is more targeted and controlled by appropriate seals or if vibrating wire piezometers are used. The benefit of vibrating wire piezometers is that the lag time in response to water level changes is very small and continuous readings can be recorded with a data logger to show groundwater spikes that otherwise might be missed due to their short duration. Sampling in landslide areas often do not follow standard procedures because of the difficulty of identifying shear zones and need of unique types of strength and correlation testing. Often, continuous sampling is desirable to locate the slide shear zone and to obtain ample soils for testing. Undisturbed samples are obtained for shear strength testing (such as triaxial undrained peak shear tests on overburden materials and repeated direct shear tests on shear zone material). If undisturbed samples are not possible to obtain from the suspected shear zones, disturbed samples could be remolded in the laboratory prior to testing. 7.

BORROW AREA INVESTIGATIONS

Test pits, trenches, and various types of borings can be used for exploration of potential Borrow areas. Samples should be obtained to permit classification, gradation, Rvalue, compaction, and chemical testing of each material type, as applicable. The extent of the exploration will depend on the size of the Borrow area, the amount of Borrow needed, and the amount of sample required to complete a full suite of specific tests. 02/14/2005



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STRUCTURE INVESTIGATIONS

The purpose of structure borings is to provide sufficient information about the subsurface materials to design the structure foundations and to provide constructionrelated recommendations. All structure borings should include Standard Penetration Testing (SPT) at regular intervals unless other sampling methods and/or testing are being performed. Undisturbed samples are often obtained to determine shear strengths in addition to material properties (such as moisture contents, unit weight, Atterberg limits, gradation). The borings can sometimes be supplemented with in situ test borings, such as the pressuremeter if field-developed p-y curves are needed for lateral pile analysis. Usually the groundwater level encountered during drilling will suffice for subsequent analysis. 8.1

Bridges

Complete at least one borehole at each pier or abutment location. The hole pattern should be staggered so that borings occur at the opposite ends of adjacent piers. Wide pier foundations or abutments that are over 100 feet wide transverse to centerline (roadway width) may require at least two borings, preferably at the extremities of the proposed substructure. For widening of existing structures, the total number of borings may be reduced, depending on the available information for the existing structure. Approximate locations of piers and abutments may be deduced based on experience and a preliminary design concept for the structure when exact support locations are unknown. Borings should be placed at no more than 100-foot intervals along the alignment when exact or approximate support locations cannot be determined. Borings should be continued to a depth that the predicted stress from the foundation and approach embankment loading is less than 10 percent of the original overburden pressure, or until all unsuitable foundation materials have been penetrated and the underlying competent bearing zone penetrated a minimum distance (i.e., 10 to 15 feet into competent bedrock). This depth should be increased, when existence of boulders are possible, to confirm that the rock is bedrock and not a large boulder. If no data is available for predicting the foundation stress, extend the boring until at least 20 feet of bedrock or other competent bearing material (N-values of 50 or greater) is encountered. Additionally, borings should be performed to a depth that the design takes into account scour and lateral loading requirements. When using the Standard Penetration Test, SPT split-spoon samples should be recovered continuously within the upper 20 feet of any boring, and then every five feet down to 60 feet. For deep foundations, an additional zone of sampling every ten feet from 60 feet deep to 100 feet deep is included where SPT samples can be recovered. When cohesive soils are encountered, undisturbed samples should be obtained at 5foot intervals in at least one boring. Undisturbed samples should be obtained from more than one boring where possible. In situ vane shear tests are recommended where soft clay, peat or other soft or highly organic materials are encountered. Representative undisturbed samples should be obtained in these materials for index testing and possible 02/14/2005



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laboratory shear strength testing. Chemical tests are required on all new bridge projects. As a minimum, one test should be conducted on each soil that will be in contact with structural steel elements. When rock is encountered, successive core runs should be made with the objective of obtaining the best possible core recovery. The RQD should be determined from rock cor es.SPT’ s shoul d be performed between core runs in soft rock, typically at 5-foot intervals. In the case of a water crossing, samples of streambed materials and each underlying stratum should be obtained for determination of the median particle diameter, D50, for scour analysis. In addition, samples should be obtained to determine Plasticity Index (PI) and particle size distribution for design of filter fabrics. 8.2

Earth Retaining Walls The following are general investigation requirements for retaining wall design:



At retaining wall locations, borings should be taken at a maximum interval of one per 100 feet of the wall with a minimum of 2 borings and as close to the wall alignment as possible.



Retaining structures with tiebacks or soil nails will need an additional row of borings where the anchor load zone is anticipated.



Borings should be continued to depths that all unsuitable founding materials are penetrated, and the proposed stress increase due to the retaining wall structure will be less than 10 percent of the original overburden pressure.



Sampling and in situ testing criteria are the same as for bridges.

8.3

Buildings

In general, one boring should be made at each corner and one in the center. This may be reduced for small buildings. For large buildings or highly variable site conditions, one boring should be taken at each support location. Refer to building foundation texts for additional guidance in planning the geotechnical investigation. 8.4

Drainage Structures (Culverts)

Borings should be taken at proposed locations of box culverts. Trenches or hand augured borings may suffice for smaller structures. For box culverts, borings should extend a minimum of 15 feet below the bottom of the culvert, or until 5 feet of firm, competent material is encountered, whichever is deeper. For smaller structures, exploration holes should extend at least 5 feet below the bottom of the structure, or until 5 feet of firm, competent material is encountered, whichever is deeper. Chemical testing must be performed for each site. Material from each stratum above the invert elevation should be tested. For drainage systems parallel to roadway alignments, tests should be performed at 1,500-foot intervals along the alignment.

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GEOTECHNICAL INVESTIGATION PLANNING GUIDELINES 8.5

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Large Load Light and Sign Structures

One boring should be made at each designated location. Borings should extend approximately 40 feet into suitable soil, or 5 feet into competent rock. Deeper borings may be required for cases with higher torsional loads, or if large boulders are anticipated. Other criteria are the same as for bridges. 8.6

Tunnels

Due to the extreme variability of conditions under which tunnels are constructed, investigation criteria for tunnels should be established for each project on an individual basis. Refer to tunneling texts for detailed guidance, or consult with an expert in tunneling. 8.7

Detention Basins

Test pits and trenches typically are adequate for the investigation of proposed detention basins. Samples should be obtained to permit classification, gradation, Plasticity Index, unit weight, moisture content, R-value, compaction, permeability test, and/or chemical testing of each material type, as applicable. The extent of the exploration will depend on the size of the detention basin area. Field tests may include infiltration tests, as applicable.

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FIGURES

5-1: Guidelines for Boring Layout Geotechnical Features Bridge Foundations

Boring Layout For piers or abutments less than 100 feet wide, provide a minimum of one boring with the hole pattern staggered so that borings occur at the opposite ends of adjacent piers. For piers or abutments over 100 feet wide, provide a minimum of two borings, one at each end of the pier or abutment. Additional borings should be provided in areas of erratic subsurface conditions.

Retaining Walls

A minimum of two borings should be performed for each retaining wall. For retaining walls more than 100 feet in length, the spacing between borings should be no greater than 200 feet. Retaining structures with tiebacks or soil nails will need an additional row of borings where the anchor load zone is anticipated to estimate lateral loads and anchorage capacities. Include additional borings outboard of the wall line to define conditions at the toe of the wall as needed. Roadways The spacing of borings along the roadway alignment generally should not exceed 200 to 500 feet. The selected spacing and location of the borings should be based on the geologic complexity and soil/rock strata continuity in the project area, with the objective of defining the vertical and horizontal boundaries of distinct soil and rock units within the project limits. Cuts A minimum of one boring should be performed for each cut slope. For longer cuts, the spacing between borings along the length of the cut should generally be between 200 and 400 feet, as needed, based on the complexity of the geology. At critical locations and high cuts, provide a minimum of two borings in the transverse direction to model the existing geological conditions for stability analyses. Embankments Use criteria presented above for cuts. Culverts A minimum of one boring at each major culvert. Additional borings should be provided for long culverts or in areas of erratic subsurface conditions. Note: This table is based on the Subsurface Investigations Manual (FHWA/NHI 01-031). Also see FHWA Geotechnical Checklist and Guidelines (FHWA-ED-88-053).

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5-2: Minimum Requirements for Boring Depth Areas of Investigation

Recommended Boring Depth

Bridge Foundations*

All borings should be extended below the estimated scour depth.

Spread Footings

For isolated footings of breadth Lf and width 2Bf, where Lf 2Bf, borings should extend a minimum of two footing widths below the bearing level. For isolated footings where Lf 5Bf, borings should extend a minimum of four footing widths below the bearing level. For 2Bf Lf 5Bf, the minimum boring length should be determined by linear interpolation between depths of 2Bf and 5Bf below the bearing level. In soil, borings should extend below the anticipated pile or shaft tip elevation a minimum of 20 feet, or a minimum of two times the maximum pile group dimension, whichever is deeper. For piles bearing on rock, a minimum of 10 to 15 feet of rock core should be obtained at each boring location to verify that the boring has not terminated on a boulder. For shafts supported on or extending into rock, a minimum of 10 to 15 feet of rock core, or a length of rock core equal to at least three times the shaft diameter for isolated shafts or two times the maximum shaft group dimension, whichever is greater, should be extended below the anticipated shaft tip elevation to determine the physical characteristics of rock within the zone of foundation influence. Extend borings to depth below final ground line between 0.75 and 1.5 times the height of the wall or to where the net increase in soil stress is less than 10% of the existing effective stress in the soil at that depth. Where stratification indicates possible deep stability or settlement problem, borings should extend to hard stratum. For deep foundations, use the criteria presented above for bridge foundations. Extend borings a minimum of 10 feet below the proposed subgrade level.

Deep Foundations

Retaining Walls

Roadways (minimal grading) Cuts

Embankments

Culverts

Boring should extend a minimum of 15 feet below the anticipated depth of the cut at the ditch line. Boring depths should be increased in locations where base stability is a concern due to the presence of soft soils or weak zones, or in locations where the base of the cut is below groundwater level to determine the depth of the underlying pervious strata. Extend borings a minimum depth equal to twice the embankment height, unless a hard stratum is encountered above this depth. Where soft strata are encountered which may present stability or settlement concerns, the borings should extend to hard material. Use criteria presented above for embankments.

Note: This table is based on the Subsurface Investigations Manual (FHWA/NHI). Also see FHWA Geotechnical Checklist and Guidelines (FHWA-ED-88-053). Requirements for highway bridges are based on AASHTO Standard Specifications for Design of Highway Bridges.

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5-3: Guideline Sampling and Testing Criteria Sand-Gravel Soils

SPT (split-spoon) samples should be taken at 5-foot intervals or at significant changes in soil strata. Continuous SPT samples are recommended in the top 15 feet of borings made at locations where spread footings may be placed in natural soils. SPT jar or bag samples should be sent to lab for classification testing and verification of field visual soil identification.

Rock

Continuous cores should be obtained in rock or shales using double or triple tube cone barrels. In structural foundation investigations, core a minimum of 10 feet into rock to insure it is bedrock and not a boulder. Percent core recovery and RQD value should be determined in field or lab for each core run and recorded on boring log.

Silt-Clay Soils

SPT and undisturbedthin wall tube samples should be taken at 5-foot intervals or at significant changes in strata. A sufficient number of samples, suitable for the types of testing intended, should be obtained within each soil layer. Take alternate SPT and tube samples in same boring or take tube samples in separate undisturbed boring. SPT jar or bag samples should be sent to lab for classification testing and verification of field visual soil identification. Tube samples should be sent to the lab for consolidation testing (for settlement analysis) and strength testing (for slope stability and foundation bearing capacity analysis). Field vane shear testing is recommended to obtain in situ shear strength of soft clay, silt, and well-rotted peat.

Ground Water

Water level encountered during drilling, at completion of boring, and at 24 hours after completion of boring should be recorded on boring log. In low permeability soils, such as silts and clays, a false indication of the water level may be obtained when water is used for drilling fluid and adequate time is not permitted after hole completion for the water level to stabilize (more than one week may be required). In such soils a plastic pipe water observation well should be installed to allow monitoring of the water level over a period of time. Seasonal fluctuation of water table should be determined where fluctuation will have significant impact on design or construction (e.g. Borrow source, footing excavation, excavation of toe of landslide, etc.). Zones of artesian water and seepage should be measured and recorded.

Soil Borrow Sources

Quarry Sites

Exploration equipment that will allow direct observation and sampling of the subsurface soil layers is most desirable for material site investigations. Equipment consisting of backhoes, dozers, or large diameter augers is preferred for exploration above the water table. Below the water table, borings can be used. SPT samples should be taken at 5-foot intervals or at significant changes in strata. Samples should be sent to lab for classification testing to verify field visual identification. Groundwater levels should be recorded. Piezometers or observation wells should be installed to monitor water levels where significant seasonal fluctuation is anticipated. Rock coring should be used to explore new quarry sites. Use of double or triple tube core barrels is recommended to maximize core recovery. For riprap source, spacing of fractures should be carefully measured to allow assessment of rock sizes that can be produced by blasting. For aggregate source, the amount and type of joint infilling should be carefully noted If assessment is made on the basis of an exiting quarry site face, it may be necessary to core or use geophysical techniques to verify that the nature of the rock does not change behind the face or at depth. Core samples should be sent to lab for rock quality tests to determine suitability for riprap or aggregates.

Note: This Table is based on FHWA Geotechnical Checklist and Guidelines (FHWA-ED-88-053).

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REFERENCES

AASHTO,“ Manual onSubsur f aceI nv est i gat i ons, ”1988 ASCE,“ Subsur f aceI nv est i gat i onf orDesi gnandConst r uc t i onofBui l di ngs, ”Manualand Report on Engineering Practice No. 56, 1976 Depar t mentoft heNavy ,“ Soi l sMechani csDesi gnManual , ”7. 1,NAVFAC DM-7.1, Naval Facilities Engineering Command, 1986 FHWA,“ Adv anc edCour seonSl opeSt abi l i t y , ”Vol .1,FHWA- SA-94, 1994 FHWA,“ Checkl i stand Gui del i nesf orRev i ew ofGeot ec hni calRepor t sand Pr el i mi nar y Pl ansandSpeci f i c at i ons, ”FHWA-PD-97-002, 1985 FHWA,“ Dr i l l edShaf t sf orBr i dgeFoundat i ons , ”FHWA-RD-92-004, 1993 FHWA,“ Geot ec hni cal Engi neer i ngNot ebook , ”( Sect i onsaddedwhenneeded) FHWA,“ Soi l sandFoundat i onsWor kshopManual , ”2ndEdi t i on,FHWAHI -88-009, 1993 FHWA,“ Subsur f ac eI nv est i gat i ons, ”NHI Course No. 132031, FHWA-HI-97-021, 1997 FHWA,“ Subs ur f aceI nv est i gations –Geot ec hni calChar act er i z at i on, ”Ref er enceManualf or NHI Course No. 132031, FHWA-NHI-01-031, 2002 FHWA,“ Geot ec hni calI nst r ument at i on, ”FHWA-HI-98-034, 1998 FHWA,“ ManualonDesi gnandConst r uct i onofDr i v enPi l eFoundat i ons, ”FHWA-HI-97-013 and 014, 1996 FHWA, “ Rock Sl opes: Desi gn, Ex cav at i on, St abi l i z at i on, Tur ner -Fairbank Highway Resear chCent er , ”FHWA-TS-89-045. 1989 NCHRP,“ Rec ommendedGui del i nesf orSeal i ngGeot echni calEx pl or at or yHol es,Nat i onal Cooper at i v eHi ghwayResear c hPr ogr am, ”NCHRPReport 378. Peck,R. B. ,Hanson,W. E. ,& Thor nbur n,T. H. ,“ Foundat i onEngi neer i ng, ”2ndEd. ,Wi l ey , 1974. Ter z aghi ,K,and Pec k,R. B. ,“ Soi lMec hani csi n Engi neer i ng Pr act i ce, ”2ndEd. ,Wi l ey , 1967 TRB,“ Landsl i des:I nv est i gat i onandMi t i gat i on, ”Speci alReport 247, 1996

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GEOTECHNICAL POLICIES AND PROCEDURES

CHAPTER 6 GEOTECHNICAL INVESTIGATION PROCEDURES

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GEOTECHNICAL INVESTIGATION PROCEDURES

6-i

TABLE OF CONTENTS 1. 2. 3. 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 4. 5. 6. 7. 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.3.4 7.3.5 7.3.6 7.3.7 7.4 7.5 7.5.1 7.5.2 7.6 7.7 8. 8.1 8.1.1 8.1.2 8.1.3 8.1.4 8.2 8.3 8.3.1 02/14/2005

PURPOSE ............................................................................................................ 1 REVIEW OF PROJECT REQUIREMENTS.......................................................... 1 OFFICE REVIEW OF AVAILABLE DATA ............................................................ 2 Topographic Maps................................................................................................ 2 Aerial Photographs ............................................................................................... 2 Geological Maps and Reports .............................................................................. 2 Soil Surveys.......................................................................................................... 3 Adjacent Projects ................................................................................................. 3 Rockfall Hazard Rating System ............................................................................ 3 Hydrogeological Surveys and Well Logs .............................................................. 3 Remote Sensing Data .......................................................................................... 3 FIELD RECONNAISSANCE................................................................................. 4 FIELD MAPPING AND MEASUREMENTS OF ROCK DISCONTINUITIES ........ 5 FIELD-DEVELOPED CROSS-SECTIONS ........................................................... 6 SUBSURFACE EXPLORATION METHODS........................................................ 6 Test Pits and Trenches ........................................................................................ 7 Hand Auger Probes .............................................................................................. 7 Exploration Drilling Techniques ............................................................................ 7 Solid Flight Auger Borings .................................................................................... 8 Hollow-Stem Auger Borings ................................................................................. 8 Wash Borings ....................................................................................................... 8 Mud Rotary Drilling ............................................................................................... 9 Air Drilling ............................................................................................................. 9 Percussion Drilling................................................................................................ 9 Coring................................................................................................................... 9 Soundings ............................................................................................................ 9 Geophysical Methods ......................................................................................... 10 Seismic Refraction and Reflection...................................................................... 10 Electrical Resistivity............................................................................................ 11 Ground Penetrating Radar (GPR) ...................................................................... 11 Nondestructive Testing - Evaluation of Existing Structures ................................ 11 SOIL SAMPLING................................................................................................ 11 Disturbed Sampling ............................................................................................ 12 Bag (Bulk) Samples............................................................................................ 12 Cuttings Samples ............................................................................................... 12 Split Spoon Sampler........................................................................................... 12 California Modified Sampler ............................................................................... 13 Undisturbed Block Sampling .............................................................................. 13 Undisturbed Sampling Using Thin Wall Samplers.............................................. 14 Shelby Tube Sampler......................................................................................... 14 NDOT Geotechnical Policies and Procedures Manual

GEOTECHNICAL INVESTIGATION PROCEDURES 8.3.2 8.3.3 8.3.4 8.3.5 8.4 8.4.1 8.4.2 8.4.3 9. 9.1 9.2 9.3 9.4 10. 10.1 10.2 10.3 10.4 10.5 10.6 10.7 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

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Stationary Piston Sampler .................................................................................. 14 Floating Piston Sampler ..................................................................................... 15 Retractable Piston Sampler................................................................................ 15 Hydraulic (Osterberg) Piston Sampler ................................................................ 15 Partially Disturbed Sampling .............................................................................. 15 Denison Sampler................................................................................................ 15 Pitcher Sampler.................................................................................................. 15 Sprague & Henwood Sampler ............................................................................ 16 ROCK SAMPLING.............................................................................................. 16 Double Tube Core Barrel.................................................................................... 16 Triple Tube Core Barrel ...................................................................................... 16 Oriented Core ..................................................................................................... 17 Borehole Television Camera .............................................................................. 17 EXPLORATION DIFFICULTIES......................................................................... 17 Improper Drilling Techniques.............................................................................. 17 Sample Recovery ............................................................................................... 18 Sample Disturbance ........................................................................................... 19 Obstructions ....................................................................................................... 19 Problematic Geologic Conditions ....................................................................... 19 Groundwater Conditions..................................................................................... 20 Contaminated Sites ............................................................................................ 20 INSTRUMENTATION ......................................................................................... 21 BOREHOLE SEALING/BACKFILLING............................................................... 21 FIELD EXPLORATION LOGS............................................................................ 22 PHOTOGRAPHIC RECORD.............................................................................. 22 SAMPLE PRESERVATION AND SHIPPING ..................................................... 22 GUIDELINES FOR INSPECTIONS OF SUBSURFACE EXPLORATIONS........ 23 EQUIPMENT FOR FIELD EXPLORATIONS...................................................... 24 SAFETY GUIDELINES....................................................................................... 25 SPECIFICATIONS AND STANDARDS .............................................................. 26 FIGURES ........................................................................................................... 27 6-1: Core Sizes (from Boart Longyear, 2000)..................................................... 27 REFERENCES ................................................................................................... 28



1.

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PURPOSE

Due to the varying complexity of projects and subsurface conditions, it is difficult to establish a rigid format to be followed in conducting geotechnical investigations. However, there are fundamental required data that should be obtained and basic steps that should be followed for any project investigation. The collected field data and assessments are the basis for all subsequent engineering decisions and, as such, are of paramount importance to the design and success of a project. By outlining and describing these requirements and steps, it will be possible to standardize procedures and considerably reduce time and expense that would be required to return to the project site and obtain important information not obtained during the initial investigation. The following are fundamental required data that should be obtained during a geotechnical investigation: 

Identification and delineation of existing soil and rock strata



Condition and performance of existing transportation structures

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Qualitative and quantitative information on the character and engineering properties of the soil and rock strata



Groundwater levels and environmental concerns



Slope stability condition, faults and other geologic hazards or constraints

The Manual for the NHI course on Subsurface Investigations (No. 132031, 2001) and the AASHTO Manual on Subsurface Investigations (1988) provide extensive information on conducting a geotechnical and subsurface investigation. 2.

REVIEW OF PROJECT REQUIREMENTS

The first step in performing a geotechnical investigation is a thorough review of the project requirements. It is important that geotechnical investigations be carefully planned, and coordinated between those who will obtain the field data and the end-users of the information. The Geotechnical Engineer should thoroughly understand the following project details and limitations before planning and performing the geotechnical investigation: 

Project location and size



Project type (realignment, improvement, bridge, embankment, rehabilitation, etc.)



Project criteria (alignment, approximate structure locations, approximate structure loads, approximate bridge span lengths and pier locations, cut and fill area locations, etc.)



Project constraints (ROW, environmental and biological assessments, permitting, etc.)



Project design and construction schedules and budgets

Depending on the stage of project development, the Geotechnical Engineer should have access to typical section, plan and profile sheets, and cross sections with a template for the proposed roadway showing cuts and fills. This project specific data aids the Geotechnical Engineer in planning the investigation to meet the project requirements. One goal of properly 02/14/2005



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planning a geotechnical investigation is to minimize exploration costs and the number of site visits needed to obtain vital design information. Prior to performing any fieldwork, the Geotechnical Engineer needs to initiate a request to obtain Entry Permits to the site through the Right of Way Division and be prepared to address any environmental concerns or limitations associated with the project. Following the identification of proposed exploration areas, utility locations and clearances need to be obtained. 3.

OFFICE REVIEW OF AVAILABLE DATA

After gaining a thorough understanding of the project requirements, all relevant available information on the project site should be collected and reviewed. Available data may consist of reports, maps, journal articles, aerial photographs, previous as built Plans, or even personal communications with individuals with local knowledge. Review of this information can provide a basis for understanding the geology, topography, and geomorphology of the area. An initial understanding of the engineering properties of subsurface materials and groundwater characteristics can often be obtained from this available data, which can help in developing the investigation program. 3.1

Topographic Maps

These maps portray physical features, configuration and elevation of the ground surface, and surface water features. Interpretations of these maps can aid the Geotechnical Engineer in determining: changes in relief and slope angles, landform and drainage characteristics, identification of potential landslide terrain, accessibility for field equipment, and possible problem areas. These maps are prepared by the U.S. Geological Survey (USGS) and are readily available. Topographic maps are sometimes prepared on a larger scale by the Department during early planning phases of a project. In addition, a review of existing data can yield information on the availability of nearby benchmarks that could be used in the field as control points for locating exploration borings. 3.2

Aerial Photographs

Aerial photographs are available from the Department and other sources. They are valuable in planning the site reconnaissance and, depending on the age of the photographs, show manmade structures, excavations, or fills that affect accessibility and the planned depth of exploration. Historical photographs can also provide a better understanding of how the project site has been modified throughout the years. 3.3

Geological Maps and Reports

Considerable information on the geological conditions of an area can be obtained from geological maps and reports. These reports and maps show the location and relative position of the different geological strata and present information on the characteristics of these materials. This data can be used directly to evaluate the rock conditions to be expected and indirectly to estimate possible soil conditions, since the parent material is one of the factors 02/14/2005



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controlling soil types. Geological maps and reports can be obtained from the USGS, Nevada Geological Survey, Nevada Bureau of Mines, university libraries, the Geotechnical Section, and other sources. 3.4

Soil Surveys

Soil surveys are compiled by the U.S. Department of Agriculture (Soil Conservation Service) usually in the form of county soils maps. These surveys can provide valuable data on surface soils including mineralogical composition, grain size distribution, and depth to rock, water table information, drainage characteristics, geologic origin, and presence of organic deposits. 3.5

Adjacent Projects

Data may be available on nearby projects from the Department, or from county or city governments. The Department may have soils data on file from State projects, as built drawings and/or pile driving records for existing structures. Existing boring information and well drilling logs, if available, can contain relevant information. This data can be useful in setting preliminary boring locations and depths and in predicting problem areas. Maintenance records for nearby roadways and structures can provide insight into subsurface conditions. For example, indications of differential settlement or slope stability problems can provide the Geotechnical Engineer with valuable information on the long-term characteristics of the site. 3.6

Rockfall Hazard Rating System

The Department ’ s Rockf al lHaz ar d Rat i ng Sy st em ( RHRS)dat abase shoul d be reviewed to identify rockfall concerns in or near a project site location. Information obtained from this database provides the Geotechnical Engineer quantitative data in this area of project development. 3.7

Hydrogeological Surveys and Well Logs

Hydrogeological surveys typically focus on the presence, depth, amount, and condition of groundwater. These resources can aid the Geotechnical Engineer by giving some indication about the presence and depth of groundwater in terms of its effect on construction conditions and its control over shear strength of soil and rock masses. The availability of water well logs produced by private drilling contractors that may be recorded by other State agencies should also be researched. In addition to groundwater information, such logs can serve as useful tools in providing general subsurface information. 3.8

Remote Sensing Data

Remote sensing data can effectively be used for large-scale regional interpretations of geologic structure, regional lineaments, drainage patterns, general soil and rock characteristics, and recognition of geologic hazards. Remote sensing methods, including such techniques as Landsat and Lidar, can be used to identify and evaluate topographic, 02/14/2005



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bathymetric, and surface features. The U.S. Army Corps of Engineers Engineering Manual EM-1110-1-1804 and the AASHTO Manual on Subsurface Investigations (1988) provide a more detailed discussion on the types and limitations of remote sensing methods. Remote sensing techniques generally have limited value for site-specific studies; however, they can be very useful for a regional or large-scale setting. The Geotechnical Engineer needs to be familiar with these methods, as well as their limitations and capabilities to determine if they are applicable for their project. 4.

FIELD RECONNAISSANCE

It is necessary for the Geotechnical Engineer to perform a field reconnaissance to develop an appreciation of the topographic, geologic and geotechnical concerns at the project site and become knowledgeable of access and working conditions. A reconnaissance should be performed only after an understanding of the project requirements has been reached, a review of the existing data has been completed, and applicable right-of-entry permit(s) have been obtained. The Geotechnical Engineer should perform the field reconnaissance with the final objective of being able to brief the project team on the key issues that will influence project design. Pertinent project information (project development documents) and other conceptual information should be obtained from the Project Designer before performing the site visit. As part of the reconnaissance, key site locations and conditions, and exploration equipment access routes should be photographed. The following factors should be defined by the field reconnaissance: 

Stratigraphy –Compare stratigraphy to information obtained from available data. Subsurface explorations and laboratory testing will ultimately define the soil and rock units.



Key Outcrops –Delineate outcrops or exposures that warrant further investigation in terms of structural mapping.



Existing Slopes –Assess the stability factors of major slope-forming geologic units. Natural slopes and any existing soil or rock slope failures should be evaluated and documented. Cut slope angles and orientations should be measured and their relative performance evaluated.



Ground and Surficial Water –Estimate the general nature of surface water and groundwater regimes at the project site. Develop concepts for future investigations.



Geologic Constraints –Identify geologic conditions that may tend to adversely affect project development plans (landslides, faults, flooding, erosion, etc.). Devise methods of investigating the degree of potential impact.



Explorations –Based on the information and the kinds of samples that may be required, determine the type(s) of exploration that would best accomplish the project needs.



Drilling Logistics –Define the type, approximate locations and depths of geotechnical borings. Determine approximate routes of access to each drilling location. Make note

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of any feature that may affect the boring program, such as accessibility, structures, overhead utilities, evidence of buried utilities, or property restrictions. Evaluate potential water sources for use during drilling operations. Evaluate potential concerns that may need to be addressed while planning an exploration program (permits, overhead utilities, equipment security, private property, etc.). If possible, exploration locations should be located with a Field Crew Supervisor. If this is not possible, a Field Crew Supervisor should be consulted regarding the use of borehole location feasibility. The Underground Services Alert (1-800-227-2600) (USADIG) must be called a minimum of two working days (preferably four days) prior to conducting subsurface explorations. It is desirable to review the proposed boring locations following utility locations to determine if any borings need to be relocated to avoid buried utilities. The presence of utilities may need to be rechecked for the adjusted boring locations. 

Environmental Considerations –Identify potential impacts the exploration program and the project may have on: subsurface materials, landforms, and the surrounding area. Determine if project areas are governed by special regulations or have protected status.

5.

FIELD MAPPING AND MEASUREMENTS OF ROCK DISCONTINUITIES

Field mapping should begin by observing road cuts, drainage courses, and bank exposures. A site plan or large-scale topographic map of the project area is essential for field mapping. The main objective of these observations is to confirm the general types of soil and rock present. Note any features that may assist in the engineering analysis, such as the angle and performance of existing slopes, or the stability of open excavations or trenches. The type and condition of vegetation may give an indication of ground and surface water regimes, as well as an indication of landslide or slope stability concerns. In addition, structures should be inspected to ascertain their foundation performance and their susceptibility to damage from construction-related ground vibrations or settlement due to embankment placement. For rock slopes, performance of slopes and the rockfall history are important indicators of how a new slope in the same material will perform. More detailed rock structural mapping entails observing and measuring lithologic contacts and the engineering characteristics and orientation of rock discontinuities that make up the rock mass. The measurements are typically made with a Brunton or Clar compass and consist of determining the strike and dip (dip and dip direction) of rock discontinuities such as faults, joints, foliation, shear and bedding planes, and contacts with other rock units. These measurements can be presented graphically on a spherical projection such as an equal area stereonet. A more detailed discussion on rock st r uct ur almappi ngi sgi v eni nt hePar t i ci pant ’ sManualf ort heNHIcour se“ RockSl opes” (Module 5: No. 132035, 1998). The AASHTO Manual on Subsurface Investigations (1988) describes the procedures for engineering geological mapping. It also provides suggestions for preparing geologic maps for different applications, such as Project Area Geologic Maps, ROW Geologic Maps, File 02/14/2005



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Geologic Maps, Site Geologic Maps, and other special mapping. 6.

FIELD-DEVELOPED CROSS-SECTIONS

Field-developed cross-sections are useful to nearly all types of site-specific geotechnical investigations. Their use can be applied to excavation and placement of materials; foundations and slopes; specific development of groundwater and aggregate resources; and for the graphic portrayal and analysis of significant features related to slope stability, seismicity, drainage, or other characteristics. Although these cross-sections lack the precision of high order engineering surveys, preparing them provides an excellent opportunity to observe the project area and apply the scientific method in resolving surface and subsurface relationships and other field observations. Standard cross-sections prepared by survey crews or taken from digital terrain models do not depict the interpreted geotechnical relationships and other features that may prove very important during the design process. Another advantage is that the sections are developed and plotted during the reconnaissance, so discrepancies can be identified and resolved immediately. This provides a high level of confidence when used later in the office. The cross-section field gear typically includes a field notebook, cloth tape, hand clinometer, calculator, and Brunton compass. Laser range finders can simplify measurements, particularly for steep inaccessible slopes. Measurements include all slope breaks and other identifiable, geological features such as landslide cracks and groundwater features. The significance of each feature is described in the field notebook. Since slope breaks commonly occur as the strength characteristics of the subsurface material changes, many times the slope breaks represent contacts between different soil and/or rock units. Measurements of the contact orientation (strike, dip and surface trace) are normally denoted where appropriate in the field notebook. The points comprising the cross-sect i onshoul dbepl ot t edongr aphpaperas“ x ”and“ y ” coordinates while in the field. The coordinates can be readily calculated from the slope distance and angle between each point with the aid of a calculator. Include the interpretations of the surface and subsurface materials and relationships on the section along with relevant estimates of engineering parameters. The section should show the distribution of soil and rock units, estimated location/elevation(s) of surface and subsurface water, and original ground lines prior to any previous excavation, filling or slope movements. As these interpretations are developed, plan any explorations that may be needed to confirm the subsurface model that will be used in the analysis and design phase. For a reference of this field technique, refer to USDA, Forest Service Publication EM-7170-13,1994,ent i t l ed“ Sl opeSt abi l i t yRef er ence Gui def orNat i onalFor est si nt heUni t edSt at es” ,Vol ume1. 7.

SUBSURFACE EXPLORATION METHODS

The information obtained from the steps discussed above is used to develop a subsurface exploration program. Field exploration can commence when right-of-entry permit and utility clearances have been issued. Many methods of field explorations exist. The 02/14/2005



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subsections below contain brief descriptions of the most common methods. 7.1

Test Pits and Trenches

Test pits and trenches are the simplest methods of observing subsurface soils. They consist of excavations performed by hand, backhoe, or dozer. Hand excavations are often performed with posthole diggers or shovels. They offer the advantages of speed and ready access for sampling. They are severely hampered by limitations of depth; and they cannot be used in soft or loose soils, boulders or below the water table. Upon completion, the excavated test pit should be backfilled with the excavated material or other suitable soil material. The backfilled material should be compacted to avoid excessive future settlements. Tampers or rolling equipment may be used ot facilitate compaction of the backfill. Excavations within existing roadways should be backfilled with granular material and compacted in lifts to restore subgrade support and the pavement should be properly patched. Any test pit or excavated area located near planned structure footings or pavement must be surveyed to determine the precise location of the excavation. This information must be presented in Construction Plans and Special Provisions to ensure the area will be re-excavated and properly compacted to the extent required. In the case of test pits excavated through existing pavements, the pavement should be properly patched. The backfilled material should be compacted to avoid excessive future settlements. Tampers or rolling equipment may be used to facilitate compaction of the backfill. Excavations within existing roadways should be backfilled with granular material and compacted in lifts to restore subgrade support. Where pits are located in agricultural areas or other areas used to support plant growth, the backhoe operator should be instructed to keep the topsoil (or at least the finer upper-layer of the profile) and overburden separate from any gravel encountered in the pit. Upon completion of the pit, the operator should backfill in a sequence (generally with the coarsest material in the bottom of the pit) such that the backfilled pit area is reestablished to support vegetation. 7.2

Hand Auger Probes

Hand auger probes are manually operated. Solid or hollow stem augers can be used to quickly and cheaply observe shallow (less than 15 feet) subsurface conditions. They cause minor disturbance to the ground surface, but are difficult to advance in rocky or dense material. 7.3

Exploration Drilling Techniques

Borings are the most common method of exploration. They can be advanced using a number of methods. Discussions of drilling methods are described in the following manuals: 1) U.S. Army Corps of Engineers, Soil Sampling Engineering Manual, 2) AASHTO, Manual on Subsurface Explorations, and 3) FHWA, Subsurface Investigations, NHI Course No. 132031. The most common methods are discussed below: 02/14/2005



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7.3.1 Solid Flight Auger Borings Auger borings are advanced into the ground by rotating the auger while simultaneously applying a downward force using either hydraulic or mechanical pressure. The auger is advanced to the desired depth and then withdrawn. Samples of cuttings can be removed from the auger; however, the depth of the sample can only be approximated. These samples are disturbed and should be used only for material identification. This method is generally used to establish shallow soil strata and water table elevations, or to advance to the desired stratum before Standard Penetration Testing (SPT) or undisturbed sampling is performed. However, it cannot be used effectively in soft or loose soils below the water table. In addition, this method has limited capabilities in dense, rocky material where it may encounter refusal. See ASTM D 1452 (AASHTO T 203). 7.3.2 Hollow-Stem Auger Borings A hollow-stem auger consists of a continuous flight auger surrounding a hollow drill st em.Acent r al“ pl ug” ,or“ but t er f l y ”bi t ,att heendofadr i l lr odi susedt opr ev entsoi lf r om entering the hollow stem as the hole is advanced between samples. The hollow-stem auger is advanced in a manner similar to Solid Flight Auger; however, removal of the hollow stem auger i snotnec essar yf orsampl i ng. The“ pl ug” ,or“ but t er f l y ”bi t ,i sr emov edand samples are obtained through the hollow drill stem, which acts like a casing to hold the hole open. This increases usage of hollow-stem augers in soft and loose soil. Usually no drilling mud is required, which could otherwise interfere with accurate groundwater level readings. In addition, this method of drilling is extremely fast, cost effective, and requires little to no water. Bel ow t hewat ert abl e,r emov aloft hecent er“ pl ug” ,or“ but t er f l y ”bi t ,candi st ur bsandand affect the validity of the SPT. One option that can be considered, when this condition develops in leading to questionable SPT results, is to add water or drill mud to the inside of the stem to create a reverse head of water and prevent heaving. Water should also be added to t hebor ehol ewhi l eaugur i ngcl ay eysoi l st ohel ppr ev ent“ baki ng”oft hemat er i alduet ot he heat generateddur i ngr api dadv ancementoft heauger s. Thi s“ baki ng”ofcl aysoi l scan adversely affect the permeability of the subsurface material. Another disadvantage of this method is that refusal may prematurely be encountered in boulders or dense rocky soils. See ASTM D 6151 (AASHTO T 251). 7.3.3 Wash Borings In this method, the boring is advanced by a combination of the chopping action of a light “ f i sht ai l ”bi tandt hej et t i ngact i onofwat erf l owi ngt hr ought hebi t .Thi smet hodi susedonl y when precise soil information is not required between sample intervals in loose, fine granular material. Generally, casing is required to stabilize the walls of the borehole. Large quantities of water are required for this method of drilling. Generally, there are better, more efficient methods available to drill a borehole.

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7.3.4 Mud Rotary Drilling This method consists of using a rotary drill with rotating thick-walled, hollow, drill rods usually attached to a tri-cone bit. Drilling mud is circulated from a mud tub, and then through the drilling rods as the drill rod is advanced. The drilling mud lifts the drilling cuttings out of the borehole while maintaining hole stability. The drill cuttings are screened and separated from the drilling mud, which is then recirculated. To collect a sample, the drill rods and bit are pulled out of the hole and are replaced with drill rods and the required sampling device. This method is fast, and provides excellent sampling and in situ testing data due to minimal disturbance to the soils at the bottom of the borehole prior to sampling. It is effective in all soil types except for very gravelly material with cobbles and boulders. No information can be reliably obtained about groundwater levels during the drilling operation, and the soil material between sampling intervals is difficult to observe from the drilling mud return. 7.3.5 Air Drilling This type of drilling uses compressed air to remove cuttings from the borehole as the drill bit is advanced. Both rotary or percussion techniques can be utilized and either open hole (rotary reverse circulation) or underreamed casing advancement (ODEX) can be used in the drilling process. SPT samples can be obtained; however, the materials between samples are highly disturbed. This type of drilling is generally fast, but expensive, and is most useful when drilling deep holes in dense gravels and boulders where traditional Hollow Stem Auger and Mud Rotary techniques cannot drill or sample. 7.3.6 Percussion Drilling In this method, the drill bit advances by power chopping with a limited amount of water in the borehole. Slurry must be periodically removed. The method is not recommended for general exploration because of the difficulty in determining stratum changes and in obtaining undisturbed samples. However, it is useful in penetrating materials not easily penetrated by other methods, such as those containing boulders. 7.3.7 Coring A sampling barrel is advanced through rock by the application of downward pressure during rotation. Circulating water removes ground-up material from the hole, while also cooling the bit. The rate of advance is controlled to obtain the maximum possible core recovery. A continuous rock core sample is sometimes obtained from this drilling method. Core drilling is the most widely used method to explore subsurface rock formations. It is preferable to perform rock coring with as large a core barrel as possible in order to optimize core recovery and minimize core damage due to drilling action. An HQ-Size System is recommended. Refer to ASTM D 2113 (AASHTO T 225). A list of core barrel sizes is shown in Figure 5.1. 7.4

Soundings A sounding is a method of exploration in which either static or dynamic force is used to

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cause a rod tipped with a testing device to penetrate soils. This method can be useful to determine the depth to harder strata or rock from the resistance to penetration. Cone penetrometers are the most common equipment that uses the sounding method. The cone penetrometer is utilized to obtain a measure of the soil resistance for the entire depth of the penetration. It is generally used for fine-grained cohesionless and cohesive soils. The disadvantage of this investigation method is that no samples are usually obtained. The resistance to penetration can be measured and correlated to various soil properties. 7.5

Geophysical Methods

Geophysical exploration methods can sometimes provide general subsurface profile information, such as the depth to bedrock, depth to groundwater, and the extent of granular/rock areas, peat deposits, or subsurface anomalies. Geophysical methods of exploration can provide a rapid and economical means of supplementing subsurface borings and test pits. These exploration techniques are most useful for extending the interpretation of subsurface conditions beyond what is determined from small diameter borings. A limitation of these techniques is that no samples are recovered. It must be emphasized that geophysical exploration methods might not be successful in all situations and should be carefully evaluated to determine whether any are appropriate for the specific project requirements and site conditions. The reliability of geophysical exploration results can be limited by several factors, including the presence of groundwater, nonhomogeneity of soil stratum thickness, gradation or density, and the range of wave velocities within a particular stratum. Subsurface strata that have similar physical properties can be difficult to distinguish with geophysical exploration methods. Because of these limitations, for most design applications, geophysics should be considered a secondary exploration method to drilling, and should generally be accompanied by conventional borings. An experienced professional should interpret the field data. For additional information, see ASTM D 6429 and U.S. Army Corps of Engineers, Engineering Manual EM-1110-1-1802. Geophysical exploration techniques can be grouped into two categories: 1) methods conducted from the ground surface, and 2) methods conducted in or between boreholes. Passive methods include the use of gravimetric, electric, magnetic, thermometric, and nuclear techniques. Active methods include the use of seismic, acoustic, electric, electromagnetic, and nuclear techniques. Geophysical exploration methods commonly used for transportation engineering purposes include: 7.5.1 Seismic Refraction and Reflection These methods rely on the fact that shock waves typically travel at different velocities through different materials. The times required for an induced shock wave to travel from the energy source to vibration detectors (geophones) after being refracted or reflected by the various subsurface materials are measured. The measured seismic velocities are used to interpret certain material properties and the thickness of the units that comprise the subsurface 02/14/2005



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profile. Seismic refraction is limited to profiles in which velocities increase with depth. Seismic investigations can be performed from the surface or from various depths within borings. For cross-hole seismic techniques, see ASTM D 4428. For the seismic refraction method, see ASTM D 5777. 7.5.2 Electrical Resistivity This method is based on the differences in electrical conductivity between subsurface strata. An electric current is passed through the ground between electrodes and the resistivity of the subsurface materials is measured and correlated to material types. Several electrode arrangements have been developed, with the Wenner (four equally spaced electrodes) being the most commonly used in the United States, see ASTM D 6431. 7.6

Ground Penetrating Radar (GPR)

The velocity of electromagnetic radiation is dependent upon the material through which it is traveling. GPR uses this principle to analyze the reflections of radar signals transmitted into the ground by a low frequency antenna. Signals are continuously transmitted and received as the antenna is towed across the area of interest. The interpreted results yield a profile of the subsurface material interfaces. The depth of signal penetration is limited in finer grained soils, see ASTM D 6432. 7.7

Nondestructive Testing - Evaluation of Existing Structures

Occasionally, the Geotechnical Engineer is involved in evaluating an existing structure foundation for new loading conditions. This typically occurs as part of a seismic or scours vulnerability assessment. An important part of the assessment is the type, depth, and condition of the structure foundation. The sources for this information may be as-built drawings, construction records, and Construction Plans for the structure. If no information is available, the Geotechnical Engineer may need to use Nondestructive Testing techniques (NDT) to characterize the foundation elements. All NDT methods are classified in two general categories, surface methods and downhole methods. Surface methods are generally less expensive, but are limited by foundation geometry and subsurface conditions. Surface methods typically cannot yield any information below the point where there is a sharp change in the impedance of a foundation element. For instance, if NDT methods were used on a bridge column, the test would not tell the Geotechnical Engineer anything about the pile or shaft elements below the pile cap. Downhole methods provide more definitive information regarding foundation geometry, but the costs are generally higher due to drilling requirements. 8.

SOIL SAMPLING

Common methods of soil sampling during field explorations include those listed below. All samples should be properly preserved and carefully transported to the laboratory to maintain sample integrity, see ASTM D 4220. 02/14/2005


GEOTECHNICAL INVESTIGATION PROCEDURES 8.1

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Disturbed Sampling

Disturbed sampling refers to methods of retrieving samples that incidentally cause the material to be remolded or at least partially altered. It should be understood that disturbed samples are generally not suitable for specialized tests requiring undisturbed soil specimens. However, disturbed samples have value for many geotechnical tests and are usually easier to obtain. 8.1.1 Bag (Bulk) Samples Bulk samples can provide a large amount of representative soil for compaction and subgrade testing. Bag samples are usually obtained from test pits. In some cases, bulk samples can be obtained during auger drilling, collecting materials as they come to the surface in the flight of the auger. The auger method is less desirable because the depths of the sample cannot be accurately defined and some mixing of the soil occurs. A preferred approach when using an auger is to drill a shallow hole, then to remove the auger and collect a sample from the sidewall of the hole (after first clearing the smear zone). The quantity of a bulk sample depends on the type of testing to be performed, but can range up to 50 pounds or more. Testing performed on these samples could include classification, moisture content, compaction maximum density, R-value and pH and resistivity (corrosivity). A portion of each sample should be placed in a sealed container in order to accurately determine the natural moisture content. The size of bulk samples obtained for testing rock quality for aggregate purposes can be significant in order to process and select representative materials. 8.1.2 Cuttings Samples In limited cases and as a last resort, samples of cuttings can be obtained from drilling operations to augment materials collected in sampling tubes. Cuttings samples can be used to try to identify major changes in lithology during drilling operations, particularly when normal tube sampling methods do not recover sufficient materials for this purpose. Examples of cuttings samples include material ejected from air rotary drilling, material that is pushed to the surface on the flights of an auger, and material that is screened from the drill mud return (mud rotary method). Cuttings samples are highly disturbed, contaminated, and sometimes altered (in size), and therefore caution and judgment must be exercised when selecting, evaluating and classifying such samples. The depths from which cutting samples are obtained can only be roughly estimated, but these estimates can be aided by noting the depths where changes in drilling action occur. 8.1.3 Split Spoon Sampler Split spoon samplers, also known as split barrel samplers, are used in conjunction with the Standard Penetration Test. The sampler is a 2-inch (O.D.) split spoon, which is driven into the soil with a 140-pound hammer dropped 30 inches. The split spoon sampler is withdrawn and the sample is removed after the sampler has been driven 18 inches. The sum of the number of hammer blows, required to drive the sampler the second and third six-inch 02/14/2005



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increments is the standard penetration value referred to as the N-value (blows per foot). Nvalues can be correlated to a number of different design parameters including relative density, angle of withdrawal, friction and shear strength. The sample should be immediately examined, logged and placed in sample jar or bag for storage. These samples are disturbed and are not suitable for strength or consolidation testing. They are suitable for moisture content, gradation, and Atterberg limits tests, and are valuable for visual identification, see ASTM D 1586. 8.1.4 California Modified Sampler California Modified Sampler (CMS) or Dames and Moore Sampler are two names for the same sampler. The split barrel samples are similar to split spoon samples used with the SPT test. The CMS is a 3-inch (O.D.) split barrel, which is driven into the soil typically with a 300-pound hammer, but the Department currently uses a 140-pound hammer, dropped 30 inches. The CMS is threaded at both ends for accepting inner rings that are 2.36-inches I.D. by .98-inches high. These ring samples can be used for various soil property tests; however, they are considered disturbed samples. Generally, this sampler is used to facilitate sample recovery in coarser-grained material due to its larger diameter as compared to the split spoon (SPT) sampler. N-values obtained from the penetration of this sampler are sometimes correlated to SPT values. However, these correlations are not standardized, and engineering judgment should be applied when they are used. The CMS can be configured many different ways. With various barrel bodies, the sampler typically ranges from 12 to 30 inches in length. Several different types of shoes (sampler tips) allow for additional accessories to be used with the sampler. Among these are br assl i ner s,soi lr et ai ner s,andt ubeex t ensi ons.Theseaccessor i esenhancet hesampl er ’ s capabilities to collect samples. The CMS can be used with a tube extension in fine-grained soils, typically clays or silts, to obtain relatively undisturbed samples. It acts similar to a Shelby Tube sampler. When the tube extension is used, the sampler is pushed into the ground with a smooth and continuous thrust. 8.2

Undisturbed Block Sampling

Samples can be carefully carved from test pits for special testing in the laboratory. The advantage of block samples is that the test pit offers a broad area to detect critical materials and ability to obtain the exact amount of the desired material. The size of the sample should be large enough to perform planned laboratory testing. The block samples should be carefully handled and should be protected with a moisture-proof barrier (i.e., plastic wrap and wax) and placed within a sturdy and stable container so the sample is fully supported/constrained. For block samples, the dimensions of the sample are controlled by the thickness of specimen of interest and by the size of the box used to hold the sample. A column of the soil is carefully exposed so that, when the sample box is centered over the column, a one-inch open space is left on all sides of the sample and a half-inch space is left at the top. The empty areas are then filled with microcrystalline wax. After the wax congeals, the top of the box is 02/14/2005



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attached and the sample is carefully detached from the underlying ground with a spade. The sample is inverted and a half-inch of material is removed. This area is filled with wax. After it congeals, the bottom of the box is attached and the sample is ready for transport to the laboratory. 8.3

Undisturbed Sampling Using Thin Wall Samplers

Undisturbed samples are required for certain tests such as peak shear, consolidation, swell potential, permeability, and density tests. There are several methods available for obtaining undisturbed samples, and would depend on the investigation equipment being used and the state of the soils in situ. Care of the samples is also critical to maintaining undisturbed conditions between drilling, transportation, storage and testing. 8.3.1 Shelby Tube Sampler A Shelby Tube is a thin walled steel tube, usually 3 inches (O.D.) by 30 inches long. The beveled cutting edge of the Shelby tube is slightly smaller in diameter than the inside of the tube, which allows the sample to slide easily in the tube with little disturbance. The thin wal l sampl eri ssui t abl ef orsampl i ngal l cohesi v esoi l s.Thet ubei spushed24”wi t hasmoot h, continuous thrust. Difficulty may be encountered in sampling very soft and wet soils that tend to drop out of the sampler. Damage to the sampling tube (resulting in a poor sample) sometimes occurs when sampling hard, cemented, or gravelly soils. Good samples must have sufficient cohesion to remain in the tube during withdrawal. Cohesionless soils will likely need improved sampling methods, as described below. If sample recovery becomes difficult, i.e., the sample stays in the ground, the tube should be left in place for roughly 10 to 15 minutes. During this waiting period, the sample will swell slightly to fill the sampler, increasing the likelihood of retaining the sample when the tube is retracted. This produces a relatively undisturbed sample. Care should be taken to not over push the sample to avoid disturbance. The ends of the Shelby Tube should be properly sealed immediately upon withdrawal. Refer to ASTM D 1587 (AASHTO T 207). The sample is suitable for unit weight, triaxial, direct shear, simple shear, and consolidation tests. 8.3.2 Stationary Piston Sampler This sampler has the same standard dimensions as the Shelby Tube described above. A piston is positioned at the bottom of the thin wall tube while the sampler is lowered to the bottom of the hole, thus preventing disturbed materials from entering the tube. The piston is locked in place on top of the soil to be sampled. A sample is obtained by pressing the tube into the soil with a continuous, steady thrust. The Stationary Piston is held fixed on top of the soil while the sampling tube is advanced. This creates suction while the sampling tube is retrieved, thus aiding in retention of the sample. This sampler is suitable for soft to firm clays and silts. Samples generally have a better recovery ratio than those obtained by use of the Shelby Tube. Care should be taken to not overdrive the sampler to avoid disturbance.

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8.3.3 Floating Piston Sampler This sampler is similar to the stationary piston sampler, except that the piston is not fixed in position but is free to ride on the top of the sample. The soils being sampled must have adequate strength to cause the piston to remain at a fixed depth as the sampling tube is pushed downward. If the soil is too weak, the piston will tend to move downward with the tube and a sample will not be obtained. This method should therefore be limited to stiff or hard cohesive materials. 8.3.4 Retractable Piston Sampler This sampler is similar to the stationary piston sampler. However, after lowering the sampler into position, the piston is retracted and locked in place at the top of the sampling tube. A sample is then obtained by pushing the entire assembly downward. This sampler is used for loose or soft soils. 8.3.5 Hydraulic (Osterberg) Piston Sampler This sampler is especially suitable for sampling soft to very soft clays and silts, and is sometimes effective in obtaining samples of cohesionless, silty sands and sands. In this sampler, a movable piston is attached to the top of a thin wall tube. Sampling is accomplished as hydraulic pressure pushes an inner sampler head and attached sample tube until it contacts a stationary piston positioned at the top of the soil sample. The distance over which the sampler is pushed is fixed. It cannot be overpushed. 8.4

Partially Disturbed Sampling

Partially disturbed sampling refers to methods of retrieving samples that incidentally cause the material to be partially altered. Hard soil conditions might make undisturbed sampling impossible, and therefore several methods were developed to obtain specimens of better quality. It should be understood that partially disturbed samples do not represent in situ conditions and generally do not provide reliable results for specialized tests such as peak shear, consolidation, swell potential, and permeability. 8.4.1 Denison Sampler This sampler is a large diameter, double tube core barrel, which is effective in obtaining 5-7/8-inch diameter samples of hard cohesive soils, soft rock, cemented soils, and soils containing gravel that cannot be obtained with push-type samplers. This sampler consists of a rotating outer barrel with cutting teeth on the bottom and an inner barrel with a smooth cutting shoe. The sample is captured in a very thin inner liner, which facilitates retrieval and handling. Core catchers should not be used unless absolutely necessary to retain the soil sample. Care should be taken not to overdrive the sample to avoid disturbance. 8.4.2 Pitcher Sampler This sampler is a double tube core barrel and is effective for the same soils as the 02/14/2005



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Denison sampler. The primary advantage the Pitcher sampler has over the Denison sampler is that the Pitcher sampler automatically adjusts the amount by which the inner barrels lead the cutting bit as the hardness of the soil varies. The Pitcher sampler can also accept a standard thin wall sample tube in lieu of the inner barrel/liner. 8.4.3 Sprague & Henwood Sampler This is a triple tube sampler designed for sampling overburden materials, and is an improvement over the Denison and Pitcher samplers. 9.

ROCK SAMPLING

Rock samples can be obtained from outcrops, test pits, or rock cores using drilling oper at i ons. Sampl esobt ai nedf r om out cr opsort est pi t sar et er med“ gr abs ampl es ” .Ty pi c al l y , the sample sizes should be small enough to carry, but large enough to be tested in a point load device or utilized as hand specimens. These samples should be labeled, and the location where they were obtained should be identified on a site map. Rock cores are obtained using core barrels equipped with diamond or tungsten carbide tipped bits. There are three basic types of core barrels; single tube, double tube, and triple tube. Use of double and triple tube core barrel systems are preferred since single tube core barrels generally provide poor recovery rates, see below. To protect the integrity of the core from damage (minimize extraneous core breaks), a hydraulic ram should be used to extrude the core from the barrel. See ASTM D 2113 (AASHTO T 225). Refer to ASTM D 5079 for practices of preserving and transporting rock core samples. 9.1

Double Tube Core Barrel

The double tube core barrel consists of an inner core barrel tube and an outer tube that serves as the drill rod. The cutting end of the core barrel is equipped with a diamond or tungsten carbide drill bit. As coring progresses, fluid is introduced downward between the inner and outer tubes to cool the bit and to wash ground-up material to the surface. The inner tube protects the core from the highly erosive action of the drilling fluid. In a rigid type core barrel, both the inner and outer tubes rotate. In a swivel type, the inner tube remains stationary while the outer tube rotates. Several series of swivel type core barrels are available. The size of core that can be recovered is governed by the size of the drill bit. For standard applications, these vary from 1.062-inch up to 3.270-inch O.D. Larger diameters generally obtain better core recovery in softer, highly erodible or highly fractured materials. The minimum diameter core obtained should be no less than A-size (1.062- to 1.185-inch O.D.). As a rule, it is recommended that a core size of H (2.406- to 3.000-inch O.D) be routinely used. Commonly used rock core sizes are included in Figure 5-1. 9.2

Triple Tube Core Barrel

Triple tube core barrel systems are similar to the double tube system, but include an additional inner liner. Two types of inner liners are used to retain the core, a clear plastic solid 02/14/2005



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tube or a thin metal split tube. This barrel best preserves recovered fractured and poor quality rock cores in their in situ state. 9.3

Oriented Core

In some rock slope applications, it is important to understand the precise orientation of rock discontinuities for the design. Orienting recovered rock core so it can be properly mapped and evaluated, as though it were still in place, requires special core barrels. In the past, core barrels were weighted on one side and used in an inclined boring. The heavier side of the barrel generally stayed on the down side of the hole allowing the core to be properly oriented when removed. Other techniques, such as using clay to make an impression of core run ends, have also been used for this purpose. Currently, specialized core barrels that scribe a reference mark (line) on the side of the core as it is drilled are more routinely used. Special recording devices within the core barrel relate known azimuth orientations to the reference mark so that when the core is subsequently removed from the core barrel, it can be oriented to the exact position it existed in situ. These specialized core barrels are relatively expensive, and require additional training for proper use and interpreting the results. 9.4

Borehole Television Camera

Boreholes can be accessed to visually inspect the condition of the sidewalls and distinguish gross changes in lithology by using specialized television cameras. These downhole cameras can also be used to identify fracture zones, shear zones, and joint patterns in rock core holes. Refer to AASHTO Manual on Subsurface Investigations, Section 6.12. 10.

EXPLORATION DIFFICULTIES

As discussed in the AASHTO Manual on Subsurface Investigations Section 7.8, limitations and difficulties may be encountered during explorations, which are common to all exploratory techniques. They are usually a result of site-specific geologic conditions and/or a function of the improper equipment or technique being utilized. Several of these limitations and difficulties are described below. 10.1

Improper Drilling Techniques

All Geotechnical Engineers and field supervisors need to be aware of potential drilling problems and to avoid them in order to properly obtain field information and samples. See AASHTO Manual on Subsurface Investigations, Section 7.12 and FHWA, Subsurface Investigations, NHI Course No. 132031, Section 3.5. The following is a partial listing of common errors: 

Not properly cleaning slough and cuttings from the bottom of the borehole. The driller should not be allowed to sample through slough. Preferably the driller should reenter the boring and remove the slough before proceeding.



Jetting should not be used to advance a split barrel sampler to the bottom of the boring.



Poor sample recovery due to improper use of sampling equipment or procedures.

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

When sampling soft or noncohesive soils with thin wall samplers (i.e., Shelby Tube), it may not be possible to recover an undisturbed sample because the sample will not stay in the barrel. The driller should be clearly instructed not to force recovery by overdriving the sampling barrel to obtain a sample.



Improper sample types or insufficient quantity of samples. The driller should be given clear instructions regarding the sample frequency and types of samples required. The field supervisor/driller must keep track of the depth of the borings and the materials being recovered at all stages of the boring to confirm the sampling interval and obtain appropriate samples of changing soil and/or rock formations.



Improper hole stabilization. Rotary wash borings and hollow-stem auger borings below the groundwater level require a head of fluid to be maintained within the drill stem at all times to prevent materials from surging up into the holes, casings, or augers. When the drill rods are withdrawn, or as the hollow stem auger is advanced, this fluid level will tend to drop, and must be maintained by the addition of more drilling fluid.



Sampler rods lowered into the boring with pipe wrenches, rather than hoisting plug. The rods may be inclined and the sampler can hit the boring walls, filling the sampler with debris.



Improper procedures for performing Standard Penetration Tests. The field supervisor and driller must assure that the proper weight and hammer drop are being used.



Catheads cannot be used on any Department projects. All hammers to be used on Department projects must be automatic, and calibrated within the last two years using a pile driving analyzer.

10.2

Sample Recovery

Occasionally, sampling is attempted and little or no material is recovered. In cases where a split barrel or some other type of sampler is used to recover a disturbed sample, it is appropriate to make a second attempt to recover the material immediately following the first failed attempt. In such instances, the sampling device may be modified to include a retainer basket, a hinged trap valve, or other measures to help retain the sample. In cases where an undisturbed sample is desired, the Geotechnical Engineer should direct the driller to drill to the bottom of the attempted (disturbed) sampling interval and repeat the sampling attempt. The sampling method should be reviewed, and the sampling equipment should be checked to understand why no sample was recovered (such as a plugged ball valve). It may be appropriate to change the sampling method and/or the sampling equipment, such as waiting a longer period of time before extracting the sampler, or extracting the sampler more slowly and with greater care, etc. If recovering a sample at a specific depth is necessary, a second boring may be advanced to obtain a sample at the prescribed depth using the improved technique. Generally, sample recovery less than 10% is considered inadequate for representative sampling. However, this criteria may be waived for the specific situation (i.e., in thick, uniform 02/14/2005



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deposits). Various sampling devices equipped with check and pressure release valves, sample retaining springs, baskets, and lifters should be used. Occasionally, sample recovery may be enhanced by modifying the equipment or the drilling techniques. 10.3

Sample Disturbance

Ther ei snowayt oobt ai nat r ul y“ undi st ur bed”sampl eusi ngav ai l abl esoi lsampl i ng techniques. Block sampling continues to be the most reliable method for minimizing sample disturbance. However, because gaining access to the zone to be sampled can be limited by the depth of overlying material and because the sampling process is fairly rigorous and time consuming, most samples are obtained via drilling. The selection of the correct sampling tool, drilling technique, and borehole stabilization method should be based on the soil type being sampled and the subsurface conditions. The incorrect preservation and shipment of samples may further disturb the specimens to the point where they are no longer usable. 10.4

Obstructions

The termination of an exploration above the required design depth due to boulders, fill material, excessively dense materials, and other obstructions may occur during any investigation. When this occurs, it usually implies that the correct exploration method might not have been selected for the anticipated subsurface conditions. Specialized tools and equipment are available to enhance the capacity of conventional drilling equipment. In some cases when obstacles are anticipated, a solution is to redrill the boring a few feet away. 10.5

Problematic Geologic Conditions

More thought and care should be given in selecting proper sampling equipment and sampling techniques when conducting subsurface exploration in problematic geologic conditions. Following is a list of some of problematic geologic conditions: 

Organic Soils



Metastable Soils (loess, alluvial deposits & mudflows )



Expansive Soils or Rocks



Sensitive Clays



Hydrocollapsible Soils



Moving Ground (slides)



Meander Loops & Cutoffs



Abandoned Mined Areas



Normally Consolidated Clays



Caliche



Loose, Granular Soils

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GEOTECHNICAL INVESTIGATION PROCEDURES 

Noxious or Explosive Gases



Artificial Fill



Weathered Shale Rocks



Wet or Saturated Soils

10.6

Groundwater Conditions

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Groundwater can affect the stability of boreholes, especially in cohesionless soils (sands and silts). Water flowing into the hole could cause caving and quick (liquefying) conditions, which would artificially reduce the SPT blow counts being measured, as well as make drilling and sampling progress difficult. Drill fluids are typically used to stabilize the borehole in such situations. Where precise water level data is important, the affects of drilling water additives (bentonite) on the permeability of certain soils should be evaluated. In soils with lower permeability and flow rates, such as in silt or silty sand, the use of bentonite mud can dramatically limit the movement of water by coating the walls of the boring. A bentonite coating can reduce the likelihood that piezometer readings will represent true ground water levels or that the water levels in the boring will respond accurately to natural groundwater changes. In these situations, alternative drilling techniques, such as using a casing advancer or hollow stem auger, should be considered to produce a stable borehole without relying on additives that can affect permeability. Following drilling, especially whenever low permeability conditions exist, the Geotechnical Engineer should wait an adequate period of time for the water level to reach equilibrium within the borehole before initiating groundwater measurements. It is preferred that a groundwater measurement be taken 24 hours after completing the boring to allow the water level to reach equilibrium. In fine-grained soils, depending on the permeability, this period may not be adequate. The installation of permanent or temporary observation wells, which provide access for measuring the groundwater table over a longer period, can be used in this case. Observation wells are generally an inexpensive safeguard against erroneous data regarding the presence and behavior of the groundwater conditions. 10.7

Contaminated Sites

When an investigation is to be performed, acquisition records for newly obtained rightof- way indicate the most recent land use for the area. On rehabilitation projects, where the only planned activities are shown on the existing right-of-way, the information available may vary from very complete to none. The Geotechnical Section does not perform HazMat explorations, testing, or evaluations. If contaminants are suspected, the Department may hire a Consultant with expertise in this field. There are many problems and issues inherent in sampling and handling contaminated soils. However, it is necessary for all involved in geotechnical investigations to be aware of the salient points of these procedures. The U.S. Environmental Protection Agency (EPA) 02/14/2005



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document number 625/12-91/ 002t i t l ed“ Descr i pt i onandSampl i ngofCont ami nat edSoi l s–A f i el dPocket Gui de”cont ai nsgui del i nes , bac k gr oundi nf or mat i on, andalist of useful references on the topic. During an investigation, if unexpected contaminants are encountered, the Field Crew staff should immediately cease explorations and inform the Geotechnical Engineer. Initial actions may require demobilization from the site. Some signs of possible contamination are: 

Prior land use (e.g., old fill, landfills, gas stations, etc.).



Stained soil or rock.



Apparent unnatural lack of vegetation or presence of dead vegetation and trees in the local site context. While in some places this could indicate contamination, in others it is just normal desert conditions.



Odors. Highly organic soils often could have a rotten egg odor that should not be construed as evidence of contamination. However, this odor may also be indicative of highly toxic hydrogen sulfide. Field Crew staff should be instructed as such.



Presence of liquids other than groundwater.



Marks of prior ground fires (at landfill sites). Established landfills emit methane gas, which is colorless and odorless, and in high concentrations in the presence of sparks or fire, explode.



Presence of visible elemental metals (i.e., mercury).



Low (<2.5) or High (>12.5) pH.

11.

INSTRUMENTATION

Geotechnical instrumentation may be required, depending on the scope of the project, the design elements, and the site conditions. Selecting and installing the proper instruments correctly are important. A discussion of installation procedures for selected instruments is provided in Appendix A of the AASHTO Manual on Subsurface Investigation, 1988. An indepth discussion on the installation of Inclinometer Casings is provided in Section 4.1.5 of Chapter 11 of the TRB Special Report 247, Landslides: Investigation and Mitigation. Such summaries are not intended to be a strict guideline, nor are they all inclusive of the variety of methods and procedures that may be used for the installation of instruments. The installation techniques may need to be customized to address particular subsurface issues. 12.

BOREHOLE SEALING/BACKFILLING

All borings should be properly backfilled at the completion of the field exploration. This is typically required for safety and to prevent contamination/commingling of groundwater. Boring closure is particularly important for tunnel projects, since an open borehole exposed during tunneling may lead to uncontrolled inflow of water or escape of compressed air. All boreholes are required to be grouted on the Department projects unless directed by the Principal Geotechnical Engineer. Holes in pavements and slabs should be filled with quick 02/14/2005



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setting concrete, or with asphalt concrete, as appropriate. Backfilling of boreholes is generally accomplished using a grout mixture. The grout mixture is normally pumped through drill rods or other pipes inserted into the borehole. In boreholes filled with water or other drilling fluids, the tremied grout will displace the drill fluid. Provisions should be made to collect and dispose of all displaced drill fluid and waste grout. National Cooperative Highway Research Program ReportNo.378( 1995)t i t l ed“ RecommendedGui del i nesf orSeal i ngGeot echni c alHol es” contains extensive information on sealing and grouting. 13.

FIELD EXPLORATION LOGS

A clear and complete record of field exploration activities and findings is essential. This should include the location of the boring, relative to the nearest Department benchmark. A station and offset from the benchmark as well as a top of the boring elevation is required. 14.

PHOTOGRAPHIC RECORD

Sites should be photographed to better describe the existing surface and surrounding condition of the project area. Photographing more details of the features of the site would better document the existing condition of the site. These photos should be included in the Geotechnical Report and the project file. Rock cores, and certain types of drive samples, are usually the only physical sample evidence of the subsurface profile that remain available for a site. In order to maintain the integrity of this record, it is useful to photograph the samples before parts are removed for testing purposes, or drying, or other disturbance occurs. Photographs assist to preserve the sampling record in the event that vandalism, negligence, or natural calamity causes loss or destruction of the physical sample. It also may be desirable to photograph specific sampling techniques and equipment for future reference. Care should be given to optimize the size of the core within the photograph in order to show as much detail as possible. Color photographs are recommended. For more details, refer to AASHTO Manual on Subsurface Investigations, Section 7.10. 15.

SAMPLE PRESERVATION AND SHIPPING

Samples of soil and rock are obtained for classification and subsequent testing to determine their various engineering properties. Rock and soil samples represent essential physical information concerning the subject site. In general, these samples can be expensive to obtain. Samples must be preserved, stored, and shipped under conditions that minimize chances of disturbance or loss. More details are provided in AASHTO Manual on Subsurface Investigations, Section 7.9. All soil samples and rock cores must be clearly, accurately, and permanently labeled to show all pertinent information which may be necessary in identifying the soil samples or rock cores, and in determining the character of the subsurface condition. The preserving, protecting and transporting of samples may be accomplished using the guidelines described as follows ; but, any method that satisfactorily protects the sample from 02/14/2005



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such things as shock, detrimental temperature changes (such as freezing), and moisture loss can be used. 

All samples should be collected from the borehole sampling sites on a daily basis and transported to the field project office or a suitable alternate location.



Rock core and thin wall tube soil samples should never be transported away from the field site in other than specially constructed wood, metal, plastic, or fiberglass shipping containers specially designed to protect them from shock and vibration.



Samples should never be left unattended in vehicles. Any undisturbed sample which is permitted to freeze, even partially, should be replaced.



Samples intended for laboratory testing should not be held at the site in excess of one week.



All sample containers should be identified as to borehole, depth interval, box number of total sequence, and project number.

16.

GUIDELINES FOR INSPECTIONS OF SUBSURFACE EXPLORATIONS

The following guidelines are summarized from the Subsurface Investigation Manual (NHI-01-031) and AASHTO Manual on Subsurface Investigations (Section 7.11): 

Thoroughly comprehend the purpose of the fieldwork in order to properly characterize the site for the intended engineering applications.



Be thoroughly familiar with the scope of the exploration program. Maintain a copy of the boring location plan.



Be familiar with site, access conditions, and any restrictions.



Review existing subsurface and geologic information before leaving the office.



Constantly review the field data obtained as it relates to the purpose of the investigation.



The field person should maintain daily contact with the Geotechnical Engineer regarding work progress, conditions encountered, problems, etc. Geotechnical Engineers log the boreholes for projects conducted in-house by the Department.



Fill out forms regularly. Obtain a sufficient supply of boring and test pit logs and any other necessary forms to cover the expected explorations.



Cl osel yobser v et hedr i l l er ’ swor katal lt i mes,pay i ngpar t i cul arat t ent i ont o:



o

Current depth (measure length of rods and samplers)

o

Drilling and sampling procedures

o

Any irregularities, loss of water, drop of rods, etc.

o

SPT counts

o

Depth to groundwater and degree of sample moisture

Do not hesitate to question the driller, or to provide direction to ensure proper procedures are being followed.

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

Classify soil and rock samples. Place soil samples in proper containers and label them. Make sure rock cores are properly boxed, photographed, stored, and protected. In handling all samples, the Geotechnical Engineer should follow the appropriate ASTM Standards. See ASTM D 4220-95, Standard Practices for Preserving and Transporting Soil Samples.



Verify that undisturbed samples are properly taken, handled, sealed, labeled, and transported.



Bring necessary tools to job.



Do not hesitate to stop work and call the Principal Geotechnical Engineer if in doubt, or if problems are encountered.



Remember field data are the basis of all subsequent engineering decisions, and as such, are of paramount importance.

The Geotechnical Engineer has the responsibility of notifying the Field Crew Supervisor when drill holes no longer need to be kept open (usually when final water table depths have been measured) and can be sealed/backfilled. The Geotechnical Engineer needs to follow up to verify that holes have been sealed/backfilled. If the holes are not sealed/backfilled within an appropriate time, the Geotechnical Engineer needs to notify the Principal Geotechnical Engineer. 17.

EQUIPMENT FOR FIELD EXPLORATIONS

The foll owi ngl i sti sf r om t heManual“ FHWA,Subsur f aceI nv est i gat i ons,NHICour se No. 132031. Geotechnical Engineers need to determine which of the listed items are applicable for each project. Paperwork/Forms

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Site Plan Technical specifications Field Instructions Sheet(s) Daily field memorandum forms Blank boring log forms Forms for special tests (vane shear, permeability tests, etc.) Blank sample labels or white tape Copies of required permits Field book (moisture proof) Health and Safety plan Field Manuals Subcontractor expense forms



6-25

Sampling Equipment

Samplers and blank tubes, etc. Knife (to trim samples) Folding rule 100-foot tape with an attachable weight so it can also be used for water level measurements Hand level Rags Proper containers and core boxes Five-gallon bucket Wire brush

Safety/Personal Equipment

Hard hat Safety boots Safety glasses Rubber boots (in some instances) Rain gear (in some instances) Work gloves

Miscellaneous Equipment

Clipboard Pencils, felt markers, grease pencils Scale/straight edge Watch Calculator Camera Compass Wash bottle or test tube Pocket Penetrometer and/or Torvane Communication equipment (two-way radio, cellular phone) Small white board and dry erase markers to make photo-labels

18.

SAFETY GUIDELINES

All field personnel, including geologists, Geotechnical Engineers , technicians, and Field Crew staff , should be familiar with the general health and safety procedures, as well as any additional requirements of the project or governing agency. Typical safety guidelines for drilling into soil and rock are presented in the Manual “ FHWA, Subsur f aceI nv est i gat i ons, NHI Cour seNo. 132031, Appendi xA.Mi ni mum pr ot ec t i v e gear for all personnel should include hardhat, safety boots, eye protection, and gloves.

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19.

6-26

SPECIFICATIONS AND STANDARDS

SUBJECT Site Characterization for Engineering, Design, and Construction Purposes Soil Investigation and Sampling by Auger Borings Penetration Test and Split Barrel Sampling of Soils Thin Walled Tube Geotechnical Sampling of Soils Diamond Core Drilling for Site Investigation Preserving and Transporting Soil Samples Cross-hole Seismic Testing Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well) Preserving and Transporting Rock Core Samples Field Logging of Subsurface Explorations of Soil and Rock Seismic Refraction Method for Subsurface Investigation Hollow-Stem Augers for Geotechnical Exploration and Soil Sampling Field Measurement of Soil Resistivity Using the Wenner FourElectrode Method Provisional Guide for Selecting Surface Geophysical Methods Descriptive Nomenclature for Constituents of Natural Mineral Aggregates Test Method for Classification of Soils for Engineering Purposes Practice for Ring-Lined Barred Sampling of Soils Practice for Description and Identification of Soils (Visual-Manual Procedure) Selecting Surface Geophysical Methods Direct Current Resistivity Method for Subsurface Investigation Surface Ground Penetrating Radar Method for Subsurface Investigation

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ASTM D 420

AASHTO T 86

D 1452 D 1586 D 1587 D 2113 D 4220 D 4428 D 4750

T 203 T 206 T 207 T 225 -

D 5079 D 5434 D 5777 D 6151 G 57

T 251 T 288

PS 78 C-294

M-146

D-2487 D-3550 D-2488

M-145 -

D-6429 D-6431 D-6432

-


GEOTECHNICAL INVESTIGATION PROCEDURES 20.

6-27

FIGURES

6-1: Core Sizes (from Boart Longyear, 2000) Core Barrel Type and Size Conventional AWG, AWM, AWL BWG, BWM, BWL NWG, NWM, NWL HW Wireline AQ BQ BQ3 NQ NQ3 HQ PQ3

02/14/2005

Rock Core Diameter (in)

Bore Hole Diameter (in)

1.185 1.655 2.155 3.000

1.890 2.360 2.980 3.875

1.062 1.433 1.320 1.875 1.775 2.406 3.270

1.890 2.360 2.360 2.980 2.980 3.783 4.828



21.

6-28

REFERENCES

AASHTO,“ ManualonSubsur f aceI nv est i gat i ons, ”Washi ngt on,D. C. ,1988 Fang, Hsai-Yang,Foundat i on“ Engi neer i ngHandbook, ”2ndEdi t i on, ”VanNost r andRei nhol d Company, New York, 1990 FHWA, “ Geot echni cal Engi neer i ngNot ebook , ”FHWARegi on10, Compi l at i onof Geot ec hni c al Guidelines, November 1986. Recent notebook issuances can be viewed at www.fhwa.dot.gov/ridge/geo.htm FHWA,“ ManualonDesi gnandConst r uct i onofDr i v enPi l eFoundat i ons, ”FHWA-HI-97-013 and 014, 1996 FHWA,“ RockSl opes,Nat i onalHi ghwayI nst i t ut e Tr ai ni ng Cour se i n Geot echni caland Foundat i onEngi neer i ng, ”NHICour seNo.132035–Module 5, 1998 FHWA," Soi l sandFoundat i onsWor kshop, ”Ref er enceManual ,NHICour seNo.132012,3rd Edition, FHWA NHI-00-045, 2000 FHWA,“ Subsur f aceI nv est i gat i ons , ”NHICour seNo.132031,FHWA-NHI-01-031, 2001 Nat i onalCooper at i v eHi ghwayResear chPr ogr am,“ RecommendedGui del i nesf orSeal i ng Geot echni calEx pl or at or yHol es, ”NCHRPRepor t378,1995 Naval Faciliti esEngi neer i ngCommand,“ Soi lMechani cs, ”NAVFACDM-7.1, Department of the Navy, 1986 OSHA,“ CodeofFeder alRegul at i ons, ”Sect i on29,OSHASt andar ds TRB,“ Landsl i des:I nv est i gat i onandMi t i gat i on, ”Speci alRepor t247,I SBN 0-309-06151-2, 1996 U.S. Army Cor psofEngi neer s,“ Geophy si cal Ex pl or at i onf orEngi neer i ngandEnv i r onment al I nv est i gat i ons,Engi neer i ngManual , ”1110-1-1802, Department of Army, 1995 U. S.Ar myCor psofEngi neer s,“ Geot echni calI nv est i gat i ons,Engi neer i ngManual , ”1110-11804, Department of Army, 2001 U. S.Ar my Cor ps ofEngi neer s,“ Soi lSampl i ng,Engi neer i ng Manual , ”1110-1-1906, Department of Army, 1996 U. S. D. A. ,“ Sl opeSt abi l i t yRef er enceGui def orNat i onal For est si nt heUni t edSt at es, ”Vol .1, Forest Service Publication EM-7170-13, ”1994 U. S. EPA,“ Descr i pt i onandSampl i ngofCont ami nat edSoi l s–AFi el dPocketGui de, ”EPA Document No. 625/12-91/002

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CHAPTER 7 IN SITU TESTING

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IN SITU TESTING

7-i

TABLE OF CONTENTS 1. 2. 3. 3.1 3.2 4. 4.1 4.2 4.3 4.4 4.5 5. 5.1 5.2 5.3 5.4 5.5 6. 6.1 6.2 6.3 7. 8.

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PURPOSE .......................................................................................................... 1 INTRODUCTION ................................................................................................ 1 CORRELATION TESTS ..................................................................................... 1 Standard Penetration Test (SPT)........................................................................ 2 Dynamic Cone Penetrometer Test (DCP)........................................................... 3 STRENGTH AND DEFORMATION TESTS........................................................ 3 Cone Penetrometer Test (CPT) and Piezocone Penetrometer Test (PQS)........ 3 Pressuremeter Test (PMT) ................................................................................. 4 Dilatometer Test (DMT) ...................................................................................... 5 Field Vane Test................................................................................................... 6 Borehole Shear Tests (BST)............................................................................... 6 PERMEABLILITY TESTS ................................................................................... 6 Pumping Test...................................................................................................... 7 Slug Test............................................................................................................. 7 Water Pressure Tests (Packer Tests)................................................................. 7 Hydraulic Conductivity Tests............................................................................... 8 Infiltration Tests .................................................................................................. 8 SPECIALIZED TESTS ........................................................................................ 8 Bearing Capacity Plate Test (PLT) ..................................................................... 8 In Situ Direct Shear Tests On Rock Discontinuities ............................................ 8 Other Tests ......................................................................................................... 9 FIGURES .......................................................................................................... 10 7-1: Specifications and Standards ................................................................... 10 REFERENCES ................................................................................................. 11


IN SITU TESTING 1.

7-1

PURPOSE

The testing described in this Chapter allows the Geotechnical Engineer to determine various soil and rock parameters under natural in-place conditions. This type of testing is useful for projects, where obtaining representative samples suitable for laboratory testing is difficult, such as those involving soft clays, loose sands and/or soils below the water table. Some benefits of in situ testing include avoidance of soil disturbance (and changes in stress) and large scale testing when size requirements exceed common sample dimensions. The discussion for each test includes a brief description of the test method, the equipment and the uses of the data. Diagrams, photographs, and example test results are included in the: AASHTO Manual on Subsurface Investigations; and FHWA Manual on Subsurface Investigations (NHI Course No. 132031). Some in situ tests are performed in conventional drilled borings, whereas other more specialized tests require a separate borehole or different insertion equipment. 2.

INTRODUCTION

Common in situ tests are performed in conventional drilled borings, whereas specialized tests require a separate borehole or different insertion equipment. Field in situ borehole tests can be grouped into three categories: 





3.

Correlation Tests o

Standard Penetration Test (SPT)

o

Dynamic Penetration Test (DPT)

Strength and Deformation Tests o

Penetrometers, such as Cone Penetrometer Test (CPT) and Piezocone Penetrometer Test (PQS)

o

Pressuremeters (PMT), such as Menard, Self-Boring, and Dilatometer

o

Stress or Shear Devices, such as Vane Shear and Borehole Shear Tests

Permeability Tests o

Pump Tests and Slug Tests

o

Water Pressure Tests

o

Hydraulic Conductivity Tests

o

Percolation Tests

CORRELATION TESTS

Data obtained through these tests may be correlated to a number of different design parameters, such as, relative density, angle of internal friction, and shear strength.

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IN SITU TESTING 3.1

7-2

Standard Penetration Test (SPT)

This test is probably the most widely used field test in the United States. It has the advantages of simplicity, the availability of a wide variety of correlations for its data, and that a sample is typically obtained with each test. The test involves advancing a standard split-barrel sampler a total of 18 inches into the bottom of a borehole by dropping a 140-pound hammer from a height of 30 inches. The number of blows required to advance the sampler for each of three 6-inch increments is recorded. The sum of the number of blows for the second and third increments is the Standard Penetration Value, or more commonly, N-value (blows per foot). Standard Penetration Tests are performed in accordance with ASTM D 1586. SPT values are sensitive to materials encountered and variations in individual drilling practices and equipment used, such as the type of hammer (hammer efficiency), diameter and length of drill rods, presence of a liner in the sampler, and diameter of the drill hole. Correction values are used to standardize the test results. Studies have indicated that SPT results are more reliable in sands than clays. Although this technique is extensively used in subsurface exploration, depending on the application, the test results should be augmented by other field and laboratory tests, particularly when dealing testing clays. Depending on the type of project, N-values can be correlated to a number of different design parameters including relative density, angle of internal friction, and shear strength. There are several methods available that use corrected N-values in the design of driven piles, embankments, spread footings, and drilled shafts. For foundation design and liquefaction studies, N-values are typically corrected for overburden pressure. This correction normalizes the N-value to an effective overburden pressure of one tsf. Testing conditions and data should be accurately recorded during exploration operations so the appropriate correction values can be applied. Noting the type of hammer used during the investigation is required on the boring logs, since this affects the actual input driving energy (hammer efficiency correction) transferred to the sampler. Because the rope and cathead method is not as consistent, only hammers using an automatic drop system are allowed on Department projects. The required method to measure the energy transfer from the hammer to the sampler using a dynamic Pile Driving Analyzer (PDA) is detailed in ASTM D 4945, which is the testing standard used in conjunction with pile driving. Since there is a wide variability in the performance of various SPT hammers, calibrations of all hammers used on Department projects are required. Calibration factors for the hammers, along with correction factors for nonstandard sized samplers, are required to be included in the boring log key in the Geotechnical Report. The procedure used to determine the hammer efficiency and resistance to pile driving is governed by stress wave propagation. Bymeas ur i ngt hehammer ’ sf or ceandv el oci t ydur i ngat est ,t het r ansmi t t edener gycanbe determined. Once the transmitted energy (Emeasured) is known, the N-values can be modified to the standard N60 equation. 02/14/2005


IN SITU TESTING 3.2

7-3

Dynamic Cone Penetrometer Test (DCP)

This Manual test consists of manually driving a cone shaped probe by dropping a 15pound hammer 20 inches. The blow count results provide an indication of the uniformity or consistency of soils. Since no samples are recovered, dynamic cone penetrometer tests should only be used as a supplement to profile interpretations determined from standard borehole sampling techniques. As the cone is driven into the soil, the number of blows required to advance the cone through a 6-inch increment is recorded. A single DCP test consists of two 6-inch increments. Tests can be performed continuously to the depth desired with an expendable cone, which is left in the ground upon drill rod withdrawal, or at specified intervals by using a retractable cone and advancing the hole by auger or other means between tests. Experience has shown that the DCP can be used effectively up to depths of 15 to 20 feet. It is extremely important to provide the full 20-inch hammer drop, per each blow, but care must be taken not to strike the weight against the handle on the upward motion. Doing so would cause the instrument to withdraw and results would be in question. If a test is performed at the bottom of an open boring, the blow counts in granular soils tend to be larger for the second 6-inch increment than for the first. In cohesive soils, the blow counts from the two increments tend to be about the same. While correlations between DCP blow counts and engineering properties of the soil exist, they are not as widely adopted as SPT values. A relationship has been developed where the blows required to drive the embedded DCP cone a distance of 1-3/4 inches yields roughly the same density/consistency values as SPT N-values. DCP results have also been correlated to California Bearing Ratio (CBR) values for use in pavement design. 4.

STRENGTH AND DEFORMATION TESTS

In situ tests for measuring strength and deformation properties include cone penetrometer, piezocone penetrometer, pressuremeter, dilatometer, vane shear, and borehole shear devices. These tests provide different methods to measure strength parameters. 4.1

Cone Penetrometer Test (CPT) and Piezocone Penetrometer Test (PQS)

The Cone Penetrometer Test (CPT) is a specialized quasi-static penetration profiling test performed independently of drilled borings. A disadvantage of this device is that no samples are obtained, so there is no positive identification of soil types. This method should only be used to supplement sampled borings, not to replace them. A cylindrical rod with a conical point is pushed through the soil at a constant rate and the penetration resistance is measured. A series of tests performed at varying depths at one location is called a sounding. Several types of penetrometers are in use, including mechanical (mantle) cone, mechanical friction-cone, electric cone, electric friction-cone, and piezocone

02/14/2005


IN SITU TESTING

7-4

penetrometers. Although many different cone configurations have been used, the current standard was developed through work performed in the Netherlands, so it is sometimes referred to as the Dutch cone. Cone penetrometers measure the resistance to penetration at the tip of the penetrometer, or the end-bearing component of resistance. Friction-cone penetrometers are equipped with a friction sleeve, which provides the added capability of measuring the side friction component of resistance. Mechanical penetrometers have telescoping tips allowing measurements to be taken incrementally, generally at intervals of 8 inches or less. Electric (or electronic) penetrometers use electric force transducers to obtain continuous measurements with depth. Piezocone penetrometers are electric penetrometers, which are also capable of measuring pore water pressures during penetration. Cones can also be equipped with timedomain sensors that allow the cone to measure shear wave velocity. For all types of penetrometers, cones with a 60-degree tip angle and a projected end area of 1.55 square inches are standard. The outside diameter of the friction sleeve is the same as the base of the cone. Penetration rates are maintained between 0.4 to 0.8 inches per second. Tests are conducted in accordance with ASTM D 3441 (mechanical cones) and ASTM D 5778 (piezocones). The penetrometer data is plotted showing the end-bearing resistance, the friction resistance and the friction ratio (friction resistance divided by end bearing resistance) as functions of depth. Pore pressures, if measured, can also be plotted with depth. The results are presented in tabular form, indicating the interpreted results of the raw data. There are published correlations relating CPT data to soil type and several engineering properties. CPT data can be used in some design methods for spread footings and piles. The penetrometer can be used in sands or clays, but not in rock, dense sands, or soils containing appreciable amounts of gravel. The piezocone penetrometer can measure the dissipation rate of excessive pore water pressure. This type of measurement, is useful in characterization, subsurface materials, such as fibrous peat or muck that are very sensitive to sampling techniques. The cone should be equipped with a pressure transducer that is capable of measuring the induced water pressure. To perform this measurement, the cone is advanced into the ground at the standard rate. Pore water pressures are measured immediately and at several time intervals thereafter. The recorded data is used to develop a plot of a pore pressure versus log-time graph. This graph can be used to directly calculate the rate of pore water pressure dissipation, which directly relates to the rate of soil settlement. 4.2

Pressuremeter Test (PMT)

The pressuremeter measures stress/strain properties of soils by inflating a probe placed at the desired depth in the borehole. The PMT provides much more direct measurements of soil compressibility and lateral stresses than do the SPT or CPT. Test

02/14/2005


IN SITU TESTING

7-5

results are interpreted based on semiempirical correlations from past tests and observation. In situ horizontal stresses, shear strength, bearing capacities, and settlement can be estimated using these correlations. The pressuremeter test is a delicate tool, and the test is very sensitive to borehole disturbance. The data may be difficult to interpret for some soils, but it provides the advantage that due to the large size of the pressuremeter cell it is less likely to be adversely affected by gravel in the soil. The test has the advantage of less likely to be adversely affected by gravels in soils due to the large size of the pressuremeter cell. This test requires a high level of technical expertise to perform, and is time consuming. Typically, 6 to 8 tests are conducted per day. The Menard type pressuremeter requires predrilling of the borehole. The self-boring type pressuremeter advances the hole itself, which reduces soil disturbance. The Menard probe contains three flexible rubber membranes. The middle membrane provides measur ement s,whi l et heout ert wocel l s,t he“ guar dcel l s, ”pr ot ectt hemeasur i ngcell from end effects. When in place, the guard cell membranes are inflated by pressurized gas, while the middle membrane is inflated with water by means of pressurized gas. The pressure in all cells is incrementally increased or decreased by the same amount. The measured volume change in the middle membrane is plotted against applied pressure. Tests are completed in accordance with ASTM D 4719. 4.3

Dilatometer Test (DMT)

The dilatometer is a 3.75-inch wide and 0.55-inch thick stainless steel blade with a thin 2.4-inch diameter expandable metal membrane on one side. While the membrane is flush with the blade surface, the blade is advanced into the soil. Rods carry pneumatic and electrical lines from the membrane to the surface. Tests are typically conducted at 8-inch intervals. Pressurized gas is used to expand the membrane. Both the pressure required to begin membrane movement and that required to expand the membrane 0.04 inches into the soil are measured. Additionally, upon venting, the pressure corresponding to the return of the membrane to its original position, which correlates to the pore water pressure in the soil, may be recorded. Each test typically requires 1 to 2 minutes to complete for each interval. The dilatometer test uses pressure readings from the inserted flat plate to determine stratigraphy and obtain estimates of at-rest lateral stresses, elastic modulus, and shear strength of sands (and to a lesser degree, silts and clays). The dilatometer test is not widely used, and the analysis and design methods based on DMT results are not yet as thoroughly developed as other techniques. However, the test provides consistent results when repeated, is useable in soils ranging from soft to moderately stiff; and provides several direct measurements of stress-strain properties. The plate can be difficult to advance into dense and hard materials. Calibration is needed to correlate to local geologic environments. Because of its relatively low cost, versatility, and compatibility with the CPT, its use may increase in the future.

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IN SITU TESTING

7-6

Through developed correlations, information can be deduced regarding material type, pore water pressure, in situ horizontal and vertical stresses, void ratio or relative density, modulus, shear strength parameters, and consolidation parameters. Compared to the pressuremeter, the dilatometer has the advantage of reduced soil disturbance during penetration. The DMT and CPT are complementary tests where the DMT is used to assess compressibility and in situ stresses and the CPT is used to evaluate soil strength. 4.4

Field Vane Test

This test consists of advancing a four-bladed vane into cohesive soil or organic deposits to the desired depth and applying a measured torque at a constant rate until the material fails in shear along a cylindrical surface. The torque measured at failure provides the undrained shear strength of the soil. A second test run immediately after the soil has failed at the same depth provides the remolded strength of the soil and, thus, information on soil sensitivity. Tests are performed in accordance with ASTM D 2573. This method is primarily intended for soft clays, and should not be used in stiff or hard soils. Vane diameters vary depending on the consistency of the soil, with larger vanes used in softer materials. Test results can be affected by the presence of gravel, roots, or sand layers. Shear strength may be overestimated in highly plastic clays, and a correction factor should be applied. Vane shear test results may be invalid for varved clays, fibrous peats, and other deposits with a high degree of anisotropy. The Geotechnical Engineer should consider the potential for shear strength anisotropy when using the test results, since the test forces a shear failure along a surface that does not represent the actual case in most geotechnical applications. 4.5

Borehole Shear Tests (BST)

Borehole shear strength tests are performed in an uncased borehole. The apparatus is positioned within the material of interest and then expanded to apply horizontal pressure against the sides of the hole. The main components of the borehole shear device are: the shear head, the pulling assembly, and the console (which contains the bottled gas and pressure gauge. The pulling assembly is hand operated by turning a worm gear to provide a uniform rate of strain, which is monitored by a strain gauge. The shear strength is determined by measuring the resistance while pulling up on the shear device. The test is repeated at increasing horizontal pressures to develop a plot of maximum shear stress to normal stress. The Mohr envelope is plotted, andshearst r engt hpar amet er sФ andcar edet er mi ned. Thi st esti sdependentonachi ev i ng“ dr ai ned”condi t i ons, and is more reliable on sand and silt soils. Tests on clay soils are possible if sufficiently long consolidation times are allowed and strain rates are applied. 5.

PERMEABLILITY TESTS Hydraulic conductivity, also referred to as permeability, is the measure of the rate of

02/14/2005


IN SITU TESTING

7-7

flow of water through soils, usually measured when the soil is saturated. The hydraulic conductivity value is corrected for the hydraulic boundary conditions, such as the hydraulic gradient. In situ hydraulic conductivity tests results are more representative of the actual soil property than test results obtained in the laboratory, since they are performed on the entire hydraulic system, with all its variables including joints, sand seams, and small fissures. Laboratory tests are performed on a small sample that may not be truly representative of field conditions. Several methods to perform in situ hydraulic conductivity tests have been developed with the most commonly used being the pumping test and the slug test. 5.1

Pumping Test

The pumping test requires one test well to pump water and one to four adjacent observation wells to monitor the changes in water levels as the pumping test is performed. Frequently, existing wells of opportunity (preexisting wells) are used for this test, but their depths and efficiency should be determined to properly use the results of the test. Often, there will be other wells within the vicinity that are not part of the test program. In this case, the influence of these wells, if they are operated during the test, must be taken into account. Pumping continues until a steady-state water level is obtained in the observation wells. The hydraulic conductivity, (k), is then computed based on the flow rate from the pumped well, the steady-state water level (total head) in the observation wells, and the configuration of the test hole relative to the observation wells, according to the principles of groundwater flow. (refer to ASTM D 4050)) Pumping tests are typically used in large-scale investigations to more accurately measure the permeability of an area for the design of dewatering systems. 5.2

Slug Test

The slug test, although less representative of the larger area typically represented by a pumping test, is quicker to perform and much less expensive because observation wells are not required. It consists of affecting a rapid change in the water level within a well by quickly injecting or removing a known volume of water or a solid object known as a slug. The natural flow of groundwater out of or into the well is then observed until equilibrium in the water level is obtained. The flow rate to equilibrium is used to compute k (refer to ASTM D 4044). 5.3

Water Pressure Tests (Packer Tests)

This test is performed in a borehole by placing packers above and below the soil/rock zone to be tested. The time rate of water flow into the isolated test zone, at a constant pressure, is recorded for 5 to 30 minutes. This procedure is repeated at higher pressure with care not to cause hydraulic fracturing. The coefficient of permeability that is calculated provides a gross indication of the overall mass permeability (refer to FHWA, “ Rock Slopes: Design, Excavation, Stabilization” ).

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IN SITU TESTING 5.4

7-8

Hydraulic Conductivity Tests

There are several methods of determining the hydraulic conductivity of water bearing materials. The tests may be performed with packers in place to isolate a specific zone; however, the test is not run with the borehole sealed or under pressure. One method is to remove water from the material being tested (Rising Water Level Method). Another method is to add water to the borehole (Falling Water Level Method and Constant Water Level Method). (refer to AASHTO,“ Manual on Subsurface Investigations” ). 5.5

Infiltration Tests

The movement of water from the surface into the soil or rock is called infiltration. Two types of infiltrometer systems are available: sprinkler type and flooding type. Sprinkler types attempt to simulate rainfall, while the flooding type is applicable for simulating runoff conditions. These methods measure the vertical flow of water, expressed in inches per hour. Applications for these tests include the design of subdrainage and dry well systems. The most common application is the falling head test, performed by filling (flooding) a test pit hole in concentric rings and monitoring the rate the water level drops (refer to ASTM D 4043). 6.

SPECIALIZED TESTS

Specialized tests are those that are not commonly used, but may have application on unique or complex projects. These tests are listed for reference, along with brief descriptions. If these tests are to be used, the Geotechnical Engineer should perform research on test details and applicability. 6.1

Bearing Capacity Plate Test (PLT)

This test is performed to determine field bearing capacities on circular plates that are subsequently used to estimate bearing capacity of shallow spread footings. The loads are applied to the bearing plates by either jacking against a dead load or against a reaction beam attached to several piles. The bearing plates vary in diameter from 12 to 30 inches, are made of steel or concrete, and are placed at the proposed footing embedment level (refer to test method ASTM D 1194). 6.2

In Situ Direct Shear Tests On Rock Discontinuities

This test is used to measure the peak and residual direct shear strength along an in situ rock discontinuity as a function of the stress normal to the sheared plane. Because of the complicated nature of the test, it is typically restricted to slope, tunnel, dam, or bridge foundation projects, where a failure along a particular discontinuity can have a significant impact. In general, the in situ test is performed on a larger specimen than the one used in a laboratory testing and is, therefore, more representative of actual conditions such as surface irregularities along the discontinuity.

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IN SITU TESTING

7-9

The test requires several pieces of equipment that typically Consultants specializing in rock mechanics would have on hand. The equipment includes rock saws, drills, hammers and chisels, formwork, and materials for reinforced concrete encapsulation for preparing the test specimen; jacks or rams and a reaction system for applying normal loads; a pump and hydraulic ram, and a reaction system for applying the shear force; and appropriate load cells and gauges for measuring the applied shear and normal forces and shear displacements. The test includes a consolidation stage during which the pore pressures within the rock and any infilling material adjacent to the shear plane are allowed to dissipate under full normal stress before shearing is initiated. During the test, corrections to the normal load may be necessary to hold the normal load constant. As in the more traditional soil shear strength testing, once the peak shear strength is obtained additional readings can be taken to determine the residual shear strength along the discontinuity (refer to ASTM D 4554). 6.3

Other Tests



Large Penetration Test (LPT) –This test is a modification of the Standard Penetration Test, which uses a larger diameter sampler for use in gravelly soils.



Becker Penetration Test (BPT) –This test is used to investigate coarse-grained materials (gravel, cobbles) by using an instrumented steel pipe pile.



Iowa Stepped Blade Test (ISB) –This test attempts to directly measure the in situ lateral stress state (Ko) in soils.



Total Stress Cells –(TSC) –This test attempts to directly measure the in situ lateral stress state (Ko) in soils.



Push-in Spade Cells –This test attempts to directly measure the in situ lateral stress state (Ko) in soils.



Hydraulic Fracturing Test (HF) - This test attempts to directly measure the in situ lateral stress state (Ko) in rock formations.

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IN SITU TESTING 7.

7-10

FIGURES

7-1: Specifications and Standards SUBJECT Dilatometer Chloride Content - Soil (Retaining Wall Backfill) Chloride Ion In Water Electrical Conductivity and Resistivity of Water Bearing Capacity of Soil for Static Load on Spread Footings pH of Water Penetration Test and Split Barrel Sampling of Soils Field Vane Shear Test in Cohesive Soil Mechanical Cone Penetration Tests of Soil Selection of Aquifer Test Method in Determining Hydraulic Properties by Well Techniques Instantaneous Change in Head (Slug Test), for determining Hydraulic Properties of Aquifers Withdrawal and Injection Well Tests for Determining Hydraulic Properties of Aquifer Systems Sulfate Ion in Brackish Water, Seawater, and Brines In Situ Determination of Direct Shear Strength of Rock Discontinuities Pressuremeter Testing in Soils Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well) High Strain Dynamic Testing of Piles Preserving and Transporting Rock Core Samples Electronic Friction Cone and Piezocone Penetration Testing of Soils Hydraulic Conductivity of Porous Materials Using Two Stages of Infiltration from a Borehole Flat Plate Dilatometer pH of Soil for Use in Corrosion Testing Soil Resistivity (ASTM –Field Procedure Using the Wenner Four-Electrode Method and AASHTO – Laboratory Procedure)

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ASTM D 512 D 1125 D 1194

AASHTO -

D 1293 D 1583 D1586 D 3441 D 4043

T 223 -

D 4044

-

D 4050

-

D 4130

-

D 4554

-

D 4719 D 4750

-

D 4945 D 5079 D 5778

-

D 6391

-

D 6635 G 51 G 57

T 289 T 288


IN SITU TESTING 8.

7-11

REFERENCES

AASHTO,“ ManualonSubsur f aceI nv est i gat i ons, ”1988 ASCE,“ Use ofI n-Si t u Test si n Geot echni calEngi neer i ng, ”ASCE Speci alTechnical Publication No. 6, 1986 Depar t mentoft heNav y ,“ Soi l sMechani csDesi gnManual7. 1, ”NAVFAC DM-7.1, Naval Facilities Engineering Command, 1986 FHWA,“ ConePenet r omet erTest , ”FHWA- SA-91-043, 1991 FHWA,“ Det er mi nat i onofHor i z ont alSt r essi nSoi l s, ”FHWA- RD-81-118, 1981 FHWA,“ Ev al uat i onofSel f -bor i ngPr essur emet erTest si nBost onBl ueCl ay , ”I nt er i m Repor t , FHWA- RD-80-052, 1980 FHWA,“ Ev al uat i onofSoi landRockPr oper t i es, ”Geot echni calEngi neer i ngCi r cul arNo.5, FHWA-IF-02-034, 2002 FHWA,“ Fl atDi l at omet erTest , ”FHWA- SA-91-044, 1991 FHWA,“ Geot echni calEngi neer i ngNot ebook, ”( sect i onsaddedwhenneeded) FHWA,“ Gr oundAnchor sandAnchor sSy st ems, ”Geot echni cal Engi neer i ngCi r cul ar ,No.4, FHWA IF-99-015, 1999 FHWA,“ Pr essur emet erTestf orHi ghwayAppl i cat i ons, ”FHWA-IP-89-008, 1989 FHWA,“ RockSl opes:Desi gn,Ex cav at i on,St abi l i z at i on, ”1989 FHWA, “ Sensi ngSy st emsf orMeas ur i ngMec hani c al Pr oper t i esi nGr oundMas s es , ”Vol s . 1 to 5, FHWA-RD-81-109 through FHWA-RD-81-113, 1981 FHWA, “ Soils and Foundations Workshop Reference Manual,”NHI Course No. 132012, FHWA NHI-00-045, August 2000 FHWA, “ Subsur f aceI nv est i gat i ons–Geotechni cal Si t eChar act er i z at i on, ”Ref er enc eManual for NHI Course No. 132031, FHWA-NHI-01-031, 2002 NCHRP,“ Tr eat mentofPr obl em Foundat i onsf orHi ghwayEmbankment s, ”Sy nt hesi s147, 1989 TRB,“ Landsl i des:I nv est i gat i onandMi t i gat ion,”Speci alRepor t247,1996

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CHAPTER 8 LABORATORY TESTS

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LABORATORY TESTING

1. 2. 3. 3.1 3.1.1. 3.1.2. 3.1.3. 3.1.4. 3.2 3.2.1. 3.2.2. 3.3 3.4 3.4.1. 3.4.2. 3.4.3. 3.4.4. 3.4.5. 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.11.1. 3.11.2. 3.12 3.12.1. 3.12.2. 3.13 3.14 3.14.1. 3.14.2. 3.14.3. 3.15 3.15.1. 3.15.2. 3.15.3. 3.16 02/14/2005

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TABLE OF CONTENTS PURPOSE ............................................................................................................ 1 INTRODUCTION .................................................................................................. 1 SOILS................................................................................................................... 1 Atterberg Limits Tests........................................................................................... 2 Liquid Limit ........................................................................................................... 2 Plastic Limit .......................................................................................................... 2 Plasticity Index...................................................................................................... 2 Shrinkage Limit..................................................................................................... 3 Grain-Size Analysis (Gradation) Tests ................................................................. 3 Sieve Analysis Test .............................................................................................. 3 Hydrometer Test................................................................................................... 3 Moisture Content Test .......................................................................................... 4 Compaction Tests ................................................................................................ 4 Standard Proctor .................................................................................................. 4 Modified Proctor ................................................................................................... 4 Relative Density Tests.......................................................................................... 5 Maximum Index Density ....................................................................................... 5 Minimum Index Density. ....................................................................................... 5 Unit Weight Test................................................................................................... 5 Specific Gravity Test............................................................................................. 5 Chemical Tests..................................................................................................... 6 Visual Classification Tests.................................................................................... 6 Organic Content Test ........................................................................................... 6 R-Value Test ........................................................................................................ 7 Strength Tests ...................................................................................................... 7 Unconfined Compression Test ............................................................................. 8 Triaxial Compression Tests .................................................................................. 8 Consolidation Tests ............................................................................................ 10 One-Dimensional Test........................................................................................ 11 Constant Rate of Strain Test .............................................................................. 12 Collapse Potential Tests..................................................................................... 12 Swell Potential Tests (Clays).............................................................................. 12 Soil Suction Test ................................................................................................ 12 Oedometer Swell Test ........................................................................................ 13 Shrinkage Limit Test........................................................................................... 13 Permeability Tests .............................................................................................. 13 Constant Head Test ........................................................................................... 13 Falling Head Test ............................................................................................... 13 Triaxial Permeability Test ................................................................................... 13 Dynamic Properties ............................................................................................ 14 NDOT Geotechnical Policies and Procedures Manual

LABORATORY TESTING 4. 5. 5.1 5.2 5.3 5.3.1. 5.3.2. 5.4 5.5 5.6 5.6.1. 5.6.2. 5.6.3. 5.6.4. 5.6.5. 5.6.6. 5.7 6. 7. 8.

9.

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CORRELATIONS of Soil Properties................................................................... 14 ROCK ................................................................................................................. 15 Visual Classifications.......................................................................................... 15 Absorption and Bulk Specific Gravity Tests........................................................ 15 Durability Tests................................................................................................... 15 Jar Slake Test .................................................................................................... 16 Slake Durability Test (2-cycle) ............................................................................ 16 Soundness Test ................................................................................................. 16 Permeability Test................................................................................................ 17 Rock Strength Test............................................................................................. 17 Point Load Strength Index Test .......................................................................... 17 Unconfined Compression Test ........................................................................... 17 Triaxial Compressive Strength Test ................................................................... 17 Elastic Moduli –Uniaxial Compressive Test....................................................... 18 Splitting Tensile Strength Test............................................................................ 18 Direct Shear Test ............................................................................................... 18 Unit Weight Test................................................................................................. 18 CORRELATIONS OF ROCK PROPERTIES...................................................... 18 SPECIFICATIONS AND STANDARDS .............................................................. 20 FIGURES ........................................................................................................... 23 8-1: Geotechnical Lab Task Sheet ..................................................................... 23 8-2: Geotechnical Lab Task Sheet, continued.................................................... 24 8-3: Summary of Results .................................................................................... 25 8-4: Line Sampling Data ..................................................................................... 26 8-5: Plasticity Index ............................................................................................ 27 8-6: Particle Size Distribution Report.................................................................. 28 8-7: Chemical Analysis ....................................................................................... 29 8-8: Consolidation Test Report........................................................................... 30 8-9: Hydrocollapse Test Report.......................................................................... 31 8-10: Direct Shear Test Report........................................................................... 32 REFERENCES ................................................................................................... 33


LABORATORY TESTING

1.

8-1

PURPOSE

The laboratory testing must be planned in advance but flexible to be modified based on subsurface findings and test results. The ideal laboratory testing program provides the Geotechnical Engineer with sufficient data to complete an economical design, yet not tie up laboratory personnel and equipment with superfluous testing. The complexity of testing required for a particular project may range from simple moisture content determinations to specialized strength testing. Chapters 7 through 10 of the Participants Manual for the NHI course on Subsurface Investigations (Module 1: No. 132031, 1997) provide an overview of testing and correlations. 2.

INTRODUCTION

For each project, a testing request form must be completed in order to plan the laboratory testing program and to convey the plan to the Geotechnical Laboratory. The form consists of two sheets, which are shown on Figures 8-1 and 8-2. Engineering judgment must be exercised in setting up a testing program that produces the information required to resolve the technical issues for each specific project. The Geotechnical Engineer should develop a prioritized and cost-effective testing program. The project budget should be verified to ensure that the recommended testing program can be accomplished, and determine if adjustments are necessary to either the budget or the testing program. Test results are provided in the Summary of Results table, shown in Figure 8-3. When planning the laboratory testing program, the Geotechnical Engineer should first examine all samples, and verify the descriptions provided in the field logs by performing visual classification tests. The following information should be considered when planning the laboratory testing program:  Project type (bridge, embankment, roadway, buildings, etc.)  Size of the project  Loads to be imposed on the foundation soil and rock materials  Types of loads ( static and dynamic cases)  Critical tolerances for project (i.e., settlement and lateral deflection limitations)  Vertical and horizontal variations in the soil profile as determined from field logs and visual identification of soil types in the laboratory  Known/suspected peculiarities of soil and rock materials at the project location (i.e., swelling soils, collapsible soils, organics, faults, erosion, degradation)  Presence of intrusions, slickensides, fissures, concretions  Project schedules and budgets 3.

SOILS

Soil tests are performed to determine specific soil properties and how the soil responds to imposed conditions. Types of behavior depend on the strength, compressibility, permeability, corrosivity, and index properties. There are a number of tests that can be used 02/14/2005


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to determine the desired properties, depending on the soil type and application. The Geotechnical Engineer should observe the quality of undisturbed samples when they are extruded from the sampling tubes in the laboratory. The Geotechnical Engineer determines the number, types, and requirements (such as site-specific confining stress levels for triaxial tests) of needed tests. The Geotechnical Engineer should be familiar with each test procedure and should verify that the tests are being performed according to his/her directions. Familiarity with testing procedures and the soil samples helps the Geotechnical Engineer to appropriately apply the test results in his/her subsequent geotechnical analyses. 3.1

Atterberg Limits Tests

Atterberg Limits Tests are index tests used to confirm visual descriptions. They are performed on fine-grained soils (clays, silts) to determine the amount of water necessary to achieve a range of behavioral states. Atterberg limits tests should be performed on each representative soil, and additional tests are advisable to confirm grouping of apparently similar soils and where project complexity justifies additional testing. These test results have been correlated with other soil properties/parameters. The liquid limit (LL), plastic limit (PL) and shrinkage limit (SL) are Atterberg limits. However, for classification purposes, the term Atterberg limits generally refers to the more common liquid and plastic limits only. The shrinkage limit test is less often included in common laboratory programs. The shrinkage limit test is performed when swelling behavior in soils are suspected that could influence design and construction. 3.1.1.

Liquid Limit

The LL is the moisture content of a soil at the boundary between the liquid and plastic states. The liquid limit is determined by ascertaining the moisture content at which two halves of a soil cake will flow together for a distance of 0.5 inch along the bottom of the groove separating the halves, when the bowl they are in is dropped between 15 to 35 times from a distance of 0.4 inches at the rate of 2 drops/second. A plot of the relationship between the water content and the number of drops is made using the results of the tests. The water content corresponding to the intersection of the line with the 25-drop abscissa is the liquid limit of the soil. Tests are performed in accordance with ASTM D 4318 (AASHTO T 89). 3.1.2.

Plastic Limit

The PL is the moisture content at the boundary between the plastic and semisolid states. The plastic limit is determined by ascertaining the lowest moisture content at which the material can be rolled into threads 0.125 inches in diameter before crumbling. Tests are performed in accordance with ASTM D 4318 (AASHTO T 90). 3.1.3.

Plasticity Index

The Plasticity Index (PI) is the difference between the LL and PL. The results are generally reported as LL and PI values on the Summary of Results table, Figure 8-3, and on the Line Sampling Data sheet, Figure 8-4. Results can also be plotted on a Plasticity chart, 02/14/2005


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which provides a visual representation of the degree of plasticity and primary soil type (silt or clay). See Figure 8-5. 3.1.4.

Shrinkage Limit

The shrinkage limit test is performed on clay soils suspected to have swell potential. Thet est det er mi nest hel i mi t sofasoi l ’ st endencyt ol osev ol umedur i ngdec r eas esi nmoi s t ur e content. The shrinkage limit is defined as the maximum water content at which a reduction in water content does not cause a decrease in volume of the soil mass. Tests are performed in accordance with ASTM D 4318 (AASHTO T 92). 3.2

Grain-Size Analysis (Gradation) Tests

The gradation tests are performed to determine the particle size distribution of the soil which could be used for soil classification. The particle size distribution information enables an evaluation of engineering properties such as permeability, filter compatibility, erosion, scour, and frost susceptibility, and also determines material suitability for earthwork construction and backfill. The tests consist of two types: sieve analysis for coarse-grained soils (sands, gravels) and hydrometer analysis for fine-grained soils (clays, silts). Materials containing both types of soils are tested by both methods and the results are merged to create one particle size distribution result. The results can be shown on the Line Sampling Data sheet (Figure 8-4). A sample of Particle Size Distribution Report is shown on Figure 8-6. 3.2.1.

Sieve Analysis Test

This test provides a direct measurement of the particle size distribution of a soil by causing the sample to pass through a series of wire screens with progressively smaller openings of known size. The amount of material retained on each sieve is weighed. See AASHTO T 87 and 88 for discussion of preparation and testing of soils containing fine-grained materials. See AASHTO T 27 for testing of coarse-grained materials including construction aggregates. When knowing the amount of fines contained in a construction material (i.e., base aggregate, drain rock, free-draining backfill) is desired, the test should be performed using a wet-sieve analysis, which entails first weighing a dry sample and then washing the sample over a No. 200 sieve prior to running over a sieve stack. Preparation of the sample for this procedure is described in AASHTO T 11. For soil classification purposes, determining the percentage of material finer than the No. 200 sieve may be desired. This simple test (often called a P200 or Wash 200) is described in ASTM D 1140. 3.2.2.

Hydrometer Test

The hydrometer test is based on Stokes Law. The diameter of a soil particle is defined as the diameter of a sphere which has the same unit mass and which falls at the same velocity as the particle. Thus, a particle size distribution is obtained by using a hydrometer to measure the change in specific gravity of a soil-water suspension as soil particles settle out over time. Hydrometer test results are sometimes needed to complete classification of soils. The resulting gradations can provide data for determining several parameters, such as effective 02/14/2005


LABORATORY TESTING

8-4

diameter (D10) and coefficient of uniformity (Cu). Results are reported on a combined grain size distribution plot as the percentage of sample smaller than, by weight, versus the log of the particle diameter. Tests are performed in accordance with AASHTO T 88. 3.3

Moisture Content Test

The moisture content, w, is defined as the ratio of the weight of water in a sample to the weight of solids. The moisture content is valuable in determining the properties of soils which can be correlated to strength, settlement, and workability. The wet sample is weighed, and then oven-dried to a constant weight at a temperature of about 230° F (110° C). The weight after drying is the weight of solids. The change in weight, which has occurred during drying, is equivalent to the weight of water. For organic soils, a reduced drying temperature of approximately 140 F (60 C) is recommended. Tests are performed in accordance with AASHTO T 265. 3.4

Compaction Tests

Compaction testing determines the optimum moisture content to achieve the maximum dry density under a designated compactive effort for a specific soil. If appropriate, the results are used in Construction Plans as the criteria necessary for the contractor to achieve a dense, competent soil mass. If needed for statistical analysis, compaction tests should be performed for each soil type likely to be used for embankment construction. The compaction testing is performed using a specified compactive effort on a soil sample in a test mold of known volume. The water content and the weight of the sample required to fill the mold are determined. Results are plotted as dry density versus water content. By varying the water content of the sample, several points on the moisture-density curve are obtained. The compactive effort used is dependent on the proposed purpose of the site and the loading to which it will be subjected. The Department requires the Harvard Miniature compaction test method. Other types of compaction test methods can be performed, if needed. The most commonly performed laboratory compaction tests are Proctor tests, with t wol ev el sofcompact i v eef f or t ,asdescr i bedbel ow.TheSt andar dPr oct ort estusesa4” di amet ermol d and t he modi f i ed Pr oct orusesa 6”di amet ermol d. Review the project requirements and specifications to determine which test(s) should be performed. Relative Density testing may be more appropriate for granular (sand) soils. 3.4.1.

Standard Proctor

This test uses a 5.5-pound rammer dropped from a height of 12 inches. The sample is compacted in three layers. Tests are performed in accordance with AASHTO T 99. 3.4.2.

Modified Proctor

This test uses a 10-pound rammer dropped from a height of 18 inches. The sample is compacted in five layers. Tests are performed in accordance with AASHTO T 180.

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8-5

Relative Density Tests

Proctor tests often do not produce a well-defined moisture-density curve for cohesionless, free-draining soils. Additionally, maximum densities from Proctor tests may be less than those obtained in the field or by vibratory methods. For these soils, it may be preferable to perform tests, which determine standard maximum and minimum densities of the soil. The density of the in situ soil can then be compared with these maximum and minimum densities and its relative density and/or percent compaction can be calculated. 3.4.4.

Maximum Index Density

This test requires that either oven-dried or wet soil be placed in a mold of known volume, and that a 2-psi surcharge load be applied. The mold is then vertically vibrated at a specified frequency for a specified time. The weight and volume of the sample after vibrating are used to calculate the maximum index density. Tests are performed in accordance with ASTM D 4253. 3.4.5.

Minimum Index Density.

This test is performed to establish the loosest condition, which can be attained by standard laboratory procedures. Several methods can be used, but the preferred method is to pour a steady stream of oven-dried soil into a mold of known volume through a funnel. Funnel height should be adjusted continuously to maintain a free fall of the soil of approximately 0.5 inches. Tests are performed in accordance with ASTM D 4254. 3.5

Unit Weight Test

The purpose of unit weight determinations is for use in several types of engineering analyses, such as settlement, shrink/swell, and stability. The unit weight is determined by dividing the weight of the undisturbed sample by its volume. It is preferable to use specimens with a uniform shape (such as cylindrical from a tube sample), because the volume can be more reliably based on measurements of diameter and length. The unit weight results are included in the Summary of Results table (Figure 8-3). 3.6

Specific Gravity Test

The specific gravity of soils (Gs) is used to relate the weight of the soil to its volume. Typically, an assumed Gs of 2.65 to 2.70 is sufficient to use in laboratory computations and geotechnical analyses. Therefore, this test is usually performed for special cases such as particle size analysis (hydrometer test) and unusual soil materials. Gs is defined as the ratio of the mass in air of a given volume of soil particles to the mass in air of an equal volume of gas free distilled water at a stated temperature (typically 60° F). The specific gravity is determined by means of a calibrated pycnometer, by which the mass and temperature of a de-aired soil/distilled water sample is measured. Tests are performed in accordance with ASTM D 854 (AASHTO T 100). This method is used for soil samples composed of particles less than the No. 4 sieve. For particles larger than this sieve, use the procedures for Specific Gravity and Absorption of Coarse Aggregate, AASHTO T 85. Test results can be shown on the Line 02/14/2005


LABORATORY TESTING

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Sampling Data sheets (Figure 8-4). 3.7

Chemical Tests

Chemical tests are performed to determine the corrosion classification of soil and water. This information is necessary to determine corrosion protection requirements for buried structures such as culverts, piles, footings, and ground anchors. A series of tests should be performed for each stream crossing and culvert location. The tests are performed to determine the pH, resistivity, chloride content, and sulfate content. The Geotechnical Laboratory performs the pH and resistivity tests. These tests require samples weighing about 15 pounds. Results are shown on the Line Sampling Data sheets (Figure 8-4). A sample chemical analysis test report is shown on Figure 8-7. 3.8

Visual Classification Tests

Visual classification tests are performed to determine primary soil constituents and material behavior, which could affect the design and construction. The Geotechnical Engineer gains a greater knowledge of the soil types and their behavior by personally performing the classification tests. The visual classification test is used to verify soil types and corresponding influence on the design. Visual classification tests assist the Geotechnical Engineer in finalizing the laboratory testing program. Refer to ASTM D 2487 and D 2488 (refer to Tables 1 through 12 in ASTM D 2488 for a quick summary of terms and categories that can be interpreted from these tests). Information that is determined by these tests includes: 

Degree of organic content (odor and visual content)



Primary constituent and the soil classification based on coarse or fine grained soil categories



Dry strength (indicates relative clay content and plasticity)



Dilatancy (indicates whether the soil is cohesive or cohesionless)



Toughness (indicates the plasticity behavior of the soil when the water content is near its plastic limit)

3.9

Organic Content Test

Organic soils demonstrate undesirable engineering characteristics, most notably low strength, high immediate compressibility, and continued long term settlements. The behavior of soils with organic contents less than 20% by weight is generally controlled by the mineral component of the soil. When organic contents are in excess of 20%, the behavior is governed by the organic component of the material. In the field, these soils can usually be identified by their dark color, musty odor and low unit weight. The most performed laboratory test for design pur posesi st heI gni t i onLosst est ,whi chmeasur eshowmuchofasampl e’ smassbur nsof f when placed in a muffle furnace. The results are presented as a percentage of the total sample mass. Tests are performed in accordance with AASHTO T 267.

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LABORATORY TESTING 3.10

8-7

R-Value Test

Pavement subgrade tests are performed for the Department Roadbed Design Section. The R-value test is used by the Department to measure subgrade strength. Other tests such as the Resilient Modulus (MR) and the California Bearing Ratio (CBR) are used by other st at es’ t r anspor t at i ondepar t ment s.Thi st esti susedt odet er mi net heabi l i t yofasoi l t or esi st lateral deformations under a vertical load. The resistance is identified as the R-value. R-values are measured with a stabilometer, which is a triaxial type device. A vertical load is applied and the lateral pressure is transmitted to the fluid filled chamber, which is measured with a pressure gauge. The test results are shown on the Line Sampling Data sheet (Figure 8-4). Currently the Department uses this test to determine suitability of material to be used as fill material. This test is also used to determine swell pressure of expansive soils. The data is used to determine the thickness of overburden necessary to prevent expansion. Refer to AASHTO T 190. 3.11

Strength Tests

Geotechnical design of embankments, cuts, walls, and foundations requires a thorough understanding of the strength properties of soils. The level of effort used to determine soil strength parameters varies, depending on the size and complexity of the project elements and consequences of failure. The shear strength of a soil is the maximum shearing stress the soil structure can resist before failure. Soils generally derive their strength from friction between par t i cl es( ex pr essed ast he angl e ofi nt er nalf r i ct i on,Ф)orcohesi on bet ween par t i cl es (expressed as the cohesion, c in units of force/unit area), or both. These parameters are ex pr essedi nt hef or m oft ot alst r ess( c,Ф)oref f ect i v est r ess( c,Ф) .The total stress on any soil layer is induced by the overburden pressure plus any applied loads. The effective stress equals the total stress less the pore water pressure. For simple projects, sufficient strength information can be obtained from strength correlations using field and laboratory index tests. However, strength testing may be needed when there is uncertainty in the knowledge of material properties, or if design loads/stresses are significant. The type of tests needed depends on whether the analysis is performed using total or effective stresses. Chapter 7, of the Participants Manual for the NHI course on Subsurface Investigations provides guidance on the selection of test types and the determination of applied loads/pressures. The general design cases and applicable stress categories are summarized below: Design Case

Analysis Type and Strength Parameters

Foundations

Total Stress –Undrained Strengths

Excavation

Effective Stress –Drained Strengths

Natural Slope

Effective Stress –Drained Strengths

Typically, at least three strength tests are performed to obtain a strength envelope and 02/14/2005


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identify any obviously erroneous test results. The confining pressures for each test should be estimated by the Geotechnical Engineer, which should be based on the range of stress levels to be experienced during various stages of construction (including the initial overburden pressures). Typically, the first test has a confining stress similar to the existing overburden pressure, and the second andt hi r dt est swoul dhav ehi gherc onf i ni ngs t r es s est odet er mi neФ. Testing pressures are commonly about 10, 20, and 40 psi (effective stresses). In cases where the Mohr envelope is not linear (because of past preconsolidation) or the project is complex, additional tests should be conducted in the lower stress range to better model the Mohr envelope and to better define the cohesion intercept. All laboratory test data and results should be scrutinized for quality of test procedures, and soil samples. In selection of strength parameters, the Geotechnical Engineer should realize that test results are indicative of a very small percentage of the soil mass, and the natural variability of these materials at the site should be considered. The results are shown on the Summary of Results table (Figure 8-3), and the detailed test specifics are often presented on graphical figures. The common methods of ascertaining shear strength parameters in the laboratory are discussed below: 3.11.1.

Unconfined Compression Test

The Unconfined Compression Test determines approximate undrained shear strengths due to the slightly relaxed in situ pressures of the sample. The lack of confinement introduces a relatively large error range. This test is a fast and economical means of approximating the shear strength at shallow depths, but the reliability decreases with increasing depth. Triaxial testing is recommended when more reliable values of cohesive shear strength are desired. The test is performed on a cylindrical sample without any confining pressure, subjected to an axial load until failure occurs. A simple hand- or motor-operated compressive load test frame is commonly used, although use of triaxial apparatus can achieve the same results. This test is typically performed on cohesive soils. Total stress parameters are obtained, which are only applicable for the sampled depths. The cohesion is taken as one-half the unconfined compressive strength, qu. Tests are performed in accordance with AASHTO T 208. 3.11.2.

Triaxial Compression Tests

Triaxial tests provide controllable stresses and reliable measurements, which are necessary for critical analyses. In this test, a cylindrical sample is subjected to an axial load until failure occurs while also being subjected to confining pressures approximating a range of in situ stress levels. Various types of triaxial tests are conducted as summarized below: 

Unconsolidated-Undrained (UU), or Q Test This test is an improved means of determining undrained shear strengths compared to the Unconfined Compressive Test, and is recommended for geotechnical analyses for short-term stability. Test results are used primarily in the calculation of immediate embankment stability as short-term (quick-loading) conditions. The test specimen is

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prevented from changing its initial water content before or during shearing. Results are total stress strength parameters, and are only applicable for the sampled depths. (Refer to ASTM D 2850, AASHTO T 296.) 

Consolidated-Undrained (CU), or R Test This test differs from the UU test by applying confining stresses to reconsolidate the specimen before testing. If the goal is to determine short-term undrained shear strengths, then no pore water pressure measurements are made, which simplifies test procedures. However, the advantage of using this test type is to determine effective stress parameters for both short-term and long-term design cases, which requires the measurement of pore water pressures and more effort in test set-up. The Geotechnical Engineer should determine the type of data needed for the design analyses and the locations and numbers of tests required. The CU test specimen is allowed to consolidate under the confining pressure prior to shearing, but no drainage is permitted during shearing. This test takes longer and is more expensive than a UU test because the sample must be backpressure saturated (to accurately measure pore water pressures and specimen response), which may take a few days. A minimum of three tests at different confining pressures is required to develop the Mohr envelope over the applicable stress range. Often a 3-stage test can be performed on one specimen, which saves time and reduces cost, as well as eliminates inconsistency between specimens. A 3-stage test might not be possible where soft/compressible soil specimens experience large deformations in the first or second shearing stages. (Refer to ASTM D 4767, AASHTO T 297.) The Bishop and Henkel reference is recommended for planning and performing this test.



Consolidated-Drained (CD), or S Test This test is not as common as the CU test because the test may require a potentially longer time to run and is primarily applicable for relatively cohesionless soils. This test is similar to the CU test except that drainage is allowed during shearing and the rate of shearing is very slow to prevent the buildup of excess pore water pressure. This test may take days to perform, making it expensive. These tests are not performed often because similar results can be obtained with the quicker CU tests. As with the CU test, a minimum of three tests (or stages) is required. Effective stress strength parameters are obtained without the need for pore water pressure measurement. Test results are used for calculating long-term stability of embankments where relatively cohesionless materials exist along potential failure surfaces. (Refer to the Corps of Engineers “ Labor at or ySoi l sTest i ngEngi neer i ngandDesi gnManual ” . )



Direct Shear Test This is a low cost test that provides reasonable strength values for undisturbed or recompacted specimens of cohesionless soils. Direct shear test apparatus is used to determine residual (remolded) shear strengths of landslide shear zone materials. To

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conduct the test, a thin soil sample is placed in a shear box consisting of two parallel blocks, and a vertical force normal to the shear surface is applied. One block remains fixed while the other block is moved parallel to it in a horizontal direction. The soil fails by shearing along a plane that is forced to be horizontal. A series of at least three tests with varying normal forces is required to determine the shear strength parameters for a particular soil. This test is typically run as a consolidated-drained test on cohesionless materials. Where the soils are cohesive, the strain rate will need to be calculated and is usually very slow to prevent the build-up of pore water pressures. Tests are performed i naccor dancewi t hASTM D3080( AASHTOT236) .Anex ampl eof“ Di r ectShearTest Repor t ”i sshownonFi gur e8-10. (Refer to the Corps of Engineers “ Labor at or ySoi l s Test i ngEngi neer i ngandDesi gnManual ” . ) 

Simple Direct Shear Test This test is conducted to measure undrained (constant volume) strength and stressstrain characteristics of cohesive soils using a constant rate of simple shear deformation mode of loading after completion of one-dimensional consolidation. This test is applicable for undisturbed and remolded soil samples. Tests are performed in accordance with ASTM D 6467.



Miniature Vane Shear and Penetrometer Tests These inexpensive tests are used as an index of the undrained shear strength (Su) of clay materials. These tests are applicable for projects that are relatively simple and lowrisk. Both tests consist of hand-held devices that are pushed into the sample and either a torque resistance (Torvane or other vane apparatus) or a tip resistance (pocket penetrometer) is measured. They can be performed in the laboratory or in the field, typically on the ends of undisturbed thin-walled tube samples, as well as along the sides of test pits. Miniature vane shear tests are performed in accordance with ASTM D 4648.

3.12

Consolidation Tests

When large loads (such as embankments and spread footings) are applied on cohesive soils, the soils consolidate, i.e., settle over time, through a combination of the rearrangement of the individual particles and the squeezing out of water. The amount and rate of settlement is of great importance in construction. For example, an embankment may settle and create a gap between the approach slab and the bridge abutment. The calculation of settlement involves many factors, including the magnitude of the load, the change in stress at the depths where compressible soils exist, the water table, and characteristics of the soil itself. Consolidation testing is performed to determine soil properties that are used in settlement analyses. Consolidation tests are conducted when embankments or structure loads are applied over deposits of relatively soft/loose or compressible fine-grained soils. Test samples should be selected after boring logs are reviewed, and subsurface cross-sections are developed. At least one consolidation test should be performed for each distinct soil unit developed in the 02/14/2005


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cross-section. Additional tests may be needed if the soil layers are thick and sub-layers are required for the analyses. The test samples should be obtained from the middle of the subject soil layers and sub-layers. Tests should preferably be performed on undisturbed samples obtained from samplers, such as Shelby Tubes or Osterberg samplers. Samples obtained by SPT, Dames & Moore, and Sprague & Henwood samplers are sometimes used for consolidation testing, but results include error because of sample disturbance. When conducting tests on disturbed samples, the preconsolidation pressure is difficult to interpret because the soil structure has relaxed t owar dst her emol dedor“ nor mal l yconsol i dat ed”st at e. The Geotechnical Engineer must determine the range of test loads (pressures) based on overburden pressures and anticipated loading conditions. This includes whether a rebound/reload cycle should be performed, and if so, at what stress levels. Soils that are organic have secondary consolidation characteristics that should be determined by continuing certain stress levels well into the secondary range (which might take hours or days in some cases). The Geotechnical Engineer needs to identify which test load levels should be applied with longer durations to determine secondary consolidation coefficients (corresponding to actual stress levels critical in the long term). 3.12.1.

One-Dimensional Test

The most often used method of consolidation testing is the one-dimensional test. In this test, a specimen is placed in a consolidometer between two porous stones, which allows flow of water. Specimen size can vary depending on the equipment used. Various loading procedures can be used during a one-dimensional test with incremental loading being the most common. With this procedure, the specimen is subjected to increasing loads; typically beginning at approximately 1/16 tsf and doubling each increment up to 48 tsf. After each load application, the change in sample height is monitored incrementally for 24 hours, generally. To evaluate the recompression parameters of the sample, an unload/reload cycle can be performed. To better evaluate the recompression parameters for overconsolidated clays, the unload/reload cycle may be performed after the preconsolidation pressure has been defined. After the maximum loading has been reached, the load is removed in decrements. Tests are performed in accordance with AASHTO T 216. An example summary graph, with calculated consolidation parameters and soil moisture/density, is shown on the Consolidation Test Report in Figure 8-8. The data from a consolidation test is usually present edonanε -log p curve, which plots per cent agest r ai n( ε )asaf unct i onoft hel ogofpr essur e( p) .Thepar amet er snecessar yf or settlement calculation can be derived from the curve: compression index (Cc), recompression index (Cr), and preconsolidation pressure (po or Pc). A separate plot is prepared of change in sample height versus log of time for each load increment. From this, the coefficient of consolidation (Cv) and coefficient of secondary compression (Cα) can be derived. These parameters are used to estimate the rate of primary settlement and amount of secondary compression. 02/14/2005



8-12

Constant Rate of Strain Test

Other loading methods include the Constant Rate of Strain Test (ASTM D 4186) in which the sample is subjected to a constantly changing load while maintaining a constant rate of strain; and measuring the pore water pressure of the soil sample, for an undrained test. A direct analogy is drawn between laboratory consolidation and field settlement amounts and rates. 3.13

Collapse Potential Tests

This test is often called a Hydrocollapse Test and is used to estimate the collapse potential of soils (under the influence of saturation). This test is primarily used on loess and loess type materials that have low dry unit weights, have low or no plasticity, have a high void r at i o,andc ant ol er at enearv er t i cal cut swhendr y .Thesemat er i al shav ea“ car dhouse”t y pe structure and collapse when saturated. Structures founded on these soils could experience serious damage if the soil becomes saturated. Collapse potential of a soil is determined by placing an undisturbed sample into a consolidation ring at its natural moisture content. Appropriate loads are applied to the sample to achieve the planned stress levels. The soil sample is saturated at the desired stress level and load is held constant to monitor the collapse before applying the next load increment. The vertical displacement is measured at each stress level, similar to performing a consolidation test. The results are graphically presented as shown on Figure 8-9. The Geotechnical Engineer needs to identify the soil samples that may be impacted by exposure to water during or after construction. The Geotechnical Engineer must determine the stress level at which the specimen should be saturated, based on expected conditions during or following construction. (Refer to ASTM D 5333 for performance of this test.) 3.14

Swell Potential Tests (Clays)

Some soils, particularly those containing montmorillonite clay, tend to increase in volume when their moisture content increases. These soils can be highly problematic resulting in costly damage to structures being supported by them. Test types include: 3.14.1.

Soil Suction Test

The soil suction test provides a characterization of the behavior of expansive soils and a reliable estimate of anticipated volume change. This is the preferred test method, according to FHWA-RD-79-51 (1979). However, conducting this test is not common and equipment needed to perform this test is typically not available in laboratories. Soil suction is the pulling force exerted on the soil-water by the soil mass and is typically measured in tons per square foot. The tendency for soil suction is directly related to the relative humidity of the soil. The simplest and most reliable technique for measuring the relative humidity of a sample is to use a thermocouple psychrometer. Undisturbed soil samples at in-place, dried and wetted moisture contents are placed in separate airtight containers fitted with a rubber stopper through which the tip of the psychrometer is inserted. The purpose of wetting and drying is to 02/14/2005


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establish a range of moisture contents over which the soil suction can be measured. The samples are allowed to stabilize for approximately 48 hours after which the psychrometer measurements are taken. The natural moisture content of each sample is then determined using the volume displacement method. 3.14.2.

Oedometer Swell Test

The swell potential of a soil can be approximated from the consolidometer test methods described in ASTM D 4546 (AASHTO T 258). It is more convenient to perform this test than Soil Suction test since the Geotechnical Laboratory is equipped with the needed apparatus to conduct this test. (Refer to FHWA-RD-79-51 (1979) for guidance on the procedure and use of the test.) 3.14.3.

Shrinkage Limit Test

This Atterberg limit test is easily performed and the obtained data can be correlated to swell potential of the soil. It does not measure swell, but rather the degree a sample shrinks when dried. Therefore, the correlation is an indirect approach to measure swell potential. FHWA-RD-79-51 (1979) describes the application of this test data, as well as its limitations. 3.15

Permeability Tests

. Soil permeability can be measured either directly from field testing or indirectly from laboratory tests, although not as accurately. The Geotechnical Engineer should evaluate whether geotechnical design for the project needs permeability data. The following are typical laboratory tests: 3.15.1.

Constant Head Test

To conduct this test, a permeameter into which the sample is placed and compacted to the desired relative density is used. Water (preferably de-aired) is introduced by an inlet valve until the sample is saturated. Water is then allowed to flow through the sample while a constant head is maintained. The permeability is measured by the quantity of flow of discharge over a specified time. This method is generally used only for coarse-grained soils. Tests should be performed in accordance with ASTM D 2434 (AASHTO T 215). Alternatively, a constant head test can be performed on a compacted specimen in a compaction mold following the procedures of ASTM D 5856. 3.15.2.

Falling Head Test

To conduct this test, an apparatus and a procedure similar to the constant-head test above are used. The test is applicable for fine-grained soils. The soil is compacted into a mold. The permeability is measured by the decrease in the head of water for a specified time. Tests are performed in accordance with ASTM D 5856. 3.15.3.

Triaxial Permeability Test

For fine-grained soils, tests using a triaxial cell are generally preferred, because Constant and Falling Head tests take too long to perform. In situ conditions can be modeled 02/14/2005


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by application of an appropriate confining pressure. The sample can be saturated using backpressuring techniques. Water flows through the sample under pressure and measurements are taken until steady-state conditions occur. Tests are performed in accordance with the Flexible Wall test procedures described in ASTM D 5084. 3.16

Dynamic Properties

Tests are performed to assess ground motion amplification parameters and liquefaction susceptibility of soils. Many dynamic properties can be obtained through in situ tests that limit sample disturbance, which is inherent in laboratory samples. (Refer to Kramer (1996) for more information.) The most common tests are listed below: 

Resonant Column Test This is a low strain test used to determine the shear modulus, shear damping, and Young’ smodul i f ordy nami cl oadi ngs.Theset est sar eusual l yper f or medoncohesi v e soils to determine the ground motion amplification parameters. This test is discussed in ASTM D 4015.



Cyclic Triaxial Test This test is usually performed on sands to determine liquefaction susceptibility although it can also be used to obtain ground motion amplification parameters. Refer to ASTM D 3999 and D 5311.



Cyclic Direct Simple Shear Test This test models large strains similar to the Cyclic Triaxial Test. This test is considered to model the earthquake stress conditions more accurately than Cyclic Triaxial Tests. See ASTM,“ Geot echni calTest i ng Jour nal , ”Vol .16,No.1,pp.36-45,and “ An Evaluation of Direct Simple Shear Tests on Clay, Geotechnique, Vol. 37, No.1, pp 2535.

4.

CORRELATIONS OF SOIL PROPERTIES

Nonhomogeneous nature of soils, finite exploration and laboratory testing budgets, sample disturbance, and the inherent empirical nature of geotechnical design procedures all make correlations essential tools for Geotechnical Engineers. Correlations are used to approximate engineering properties and to check the reasonableness of test results and assumptions. The use of correlations enables greater application of data obtained from the geotechnical exploration program. Many correlations are based on common tests, such as moisture contents, Atterberg limits, SPT values, and general soil descriptions. The Participants Manual for the NHI course on Subsurface Investigations provides a discussion of the most commonly used correlations. Common correlations include the following: 

Unit weights as a function of void ratios for typical soil types



Relative density of cohesionless soils as a function of SPT values



Consistency of cohesive soils as a function of SPT values



Consolidation parameters based on general soil classifications

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8-15



Consolidation parameters based on moisture contents, liquid limits, and Plasticity Indices



Permeability parameters based on general soil classifications



Permeability parameters based on soil gradations, void ratios, and unit weights



Cohesive shear strengths based on SPT values for silt and clay soils



Classifications of cohesive soils based on Atterberg limits and SPT blow counts



Angl esofshear i ngr esi st ance,Φ,basedonSPTval uesf orcohesi onl esssoi l s



Angl esofshear i ngr esi st ance( peakandr esi dual ) ,Φ,andΦr ,basedonPl ast i ci t y Indices for cohesive soils



Shear strengths of compacted soils, based on general soil classifications



Compaction optimum moistures, based on Plastic Limits

5.

ROCK

Laboratory testing on rock samples is for determining certain properties such as strength, elasticity, and degradation potential. The results are applied to the design of rock slopes and foundations. Typically, the properties of in situ rock are determined by the presence of joints and bedding planes. These features cannot be modeled in the laboratory, since laboratory tests are performed on samples of limited size. Therefore, the application of the laboratory test results should be used only with a thorough understanding of the affects the in situ characteristics of the rock mass, especially the structural discontinuities, have on the design performance. Test descriptions are briefly described in the following sections: 5.1

Visual Classifications

The Rock Quality Designations (RQD) is determined in the field when core barrels are opened. In the laboratory, a closer examination can be made of joint surfaces and infilling conditions, as well as a confirmation of RQD and Joint Roughness Coefficient (JRC) values. In some cases, soil-like zones may exist within the rock unit (i.e., decomposed rock, gouge zones, interbed contact zones, or poorly indurated material). When soil-like materials are encountered, consideration should be given to performing soil tests to properly characterize these zones, such as moisture contents and Atterberg limits. 5.2

Absorption and Bulk Specific Gravity Tests

Absorption is a measure of the amount of water a dry specimen can absorb during a 48-hour soaking period. The amount of absorbed water is indicative of the porosity of the sample. Bulk specific gravity is used to calculate the unit weight of the material. Tests are performed in accordance with ASTM C 97. 5.3

Durability Tests

Durability tests are conducted to determine the relative durability of rock, which are useful for evaluating whether the rock potentially degrades when exposed to alternating cycles of wetting and drying. 02/14/2005



8-16

Jar Slake Test

This is a simple, qualitative test used to assess durability of weak rocks, such as shales or mudstones, when exposed to atmospheric conditions. Performance of a rock sample in this test determines if a rock is relatively nondurable. More quantitative tests may need to be performed depending on the environmental conditions and application. To conduct the Jar Slake Test, a rock sample is immersed in water for a minimum of 24 hours. If degradation in the form of fractures, chips, flakes occurs, the condition is described, including the approximate percentage of material that sloughed. There is no ASTM or AASHTO procedure for this test. The following are rock durability categories based on the results of the Jar Slake Test (per Wood and Deo, 1975): Jar Slake Value Behavior 1 Degrades to a pile of flakes or mud 2 Breaks rapidly, forms many chips, or both 3 Breaks slowly, forms few chips, or both 4 Breaks rapidly, forms several fractures, or both 5 Breaks slowly, develops few fractures, or both 6 No visible change 5.3.2.

Slake Durability Test (2-cycle)

This test is performed on shales, mudstones, or other weak rocks that may be susceptible to degradation when exposed to atmospheric conditions. This test is useful for an assessment of degradations of rocks after the first-time atmospheric exposure. Examples would be exposed rock surfaces of excavated holes when socketing a drilled shaft, or exposed newly constructed rock cut surfaces. Degradation assessments are also used to evaluate long-term performance of embankment fill materials. This test consists of rotating oven-dried rock fragments submerged in water in a drum. Two cycles of rotation/submersion are performed and the final oven dried mass is compared to the initial oven dried mass. This mass ratio along with the size and shape of the remaining sample are used to determine the Slake Durability Index (SDI). Low SDI values indicate that the sample is susceptible to degradation. This test is described in ASTM D 4644. The SDI values are grouped into the following categories: Slake Durability Index, SDI Material Classification 0 to 60% Soil-like 60% to 90% Intermediate 90% to 100% Rock-like 5.4

Soundness Test

This test is used to determine the suitability of aggregate for use as MSE backfill. The test consists of four or five cycles of drying and immersion of rock slabs in a sodium or magnesium sulfate solution (AASHTO T-104). The percent of weight loss is expressed as percent soundness. Refer to ASTM D 5240. 02/14/2005


LABORATORY TESTING 5.5

8-17

Permeability Test

The permeability of rock masses is depended on quantity of fluid flowing through discontinuities. It is therefore most appropriate to determine permeability by in situ tests such as variable head tests or pumping tests. Laboratory permeability tests can be performed by methods using flowing air. The test is performed on a small sample in accordance with ASTM D 4525. 5.6

Rock Strength Test

Laboratory tests, except for Point Load tests, to determine strengths of rocks are relatively uncommon for most highway applications. In most highway designs, the strength of intact rock pieces is usually not a controlling factor. Point Load test data helps to characterize strength of the rock, which is useful for evaluating excavatability. Compressive strength tests may be needed for design of tunnels and highly loaded structure foundations on rock. Typically, the Department sends rock samples to the University of Nevada, Reno, to have these tests performed. 5.6.1.

Point Load Strength Index Test

This inexpensive test can be performed in the field or the laboratory. Numerous tests can be performed in a short time. Estimates of uniaxial compressive strengths using the point load strength index test results are approximate and should be used with engineering judgment when making general rock strength classifications. Point Load strength index is an indicator of intact rock strength and hardness. The test subjects the rock specimen to an increasing concentrated point load, applied through a pair of truncated, conical platens, until failure. The failure load is used to calculate the size corrected point load strength index (Is(50)), and to estimate the uniaxial compressive strength of the rock core specimen. Rock core samples are typically tested diametrically (load applied along the axis of the diameter). Irregular rock fragments and lumps can also be tested, with some preparation. Tests can be performed both parallel and perpendicular to inherent planes of weakness within the rock mass. Tests are performed in accordance with ASTM D5731 and the International Society for Rock Mechanics (ISRM). 5.6.2.

Unconfined Compression Test

This test is performed on intact rock core specimens, which preferably have a length of at least two times the diameter. The specimen is placed in the testing apparatus and loaded axially at an approximately constant rate such that failure occurs within 2 to 15 minutes. Tests are performed in accordance with ASTM D 2938. 5.6.3.

Triaxial Compressive Strength Test

This test is performed to measure the ultimate compressive shear strength and elastic properties, such as Young's modulus and Poisson's ratio, of rock under a confining pressure. The application of confining pressure to the rock sample to be tested is to simulate the stress conditions under which the rock existed in the field. Tests are performed in 02/14/2005


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accordance with ASTM D 2664 (AASHTO T 226). Elastic Moduli –Uniaxial Compressive Test

5.6.4.

This test is performed to determine the stress-deformation characteristics of rock, cal cul at et heYoung’ sModul us,andt oev al uat et hesui t abi l i t yoft her ock to support structure foundations. (Refer to ASTM D 3148.) 5.6.5.

Splitting Tensile Strength Test

This is an indirect tensile strength test similar to the Point Load Strength Index test. However, the compressive loads are line loads applied parallel to the core’ sax i sbyst eel bearing plates between which the specimen is placed horizontally. Loading is applied continuously such that failure occurs within one to ten minutes. Tests are performed in accordance with ASTM D 3967. 5.6.6.

Direct Shear Test

This test is performed to determine the shear strength of a rock discontinuity, such as joints and bedding contacts. Test results are used for stability analysis of rock slopes. The test is similar in concept to the direct shear test for soils. The rock sample is grouted in the lower platen of the shear box. The line of force is directed to act along the discontinuity in the rock. Irregularities in the surface of the discontinuity can create misleading results because the mode of failure may vary to that in the field. An asperity in the discontinuity surface results in either shearing or overriding of the asperity, depending on the normal load applied. (Refer to ASTM D 5607.) Depending on the application, an in situ direct shear test may be warranted/preferred (see Figure 8-10). 5.7

Unit Weight Test

This test is performed to measure the total/moist or oven-dried unit weight of a rock core sample. The total/moist or oven-dried unit weight is directly determined by dividing the total/moist or oven-dried weight by the cylindrical volume of the intact sample respectively. The volume measurement includes any voids or pore spaces in the sample. Samples should be preserved and tested at the moisture content representative of field conditions. Moisture contents are performed in accordance with ASTM D 2216. 6.

CORRELATIONS OF ROCK PROPERTIES

Rock property correlations utilize limited databases and the rock formation used to develop the correlation likely differs from the mass being studied. Therefore, experience and engineering judgment is necessary when correlating test results to rock properties. The controlling factors in the behavior of a rock mass are the structural discontinuities. The NHI course on Subsurface Investigations, Chapter 10, provides a discussion of the most commonly used correlations. Common correlations include the following: 

Compressive strength based on rock types



Uniaxial compressive strength based on Point Load tests

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LABORATORY TESTING 

Modulus of elasticity based on rock types



Shear strength based on rock types



Joint Roughness Coefficients based on visual examination of specimen

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8-19


LABORATORY TESTING

7.

8-20


The appropriate test method (ASTM, AASHTO, or Nevada) is determined by the Principle Geotechnical Engineer. SOIL TESTS Test Category Visual Identification

Index Properties

Tests

ASTM

AASHTO

Classification of Soils for Engineering Purposes (Unified Classification System Description and Identification of Soils (VisualManual Procedure) Specific Gravity of Soils

D 2487

-

D 2488

-

D 854

T 100

Materials Finer than No. 200 Sieve in Mineral Aggregates by Washing Sieve Analysis of Fine and Coarse Aggregate

C 117

T 11

C 136

T 27

Particle-Size Analysis of Soils

D 421 D 422

T 87 T 88

Materials Finer than No. 200 Sieve in Mineral Aggregates by Washing Resistance R-Value & Expansion Pressure of Compacted Soils

D 1140

-

D 2844

T 190

-

T 292

Shrinkage Factors of Soils by the Mercury Method

D 427

T 92

Liquid Limit, Plastic Limit, and Plasticity Index of Soils

D 4318

T 89 T 90

Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 [600 kN-m/m]) Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft3 [2,700 kN-m/m3])

D 698

T 99

D 1557

T 180

Resilient Modulus- Soil

Harvard Miniature Compaction Device

Chemical Tests

Water (Moisture) Content of Soil and Rock

D 2216

T 265

Maximum Index Density and Unit Weight of Soils Using A Vibratory Table

D 4253

-

Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density

D 4254

-

Crumb Test to Identify Dispersive Clays

D 6572

pH of Peat Materials

D 2976

pH of Soils

D 4972

pH of Soil for Use in Corrosion Testing Sulfate Content 02/14/2005

T 272

NDOT

T 206F

T 106B T 115D T 166A

T 210F T 211F T 212F

T 101E T 112D

T 238A

G 51

T 289

D 4230

T 290


LABORATORY TESTING Resistivity

8-21 D 1125

T 288

T 235B

& G 57

Strength Testing

Dynamic Properties

Permeability

Compression Properties

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Chloride Content Moisture, Ash, and Organic Matter of Peat and Other Organic Soils

D 512 D 2974

T 291 T 267

Unconfined Compressive Strength of Cohesive Soil Unconsolidated, Undrained Compressive Strength of Cohesive Soils in Triaxial Compression Consolidated Undrained Triaxial Compression Test for Cohesive Soils Consolidated Drained Triaxial Compression Test Direct Shear Test of Soils Under Consolidated Drained Conditions Miniature Vane Shear Test for Saturated FineGrained Clayey Soil Consolidated Undrained Direct Simple Shear

D 2166 D 2850

T 208 T 296

D 4767

T 297

D 3080

T 236

D 4648

-

Modulus and Damping of Soils by the ResonantColumn Test

D 4015

-

Modulus and Damping of Soils by the Cyclic Triaxial Apparatus

D 3999

-

Load Controlled Cyclic Triaxial Strength of Soil

D 5311

-

Consolidated Undrained Direct Simple Shear

D 6528

-

Permeability of Granular Soils (Constant Head)

D 2434

T215

Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter

D 5084

-

Hydraulic Conductivity of Porous Materials Using a Rigid-Wall, Compaction-Mold Permeameter

D 5856

-

One-Dimensional Consolidation Properties of Soils

D2435

T 216

One-Dimensional Consolidation Properties of Soils Using Controlled-Strain Loading

D 4186

-

One-Dimensional Swell or Settlement Potential of Cohesive Soils

D 4546

T 258

Measurement of Collapse Potential of Soils

D 5333

-

D6528


LABORATORY TESTING

8-22

ROCK TESTS Test Category Index Properties

Point Load Strength Compressive Strength

Direct Shear Tensile Strength Permeability Durability

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Tests

ASTM

AASHTO

Absorption and Bulk Specific Gravity of Dimension Stone Specific Gravity and Absorption of Coarse Aggregate Preserving and Transporting Rock Core Samples Point Load Strength Index of Rock

C 97

-

C 127

T 85

D 5079

-

D 5731

-

D 2664

T 226

D 2938

-

D 5607

-

D 3967

-

D 4525 D 4644

-

D 5240

-

Triaxial Compressive Strength of Undrained Rock Core Specimens Without Pore Pressure Measurements Unconfined Compressive Strength of Intact Rock Core Specimens Laboratory Direct Shear Strength Tests – Rock Specimens Under Constant Normal Stress Splitting Tensile Strength of Intact Rock Core Specimens Permeability of Rocks by Flowing Air Slake Durability of Shales and Similar Weak Rock Rock Slab Testing – Riprap Soundness, By Use of Sodium/Magnesium Sulfate


LABORATORY TESTING

8.

8-23

FIGURES 8-1: Geotechnical Lab Task Sheet

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LABORATORY TESTING

8-24

8-2: Geotechnical Lab Task Sheet, continued

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LABORATORY TESTING

8-25

8-3: Summary of Results

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LABORATORY TESTING

8-26

8-4: Line Sampling Data

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LABORATORY TESTING

8-27

8-5: Plasticity Index

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LABORATORY TESTING

8-28

8-6: Particle Size Distribution Report

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LABORATORY TESTING

8-29

8-7: Chemical Analysis

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LABORATORY TESTING

8-30

8-8: Consolidation Test Report

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LABORATORY TESTING

8-31

8-9: Hydrocollapse Test Report

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LABORATORY TESTING

8-32

8-10: Direct Shear Test Report

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LABORATORY TESTING

9.

8-33

REFERENCES

AASHTO,“ ManualonFoundat i onI nv est i gat i ons, ”1988 AASHTO,“ ManualonSubsur f aceI nv est i gat i ons, ”1984 ASTM,“ Geot echni calTest i ngJour nal , ”Vol .16,No.1,pp.36-45, 1993 Airey, D.W. and Wood, D.M. “ An Ev al uat i on ofDi r ectSi mpl e ShearTest s on Cl ay , ” Geotechnique, Vol. 37, No.1, pp 25-35, 1987 Bi shop,A. W. ,andHenkel ,D. J,“ TheTr i ax i alTest , ”2ndEd. ,1962 Boul anger ,R. W. ,Chan,C. K. ,Seed,H. B. ,Seed,R. B. ,and Sousa,J. ,( 1993) .“ Al ow Compl i ance Bi di r ect i onalCy cl i c Si mpl e ShearAppar at us, ”Geot echni calTest i ng Journal, ASTM, Vol. 16.No.1, pp 36-45, 1993 Canadian Geotechni calSoci et y ,“ Canadi anFoundat i onEngi neer i ngManual , ”1985. Cor psofEngi neer s, “ Labor at or ySoi l sTest i ng, Engi neer i ngandDesi gnManual , ”No. 1110-21906, Waterways Experiment Station, 1970 FHWA,“ Desi gnandConst r uct i onofCompact edShal eEmbankment s” ,Vol s.1t o5,FHWARD-75-61, FHWA-RD-75-62, FHWA-RD-77-1, FHWA-RD-78-140, and FHWA-RD-78141, ”1978 FHWA,“ Ev al uat i onofSoi landRockPr oper t i es, ”Geot echni calEngi neer i ngCi r cul arNo.5, FHWA-IF-02-034 FHWA,“ Geot echni calEngi neer i ngNot ebook” . FHWA,“ Soi l andBaseSt abi l i z at i onandAssoci at edDr ai nageConsi der at i ons, ”Vol s. 1and2, FHWA-SA-93-004 and FHWA-SA-93-005, 1993 FHWA,“ Soi l sandFoundat i onsWor kshopManual , ”FHWA-HI-88-009, 2nd Ed., 1993 FHWA,“ Subsurface Investigations, Participants Manual for Geotechnical and Foundation Engi neer i ng, ”Modul e1,NHICour se13221,FHWA-HI-97-021, 1997 FHWA,“ Techni calGui del i nesf orEx pansi v eSoi l si nHi ghwaySubgr ades, ”Fi nalRepor t , FHWA-RD-79-51, 1980 Kr amer ,S. L. ,“ Geot echni calEar t hquakeEngi neer i ng, ”1996. NAVFAC,“ Desi gnManualDM-7:Soi lMechani cs, ”1982. TRB,“ Gui det oEar t hwor kConst r uct i on:St at eoft heAr tRepor t , ”TRBRepor tNo.8,I SBN0309-04957-1, 1990

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CHAPTER 9 MATERIALS DESCRIPTION

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MATERIALS DESCRIPTION

1. 2. 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 3. 3.1 3.1.1. 3.1.2. 3.1.3. 3.1.4. 3.1.5. 3.1.6. 3.1.7. 3.1.8. 3.2 3.2.1. 3.2.2. 4. 4.1 4.2 4.3 5. 6.

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TABLE OF CONTENTS INTRODUCTION.................................................................................................. 1 SOIL ..................................................................................................................... 1 Soil Type .............................................................................................................. 2 USCS Designation ............................................................................................... 3 Color..................................................................................................................... 3 Plasticity ............................................................................................................... 3 Moisture ............................................................................................................... 3 Relative Density and Consistency........................................................................ 3 Texture ................................................................................................................. 4 Cementation......................................................................................................... 4 Structure............................................................................................................... 4 Other Constituents/Characteristics....................................................................... 4 Origin.................................................................................................................... 5 ROCK................................................................................................................... 5 Intact Character.................................................................................................... 5 Rock Name .......................................................................................................... 6 Color..................................................................................................................... 6 Degree of Weathering.......................................................................................... 7 Relative Hardness ................................................................................................ 7 Structure/Discontinuities ...................................................................................... 7 Core Recovery and Rock Quality Designation (RQD).......................................... 9 Other Rock Characteristics ................................................................................ 10 Formation Name ................................................................................................ 10 In Situ Character ................................................................................................ 11 Discontinuity Orientation .................................................................................... 11 Roughness ......................................................................................................... 11 EXPLORATION LOG ......................................................................................... 12 Field Log ............................................................................................................ 12 Drilling Remarks ................................................................................................. 13 Final Exploration Log ......................................................................................... 13 SPECIFICATIONS AND STANDARDS.............................................................. 14 FIGURES ........................................................................................................... 14 9-1: Soil Constituents –Definitions ................................................................... 14 9-2: Silt and Clay Characteristics ...................................................................... 15 9-3: Examples of Fine-Grained Soil Field Identification .................................... 16 9-4: Fine-Grained Soil Subclassification ........................................................... 16 9-5: Coarse-Grained Soil Subclassification....................................................... 17 9-6: Unified Soil Classification Summary .......................................................... 18 9-7: Degree of Plasticity .................................................................................... 19



7.

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9-8: Moisture Designations................................................................................ 19 9-9: Consistency of Cohesive Soils................................................................... 20 9-10: Relative Density for Granular Soils .......................................................... 20 9-11: Gradation Categories ............................................................................... 21 9-12: Criteria for Describing Structure............................................................... 21 9-13: Common Igneous Rocks.......................................................................... 22 9-14: Pyroclastic Rocks..................................................................................... 22 9-15: Igneous Rock Textures ............................................................................ 22 9-16: Common Sedimentary Rocks .................................................................. 23 9-17: Common Metamorphic Rocks.................................................................. 23 9-18: Scale of Relative Rock Weathering ......................................................... 24 9-19: Scale of Relative Rock Hardness............................................................. 25 9-20: Stratification Terms .................................................................................. 26 9-21: Joint and Bedding Spacing Terms ........................................................... 26 9-22: Standardized Volume Percentage Chart.................................................. 27 9-23: Graduation Chart ..................................................................................... 28 9-24: Measurement of Joints............................................................................. 29 9-25: Field Log Form......................................................................................... 30 9-26: Example, Final Exploration Log ............................................................... 31 9-27: Key to Boring Logs................................................................................... 32 REFERENCES................................................................................................... 33


MATERIALS DESCRIPTION 1.

9-1

INTRODUCTION

Consistency when describing materials is essential so that users of the information can properly understand and interpret the subsurface conditions. Material descriptions are based on the visual-manual method, which uses visual observations and simple manual index tests to estimate the physical and behavioral properties of the material (ASTM D 2488). Material classifications are based on more detailed, visual-manual observations and inspections, as well as the results of specific laboratory tests (ASTM D 2487). Physical and engineering properties of materials are considered in classifications of soils and rocks. The detail of the classification should not be dictated by the complexity or objectives of the project. Classification should always be as complete as possible and based on factual information. Interpretive information should be kept to a minimum and always put in parentheses. Discussions of interpretive information can be provided in the text of Geotechnical Reports. Material classifications, and information obtained during the subsurface explorations are heavily relied on throughout the remainder of the investigation program and during the design and construction phases of a project. They also have significant importance in resolving claims disputes. It is therefore necessary for the method of reporting this data to be standardized. Records of subsurface explorations should follow the format presented in this Chapter. 2.

SOIL

Soil classifications are based on the distribution and behavior of fine-grained (passing No. 200 sieve) and coarse-grained (retained No. 200 sieve) soil constituents, as described in ASTM D 2487 and D 2488. These procedures employ visual examination and simple manual tests to identify soil characteristics, which are then included in the material description. For example, estimates of grain-size distribution by visual examination indicate whether the soil is fine-grained or coarse-grained. Manual tests for dry strength, dilatancy, toughness, and plasticity indicate the type of fine-grained soil. Organics are generally identified by their color, odor, and spongy feel. The general descriptive sequence for soil materials is listed below. As a minimum, the first seven items should be included on the exploration logs.  Soil Name  USCS Designation  Color  Plasticity  Moisture  Consistency/Relative Density  Texture  Cementation  Structure  Other Constituents/Characteristics (unit weight, sensitivity, etc.)  Origin

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MATERIALS DESCRIPTION 2.1

9-2

Soil Type

Definitions of various soil constituents are presented in Figure 9-1. To describe a soil, the Geotechnical Engineer should determine whether the soil is predominantly fine or coarsegrained. A mixed-grained soil, which contains both fine and coarse-grained constituents, is categorized by determining its predominant engineering behavior. The procedures for describing and classifying fine-grained and coarse-grained soils are as follows:  Fine-grained Soils - Fine-grained soils are described by their engineering behavior considering characteristics such as dilatancy, dry strength, toughness, dispersion, and plasticity, as summarized on Figure 9-2. The index tests used to determine these characteristics are described in ASTM D 2488. Examples of soil descriptions based on index tests are shown on Figure 9-3. Figure 9-4 summarizes the subclassification order for fine-grained soils. For example, a soil that contains 80% fine-grained constituents (medium dry strength, slow dilatancy, medium toughness, low plasticity) and 20% sand woul dbedescr i bedas“ cl ay eysi l twi t hsomesand. ”  Coarse-grained Soils - Coarse-grained soils are described based on an estimation of particle-size distribution, as shown on Figure 9-5. Where no constituent exceeds 50% of the total sample, the coarse-grained constituent having the largest percentage becomes the primary constituent. If the soil contains no discernable fines, then the soil i sdescr i bedas“ cl ean. ”Wher et he secondary or additional constituent is fine-grained, t het er m“ cl ay ”or“ si l t ”i ssel ect edbasedont hepr edomi nantpl ast i ci t ychar act er i st i cs from index tests. For example, a soil with 48% sand, 42% gravel, and 10% fine-grained constituents (nonplastic,l owdr yst r engt h)woul dbedescr i bedas“ gr av el l ysandwi t h somesi l t . ”  Organics - Organics can generally be identified by their distinctive dark color and by their spongy feel. Fresh, wet organic soils usually have a distinctive odor of decomposed organic matter. This odor can be made more noticeable by heating the wet sample. The estimated percent and type of organic material present should be included as part of the visual sample description. The percentage of organics or any other constituent in a sample can be estimated visually by comparing the sample to standardized volume percentage charts, Figure 9-22. Based on the percentage of organics present, the material classification is as follows: Peat

50 to 100%

Primary Constituent

Organic (Soil Name)

15 to 50%

Secondary Organic Constituent

(Soil Name) with some organic

5 to 15%

Additional Organics Constituent

Secondary soil constituents should be described for peat. For example, a soil containing greater than 50% organics by volume and more than 12% silt by weight would be descr i bedasa“ si l t ypeat . ”Thet y peofor gani cmat er i al ( peat ,woodf i ber s,r oot s,car boni z ed wood, grass, leaves, etc.) should be identified if at all possible. Organics may range from 02/14/2005



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fibrous to amorphous and, at times, it may be very finely divided and hard to identify if a strong organic odor is not present. If the presence of organics is suspected, the natural moisture content or liquid limit of samples before and after oven drying can be determined and used to verify the assumption. However, Atterberg limits tests are not applicable for peat. 2.2

USCS Designation

The USCS (Unified Soil Classification System) designation should be determined by following the procedures specified in ASTM D 2487. The USCS designation, as reported on exploration logs, will be an approximation based on the visual-manual soil description (ASTM D 2488). Where classifications are based on grain-size and Atterberg limits tests, the USCS designation will be more precisely defined. Figure 9-6 is a summary of the Unified Soil Classification System. 2.3

Color

The color of a soil is of minor importance except to provide a clue as to its origin, presence of organics, or for correlation with adjacent boreholes. The Geotechnical Engineer should use the Munsell Soil Color Chart to describe soil colors. 2.4

Plasticity

Plasticity is a significant indicator property for cohesive soils. Field estimates of plasticity should be based on dry strength and toughness tests (as described in Figure 9-2 and discussed in ASTM D 2488). The relationship between these index tests and plasticity are shown on Figure 9-7. An accurate measurement of plasticity is typically made in the laboratory by means of the Atterberg limits test. A series of Atterberg limits tests should be performed on representative samples to confirm visual-manual soil descriptions. 2.5

Moisture

A visual estimation of the relative moisture content of a soil sample should be included as part of the field description (refer to ASTM D 2488). The in situ moisture content of a soil should be described as dry, damp, moist, or wet (Figure 9-8). Natural moisture contents should be determined in the laboratory for all soil samples. 2.6

Relative Density and Consistency

Consistency refers to the stiffness of a fine-grained soil. Relative density refers to the degree of compactness of a coarse-grained soil. Standard Penetration Test (SPT) N-values (blows per foot) are typically used to define the relative density and consistency (Tables 9-9 and 9-10). Nonplastic silt soils that exhibit the general properties of a granular soil are given a relative density description. Consistency is an important index property of cohesive (plastic) soils and is an indicator of the shear strength (Su). If SPT data is not available, consistency can be estimated based on visual-manual examination of the material. (Refer to ASTM D 2488 for consistency criteria).

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9-4

Texture

Texture refers to the actual size, shape, and gradation of the constituent grains. The maximum coarse-grained size recovered in soils should be noted. The gradation definitions are presented in Figure 9-11, and a gradation chart is included as Figure 9-23. Coarsegrained soils with less than 12 percent passing the No. 200 sieve require gradation descriptions (i.e. well-graded, poorly-graded, uniformly-graded, or gap-graded). 2.8

Cementation

Cementation is the bonding of grains by secondary minerals (e.g., calcium carbonate, iron oxide) or degradation products (e.g., clay). The presence of calcium carbonate cementation can be detected by its reaction to hydrochloric acid. The relative degrees of cementation of undisturbed soil samples are defined as: Weak

Crumbles or breaks with handling or light finger pressure and rubbing

Moderate

Crumbles or breaks with considerable finger pressure and rubbing

Strong

Will not crumble or break with finger pressure and rubbing

2.9

Structure

Structural features include stratifications, varves, lenses, fissures, seams, slickensides, striations, blocky structure, relict rock structure, and voids (root or worm holes, cavities). The thickness, frequency, and inclination of these features should be noted. Figure 9-12 presents criteria for describing structures. 2.10

Other Constituents/Characteristics

 

Other constituents/characteristics include the following: Unit Weight. The total and dry unit weight should be determined on undisturbed soil samples. Sensitivity. Sensitivity refers to the significant loss of strength when a fine-grained soil is remolded. A sensitive soil may be highly compressible, andt he soi l ’ snat ur al moisture content often is above its liquid limit. Sensitivity is a function of the primary structure of the soil (i.e., dispersed, dense or flocculated), strength of grain bonding, and water content. A measure of the sensitivity (St) is the ratio of the undrained shear strength (Su), or unconfined compressive strength (qu) of the undisturbed sample to the remolded sample. When it is noticed in the field that a fine-grained soil might be sensitive, it should be noted on the field log as“ pot ent i al l ysensi t i v e. ” Quality of Coarse-grained constituents. Where the soil is predominantly coarsegrained, the nature, such as for the parent rock type(s) and hardness (soft or hard), and condition, such as weathering (fresh, weathered, or decomposed), of the coarse grains should be described.





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Origin

The origin of the soil is generally interpreted based on knowledge of geologic site conditions and the soil description. A generic name for soil origin may be provided at the end of the soil description in parentheses, such as (Alluvium), (Colluvium), (Terrace Deposit), (Decomposed [rock name]), and (Fill). All soils should be examined to see if they contain nonnative materials indicative of man-made fills. Undocumented fills often cause problems. Manmade items such as glass, brick, dimensioned lumber, concrete, metal, plastics; plaster in fills should be listed in each of the soil descriptions. Other items that could suggest existence of fill include buried vegetation mats, tree limbs, and stumps. The soil description for a fill material shoul dbef ol l owedbyt het er m“ ( Fi l l ) ” .Forex ampl eacl ay eysi l tf i l l wi t hsomebr i ckf r agment s woul dbedescr i bed“ cl ay eySi l t ,ML,wi t hbr i ckf r agment s( Fi l l ) . ”Thesi z eanddi st r i but i onof miscellaneous items should be noted. The limits (depth range) of fill material should be determined and identified at each exploration location. 3.

ROCK

Rock descriptions for engineering purposes consist of two basic assessments: intact and in situ characters of the rock mass (FHWA HI-88-009, 1993). Both characteristics are the basis for rock slope design and excavation. 

Intact character: Description of the intact rock, such as hand specimens or core, in terms of its origin, mineralogical makeup, texture, degree and nature of chemical and physical weathering or alteration, and strength.



In situ character: Description of in-place rock masses that includes the nature and orientation of its constituent interlocking blocks, plates, or wedges formed by bounding discontinuities such as bedding, foliation planes, fractures, joints, shear planes, shear zones and faults.

3.1

Intact Character

The general descriptive sequence for intact rock materials is listed below, as they should appear on the exploration logs.  Rock Name  Color  Degree of Weathering  Relative Hardness  Structure/Discontinuities (joints, stratification, faults, separation, infilling, continuity, vesicularity)  Core Recovery and RQD  Other Characteristics, as applicable (mineralization, slaking, field unit weight, discontinuity surface condition, voids)  Formation Name

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MATERIALS DESCRIPTION 3.1.1.

9-6

Rock Name

Rocks are classically divided into three general categories: igneous, sedimentary and metamorphic (Figures 9-13 through 9-17). Igneous rocks form from magma (molten rock) and are classified based on mineralogy and genesis (intrusive, extrusive or pyroclastic). Names of common igneous rocks are included on Figure 9-13. Pyroclastic rocks form when magma is ejected into the atmosphere, and includes cinder, tuff and volcanic ash materials. Characteristics of pyroclastic rocks are included on Figure 9-14. Texture is the most conspicuous feature of genetic occurrence (Figure 9-15). Due to the length of time available for crystal growth, intrusive rocks tend to be phaneritic (contain coarser crystals visible with the naked eye), such as granite, while extrusive rocks are commonly aphanitic (contain fine-grained crystals not distinguishable with the naked eye), such as basalt or glassy like obsidian. Sedimentary rocks include those formed through the induration (hardening) of accumulated sediments or clastic (sandstone, siltstone), chemical rock (rock salt, gypsum) formed by precipitation from solution, or biogenic rock (limestone, dolomite) consisting of the remains or secretions of plants and animals. Sedimentary rocks are classified based on grain size, mineralogy and on the relationship between grains (Figure 9-16). A modifier may be necessary to describe a sedimentary rock formed from a combination of different grain sizes only if the modifier has engineering significance. For example, “ si l t ysandst one”woul dbe predominantly composed of sand grains with a lesser amount of silt grains. The term mudstone could be used when the composition of a fine-grained sedimentary rock is uncertain or variable. Metamorphic rocks have been derived from mineralogical, chemical, and/or structural changes of rocks (predominantly while in the solid state) in response to significant changes in temperature, pressure, or the chemical environment. The most conspicuous features of metamorphic rocks are typically the aligning of minerals that cause distinctive fissile or platy structure (splits easily along closely spaced planes) as in slate or phyllite, or the visible banding of minerals as in schist or gneiss (Figure 9-17). The complete name of a rock specimen or rock unit should include texture and lithologic name. The rock name should be in simple geologic terms and should be written in capital letters. 3.1.2.

Color

Rock color is not in itself a specific engineering property, but may be an indicator of the influence of other significant conditions such as groundwater (e.g., mottling indicating wetting and drying cycles), and alteration/weathering. Color may also be an aid in subsurface correlation between soil layers. The color should be determined from fresh samples. Describe t he“ net ”col oroft her ockmass.Wet t i ngt her ocksampl emaybenecessar yi fdr y i nghas occurred. Use the Munsell Rock Color Chart to describe rock color.

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MATERIALS DESCRIPTION 3.1.3.

9-7

Degree of Weathering

Weathering is the process of mechanical and/or chemical breakdown of rocks through exposure to the elements, which include rain, wind, plant action, groundwater, ice, and changes of temperature. In general, the strength of rock tends to decrease as the degree of weathering increases. In the early stages, weathering is manifested by discoloration of intact rock and only slight changes in rock texture. With time, significant changes in rock hardness, strength, compressibility and permeability occur, and the rock mass is altered until the rock is decomposed to soil. For determining stages of weathering for rock, use Figure 9-18, Scale of Relative Rock Weathering. For example, granite that is more than 50 percent decomposed ( butnotcompl et el y )woul dbedescr i bedas: “ gr ani t e;pr edomi nant l ydecomposed. ” The degree of weathering should be determined for each rock core sample. Multiple designations would be required for variable rock conditions. I nsel ect cases, t het er m“ al t er at i on”maybeus ed, whi c happl i ess pec i f i c al l yt oc hanges in the chemical or mineral composition of rock due to hydrothermal or very low grade or localized metamorphic activity. Alteration may occur as zones and pockets and can be found atdept hsf arbel ow t hatoft y pi calr ockweat her i ng.Separ at et het er ms“ weat her i ng”and “ al t er at i on” ,si nceal t er at i ondoesnotst r i ct l yi nf erar educt i oni nr ockst r engt h.Forex ampl e, a gray basalt that is closely jointed with extensive hydrothermal alteration and secondary mineralization, may exhibit only slight weathering along joint surfaces and would be described as“ basal t ;gr ay ;sl i ght l yweat her ed;cl osej oi nt ed;ex t ensi v ehy dr ot her malal t er at i onwi t h secondar ymi ner al i z at i on. ” 3.1.4.

Relative Hardness

Differentiating between rock and soil, for engineering purposes, is based primarily on values of unconfined compressive strength. Rock hardness is a measure of rock strength, and is controlled by many factors including degree of induration, cementation, crystal bonding, and/or degree of weathering. Rock hardness may be estimated through manual field tests, y i el di nga“ f i el ddescr i pt i on, ”whi chcanber ef i nedt hr oughl abor at or yt es t i ng.Thes c al eof r oc k hardness to be used is presented on Figure 9-19. The relative hardness of rock should be determined for each rock core sample. The methods given in Figure 9-19 can be used to describe rock hardness and is suitable for use on core and hand specimens. If samples were recovered as part of an SPT sampling program, a hardness description based on blow count would be used. This would include situations where materials like caliche are recovered. In some instances, these intermediate materials behave like soil, while in other deposits they exhibit properties similar to rock. In these cases, it is principally the method of sampling that governs how the hardness is described. 3.1.5.

Structure/Discontinuities

Discontinuities refer to large-scale (megascopic) planar or non-planar features of various orientations, which are significant to the overall strength, permeability, and breakage characteristics of the rock unit. Structural features (discontinuities) include rock breaks 02/14/2005



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(fractures), joints, bedding planes, and faults. Structural features, properties, and descriptive terms are defined below. 

Joints - Planar breaks or fractures where no movement has occurred parallel to the fracture surface are defined as joints. They may range from perpendicular to parallel in orientation with respect to bedding. Repetitive patterns of relatively parallel joints are called a joint set. A joint system is defined by two or more joint sets. The number of joint sets is most reliably obtained from rock exposures.



Stratification - Rock stratification is evidenced by changes in texture, composition, age or unique forms. Bedding applies primarily to sedimentary and pyroclastic rocks. For other stratigraphic terms, refer to Figure 9-20.



Faults - Planar breaks or fractures, where displacement has occurred parallel to the fracture surface are defined as faults. The presence of gouge (pulverized rock), bedding offset, and/or slickensided surfaces (commonly with mineral or clay coating), may be indicators of fault movement. However, not all slickensides are caused by faulting. Slickensides can be caused by deformation (i.e., folds, flows) or landsliding.



Spacing - In determining the range of distances between individual joints or beds, keen observation must be made to distinguish between joints and mechanical breaks that are caused by handling or drilling. Mechanical breaks are more likely to be rough and irregular, showing a fresh rock surface and are disregarded for description. Some mechanical breaks, caused by handling or drilling, may occur along existing joints or fractures, and should be described accordingly. Joint/bedding spacing terms are shown on Figure 9-21.



Separation - The separation or openness of joints may be described as:



a.

Open: an existing planar surface that is separated or separates easily when handled, and may have mineralization or staining/weathering on the joint surfaces. Where measurable, identify the opening width (aperture). Open joints typically act as conduits for groundwater.

b.

Closed: an existing planar surface that separates with greater difficulty than “ Open”t y pe separ at i on,seen as a “ hai r l i ne”t r ace on t he out si de oft he sample/core, and usually does not have soil or mineral surface coating.

c.

Healed: an existing planer surface that breaks open easily or with difficulty, seen either as a hairline trace or a seam of some thickness on the outside of the sample/core, and usually contains soil or minerals as a filling between joint surfaces.

Infilling - This term refers to the material separating the adjacent walls of discontinuities in rock. The filling material may consist of weathered or hydrothermally altered products, secondary mineralization or precipitates, or fault gouge (ground up rock). The wide variety of conditions and types of fillings that may occur can significantly influence the strength of the discontinuity and the stability of the rock mass. For structurally important discontinuities, the infilling observations may be a critical aspect of the

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analytical model and the stability analyses. The extent of the infilling description should be consistent with the project design and the significance of the feature. 

Continuity - The extent of continuity (or persistence) of a discontinuity is an expression of the lateral extension of the structural feature as measured or projected along its plane. Continuity is a very important property of the rock mass, as a single continuous joint may actually control the behavior of the entire mass. Commonly, the only clue to the persistence of a discontinuity is the trace of the discontinuity on the surface of a rock exposure. Where deemed important, continuity can be verified using test pits (if practical) or additional boreholes. The description of joint continuity should include an indication of certainty and the method of observation. The degrees of continuity should be reported according to the following: Discontinuous 0 – 5 ft. in length Slightly continuous 5 –10 ft. in length Continuous 10 –40 ft. in length Highly continuous > 40 ft. in length



Vesicularity - Small to large rounded cavities in volcanic rocks (vesicles) are created by gas bubbles in the molten lava that become incorporated in the cooled rock. Cavities or openings in other rocks, such as intergranular space, should be described by other terms, such as porosity. The occurrence of vesicles is to be reported using the Comparison Chart (Figure 9-22) to estimate the relative percent of area occupied by vesicles and the following corresponding descriptive designations: Some Vesicles 5 - 25% Highly Vesicular 25 - 50% Scoriaceous > 50%

3.1.6.

Core Recovery and Rock Quality Designation (RQD)

Core recovery measurements and Rock Quality Designations are indicators of the quality and structure of rock. Both the percent core recovery and the RQD should be determined and recorded on the boring log for each core run. The core recovery is calculated by dividing the length of core retained (recovered) in the core barrel by the total run length expressed as a percent. The RQD provides a subjective estimate of rock mass quality/structure. The RQD is a modified core recovery percentage in which only pieces of intact core 4 inches or greater in length (average length) are included in the measurement. Pieces smaller than 4 inches are considered a result of close jointing, fracturing or weathering in the rock mass, and are excluded from the RQD determination. The RQD is defined as the cumulative total length of all pieces 4 inches long or longer divided by the total run length, expressed as a percentage. Mechanical breaks, caused by handling or drilling, should be noted as such and not included in the RQD calculations. Where significant soil is encountered at one end of the core run, the soil portion is excluded from the run length measurement and should be clearly described on the log. The RQD is based solely on that portion of the run where rock was encountered. RQD is not 02/14/2005



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applicable to fissile rocks such as shales. Difficulties such as distinguishing natural fractures in the rock core from mechanical breaks and the insensitivity of the RQD to the tightness of individual joints may limit the use of the RQD in evaluating in situ rock properties. 3.1.7.

Other Rock Characteristics

Other physical characteristics of rock should be described, depending on the scope and objectives of the project. These may include the following: 

Mineralization - Secondary mineralization is the introduction of new minerals to a rock mass from an outside source, or through alteration of existing minerals. Mineralization may occur in voids, along joints or within the groundmass. The presence of Iron oxide staining typically indicates the static groundwater level may be fluctuating within the discolored zone. The iron oxide may only be a discoloration of surfaces, or an accumulation of bright orange material several inches thick and varying in hardness. Sulfide or carbonate minerals, such as pyrite or calcite, may be present and could denote groundwater of high mineral or bicarbonate content. Alteration products may indicate an increase in hardness or brittleness if high strength minerals such as quartz have formed, or reduction of rock strength if soft clay minerals have developed along joints or have replaced major constituent minerals (e.g., the feldspar crystals in basalt altered to clay).



Slaking - Slaking is the tendency for rock to disintegrate under conditions of wetting and drying, or when exposed to air. This behavior is related primarily to the chemical composition of the material. It may be identified in the field if samples shrink and crack, or degrade upon drying, or upon being exposed to the air for several hours. If degradation occurs, and slaking is suspected, an air-dried sample may be placed in clean water to observe the reaction. The greater the tendency for slaking, the more rapidly degradation or disintegration occurs. This tendency should be expressed on f i el dl ogsas “ pot ent i alf orsl aki ng, ”and,i fcr i t i cal ,shoul d be conf i r med t hr ough laboratory testing. The Slake Durability Index of shales and similar weak rock can be determined using ASTM D 4644.



Field Unit Weight - Unit weight of rock can be important in the stability analyses. Unit weight of rock is determined from multiplying the weight of the sample in air by the unit weight of water and dividing the product by the difference between the weight of the sample in air and in water.



Voids - Open spaces in sedimentary and metamorphic rock are generally caused by chemical dissolution or running water. Since most of these voids result from groundwater, the openings are commonly elongated in the horizontal plane. The size of voids, where significant, should be measured and recorded with the rock classification.

3.1.8.

Formation Name

Various rock units are typically known by formational names, which can be identified within project boundaries by examination of core samples, rock outcrops, and geologic 02/14/2005



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literature. Where the formation name is determined or known, it should be included at the end of the rock classification in parentheses. 3.2

In Situ Character

While the intact character of a rock is what is used to classify a rock material as to type or origin, it is the in situ character that primarily controls how a rock performs in most engineering applications. The intact character is defined in terms of the structural discontinuities that divide nearly all rock bodies into discrete planar, wedge or block-shaped pieces. The orientation of and the resistance to move along these discontinuities are what control the stability of rock. The intact strength rarely controls stability. Most structural information is obtained from outcrops since it is easier to observe and measure these features on larger samples that are more representative of the rock structure. However, important in situ information can be obtained from borings, especially if the borings are oriented so recovered rock cores can be aligned, evaluated and described as though they were in place. 3.2.1.

Discontinuity Orientation

The orientation of a discontinuity is described by the dip and dip direction of the plane representing the discontinuity. The dip is the maximum downward inclination angle on the plane measured from the horizontal. The azimuth paralleling the direction of maximum dip is the dip direction and is measured from north. In addition to dip and dip direction, there are additional joint features that should be identified/measured, as shown in Figure 9-24. The angle that striat i ons( sl i ckensi des)makewi t hahor i z ont all i nei sknownast he“ r ake. ” Both primary and secondary joint sets should be defined where possible and appropriate. Typically, one joint set may yield slabs, two intersecting joint sets may yield wedges, and three or more intersecting joint sets may yield blocks or highly fragmented rock. The orientation of discontinuities as they relate to adjacent engineering works, such as excavations or, in some cases, structure foundations, predominantly controls the potential for developing an unstable condition. 3.2.2.

Roughness

Roughness significantly contributes to the shear strength along discontinuities, particularly if the rock is undisplaced or has interlocking features. Roughness is divided into two main categories based on the scale of the roughness relative to the size of the discontinuity. Small-scale features (asperities) and the surface texture are referred to as micro roughness, while large-scale features (such as steps or undulations along the discontinuity surface) are referred to as macro roughness. Micro roughness provides resistance to sliding along discontinuity contacts and is the principal contributor to sliding resistance along planar contacts. As the micro roughness increases, the friction between adjoining surfaces increases. This frictional resistance must be overcome before movement can occur. Typically, once movement occurs, the micro r oughness( f r i ct i on,Φ)i sdecr easedt or esi dual ( r educed)shearst r engt hduet ot hegr i ndi ng 02/14/2005



9-12

action. If the applied loads are large enough, a visibly polished or slickensided surface can develop. For larger roughness features (macro roughness), dilation (movement normal to the contact between the rock surfaces forming the discontinuity) or a failure through intact rock, which is relatively unusual for near surface loading conditions, must occur for movement to take place. This condition applies to discontinuities that have interlocked steps and to undulating surfaces. When estimating the effects of macro roughness, it is important to determine the alignment of the features relative to the potential direction of movement. Although stepped or undulating surfaces may be present, these macro features do not increase sliding resistance if they are oriented parallel to the direction of movement, so no dilation or failure of intact rock is required for movement to occur. Conversely, these roughness features provide the greatest sliding resistance when they are oriented perpendicularly to the potential direction of movement. Surface roughness can be defined in terms of a Joint Roughness Coefficient (JRC), which requires estimation or measurement of the surface unevenness. The JRC should be determined in the direction of anticipated block movement. Surface roughness is best determined on in-place discontinuities, rather than core samples. 4.

EXPLORATION LOG

An“ Ex pl or at i onLog”shoul dbemadef oreachex pl or at or ybor i ng,hand-auger hole, probe hole and test pit. The log can also be used to describe inspected cut slopes. Soil and rock descriptions/classifications and terminology should be consistent with this Manual. Abbreviations are to be avoided unless they are defined in this Manual. The logs for drillhole borings must contain basic reference information at the top of each sheet, including project name, project location, boring ground surface elevation, boring number, boring location (station and offset), groundwater level with date measured, start and end dates, drilling equipment, drilling method, on-site Engineer, drill rig operator, and if backfilled (including date).The boring location relative to the roadway alignment can be determined by measuring from the nearest Department benchmark. Benchmarks are typically located on Department bridges. Each sample should be fully described. Referencing a previous sample is not recommended since rarely are any two samples identical. The depth of each stratum contact, discontinuity, and lens should be recorded. The reason for terminating an exploration hole and a list/description of instrumentation installed should be written at the end (bottom) of each exploration log. 4.1

Field Log

The field log is a record, which should contain all of the information obtained from an exploratory hole, whether or not it may seem important at the time of exploration (see Figure 925). It is important to record all information in an accurate manner. All soil and rock samples are to be fully described immediately on recovery. Depths of samples, top and bottom of each stratum/layer, discontinuities, field tests, and groundwater level(s) should be measured to the 02/14/2005



9-13

nearest 0.1-foot. The depth(s) of drilling, the date of drilling, and the times that drilling began and ended should be recorded. 4.2

Drilling Remarks

The material that is not recovered is frequently significant in the design of foundations, excavations, performance of fills, and other geotechnical applications. Subsurface conditions are not always fully described based solely on material descriptions. Therefore, any comments with regard to the character of drilling and difficulties encountered while advancing the boring should be included on the exploration log. Drilling remarks may include: 

Obstruction



Difficulty in drilling (caving, surging sands, caverns, heaving, etc.)



Estimated drilling fluid return and applied water pressure



Color of drilling fluid return



Return fluid constituents



Relative drilling down-pressure and exact depth of major pressure changes



Drilling action (drill chatter, smooth, bouncy, etc.)



Drilling rate and the length of time for each core run



Explanation for incomplete recoveries regardless of sampling method (SPT, Shelby tube, core, etc.)



Artesian water pressure or elevation head, and depth where encountered



Reason for using drilling muds, casing, or special drill bits

4.3

Final Exploration Log

The final log is prepared from the field log after completing laboratory tests. Information provided on the logs should be typed. Compare soil classifications obtained from the results of lab testing with the original field classifications (Figure 9-26). The final log includes descriptions of all materials, conditions, drilling remarks, and results of field tests and any instrumentation. Where groundwater observation wells or piezometers are installed, several measurements are usually necessary following drilling to verify that measured groundwater levels or pressures have achieved equilibrium. For instance, if drill water is used in finegrained soils, and the exploratory hole is not bailed, then the observation well levels are initially high, dropping with time to the actual groundwater level. It is desirable for final logs to include measurements of groundwater levels during different seasons in order to establish the range of groundwater fluctuation. An explanation key (Figure 9-27) should always accompany Exploration Logs whenever they are presented.

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9-14

SPECIFICATIONS AND STANDARDS Subject

ASTM

AASHTO

Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System)

D 2487

-

Description and Identification of Soils (Visual-Manual Procedure)

D 2488

-

Standard Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes

D 3282

M 145

Slake Durability of Shales and Similar Weak Rock

D 4644

-

Field Logging of Subsurface Explorations of Soil and Rock

D 5434

-

6.

FIGURES

9-1: Soil Constituents –Definitions Boulders

Particles of rock that will be retained on a sieve with a 12-inch square opening

Cobbles

Particles of rock that will pass a sieve with a 12-inch square opening, but be retained on a 3-inch sieve.

Gravel

Particles of rock that will pass a 3-inch sieve, but be retained on a No. 4 sieve.

Sand

Particles of Rock that will pass a No. 4 sieve, but be retained on a No. 200 sieve.

Silt

Soil passing a No. 200 sieve that is nonplastic or very slightly plastic and exhibits little or no strength when air dry.

Clay

Soil passing a No. 200 sieve that can be made to exhibit plasticity (puttylike properties) within a range of water contents and has considerable strength when air dry.

Organic Soil

A soil with sufficient organic content to influence the soil properties.

Peat

A soil composed primarily of vegetable matter in various stages of decomposition usually with an organic odor, a dark brown to black color, spongy consistency, and a texture ranging from fibrous to amorphous.

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9-15

9-2: Silt and Clay Characteristics Characteristics

Silt

Dilatancy (Movement of water in voids due to shaking.)  None  Slow  Rapid Dry Strength (Cohesiveness in dry state.)  None  Low  Medium  High  Very High Toughness (Plasticity in moist state.)  Low  Medium  High Dispersion (Settlement in water.) Visual Inspection and Feel

Rapid reaction. Water appears on the surface to give a livery appearance when shaken. Squeezing the soil causes water to disappear rapidly.

Sluggish or no reaction. Surface of the samples remain lustrous. Little or no water appears when hand is shaken. Sample remains lustrous during squeezing.

None to low. Even oven-dry strength is low. Powder easily rubs off surface of the sample. Little or no cohesive strength –will crumble and slake readily.

High to very high. Exceptionally high if oven-dry. Powder will not rub off the surface. Crumbles with difficulty. Slakes slowly.

Plastic thread has little strength. Dries quickly. Crumbles easily as it dries below plastic range. Seldom can be rolled to 1/8thread without cracking. Settles out of suspension in 15 to 60 minutes. (Sands settle in 30 to 60 seconds.) Only coarsest individual silt grains are visible to the naked eye. Feels slightly gritty when rubbed in fingers. Dries quickly and dusts off easily.

Plastic thread has high strength. Dries slowly. Usually stiff and tough as it dries below plastic range. Can easily be rolled to 1/8thread without cracking.

Bite Test (Caution: Eating contaminated soil may be hazardous to your health.)

Gritty feeling between the teeth, does not stick to the teeth.

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Clay

Settles in several hours or days, unless it flocculates (rapidly precipitates out in small clumps). Individual grains cannot be observed by the naked eye. Feels smooth and greasy when rubbed in fingers. Dries slowly and does not dust off; must be scraped off. No gritty feeling between the teeth; tends to stick to the teeth.



9-16

9-3: Examples of Fine-Grained Soil Field Identification FIELD INDEX TESTS Typical Name Silt

Dry Strength none, low

Dilatancy Reaction

Toughness of Plastic Thread

Plasticity

rapid

low

nonplastic, low

Silt w/some clay low, medium

rapid, slow

low, medium

low

clayey Silt

medium

slow

medium

low, medium

silty Clay

medium, high

slow, none

medium, high

medium

Clay w/some silt

high

none

high

high

Clay

very high

none

high

high

organic Silt

low, medium

slow

low, medium

nonplastic, low

organic Clay

medium to very high

none

medium, high

medium, high

9-4: Fine-Grained Soil Subclassification Terms Percent of Total Sample by Weight Silt, Clay Primary Constituent* clayey, silty Secondary fine-grained constituents* with some silt, some clay Additional fine-grained constituents* sandy, gravelly 30 –50% Secondary coarse-grained constituents with some sand, some gravel 15–30% Additional coarse-grained constituents with trace sand, trace gravel 5–15% Additional coarse-grained constituents * The relationship of clay and silt constituents is based on plasticity and normally determined by performing index tests. Refined classifications are based on Atterberg limits tests and the Plasticity Chart (ASTM D2487).

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9-17

9-5: Coarse-Grained Soil Subclassification Terms Gravel, Sand

Percent of Total Sample by Weight

gravelly, sandy

Predominant constituent >50% 30 –50

w/some (gravel, sand) w/trace (gravel, sand) silty, clayey *

15 –30 5 –15 12 –50

w/some (silt, clay) * w/trace (silt, clay) *

5 –12 < 5

Primary constituent* Secondary coarse-grained constituents Additional fine-grained constituents Secondary fine-grained constituents Additional fine-grained constituents

*I ndext est sand/ orpl ast i ci t yt est sar eper f or medt odet er mi newhet hert het er m“ s i l t ”or “ cl ay ”i sused.

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9-18

9-6: Unified Soil Classification Summary Group Symbols*

Highly Organic Soils

Clean Gravels

GP

Poorly graded gravels, gravel-sand mixtures, little or no fines.

GW

Silty gravels. Poorly graded gravel-sand-silt mixtures.

GC

Clayey gravels, poorly graded gravel-sand-clay mixtures.

SW

Well graded sands, gravelly sands, little or no fines.

SP

Poorly graded sands, gravelly sands, little or no fines.

Clean Sands

Well graded gravels, gravel-sand mixtures, little or no fines.

Gravels With Fines

Typical Names

GW

Sands with Fines

Sands Gravels More than half of coarse More than half of coarse fraction is smaller than No. 4 fraction is larger than No. 4 sieve size sieve size Silts and Clays Silts and Clays Liquid limit Liquid limit greater than 50 less than 50

Fine Grained Soils More than half of material is smaller than 200 sieve size

Coarse Grained Soils More than half of material is larger than 200 sieve size

Major Divisions

SW

Silty sands, sand-silt mixtures.

SC

Clayey sands, sand-clay mixtures.

ML

Inorganic silts and very fine sands, rock flour, silty or clayey fine sands with slight plasticity.

CL

Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays.

OL

Organic silts and organic silt-clays of low plasticity.

MM

Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts.

CH

Inorganic clays of high plasticity, fat clays.

OH

Organic clays of medium to high plasticity.

PT

Peat and other highly organic soils.

* Boundary classifications. Soils possessing characteristics of two groups are designated by combinations of group symbols, for example GW-GC, well graded gravel-sand mixture with clay binder.

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MATERIALS DESCRIPTION 9-7: Degree of Plasticity Plasticity Term Index, PI% Nonplastic 0-3 Low plasticity

3 - 15

Medium plasticity High plasticity

15 - 30 30 or more

9-19

Dry Field Test (approximation) Strength Very low Dry specimen ball falls apart easily. Cannot be rolled at any moisture content. Low Dry specimen ball easily crushed with f i nger s. 1/ 8”t hr ead can bar el ybe r ol l ed within its plastic range. Medium Difficult to crush dry specimen ball when dry. 1/ 8”t hr eadi seasyt or ol l . High Impossible to crush dry specimen ball with f i nger s.1/ 8”t hr eadt akesconsi der abl et i me to roll/knead to reach plastic limit. Can be re-rolled several times without breaking after reaching plastic limit.

9-8: Moisture Designations Term

Field Identification

Dry

Absence of moisture. Dusty. Dry to the touch.

Damp

Soil has moisture. Cohesive soils are below plastic limit (BPL) and usually moldable.

Moist

Grains appear darkened, but no visible water. Silt/clay will clump. Sand will bulk. Soils are often at or near plastic limit.

Wet

Visible water on larger grain surfaces. Sand and cohesionless silt exhibit dilatancy. Cohesive silt/clay can be readily remolded. Soil leaves wet nessont hehandwhensqueez ed.“ Wet ”i ndi cat est hatt hesoi li s much wetter than the optimum moisture content and above plastic limit (APL).

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9-20

9-9: Consistency of Cohesive Soils Consistency

SPT N-Value (Blow/Foot)

Field Approximation

Very soft

Less than 2

Squeeze between fingers when fist is closed; easily penetrated several inches by fist.

Soft

2 –4

Easily molded by fingers; easily penetrated several inches by thumb.

Medium stiff

4 –8

Molded by strong pressure of fingers; can be penetrated several inches by thumb with moderate effort.

Stiff

8 –15

Molded by strong pressure of fingers; readily indented by thumb but can be penetrated only with great effort.

Very Stiff

15 –30

Readily indented by thumbnail.

Hard

Greater than 30

Indented with difficulty by thumbnail.

9-10: Relative Density for Granular Soils Safety Hammer Relative SPT Field Approximation Density N-Value (Blow/Foot) Very loose 0-4 Easily penetrated many inches (>12) with ½ inch rebar pushed by hand. Loose 5 –10 Easily penetrated several inches with ½ inch rebar pushed by hand. Medium Dense 11 –30 Easily to moderately penetrate with ½ inch rebar driven by 5 lb. hammer. Dense 31 –50 Penetrated 1 foot with difficulty using ½ inch rebar driven by 5 lb. hammer. Very Dense Greater than 50 Penetrated only a few inches with ½ inch rebar driven by 5 lb. hammer.

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MATERIALS DESCRIPTION 9-11: Gradation Categories Gradation Term Description (USCS) Well-graded Full range and even distribution of grain (GW, SW) sizes present. Poorly-graded Narrow range of grain sizes present (GP, SP) Uniformly-graded Consists predominantly of one grain (GP, SP) size.

Example Coarse to fine Sand with trace silt, SW Fine to medium Sand, SP Clean fine Sand,

SP Within the range of grain sizes present, Fine Sand with some coarse one or more sizes are missing. gravel, SP

Gap-graded (GP, SP) Coefficients:

D60 D10

Cu 

9-21

Cc 

( D30 ) 2 D10 xD60

Uniformity Coefficient Requirements SW 5% Cu > 6 and Cc 1 GW to 3 5% Cu > 4 and Cc 1 to 3 Note: If 5 to 12% passes the No. 200 sieve, then use a dual classification with the predominant fine-grained constituent, i.e., SW-SM, etc. % Passing No. 200 Sieve

USCS Term

9-12: Criteria for Describing Structure Term Stratified

Criteria Alternating layers of varying material or color with layers at least ¼-inch.

Laminated

Alternating layers of varying material or color with layers less than ¼-inch.

Fissured

Contains shears or separations along planes of weakness.

Blocky

Cohesive soil that can be broken down into small angular lumps which resist further breakdown.

Lensed

Inclusion of small pockets of different soils, such as small lenses of clay; note thickness.

Homogeneous

Same color and appearance throughout.

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MATERIALS DESCRIPTION 9-13: Common Igneous Rocks Intrusive (coarse-grained) Essential Minerals Granite Quartz K-feldspar

Diorite

Plagioclase

Gabbro

Plagioclase Pyroxene

9-22

Common Extrusive Accessory Minerals (fine-grained) Plagioclase Rhyolite Mica Amphibole Pyroxene Mica Andesite Amphibole Amphibole Basalt

9-14: Pyroclastic Rocks Rock Name Cinders

Characteristics Uncemented glassy and vesicular ejecta 4-32 mm size.

Tuff Breccia (agglomerate) Lapilli Tuff Tuff Pumice

Composed of ejecta >32 mm size, in ash/tuff matrix, indurated. Composed of ejecta 4-32 mm size, in ash/tuff matrix, indurated. Cemented volcanic ash particles <4 mm size, indurated. Excessively vesicular glassy lava.

9-15: Igneous Rock Textures Texture Pegmatitic

Phaneritic

Grain Size Very large; diameters measured in inches or feet. Wide range of sizes.

Rock Type Intrusive

Intrusive or Extrusive

Aphanitic

Can be seen with naked eye Cannot be seen with naked eye

Amorphic Glassy

No grains present

Extrusive

Porphyritic

Grains of two widely different sizes

Intrusive and Extrusive

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Intrusive or Extrusive



9-23

9-16: Common Sedimentary Rocks Rock Name Conglomerate Sandstone

A. Mechanical Sedimentary Rocks Original Sediment Gravel, or sand and gravel Sand Silt

Siltstone Claystone

Clay

Mudstone

Silt, clay, possibly with sand and/or gravel inclusions, nonoriented Oriented, laminated, fissile, clay and silt

Shale (laminated claystone/siltstone) B. Chemical Sedimentary Rocks Rock Name Main Mineral Limestone Calcite Dolomite Dolomite Chert

Quartz

9-17: Common Metamorphic Rocks A. Foliated Metamorphic Rocks Rock Name Texture Formed From Slate Platy, fine-grained Shale Schist Irregular layers, Slate, igneous rocks medium-grained Gneiss Layered, Igneous rocks, coarse-grained schist, sandstone B. Nonfoliated Metamorphic Rocks Rock Name Texture Formed From Marble Crystalline Limestone, dolomite Quartzite Crystalline Sandstone Serpentinite Massive to layered, Ultramafic rocks, fine-to coarsei.e., peridotite, grained gabbro

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Main Minerals Mica, quartz Mica, quartz, feldspar, amphibole Mica, quartz, feldspar, amphibole Main Minerals Calcite, dolomite Quartz Serpentine



9-24

9-18: Scale of Relative Rock Weathering Designation

Field Identification

Fresh

Crystals are bright. Discontinuities may show some minor surface staining. No discoloration in rock fabric.

Slightly Weathered

Rock mass is generally fresh. Discontinuities are stained and may contain clay. Some discoloration in rock fabric. Decomposition extends up to 1 inch into rock.

Moderately Weathered

Rock mass is decomposed 50% or less. Significant portions of rock show discoloration and weathering effects. Crystals are dull and show visible chemical alteration. Discontinuities are stained and may contain secondary mineral deposits.

Predominantly Decomposed

Rock mass is more than 50% decomposed. Rock can be ex cav at ed wi t h geol ogi st ’ s pi ck. Al ldi scont i nui t i es ex hi bi t secondary mineralization. Complete discoloration of rock fabric. Surface of core is friable and usually pitted due to washing out of highly altered minerals by drilling water.

Decomposed

Rockmassi scompl et el ydecomposed.Or i gi nalr ock“ f abr i c” may be evident. May be reduced to soil with hand pressure.

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9-25

9-19: Scale of Relative Rock Hardness Term

Hardness Designation

Field Investigation Methods

Approximate Unconfined Compressive Strength < 100 psi

Extremely soft

R0

Can be identified with difficulty by thumbnail. May be moldable or friable with finger pressure.

Very soft

R1

Crumbles under firm blows with point of a geology pick. Can be peeled by a pocketknife and scratched with fingernail.

100-1000 psi

Soft

R2

Can be peeled by a pocketknife with difficulty. Cannot be scratched with fingernail. Shallow indentation made by firm blow of geology pick.

1000-4000 psi

Medium hard

R3

Can be scratched by knife or pick. Specimen can be fractured with a single firm blow of hammer/ geology pick.

4000-8000 psi

Hard

R4

Can be scratched with knife or pick only with difficulty. Several hard hammer blows required to fracture specimen.

8000-16000 psi

Very hard

R5

Cannot be scratched by knife or > 16000 psi sharp pick. Specimen requires many blows of hammer to fracture or chip. Hammer rebounds after impact.

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9-26

9-20: Stratification Terms Term

Characteristics

Laminations

Thin beds (< 1 cm.).

Fissile

Tendency to readily break along laminations.

Parting

Tendency to break parallel to bedding.

Foliation

Nondepositional, e.g., segregation and layering of minerals in metamorphic rocks.

9-21: Joint and Bedding Spacing Terms Spacing

Joint Spacing Terms

Bedding/Foliation Spacing Terms

Less than 2 in.

Very close

Very thin (laminated)

2 in. –1 ft.

Close

Thin

1 ft. –3 ft.

Moderately close

Medium

3 ft. –10 ft.

Wide

Thick

More than 10 ft.

Very wide

Very thick (massive)

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9-27

9-22: Standardized Volume Percentage Chart

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MATERIALS DESCRIPTION 9-23: Graduation Chart

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9-28


9-29

9-24: Measurement of Joints

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9-30

9-25: Field Log Form

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9-31

9-26: Example, Final Exploration Log

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9-32

9-27: Key to Boring Logs PARTICLE SIZE LIMITS CLAY

SILT

SAND FINE

.002 mm

#200

GRAVEL

MEDIUM

#40

COARSE

#10

USCS GROUP GW GP GC SW SP SM SC ML CL OL MH CH OH CS PT

FINE

#4

COBBLES

BOULDERS

COARSE

¾ inch

3 inch

12 inch

TYPICAL SOIL DESCRIPTION Well graded gravels, gravel-sand mixtures, little or no fines Poorly graded gravels, gravel-sand mixtures, little or no fines Clayey gravels, poorly graded gravel-sand-clay mixtures Well graded sands, gravelly sands, little or no fines Poorly graded sands, gravelly sands, little or no fines Silty sands, poorly graded sand-silt mixtures Clayey sands, poorly graded sand-clay mixtures Inorganic silts and very fine sands, rock flour, silty or clayey fine sands with slight plasticity Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays Organic silts and organic silt-clays of low plasticity Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts Inorganic clays of high plasticity, fat clays Organic clays of medium to high plasticity Claystone/Siltstone Peat and other highly organic soils

MOISTURE CONDITION CRITERIA SOIL CEMENTATION CRITERIA Description Description Dry Weak handling or little to touch. finger pressure. Moist Moderate considerable Wet below





Symbols

Criteria Criteria Absence of moisture, dusty, Crumbles or breaks with dry Damp, no visible free water. Crumbles or breaks with Visible free water, usually finger pressure. groundwater table.

Strong

Wont break or crumble w/finger pressure

Groundwater Elevation

STANDARD PENETRATION CLASSIFICATION* GRANULAR SOIL BLOWS/FT

DENSITY

CLAYEY SOIL BLOWS/FT

CONSISTENCY

0-4

VERY LOOSE

0-1

VERY SOFT

5 –10

LOOSE

2-4

SOFT

11 - 30

MEDIUM DENSE

5-8

MEDIUM STIFF

31 - 50

DENSE

9 - 15

STIFF

OVER 50

VERY DENSE

16 - 30

VERY STIFF

*Standard Penetration Test (N) 140 lb hammer 30 inch free fall on 2 inch O.D. x 1.4 inch I.D. sampler.

31 - 60

HARD

OVER 60

VERY HARD

Blow counts on Calif. Modified Sampler (NCMS) can be converted to NSPT by: (NCMS)(0.62) = NSPT Blow counts from Automatic or Safety Hammer can be converted to Standard SPT N60 by: (NAUTOMATIC)(1.25) =N60 (NSAFETY)(1.17) =N60

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9-33

REFERENCES

AASHTO,“ ManualonSubsur f acei nv est i gat i ons, ”1988 AASHTO, “ St andar dSpeci f i cat i onsf orTr ans por t at i onMat er i al sandMet hodsof Sampl i ngand Test i ng, ”Par tI I :Test s ASTM,“ AnnualBookofASTM St andar ds, ”Section 4: Construction, Vol. 04-08: Tests D420 through D5779 FHWA, “ Soils and Foundations Workshop Reference Manual,”NHI Course No. 132012, FHWA NHI-00-045, August 2000 FHWA,“ Det er mi nat i onofConsi st encyChar act er i st i csofSoi l s, ”FHWA-RD-77-101, 1977 FHWA,“ Tr ai ni ng Cour se i n Geot echni caland Foundat i on Engi neer i ng:Rock Sl opes, ” Participants Manual, and Student Exercises, FHWA-HI-99-007 and NHI-99-036, 1999 FHWA,“ Ev al uat i onofSoi landRockPr oper t i es, ”Geot echni calEngi neer i ngCi r cul arNo.5, FHWA-IF-02-034 FHWA,“ RockandMi ner alI dent i f i cat i onf orEngi neer s, ”FHWA-HI-91-025, 1991 FHWA,“ Subsur f aceI nv est i gat i ons , ”FHWA-HI-97-021, 1997 NAVFAC DM-7. 1,“ Soi lMechani c s , ”Depar t mentoft heNav y ,Nav alFaci l i t i esEngi neer i ng Command, 1986 NDOT, Testing Manual, http://test.nevadadot.com/reports_pub/test_manual/list.asp Or egonDOT,“ Soi landRockCl assi f i cat i onManual , ”1987 Wy l l i e,“ Foundat i onsonRock, ”ChapmanandHal l ,1992

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CHAPTER 10 FIELD INSTRUMENTATION

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FIELD INSTRUMENTATION

10-i

TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 6.1 6.2 6.3 6.4 7. 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 8. 8.1 8.2 8.3 8.4 8.5 9. 10. 11. 12. 13. 14. 15.

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PURPOSE.............................................................................................................. 1 INTRODUCTION.................................................................................................... 1 USES OF INSTRUMENTATION ............................................................................ 2 PLANNING INSTRUMENTATION PROGRAMS.................................................... 3 INSTRUMENTATION, MONITORING, AND DATA INTERPRETATION ............... 4 GROUNDWATER LEVEL AND PORE PRESSURE MEASUREMENT ................. 5 Observation Wells .................................................................................................. 6 Open Standpipe Piezometers ................................................................................ 6 Vibrating Wire Piezometers .................................................................................... 7 Pneumatic Piezometers ......................................................................................... 7 LATERAL GROUND MOVEMENT INSTRUMENTATION ..................................... 8 Telltale Stakes........................................................................................................ 8 Survey Hubs........................................................................................................... 8 Portable Crack/Deformation Gauges...................................................................... 8 Inclinometers .......................................................................................................... 8 ShearPl aneI ndi cat oror“ Poor -Man’ s”I ncl i nomet er ............................................... 9 Time Domain Reflectometry (TDR) ...................................................................... 10 Lateral Extensometers ......................................................................................... 10 Webcams ............................................................................................................. 10 SETTLEMENT/HEAVE MONITORING ................................................................ 11 Settlement Plate/Platform..................................................................................... 11 Remote Settlement (Gauge Monitoring Tubes) .................................................... 11 Inductive Coil Gauge (Deep Settlement Monitoring) ............................................ 12 Borehole Extensometer (Deep Settlement Monitoring) ........................................ 12 Horizontal Inclinometer (Settlement Monitoring)................................................... 12 TILTMETERS ....................................................................................................... 13 LOAD CELLS AND STRAIN GAUGES ................................................................ 13 EARTH PRESSURE CELLS ................................................................................ 13 VIBRATION MONITORING.................................................................................. 13 GROUND TEMPERATURE ................................................................................. 14 SPECIFICATIONS AND STANDARDS................................................................ 14 REFERENCES..................................................................................................... 15


FIELD INSTRUMENTATION 1.

10-1

PURPOSE

Field instrumentation is used for two primary purposes: to determine ground in situ conditions for design, and to monitor performance of critical elements of a project. During the investigation and design phase, instrumentation can be used to determine ground in situ conditions. Instrumentation monitoring can be extended over several months, as needed, to measure seasonal effects. During construction, instruments can be used to monitor in situ conditions to verify design assumptions and to warn of possible changed conditions or impending hazards. In addition, instrumentation may be used to monitor performance of embankments, slopes and foundation soils in response to construction (such as stability and the magnitude and time rate of settlement of new embankments). 2.

INTRODUCTION

Geotechnical instruments are used to characterize site conditions, verify design assumptions, monitor the effects of construction, enforce the quality of workmanship, and provide early warning of impending failures. In these regards, they are used to augment standard investigation practices and visual observations where conditions would otherwise be difficult to evaluate or quantify due to their location, magnitude or rate of change. Ralph Peck’ spaperont he“ Obser v at i onalMet hod”( Ni nt hRanki neLect ur e,1969) ,descr i beshow instrumentation should be utilized during critical parts of construction to supplement the observations. Instruments should be used to answer specific questions and provide engineering insight to a problem. There are a multitude of instruments available that can be grouped into the following functional applications: 

Groundwater Level and Pore Pressure

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Lateral Ground Movement and Deformation

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Settlement/Heave

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Tilt/Rotation

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Load/Stress on Structural Members

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Earth Pressure

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Vibration

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Ground Temperature

The Geotechnical Engineer should become familiar with the different types of instrumentation available in order to understand their uses; how they are installed and operated; instrument accuracy, precision, and sensitivity; monitoring requirements; potential errors; environmental limitations, and the effects of nearby activities. Consultation with equipment suppliers and instrumentation Consultants is advisable when complex types of instruments are required. References providing detail and schematics regarding instrumentations include: 

FHWA,Manual on“ Geot ec hni calI ns t r ument at i on” ,( NHICour se132041,Modul e11)

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AASHTO,Manual on“ Subsur f aceI nv est i gat i ons” ,Appendi xG –Instrumentation

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“ Geot ec hni calI nst r ument at i onf orMoni t or i ngFi el dPer f or mance”( Dunni cl i f f )

3.

USES OF INSTRUMENTATION

In the design phase, instrumentation can be used to determine groundwater levels/pressures at various depths, or to obtain data on existing slopes, landslides, structures or embankments. For example, piezometers and inclinometers, placed within an unstable area of an existing slope, can provide the Geotechnical Engineer with information that is valuable in assessing the cause of the problem and in designing the necessary remedial measures. The following list describes examples when instrumentation can be useful in the design phase: 

Testing constructed embankments to assist settlement prediction (survey hubs, settlement plates, piezometers)

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Evaluating landslides (inclinometers and piezometers)

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Evaluating excavations and earthworks including cuts and fills (observation wells)

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Mitigating rockfall (crack monitors and strain gauges)

On projects where analysis has indicated potential problems with embankment or structure settlement or stability, geotechnical instruments should be used to monitor, evaluate and control construction progress. The location and types of instrumentation should be well defined as an integral part of earthwork and foundations. The contract documents should include special provisions regarding the application of instruments and construction requirements. For example, instrumentation allows the engineer to evaluate settlement rate and stability as construction proceeds. The Geotechnical Engineer should install these instruments and interpret the obtained data in consultation with the Resident Engineer. The following list describes examples when instrumentation can be beneficial: 

Monitoring the effects of blasting or heavy construction (vibration monitoring of adjacent facilities)

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Monitoring movements in adjacent slopes and structures (survey hubs, tiltmeters)

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Monitoring ground stability during and after construction (piezometers, survey hubs/stakes, and inclinometers)

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Monitoring embankment settlement and confirming improved ground conditions bef or epr oceedi ngt osubsequentst agesoff i l l i ng,usi ngt he“ Obser vat i onalMet hod” (settlement plates and piezometers)

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Monitoring applied loads in reinforced wall systems, such as ground anchors, soil nails, and MSE wall reinforcing strips (load cells, strain gauges, extensometers)

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Monitoring deflection, displacement, and loads of flexible wall systems, such as sheetpiles (inclinometers, survey points, earth pressure cells)

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Monitoring loads and deflections at the base of drilled shafts (load cells, extensometers)

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Monitoring the effectiveness of dewatering (piezometers or observation wells to determine drawdown at various distances from the dewatering wells)

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Monitoring temporary stability during excavations for landslide stabilization (survey hubs, stake lines, inclinometers)

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Monitoring stability of tunnel cuts, rock slopes, and rockbolts (extensometers, load cells, strain gauges)

4.

PLANNING INSTRUMENTATION PROGRAMS

When ordinary inspection, investigation, and testing are insufficient to verify the intended performance, there may be a need for instrumentation. A successful instrumentation program involves creating a plan that matches appropriate instruments to the project needs and the resources available for implementation, monitoring and data reduction. The instrumentation plan should take into consideration the anticipated construction process/schedule from beginning to end. The planning task should consider several factors, which include the following: 

Objectives for instrumentation (What is the performance, property, or behavior that needs to be known?)

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Identification of instruments (What instrument functional applications are needed? Which instruments provide measurement of the desired objectives? What accuracy and reliability are needed? What are the simplest instruments that meet the objectives and get the job accomplished?)

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Location (Determine instrument locations in safe places. Identify installation depths. Determine if monument covers and other warning/protection devices are needed to protect instruments.)

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Acquisition of instruments (Will the Department acquire the instruments directly or will the construction contractor or a Consultant be asked to provide instruments? Providing specifications may be necessary to acquire equipment or results desired. Cost considerations could affect the types and extent of instrumentation selected.)

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Calibration (Is this necessary for the selected types of instruments?)

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Installation (Identify who will perform and supervise the installations. Are there installation procedures that are unique for this project? Verify that the installation approach will not compromise the quality of the expected data. Are protective measures needed?)

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Training personnel (Will the new instrumentation require training by the Geotechnical Engi neer or manuf act ur er ’ sr epr esent at i v e? Ar e t he av ai l abl e Depar t ment technicians familiar with the selected instruments?)

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Monitoring (Determine the monitoring requirements and frequency, which could be variable depending on construction progress and ground behavior. Determine the means of collecting and storing data. Should monitoring be done manually each time, or should continuous data collection systems be used?)

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Data analysis (Determine how the data will be reduced, evaluated, and plotted. Identify the types of plots that are relevant to meet the objectives of the engineering evaluation.)

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Documentation (Determine how the data and interpretations, including graphical plots, should be prepared and displayed. Determine the scheduling and recipients of reports/memorandums.)

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Follow-Up (Plan to verify construction practices in response to instrumentation results, and be prepared to respond to potential concerns.)

5.

INSTRUMENTATION, MONITORING, AND DATA INTERPRETATION

Proper installations are important to getting useful results that can be readily interpreted for the intended pur pose.Thei nst r umentmanuf act ur er ’ si nf or mat i onshoul dbe r ev i ewed and,i fnec essar y ,t he manuf act ur er ’ sr epr esent at i v e shoul d be cont ac t ed t o obtain advice for less frequently used instruments. Unfortunately, many instruments have been installed improperly and have resulted in obtaining questionable and misleading data. Installation requires significant attention to details and using the procedure suitable for the geologic conditions and the instrument program objectives. Some instruments need to be calibrated, such as load and pressure devices, inclinometer probes, vibrating wire pi ez omet er s. ( Ref er t o t he manuf act ur er ’ s r ecommendat i ons) . The i nst al l at i on of instruments should be under the direction of the Geotechnical Engineer or trained and experienced technician. Instruments are often exposed to the environment and are susceptible to damage due to accidental impacts (human, animal, and equipment) or vandalism. Environmental factors can affect instrument performance. Therefore, consider the installation location and whether the instrument may be affected by conditions such as water, melting snow, heat, or subfreezing temperatures. Many instruments having equipment such as inclinometer casing, settlement platform risers, or junction boxes, which protrude above ground in the construction area, are particularly susceptible to damage from construction equipment. The requirement for the Contractor to protect and maintain them, as needed, throughout contact period should be clearly described in the contract documents. Protective casings and monument covers may be installed for protecting instruments that are exposed near the ground surface. In addition, placing barricades, posts and warning flags around the instrument location can achieve further protection. The Geotechnical Engineer must work with the Resident Engineer to ensure that the Contractor understands the importance of these instruments, the need to protect them, and the possible impacts to construction, such as work stoppage near damaged instruments. Maintenance of instruments and readout devices should be performed at recommended intervals in order to maintain accuracy and dependability. Electrical and pneumatic systems need to be free of moisture, dirt and dust. Deteriorated or damaged components should be immediately repaired. Periodic calibrations are required for some instruments and readout devices. 02/14/2005



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Most instruments require initial readings to be repeated (duplicate set) to crosscheck that the reference data set is accurate and dependable. The monitoring frequency should be determined by the Geotechnical Engineer to fit the anticipated construction schedule and ground behavior. The Geotechnical Engineer should reevaluate the monitoring program, as construction proceeds, to determine if monitoring frequency should be changed. The data will need to be stored in digital and/or hard copy. When using portable electric data systems, the data should be immediately transferred to a workstation computer. It is advisable to print a back-up copy to provide a redundancy in the stored data. Data analysis should usually be performed immediately, according to the most recent guidance provided by FHWA, AASHTO, geotechnical instrumentation publications, and the manufacturer. Comparing them to previous data sets and known site conditions, as well as performing error checks should verify the reasonableness of the data and the analysis results. Compare the results to previously projected scenarios and determine if there are any concerns. Apply correction factors, if necessary, to make the data relevant and usable. Data results are most useful when plotted in a form that is easily understood and relates to the construction and instrumentation program objectives. Typically, graphs compare the specific measured results against time; however, results can be shown in other ways. For example, for settlement monitoring, graphs can relate and compare such things as fill placement height versus settlement, static groundwater level or pore pressure head versus fill placement height, or settlement versus time. Trends in the data should be evaluated to determine if there is an unusual condition or a common theme demonstrated by the results. A determination should be made if there is a performance hypothesis that is consistent with the instrumentation results. This will help evaluate the validity of data and interpretations. Results should be reviewed by experienced personnel to recommend changes in construction, if necessary. Instrumentation results should be documented promptly. The timing of the reports/memorandums should be established to fit the construction schedule in order to be of value. Sometimes, the reports may need to be made the same day as the readings, or possibly the next morning. If concerns or issues arise that could affect construction, they should be immediately communicated by the Geotechnical Engineer to the Resident Engineer or Inspector. 6.

GROUNDWATER LEVEL AND PORE PRESSURE MEASUREMENT

Piezometric pressures influence the strength of soil or rock. Critical pore water pressures should be estimated during design of embankment fills and other structures. During construction, piezometers can be installed to monitor the pore water pressures. The dissipation of the pore water pressure over time is used as a guide to consolidation rate. Thus, piezometers can be used to control the rate of fill placement during embankment construction over soft soils. Piezometers should be placed prior to construction in the 02/14/2005



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strata/zones that contribute to settlement or shear strength. If the strata or zones are more than 10 feet thick, more than one piezometer should be placed to provide adequate coverage with depth. It is possible to install several piezometers in the same borehole; however, this requires more complex installation and introduces the possibility of crossflows from inadequate seals. Single piezometer installations are generally recommended. The pore water pressure should be measured often during embankment construction. After the fill is in place, and critical conditions have passed, pore water pressures can be monitored at a decreasing frequency. The data should be plotted (as pressure or elevation of water head) as a function of time. A recommended practice is to plot pore water pressure, settlement, and embankment elevation on the same time-scale plot for comparison. Instruments commonly used to measure groundwater pressures include observation wells, open standpipe piezometers, vibrating wire piezometers and pneumatic piezometers. 6.1

Observation Wells

An observation well consists of a perforated section of pipe attached to a riser pipe installed in a borehole backfilled with sand. A pipe cap on top of the riser pipe and, typically, a cement seal around the top of the pipe are used to prevent surface water from entering the monitoring system. A vent is required in the cap to allow pressures in the pipe to equalize. Groundwater levels in standpipes and wells are read using an electronic dipmeter, which emits an audible (beep) and visible (red light) signal when the surface of groundwater is encountered. The red light signal can be very handy when working around noisy equipment. The depth is measured using a graduated cable. Observation wells are used for monitoring the groundwater levels. Observation wells are also used to monitor the changes of ground water levels due to conducting a pump test to determine permeability. If an observation well is installed across several zones of permeability, the measurement will correspond to the zone of highest permeability. Observation wells should preferably be installed in materials of high permeability so that the lag time related to changes in groundwater levels is minimized and reasonably accurate results are obtained. Observation wells in silt and clay soils could experience long lag times and therefore should be used cautiously. Where these conditions exist, it is advisable to use an alternative type of piezometer. 6.2

Open Standpipe Piezometers

Open standpipe piezometers are similar to observation wells, except that the perforated portion of the pipe and sand filter region (backfill) is sealed in a discrete zone and the riser pipe is much smaller in diameter. The smaller diameter of the pipe reduces the lag time related to changes in ground water levels. Above the sand filter, the remaining backfill should include a seal (either cement/bentonite or bentonite pellets). Surface runoff should be prevented from entering the standpipe by installing a box or monument that does 02/14/2005



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not restrict the pipe from venting. Groundwater levels in standpipes are read using an electronic dipmeter which signals when the water surface inside the pipe is encountered. The depth is measured using the graduated cable. Open standpipe piezometers have a long successful performance record and are preferable to observation wells in most applications. Open standpipe piezometers should be used only in materials of high to moderately high permeability so that lag time remains relatively short. Standpipe piezometers are less effective in low-permeable silts or clayey soils to measure fluctuations in groundwater levels. 6.3

Vibrating Wire Piezometers

Vibrating wire piezometers are pressure transducers that operate using the frequency of vibration of a wire connected to a flexible metallic diaphragm. As the pressure changes, the length of the wire changes, resulting in a different vibrating frequency, which can be correlated to a specific water pressure. Each uniquely calibrated piezometer is contained in a protective housing with a porous filter. There are several manufacturers of vibrating-wire piezometers. Each manufacturer sells readout devices that are generally able to read other brands of piezometers as well. Vibrating wire piezometers are installed in a similar manner as open standpipe piezometers. It is recommended that the wire leads be kept taut during installation, especially when using hollow-stem auger drilling systems, to avoid abrasions and breakage. This can be performed by taping the leads to a solid rod or PVC pipe. Vibrating wire piezometers have several significant advantages over open standpipe piezometers including: (1) require very short lag time related to changes in groundwater levels in all types of soils, (2) cause minimum interference to construction equipment due to flexibility of wire placement, and (3) are easily adapted for use with an inexpensive datalogger for automated readings. Disadvantages include: (1) more care is required to assure proper installation, and (2) the electronic units are susceptible to damage by lightning, transient electricity, and shorting if the leads become abraded and the wires are exposed to moisture. The power source needs to be maintained (i.e., periodic replacement of batteries). 6.4

Pneumatic Piezometers

Pneumatic piezometers consist of a sensor body with a flexible diaphragm, and inlet and outlet tubes. The junction box outlet is connected to a readout unit and pressurized gas is applied to the inlet tube. As the applied gas pressure equals and then exceeds the pore water pressure, the diaphragm deflects allowing gas to vent through the outlet tube. The gas supply is then turned off and the diaphragm returns to its original position. The pressure in the inlet tube equals the pore water pressure and is measured and recorded. Pneumatic piezometers are installed in a similar manner as vibrating wire piezometers. Pneumatic piezometers have many of the same advantages that vibrating-wire piezometers have. Disadvantages include: (1) require more equipment, (2) require more 02/14/2005



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complex setup and operator training, and (3) the quality of the readings is more operatordependent. 7.

LATERAL GROUND MOVEMENT INSTRUMENTATION

Movements can be identified by visual observations, or can be measured using surveying equipment to monitor tag lines comprised of hubs/stakes, or permanently/temporarily installed reflectors. Movements can also be measured by more sophisticated instruments such as inclinometers. Survey instrumentation, telltale stakes, and crack monitoring devices measure movements only on the surface, whereas inclinometers measure movements below the ground surface. 7.1

Telltale Stakes

The simplest means of monitoring ground movement is a row of stakes along a lineof-sight. If any of the stakes are observed to veer from the line-of-sight, ground movement may be occurring. This system serves as an early warning method and can be checked frequently with ease. For this system to be effective, the stakes at each end must be on stable ground and safe from being disturbed. 7.2

Survey Hubs

Survey hubs (stakes or pins) could be used to monitor horizontal and vertical movement of the ground surface George, this is in Lateral Ground Movement Instrumentation Section so I crossed it out, where the hubs can be installed and maintained with essentially no disturbance. Surveying of one or a series of hubs (tag line) can help determine rates and direction of ground surface movement, and the lateral extent of landslides. Typical hubs survey monitoring can identify gross movements of ¼ inch or more. For greater dependability, use deeply installed steel pins/rebar that are not as easily disturbed by surface activities and freeze/thaw. The reference datum (benchmark) should be located where it is not subject to movement. 7.3

Portable Crack/Deformation Gauges

Cracks on rock slopes, buildings, walls, and slides can be monitored using a strain measuring tool. Tools include: A transparent graduated grid/scale, calipers, survey tape, micrometer, dial gauge, mechanical strain gauge, or electrical crack gauge. One simple monitoring method is to firmly place a stake/hub on each side of a crack and then measure the distance between the two. The magnitude and time rate of movement is monitored. Commonly, as the rate of movement accelerates, the likelihood of an imminent failure increases and concern should be raised. 7.4

Inclinometers

Inclinometers are used to monitor ground deformation below the ground surface. The installation includes placing a grooved plastic tube (inclinometer casing) within a borehole and backfilling the annular space outside the casing. To accurately measure 02/14/2005



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lateral displacements, the bottom of the tube must be socketed at least ten feet below the failure zone where the bottom of the tube does not experience any movement, thereby achieving a stable point of fixity. An inclinometer probe contains two transducers for taking measurements. The probe should be carefully handled and periodically calibrated and verified for proper performance. The inclinometer probe is lowered down to the bottom of the tube with the probe wheels following the grooves within the tube. The orientation of the tube (degree of tilt) is measured as the probe is pulled up (usually in 2-foot increments). The measurements are taken with a portable electronic readout device. Readings are plotted relative to an initial set of readings taken immediately after installation to show any displacements that have occurred versus depth. Subsequent readings can be included on the same plot to show the rate of displacement over time. Vector sums can be used to determine the direction of movement. Depending on the rate of landslide movement, it is important to take readings often enough to pick up the depth(s) of slide movement before the casing pinches off, becoming unusable. Inclinometers are routinely used to monitor landslides. Inclinometers are placed at several locations along the length of the slide to develop a cross-section showing the depth and orientation of the slide shear zone. The cross-section should be aligned along the axis of landslide movement based on the calculated direction of movement. Inclinometers can also be installed to monitor critical embankment and excavation slopes where stability is a concern. Fill operations should be halted if unacceptable movements (as determined by the Geotechnical Engineer) are detected. In installation of an inclinometer, the annulus space between the borehole wall and the casing should be backfilled with a firm grout as recommended by the manufacturer. The grout should be placed either by Tremie tube into the annular space starting at the bottom of the hole, or pumped through a pipe connected to a one-way valve at the bottom of the inclinometer casing. In some cases, sand or gravel is used as a backfill material. However, granular material can bridge within the hole, or result in loose backfill zones, which could cause casing deflections that are not related to ground movement. Granular fill should only be used in boreholes that cannot be grouted, or where the rate of movement is high enough to be readily distinguishable from other casing disturbances. For installations in highly compressible soils, telescoping couplings should be used to prevent damage to the casing due to ground settlement. 7.5

ShearPl aneI ndi cat oror“ Poor -Man’ s”I ncl i nomet er

A shear plane indicator consists of a plastic pipe installed in a borehole, similar to an observation well. Depending on the size of the plastic pipe, a short steel rod is lowered into the pipe on a fishing line, wire or cable. Typically, rod lengths range from six inches to two feet. Monitoring consists of pulling the rod up from the bottom of the hole to see if it begins to bind up in the hole where the pipe is bent by slide movement. Often, slide movements occur within a zone, not as a discrete failure plane. In this case, the rod typically binds up at 02/14/2005



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the bottom of the failure zone. To determine if the failure is occurring discretely or as a failure zone, a second steel rod could be lowered into the pipe (top-down) to determine the upper limit of slide movement. This instrument is an approximating tool, which could be considered where funds are limited; however, it is not as accurate or dependable as the regular inclinometer. 7.6

Time Domain Reflectometry (TDR)

This relatively new method provides a basic subsurface movement identification system. The TDR instrument utilizes a coaxial cable installed in a borehole, which is monitored by applying a voltage pulse. Wherever there is a change in electrical properties, such as the one caused by deformations of the cable due to ground movements, a portion of the voltage is reflected back to the source and relative magnitudes of distortion are measured for interpretation. The depths to possible deformation zones can be approximated. Use of TDR is most valuable in cases where the location of the instrumented boring is in the roadway, where setting up and reading an inclinometer may be unsafe. The TDR cable can be routed in a narrow trench to beyond the edge of pavement and the readings can be made at that location. Advantages over an inclinometer are that the TDR cable may continue to function for a longer period than an inclinometer casing, (which may become too distorted for the probe to be inserted after only several inches of movement), and multiple zones of movement can be detected over time. Disadvantages to use of TDR are that accurate movement magnitudes, rates, and direction cannot be determined; that the system is complex; and the supply and technical suppor tar el i mi t ed.Ref ert ol i t er at ur ebyKaneandO’ Connerf orf ur t heri nf or mat i on. 7.7

Lateral Extensometers

Extensometers can be used to measure displacement and deformations of rock cuts, tunnel cuts, and retaining systems. The extensometer rods or cables are placed in holes that are generally perpendicular to the cut or wall surface to determine whether material or blocks of rock are being displaced. Relative displacements of the extensometer rods in relation to each other or to the ground surface can be measured with strain gauges. 7.8

Webcams

Webcams have been used as warning devices for real-time monitoring of areas that have high risks of sliding, rockfall or other geotechnical problems that can be identified visually. The objective is to spot a problem occurring and to take action before significant harm occurs. It is typically not feasible to have inspectors or maintenance staff on site all the time, particularly during evenings and weekends. The benefits of the webcam instrumentation are that high risk areas can be monitored remotely around the clock (possibly by maintenance staff in traffic control centers). Limitations include: (1) visibility can be hindered during dark, rain and fog conditions, (2) small movements/events may not be detected, and (3) potential delay time before staff recognizes that a problem condition is 02/14/2005



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occurring or has occurred. This application is a reactive method, but could help prevent greater problems from occurring. The Geotechnical Engineer should determine when geologic conditions are too hazardous or dangerous to require a full-time watchperson, warning signs, and possibly control and/or restriction of traffic, in addition to remote visual monitoring. 8.

SETTLEMENT/HEAVE MONITORING

The most common settlement monitoring instrumentation is the settlement plate. Less common instruments include the inductive coil gauge, the borehole extensometer, and inclinometer casing installed horizontally on the embankment foundation. To augment settlement deformation measurements, piezometers are used to provide a measure of the dissipation of pore pressure associated with consolidation. 8.1

Settlement Plate/Platform

Settlement instruments record elevations, which are used to calculate the amount of settlement under a load. They are most commonly used on projects with high fill embankments, where significant settlement is predicted. The simplest device is the settlement platform or plate, which consists of a square wooden platform or steel plate placed on the existing ground surface prior to embankment construction. A reference rod and protecting pipe are attached to the platform. As fill operations progress, more segments of l rods and pipes are added. Settlement is determined by periodically measuring the elevation of the top of the reference rod. The platform elevation must be measured before embankment construction commences. . Subsequent readings should be taken periodically during embankment construction and whenever additional riser pipes are attached. Stable benchmarks should be used for a reference elevation datum, and should be located away from all possible vertical movement or other disturbance. The Geotechnical Engineer should determine locations of the benchmarks. It may be necessary to use multiple benchmarks for redundancy and to survey elevations between them at regular intervals for confirmation. Settlement plates should be placed at locations under the embankment where maximum settlement is predicted. On large projects, two or more settlement plates per embankment should be installed. The settlement data should be plotted as a function of time. The Geotechnical Engineer should analyze this data to determine when the rate of settlement has slowed sufficiently for other construction operations to commence, such as subsequent embankment or base course placement for paving. Concerns with settlement plate instruments are potential for damage to the reference rods by construction equipment, and difficulty in properly compacting around the pipes/rods as subsequent embankment lifts are placed. Protection and warning devices are required. 8.2

Remote Settlement (Gauge Monitoring Tubes)

Settlements can be monitored by using manometer technology, which eliminates the need for riser pipes within the fill as the embankment is being constructed. The change 02/14/2005



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in piezometric head within the manometer tube can be translated to settlement magnitude. This system, while less susceptible to construction traffic, is more complex than the settlement plate and requires calibration and specialized maintenance, as well as care and protection during installation. 8.3

Inductive Coil Gauge (Deep Settlement Monitoring)

A more technically complex alternative to a settlement plate is the inductive coil gauge in which a probe lowered down a flexible compressible pipe can identify points along the pipe either mechanically or electrically. Distances between these points are determined, and then used to calculate the magnitude and rate of settlement at various depths. An alternative system includes magnet and reed switch gauges. This method of settlement measurement allows a profile to be obtained within the compressible soil layer. Ref ert oFHWA,“ Geotechnical Instrumentation –St udentWor kbookf orTr ai ni ngCour se, ” 1981. Surveying the top of the pipe elevation needs to be performed if the pipe is not seated into an incompressible soil layer. Care must be taken during installation and grouting the pipe in the borehole so that the flexible pipe is allowed to settle in the same fashion as the surrounding soil. 8.4

Borehole Extensometer (Deep Settlement Monitoring)

The borehole extensometer is an alternative to the inductive coil gauge, which consists of one or several steel rods placed within a borehole and anchored at specified depths to monitor localized settlement within specific layers. Anchors are attached to the bottom of extensometer rods, as a stationary reference point at the deepest location desired in the borehole. The mechanical anchoring system (Borros) consists of a device with expandable steel members that are pushed into the borehole sidewall. Grout backfilling the borehole is an alternative to anchor the steel extensometer rods. Elevation measurements are related to the lowermost anchored-rod or surveyed datum. System redundancy can be provided by surveying the ground surface elevation and the instrument measuring plate. The relative displacements of each rod are measured with a dial gauge mounted on a pedestal. 8.5

Horizontal Inclinometer (Settlement Monitoring)

Inclinometers can be used to measure vertical deformation (settlement) when the grooved inclinometer casing is placed horizontally beneath a proposed embankment. One end of the casing must terminate at a fixed datum (or the datum should be accessible for resurveying each time measurements are taken). A pulley system is required to move the inclinometer probe along the casing. It is preferable that both ends of the casing daylight to simplify monitoring operations and to provide a more reliable means of maintaining the system. Taking measurements using horizontal inclinometers takes longer time than using settlement plates. This instrument is used sparingly, primarily where settlement plate instruments are too likely to be damaged or when settlement profiling under the embankment cross-section is required. 02/14/2005



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TILTMETERS

Tiltmeters measure the inclination (tilt or rotation) of discrete parts of rock cuts and structures from the established datum. They are most commonly used to monitor tilting of bridge abutments, retaining walls and marginally stable slopes or rock outcrops. Types of tiltmeters range from a simple plumb line to more sophisticated electrical equipment with accelerometer or electrolytic level transducers. The fixed-in-place tiltmeter is more accurate than the portable version because there is no inaccuracy associated with the direct anchoring system. The portable instrument introduces some inaccuracy due to the use of an intermediate reference plate and mechanical connections. 10.

LOAD CELLS AND STRAIN GAUGES

Load cells and strain gauges are used to measure forces and deformation of critical structural elements, such as high capacity ground anchors, heavily loaded drilled shafts, and tunnel supports. Strain gauges could be used solely for measuring strain, or can be incorporated into structural members to measure loads (which require computations relying on elastic properties of the device). Calibration is typically required. Electrical resistance and vibrating wire type load cells are more reliable and accurate (accuracy within ±2 to ±10%) than proof ring type load cells. A common load applying device is a calibrated hydraulic jack; however, its accuracy to measure the applied load is within about ±10 to ±25%. For many engineering applications, higher measuring accuracy is required. . 11.

EARTH PRESSURE CELLS

“ Embank mentear t hpr essur ecel l s”ar ei nst al l edwi t hi nembank ment st odet er mi ne the magnitude and direction of total stress. In addi t i on,“ Cont ac tear t hpr essur ecel l s”ar e used to measure total stress acting against retaining walls, foundations, and culverts. Both of these types of earth pressure cells are primarily used in research and verifying design assumptions of special applications, and are rarely used for construction control. In general, these instruments are expensive and accurate earth pressures are difficult to obtain. 12.

VIBRATION MONITORING

It is sometimes desirable to monitor the ground vibrations induced by blasting, pavement breaking, pile driving, rock excavation (ripping, chiseling, hammering), operation of construction equipment, or traffic loading. This is especially critical when construction is in close proximity to sensitive structures or equipment, which may become damaged if subjected to excessive vibration. A visual survey of structures that may potentially be damaged due to vibration should be conducted prior to the construction. Structures should be photographed. Video cameras are typically used for visual recording with a commentary ofobser v at i ons.I nbl ast i ngoper at i ons,t hi si sr ef er r edt oast he“ Pr ebl astSur v ey . ” Thi s may include land survey of very significant structures. A vibration monitoring device typically consists of a recording unit, one or more geophones, and connecting cables. Instrument types include: seismographs, peak meters, 02/14/2005



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and air blast sensors. Sound sensors to detect noise levels are also available. Geophones and/or sound sensors are placed at locations where data on vibration levels is desired. Peak particle velocities, principle frequencies, peak sound pressure levels, and actual waveforms can be recorded. Results are compared with preestablished vibration limiting criteria, which are based on structure conditions, equipment sensitivity, or human tolerance. 13.

GROUND TEMPERATURE

Measurements of ground temperature could be accomplished by installing thermistors into boreholes. Multiple installations are possible. An electronic readout instrument is required. Initial readings should be made over a period of several days to verify that temperature measurements have reached equilibrium. Ground temperature can be a factor in addressing viscoelastic behavior of embedded materials, impacts on grout curing, and potential frozen ground issues. Vibrating wire piezometers commonly come equipped with thermistors. 14.


SUBJECT Settlement Plate/Platform

ASTM -

AASHTO -

-

T 252

D 4403

-

Installing, Monitoring, and Processing Data of the Traveling Type Slope Inclinometer

-

T 254

Subsurface Liquid Levels in a Borehole or Monitoring Well (Observation Well)

D 4750

-

Design and Installation of Groundwater Monitoring Wells in Aquifers

D 5092

-

Static Calibration of Electronic Transducer Based Pressure Measurement Systems for Geotechnical Purposes

D 5720

-

Monitoring Well Protection

D 5787

-

for

D 6027

-

Type

D6230

-

Pore Pressures in Soils Extensometers Used in Rock

Calibrating Linear Displacement Geotechnical Purposes Monitoring Ground Inclinometers

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Movement

Transducers

Using

Probe



10-15

REFERENCES

AASHTO,“ Manual onSubsur f aceI nv est i gat i ons, ”Appendi xG:I ns t r ument at i on,1984 AASHTO,“ I nSi t uI mpr ov ementTechni ques, ”TaskFor ce27Repor t ,1990 Dunni cl i f f ,J ohn,“ Geot echni calI nst r ument at i onf orMoni t or i ngFi el dPer f or mance, ”Wi l ey Interscience, New York, 1993 FHWA,“ Geot echni calI nst r ument at i on, ”Ref er ence Manual ,NHICour se No.13241 – Module 11, FHWA-HI-98-034, 1998 FHWA,“ Geot ec hni calI nst r ument at i on–St udentWor kbookf orTr ai ni ngCour se, ”1981 FHWA,“ Adv anced Cour se on Sl ope St abi l i t y , ”Vol .1,Chapt er9,I nst r ument at i on and Monitoring, FHWA- SA-94-005, 1994 FHWA,“ Tol er abl eMov ementCr i t er i af orHi ghwayBr i dges, ”FHWA- RD-85-107, 1985 FHWA,“ Foundat i onI nst r ument at i on–I ncl i nomet er s, ”FHWA-TS-77-219, 1977 FHWA,“ RockSl opes–Desi gn,Ex cav at i on,St abi l i z at i on, ”FHWA-TS-89-045, 1989 Kane, W. F. , Per ez , H. , and Ander son, N. O. ,“ Dev el opment of a Ti me Domai n Ref l ect omet r ySy st em t o Moni t orLandsl i de Act i v i t y , ”Fi nalRepor tFHWA/ CA/ TL96/09, Department of Civil Engineering, University of the Pacific, Stockton, California, June 1996 NCHRP,“ Tr eat mentofPr obl em Foundat i ons f orHi ghway Embankment s , ”Chapt er7, Construction and Performance Monitoring, Synthesis 147, 1989 O’ Conner ,K. M. ,“ RealTi me Moni t or i ng ofI nf r ast r uct ur e Usi ng TDR Tec hnol ogy , ”25t h FHWA Northwest Geotechnical Workshop, Bismarck, North Dakota, August 1999 Peck,R.B. ,“ Adv ant agesand Li mi t at i onsoft he Obser v at i onalMet hod i n Appl i ed Soi l Mechani cs, ”Ni nt hRanki neLec t ur e,Geot ec hni que,Vol .19,No.2,pp171–187, 1969 TRB,“ Gui det oEar t hwor kConst r uct i on:St at eoft heAr tRepor t , ”TRBRepor tNo.8,I SBN 0-309-04957-1, 1990 TRB,“ Landsl i des :I nv est i gat i onandMi t i gat i on, ”Chapt er11,Fi el dI nst r ument at i on,Speci al Report 247, 1996 USDA,“ Sl opeSt abi l i t yRef er enceGui deForNat i onalFor est si nt heUni t edSt at es , ”Vol .I , Section 3, Site Investigations, EM-7170-13, 1994

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CHAPTER 11 ANALYSIS AND DESIGN

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ANALYSIS AND DESIGN

1. 2. 3. 3.1 3.2 3.3 3.4 3.5 3.6 4. 5. 5.1 5.2 6. 6.1 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.3 6.3.1 6.3.2 6.3.3 6.3.4 7. 8. 8.1 8.2 8.3 8.4 8.5 8.6 9. 9.1 9.2 9.3 9.4 9.5 02/14/2005

11-i

TABLE OF CONTENTS PURPOSE ............................................................................................................ 1 INTRODUCTION .................................................................................................. 1 ROADWAY EMBANKMENT MATERIALS ........................................................... 1 Suitable use of Materials within Project................................................................ 1 Limits of Usable Materials .................................................................................... 2 Corrosivity............................................................................................................. 2 Drainage ............................................................................................................... 2 Earthwork Factors ................................................................................................ 3 Other Considerations............................................................................................ 3 EMBANKMENT SETTLEMENT ........................................................................... 3 SOIL CUT AND FILL SLOPE STABILITY ............................................................ 5 Embankments Over Liquefiable Ground .............................................................. 6 Reinforced Soil Slopes ......................................................................................... 6 ROCK CUT SLOPES ........................................................................................... 7 Predesign Tasks................................................................................................... 8 Slope Stability Analyses ....................................................................................... 9 Kinematic Analyses .............................................................................................. 9 Stability Analyses ................................................................................................. 9 Factor of Safety .................................................................................................. 10 Computer Programs ........................................................................................... 10 Rock Slope Design ............................................................................................. 10 Design Standards and Policies........................................................................... 11 Selecting Slope Angle ........................................................................................ 11 Construction Considerations and Mitigation Measures ...................................... 11 Rockfall Control Design ...................................................................................... 13 LANDSLIDES ..................................................................................................... 13 GEOTECHNICAL EARTHQUAKE ENGINEERING DESIGN............................. 14 Seismicity ........................................................................................................... 15 Seismic Response of Soils ................................................................................. 16 Dynamic Response Characteristics of Structures .............................................. 16 Liquefaction ........................................................................................................ 16 Seismic Slope Stability ....................................................................................... 17 Seismic Analysis of Retaining Structures ........................................................... 17 FOUNDATIONS ................................................................................................. 18 Service Load vs. Load and Resistance Factor Design ....................................... 18 Foundation Feasibility......................................................................................... 18 Spread Footings ................................................................................................. 19 Foundations on Rock ......................................................................................... 19 Deep Foundations .............................................................................................. 19 NDOT Geotechnical Policies and Procedures Manual

ANALYSIS AND DESIGN

9.5.1 9.5.2 9.5.3 9.5.4 9.5.5 9.5.6 9.6 9.7 9.8 9.9 10. 10.1 10.2 10.3 10.4 10.5 10.6 11. 12.

13.

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11-ii

Axial Capacity..................................................................................................... 20 Lateral Capacity.................................................................................................. 20 Seismic Analyses ............................................................................................... 20 Liquefaction Potential and Mitigation.................................................................. 20 Scour Considerations ......................................................................................... 21 Design Phase Load Testing ............................................................................... 21 Driven Piles ........................................................................................................ 21 Drilled Shafts ...................................................................................................... 22 Auger Cast Piles (ACP) ...................................................................................... 22 Micropiles ........................................................................................................... 22 RETAINING WALL SELECTION AND DESIGN ................................................ 22 Standard Cantilever Walls.................................................................................. 23 Modular Gravity Walls ........................................................................................ 24 Mechanically Stabilized Earth (MSE) Walls........................................................ 24 Soil Nail Walls .................................................................................................... 25 Cantilevered Soldier Pile and Sheet Pile Walls .................................................. 26 Ground Anchor Wall Systems ............................................................................ 26 DEWATERING ................................................................................................... 27 FIGURES ........................................................................................................... 28 11-1: Policies and Procedures Memorandum .................................................... 28 11-2: List of Landslide Mitigation Methods ......................................................... 35 11-3: AASHTO Factors of Safety ....................................................................... 35 11-4: Computer Programs .................................................................................. 36 11-5: Guidelines for Geotechnical Engineering Analysis.................................... 42 REFERENCES ................................................................................................... 44


ANALYSIS AND DESIGN 1.

11-1

PURPOSE

After exploration and testing have been completed, the Geotechnical Engineer must organize and analyze all existing data and provide design recommendations. The extent of the analysis depends upon the scope of the project and the soils/rock involved. 2.

INTRODUCTION

Many factors must be considered during the analysis and design phase of projects. Figure 11-5 provides guidelines for types of analyses that should be performed. The references cited in the text provide suggested methods of analysis and design. Figure 11-4 provides a list of computer software programs used by the Department. In using these references and software programs, be aware that engineering technology progresses rapidly and those methods and software programs are being improved or new methods or programs introduced frequently. The Geotechnical Engineer should keep abreast of the state-of-the-art practice for appropriate and economical designs. The Geotechnical Engineer needs to consult with the Principal Geotechnical Engineer when new techniques are to be utilized. 3.

ROADWAY EMBANKMENT MATERIALS

The suitability of in situ materials for use as roadway Embankment Borrow is determined by analysis of the results of reconnaissance and subsurface exploration. Embankment materials must meet the Department Standard Specifications for Road and Bridge Construction, unless alternate specifications are needed. The subsurface materials encountered during soil explorations should be classified, and interpretations of the stratigraphy should be made. Soils should be grouped if they belong within the same stratum. If planned testing identifies dissimilar types of soils within the same stratum, additional sampling and testing may be required to better define the in situ materials and potential variabilities. On occasion, dissimilar soil types may be grouped for such reasons as borderline test results, or insufficient quantities of in situ material to economically justify separation of the material during construction. Some engineering judgment must undoubtedly be used in grouping and stratifying soil types. Conclusions should be clearly explained and justified in the Geotechnical Report. Each stratum should be analyzed to define characteristics that may affect the design. 3.1

Suitable use of Materials within Project

The Geotechnical Engineer should determine the appropriate suitability of materials to be excavated in the project. The uses of specific materials are typically based on classifications and tests, such as gradations, R-value, plasticity, moisture, rock durability, and degree of weathering. The Geotechnical Engineer should determine if materials within the proposed project excavations meet required specifications of Borrow Embankment materials. Estimates should be made of available quantities of each identified material type. The 02/14/2005


ANALYSIS AND DESIGN

11-2

location of material types should be identified in order to provide information for project designers, construction schedule planners, and contractors regarding potential earthwork issues. Sometimes the sequencing of cross-hauls to excavate, process and deliver materials can be complex and therefore specific information can be beneficial during project development and construction. Borrow Embankment materials have R-values greater than or equal to 45. Typically roadway embankment materials must meet required specifications for Borrow Embankment materials. The Geotechnical Engineer must provide detailed and accurate information on the boring logs and in the Geotechnical Report regarding the drilling process and description of encountered soils during the subsurface investigation. This will assist the Contractor to make a reasonable interpretation of the subsurface conditions to be encountered and avoid a change of conditions when excavating. Contractors review boring logs and Geotechnical Reports to make their assessments of excavatability requirements. The Geotechnical Engineer should evaluate whether controlled blasting techniques are to be used to develop appropriate cut slopes in rock. Rock excavation and blasting are described in greater detail in Section 6. 3.2

Limits of Usable Materials

The limits of in situ materials considered unsuitable, for use on the project, or as a foundation to support structural elements of the project, should be defined, and the effect of each material on roadway performance should be assessed. Refer to Sections 203 and 207 of the Department Standard Specifications for Road and Bridge Construction for requirements on excavation and replacement of these materials. In areas where excavation may be excessive, but the potential for problems exists if not excavated, possible stabilization methods to be considered include placement of geotextile, surcharging, mixing the soil with lime, cement, or fly ash, or a combination of these. 3.3

Corrosivity

Results of field and/or laboratory tests should be reviewed and the potential for corrosion of the various foundation and drainage system components should be assessed. The Structural/Chemical Section of the Materials Division provides the recommendation. 3.4

Drainage

The permeability and infiltration rates of cut slopes and embankment materials should be estimated based on test results or knowledge of the material characteristics. This information, along with data on the depth to groundwater, can be used in assessing the need and design of a drainage system. Subsurface drainage systems may include pavement underdrains and interceptor drains. Surface drainage systems may include retention, detention, and infiltration basins. TheHy dr aul i csSect i onoft heDepar t ment ’ sRoadway Design Division designs surface drainage systems.

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ANALYSIS AND DESIGN 3.5

11-3

Earthwork Factors

Earthwork factors (shrink/swell) used in estimating cut and fill quantities are typically based on local experience. Shrink/swell is the percent decrease or increase in volume that occurs when a material is excavated from an in situ location and used to construct an embankment. In general, rock that is blasted from in place and used in an embankment will swell. The Geotechnical Engineer should determine the shrink/swell factors for the materials to be excavated, and estimate average values according to roadway excavation plans. The roadway alignment can be divided into sections to group excavated materials that are similar. Thesef act or saf f ectt heRoadwayDesi gnEngi neer ’ smat er i al squant i t i esest i mat ef ort he project (refer to Church, (1981). The values of shrink/swell factors vary considerably depending on the method of fill construction and the level of compaction effort applied. Typically, material to be wasted from a project is placed in a disposal area by end dumping using gravity compaction. For highway construction, earth materials are placed and compacted using heavy compaction equipment as specified in the Department Standard Specifications for Road and Bridge Construction. For most hard rock, such as granite or limestone, the swell can range up to 36 percent. Conversely, due to the compaction effort, soils that are removed from in place and then placed and compacted in an embankment tend to shrink, typically averaging about 10 percent. If the Geotechnical Engineer cannot determine the shrinkage factor for excavated soil used as Borrow Embankment material, a value of 15% should be recommended. 3.6

Other Considerations

Presence of characteristics and features determined from soil explorations that affect the roadway design, include expansive soils, springs, sinkholes, rock, or soft subgrade. The effect of these characteristics on roadway performance should be assessed. 4.

EMBANKMENT SETTLEMENT

The magnitude and time rate of settlement of embankments are typically estimated using one-dimensional consolidation theory and strip loading stress distributions. Several conditions that can cause settlement include loading due to new embankments, embankment widening, lowering of groundwater (including temporary dewatering), temporary fills and stockpiles. FHWA publications (Soils and Foundations Workshop, 2000; and Advanced Course on Slope Stability, 1994) provide technical guidance for estimating settlement at abutments, along embankment centerline and edge of pavement, and at locations beyond embankment toes where sensitive structures or facilities might exist. The Geotechnical Engineer may use FoSSA software, provided by the Federal Highway Administration to estimate settlements. Other software programs such as EMBANK or SIGMA/W (a finite element program) are available. If design analyses indicate excessive settlement magnitude or time, mitigation measures should be evaluated. Mitigation measures could include: (1) surcharging, (2) 02/14/2005


ANALYSIS AND DESIGN

11-4

removal of settlement-prone material, (3) installation of vertical drainage systems such as wick drains, sand drains, or stone columns, (4) ground improvement such as jet grouting, dynamic compaction, deep soil mixing, vibroflotation, and placing piles, (5) reducing loads by decreasing the height of embankments, substituting lightweight fill (sawdust, shredded tires, baked shale, extruded polystyrene-EPS), (6) spanning the compressible area with a pilesupported structure (bridge or viaduct), and (7) column supported embankments. The use of surcharging is a very common mitigation measure. The principle is to overconsolidate the foundation soil to reduce postconstruction settlement. The postconstruction settlement is estimated by comparing the settlement versus time graphs for both the design embankment and for the embankment plus surcharge condition. Sometimes, surcharging does not produce the desired amount of preloading settlement within the timeframe constraints. If this is the case, then the alternative mitigation measures are evaluated. Vertical drainage systems can be used to speed the rate of settlement of a fill placed on top of a soft soil deposit. This method effectively shortens the drainage path that pore water must travel during consolidation under an applied load. The Geotechnical Engineer selects the drain spacing that results in a consolidation that meets the project design and construction requirements (i.e., settlements have occurred to an acceptable magnitude prior to construction of a settlement sensitive element, such as a bridge abutment). A wick drain consists of a plastic drainage core wrapped in a nonwoven geotextile. The drains are installed by a mandrel on a rig that drives the mandrel with continuous down pressure or vibration. The mandrel is extended to the design elevation and then retracted. An anchor plate at the bottom of the drain prevents the drain from being pulled upwards with the mandrel. After installation of the drains, a free draining sand blanket is installed on the ground surface to enable free flow of water from the drains. The fill embankment is then constructed on top of the sand blanket. Jet grouting mixes cement with the native soil to create a higher capacity and less compressible foundation. Silt and sand soils are best suited for this type of mitigation technique since they are readily cut and mixed by the water jets. Clay soils may not break down sufficiently. Dynamic compaction and vibroflotation (including stone columns) increase the density of subsurface soils. Silt and sand soils are best suited for these types of mitigations techniques since they relieve excess pore water pressures generated by the dynamic motions. Placing piles can be used (although infrequently in practice) to distribute embankment loads to a lower, less compressible stratum. Sometimes a proposed roadway alignment can be modified to reduce embankment heights in critical settlement-prone areas. If not, another option to reduce embankment weight is to substitute lightweight materials instead of soils in the embankment. Sawdust or wood fiberfills have been used for decades. Since the 1980s, shredded tires have also been used in embankments. Drawbacks for these lightweight materials are: (1) having the potential for combustion, and (2) occurrence of surface deflections/rebound under traffic loads. Baked shale and extruded polystyrene (EPS) do not have these drawbacks; although EPS needs to 02/14/2005


ANALYSIS AND DESIGN

11-5

be encapsulated to prevent damage from solvent spills, such as gasoline. EPS is the lightest of the lightweight construction fill materials, with a density of about 2 lbs/cu. ft. On some projects such as those in wetlands, much mitigation may not be permitted due to environmental constraints. Use of a bridge or viaduct may be acceptable because of having minimal environmental impacts, as well as avoiding need of support on compressible soils. Structural mitigations are typically the most expensive options. 5.

SOIL CUT AND FILL SLOPE STABILITY

Short cut and fill slopes are typically evaluated using precedence, experience, and judgment. The Geotechnical Engineer needs to recognize when the height of a cut/fill slope or poor subsurface conditions warrant performing stability analyses. A quick form of analysis is the use of stability charts and graphs that solve relatively simple and common cases. The U.S. Forest Service Slope Stability manuals provide a compilation of stability charts. Also, r ef ert oFHWA’ sAdv ancedCour seonSl opeSt abi l i t ymanual . Cuts and fills that have irregular geometry, intermediate groundwater levels, or low-strength soils may justify the use of limit equilibrium stability analyses. Most landslides should be evaluated with stability analysis. For decades now, FHWA has endorsed XSTABL, which is a stability analysis software based on the STABL programs developed by Purdue University in the 1970s. This program has been modified into the user-friendly program PCSTABL. There are several other software packages which some have greater capabilities and output formats, such as Slope-W, UTEXAS, and PC-Slope. Refer to FHWA publications (Soil and Foundation Workshop and Advanced Course on Slope Stability). Typical cut and fill slopes have inclination angles of 2H:1V. Steeper slopes can be used based on analyses using representative shear strength or based on local precedence. When the analyses indicate that slope angles do not have a sufficient level of stability (Factor of Safety, F.S.), mitigation measures may be necessary. The following is a list of possible mitigations for cut and fill slopes. Cut Slope Mitigation 

Flatten the cut slope angle



Lower the groundwater level using drainage methods (trench drains, interceptor drains)



Replace some of the cut slope material with higher strength material, such as rock fill (rock inlay)



Reinforce cuts (soil nails) Fill Slope Mitigation



Flatten the fill slope angle



Install drainage measures (underdrain blankets, trench drains)



Use an embankment fill material with higher shear strength properties (for example,

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ANALYSIS AND DESIGN

11-6

embankments constructed with rock fill can generally support 1.5H:1V slopes) 

Place toe counterberms



Place rockfill shear key



Improve the foundation materials (overexcavate and replace)



Use staged embankment placement (allowing excess pore water pressures to dissipate in the foundation soils between each fill stage)



Reinforce the fill slopes (RSS)

5.1

Embankments Over Liquefiable Ground

Foundation soils that are potentially liquefiable (typically saturated, loose silts and sands) can lose strength during earthquake shaking or possibly from blasting-induced vibrations. Embankments overlying soils that liquefy can experience stability problems including slumping, lateral spreading, and subsidence. The simplified analyses methods involve comparing the cyclic strength of the soil to the cyclic stresses caused by the earthquake. If the stresses exceed the strength, the material has a factor of safety of less than 1.0 against liquefaction and is determined to be potentially liquefiable. An estimate of the cyclic strength (termed the cyclic resistance ratio or CRR) is commonly obtained from in situ tests including the Standard Penetration, Cone Penetrometer, or geophysical. An estimate of the cyclic stresses caused by an earthquake (termed the cyclic stress ratio or CSR) is obtained from a simplified formula developed by Seed and Idriss (1971). More detailed evaluations of cyclic stresses and in situ static stresses can be obtained from one-dimensional ground response programs such as SHAKE, or from twodimensional, nonlinear, finite-difference programs such as FLAC (Itasca Consulting Group, 1995). Estimates of potential lateral spread can be obtained from empirical procedures developed by Youd, et al. (2002). Mitigation measures can include dynamic compaction, blasting and vibroflotation, placing stone columns, permeation and jet grouting, removal of the potentially liquefiable layer, or possible relocation of the project. Refer to the 1997 FHWA, Geotechnical Engineering, Circular No. 3, “ Des i gnGui danc e: Geot echni cal Ear t hquak eEngi neer i ngf orHi ghway s , ”Vol . 1; and by recent NCEER workshops ( see,“ Li quef act i onResi st anceofSoi l s:Summar yRepor t ”f r om t he1996NCEER;1998 NCEER/ NSF, “ Wor k s hopsonEv al uat i onof Li quef ac t i onRes i s t anc eof Soi l s , ”YoudandI dr i s s , andASCE,“ Geot echni calandGeoenv i r onment alEngi neer i ng, ”Apr i l ,2001) . 5.2

Reinforced Soil Slopes

Reinforced Soil Slopes (RSS) consist of tensile reinforcements in soil backfill allowing the slope to be constructed steeper than without the reinforcement. Depending on the materials used, the slope inclinations can be constructed up to 70 degrees from the horizontal. Primary reinforcing elements provide overall stability, while secondary (shorter) reinforcing elements are used to provide near face stability. Typically, various types of slope facing such 02/14/2005


ANALYSIS AND DESIGN

11-7

as erosion control blankets, geogrids, gabions, or shotcrete are used to prevent near surface erosion and raveling, especially for steep slopes. All RSS must be designed for external stability such as sliding and deep seated, local bearing capacity failure, and excessive settlement from both short- and long-term conditions. Reinforcement requirements must be designed to adequately account for the internal stability of the slope. Mechanically Stabilized Earth (MSE) walls and Reinforced Soil Slopes (RSS) – Design and Construction Guidelines (FHWA-NHI-00-043) provide detailed design procedures for reinforced soil slopes. The design concepts are similar to MSE walls. RSS are relatively easy to construct, and have a lower cost relative to MSE walls. Proper drainage is needed behind the reinforced mass to prevent development of hydrostatic pressures. Design of reinforced slopes requires that sufficient width be provided to install reinforcing elements. In road rehabilitation projects, construction of the required backfill zone could impact the travel lanes or may necessitate acquiring additional right-of-way. Reinforced soil slopes have a number of advantages including: 

Requiring less fill material and having a smaller overall footprint, which can reduce right-of-way acquisition and environmental impacts in sensitive areas.



Often allowing, onsite materials to be used for construction.



Assisting growth of vegetation on slope face for a more environmentally acceptable appearance.

6.

ROCK CUT SLOPES

The Geotechnical Engineer should take into account the structural and strength properties of the rock to develop designs that address the constructability concerns and longterm performance of the finished cut slopes. The objective of the design process is to determine the cut slope angle for the steepest continuous slope without intermediate slope benches that addresses cut slope performance (reduced rockfall) and safety while reducing excavation quantities. Rock slope stabilization and rockfall protective measures may be required to reduce rockfall hazards, minimize environmental and right-of-way impacts, and meet other project goals. The Geotechnical Engineer should review: 

FHWA, “ RockBl ast i ngandOv er br eakCont r ol , ”NHI Cour seNo. 13211, FHWA-HI-92001



FHWA,“ RockSl opes, ”NHICour seNo. 130235 - Module 5



FHWA,“ RockSl opes:Desi gn,Ex cav at i on,St abi l i z at i on, ”FHWA-TS-89-045



FHWA,“ Rockf al lHaz ar dMi t i gat i onMet hods- Par t i ci pantWor kbook, ”FHWASA-93085



FHWA,“ Rockf al l Haz ar dRat i ngSy st em - Par t i ci pant ’ sHandbook, ”FHWASA-93-057



Pierson, L.A., Gullix son,C. F. ,andChassi e,R. G. ,“ Rockf al lCat chmentAr eaDesi gn Guide, Final Report SPR-3( 032) , ”Repor tNo. FHWA-OR-RD-01-04

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ANALYSIS AND DESIGN 

FHWA,“ Gui deCont r ol l edBl ast i ngSpeci f i cat i on”(1985)

6.1

Predesign Tasks

11-8

A general knowledge of the geology of the area can be obtained by examining published geologic maps and reports along with any available aerial photographs. Slope angles and slope heights are determined using topographic maps and cross sections. If site topographic maps are not available, topographic surveys need to be performed. The Geotechnical Engineer needs to characterize the rock in the slope and consider rock classification, degree of weathering, presence of discontinuities, and degradability. Degradability of rock, such as the weathering potential and erodibility, needs to be considered in the design because these characteristics can adversely affect the long-term stability of the slope. Discontinuities, such as joints, foliations, shears, and faults, are important factors in the stability of rock slopes. The orientation, frequency, persistence, and shear strength of rock discontinuities are obtained from existing cuts, outcrops or rock core. The measurements of the strike and dip (dip and dip direction) of the discontinuities along with their shear strength are typically presented and evaluated on stereonets to determine if rockfall is kinematically possible. When rock properties and discontinuities need to be investigated beyond their ground surface expressions or when no outcrops are available, coring exploration is used to obtain rock cores. The cores provide information on the roughness and infilling of discontinuities. Oriented coring exploration may be used to obtain information on the dip and dip direction of discontinuities. The shear strength of rock along the discontinuities that separate the rock mass into discrete blocks is a much more critical rock slope stability parameter than the strength of the intact rock. In simplest terms, the shear strength governs the angle at which one rock block will begin to slide over an adjoining block. The resistance to sliding is controlled by both the macro roughness (irregularities such as steps or undulations on the joint surfaces) and the micro roughness. The micro roughness is related to the texture of the rock and any movement that may have occurred between adjacent blocks that may have created slickensides or gouge. The resistance to sliding can be determined by performing shear tests in the field or laboratory, or it can be estimated in the field by observing the inclinations of preexisting failure surfaces. Groundwater conditions must be evaluated for the design and analysis of rock cut slopes. Groundwater pressure acting within the discontinuities can cause significant destabilization by decreasing the shear strength due to uplift and/or increasing the driving forces acting on the block. Typically, the groundwater level within a slope can be estimated by observing seepages from and around the rock slope. When groundwater conditions are unknown and groundwater is expected to influence the stability of the slope, groundwater pressures can be measured using piezometers.

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ANALYSIS AND DESIGN

11-9

Rockfall hazards and potential rock slope problems have been evaluated for many of t heDepar t ment ’ shi ghway st hr ought hei mpl ementation of the Rockfall Hazard Rating System (RHRS). The maintenance history, including a description of past problems and interim mitigations measures are included in the RHRS database. The Geotechnical Engineer should refer to FHWA, Rockfall Hazard Rating System - Participant's Manual, FHWA-SA-93-057, 1993. 6.2

Slope Stability Analyses

The stability of hard rock slopes is highly controlled by discontinuities (joint and joint sets) within the rock. Failures tend to occur as discrete blocks. Discontinuities form planes of weakness. Without discontinuities, rock slopes, even those composed of relatively weak rock, could stand hundreds of feet tall without potential of failure. Kinematic analysis of the discontinuities is performed to determine the most likely mode of failure. This is followed by slope stability analyses to determine the factor of safety. 6.2.1 Kinematic Analyses A kinematic analysis is the first step in evaluating slope stability. This analysis establishes the possible failure modes of the blocks that comprise the slope. The analysis determines if the orientations (dip and dip direction) of the various discontinuities will interact with the cut slope orientation and inclination to form discrete blocks with the potential to fail without regard to any forces that may be involved. Failure modes typically fall within one of three categories: plane failure, wedge failure, or toppling. Where a rock mass is highly fractured by randomly oriented discontinuities or composed of very weak rock, the mode of failure may be circular as in a soil slope. The analysis involves a comparison of the orientations of the dominant discontinuity sets with the orientation of the cut slope. Where discrete blocks are formed and where the failure surfaces that bound these blocks dip out of the slope at an angle steeper than the shear strength along the discontinuity, failure is kinematically possible. A stereonet is used to display the discontinuity and slope data in this analysis. For detailed discussions of stereographic analysis, refer to Hoek and Bray (1981), Hoek and Brown (1980), and Goodman (1976). 6.2.2 Stability Analyses After the kinematic analyses have identified the most likely mode(s) of failure, the next step is to perform a stability analysis using the shear strength of discontinuities and groundwater conditions. The objective is to calculate the factor of safety of the slope or individual block being analyzed. Each of the failure modes follows. 

Plane Failure –The reference discusses general procedures, influence of groundwater and tension cracks, and reinforcement of slopes (use of rock bolts and anchors) and has several practical examples that are helpful in understanding the procedures

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ANALYSIS AND DESIGN

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involved. 

Wedge Failure –The reference contains wedge stability charts that can be used when the two discontinuity planes forming the wedge have frictional strength only and the slope is fully drained. These charts may be suitable for a preliminary design of highway cut slopes. Wedge failure stability analyses are more complex than plane failures. Computer programs (SWEDGE, YAWC, GOLDPIT, and Key Block Theory) may be used to perform the analyses. Appendix IV of the reference describes analytical solutions that may be used with computers and programmable calculators.



Toppling Failure –The reference contains an analytical method that may be applied to a few special cases of toppling failures.



Circular Failure –Slope failures in decomposed rock, closely fractured rock, or rock fills generally occur along a curved surface and are not controlled by discontinuities. These slopes may be analyzed using circular failure surfaces similar to the method used in analyzing soil slopes. Computer programs, such as XSTABL are routinely used for the analysis.

6.2.3 Factor of Safety The minimum factor of safety (FS) to be used in stability analyses for a specific rock slope depends on factors such as: 

The degree of uncertainty in the stability analysis inputs; the most important being the amount of intact rock, shear strength and groundwater conditions



Costs of constructing the slope to be more stable



Costs and other consequences of the slope failure



Whether the slope is temporary or permanent

Typical FS values range from 1.3 to 1.5; however, based on engineering judgment, values outside of this range may be appropriate, depending on the circumstances. 6.2.4 Computer Programs Computer programs such as Rocscience and Rockpack III are available to perform rock slope stability analyses. Rockfall events can be simulated using computer programs such as CRSP (Colorado Rockfall Simulation Program), Version 4.0 and Rocfall, Version 4.0. These programs allow hundreds or even thousands of rockfall events to be quickly simulated. This number of events typically represents many years of actual rockfall. The output includes rockfall trajectories and the bounce heights and total kinetic energies at selected locations on or beyond the base of the slope. The results are useful in determining the optimum location and capacity of certain mitigation measures, such as rockfall barriers and catch fences. 6.3

Rock Slope Design Rock slope design consists of determining (1) the orientation of the cut, (2) the

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steepness of the cut, and (3) the need for mitigation measures if the resulting factor of safety is deemed too low or the rockfall potential onto the facility is unacceptably high. 6.3.1 Design Standards and Policies The Geotechnical Engineer should verify the applicable Department standards and policies to confirm the practices to be followed. The Department Standard Specifications for Road and Bridge Construction includes standard requirements for rock construction, including the following sections: 

203.03.03, Blasting



203.03.04, Rock Cuts



203.03.05, Overbreak

Although thorough engineering analyses should be performed, it is important to note that due to uncertainties in defining the controlling conditions present within a rock mass, sound engineering judgment should be applied in the design of rock slopes. Experience is the best predictor of the effectiveness of a rock slope or rockfall remedial design. Case histories in similar rock conditions should be consulted to provide additional guidance. 6.3.2 Selecting Slope Angle Several factors affect how steep a rock slope should be cut including the orientation and strength of the discontinuities within the slope, the anticipated method of construction, and whether additional measures will be used to enhance slope stability. Some methods of slope construction damage the rock such that the finished cut slope has an increased likelihood of long-term rockfall. Uncontrolled blasting, for example, can cause fracturing and open existing fractures tens of feet into the slope. A finished cut slope can be constructed by excavating the rock using heavy equipment ripping or production blasting techniques, or it can be augmented with controlled blasting methods. The use of controlled blasting, either presplitting (preshear) or trim (cushion) blasting, produces a cut slope with significantly less potential for rockfall. Local experience with similar rock type should be investigated. In some cases, right-ofway limitations or other factors, such as economics, may require the design slope to be steeper than desirable. If the resulting factor of safety is determined to be too low, or the potential for rockfall is estimated to be unacceptably high during the design life, rock slope stabilization and rockfall mitigation measures should be included in the design. 6.3.3 Construction Considerations and Mitigation Measures In addition to the natural rock discontinuities that control the stability of rock slopes, fractures caused by poor blasting techniques could increase the rockfall potential. Mitigation measures to enhance stability include installation of reinforcement, drainage, and erosion protection systems. The following is a partial list of available techniques: 

Controlled Blasting - Lightly loaded, aligned and closely spaced blast holes are used to

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form the final cut slope face in a manner that minimizes the affects of the intense detonation gas pressures caused by production blasting. The controlled blasting is performed either before the main production blasting is detonated (presplit blasting) or after the production blasting (cushion blasting). In presplit blasting, the row of control blast holes is detonated to form a break in the slope along the final cut slope, which serves to vent production gas pressure and keep it from penetrating and damaging the rock that will form the final cut face. In cushion blasting, the row of control blast holes is detonated last to trim off the rock outside the cut slope. The cushion blasting technique is most commonly used in weaker rock conditions or wherever the thickness of rock to be excavated is less than 15 feet. Controlled blasting is routinely used for rock cuts that are 0.75H:1V or steeper. The limiting factor is the inability to maintain proper blast hole alignments on flatter slopes. 

Rock Removal - One method to mitigate an unstable rock slope is to remove the potentially unstable rock by hand scaling, blast scaling, or excavation equipment techniques. In the construction of new rock cuts, rock scaling is generally required and treated as incidental to the payment for the type of excavation performed.



Screening and Barrier Systems –Draped mesh system (slope screening) applies limited normal force against the rock face, and primarily serves to control the descent of falling rocks into the roadside collection area. Barrier systems can range from concrete or gabion wall barriers to proprietary systems, such as the Brugg Barrier Fences.



Reinforcement - Structural reinforcement can be provided by rock bolts, dowels, and cable lashing. Tensioned rock bolts are used to increase the normal stress along the discontinuity where sliding is possible, thus increasing the shear strength of the discontinuity. They may also be used to anchor potentially unstable rock blocks in place. Dowels are untensioned rock bolts or shear pins used to resist lateral movement of rock blocks by their lateral capacity. Cable lashing uses tensioned cable(s) to increase the normal force against the face of an isolated block to increase sliding resistance.



Drainage - Dewatering to reduce groundwater pressures acting within the rock slope improves slope stability. Reduced groundwater pressure within a discontinuity increases the shear strength, while lowering the groundwater height within tension cracks reduces the driving force on a rock block. Proper drainage of rock slopes could be achieved by installing drain holes (weep holes, horizontal drains) or vertical relief wells. Various measures, such as construction of surface drains and ditches minimize water infiltration and therefore prevent build up of groundwater pressures.



Erosion Protection - Soils, decomposed rocks, highly fractured rocks, and certain types of rocks are susceptible to erosion or degradation. When hard rock, resistant to erosion, is underlain by an erodible or degradable layer, loss of support for the overlying rock may develop over time. This may create an unstable condition.

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Stopping this process can be accomplished by applying shotcrete to the surface of the less resistant zones. Weep holes are installed to prevent buildup of groundwater pressures behind the shotcrete. To improve the performance of shotcrete, wire mesh or steel fibers are routinely used to reinforce the shotcrete. 

Buttresses - When an overhanging rock is large and it is impractical to remove or reinforce it, buttresses can be used to support the overhanging rock and increase its stability. Buttresses serve two functions: (1) protect or retain underlying erodible material, and (2) support the overhang.

6.3.4 Rockfall Control Design In many rock slopes, the potential for rockfall remains even after mitigation measures are in place. It may be impractical to stabilize all potentially unstable rocks. In these situations, the likelihood of rocks reaching the road should be evaluated and appropriate control or protection measures should be recommended. The consequences and probabilities of falling rocks reaching the road or facilities should be weighed against the cost of installing control measures. Rockfall mitigation measures generally fall into two major categories: (1) measures to prevent rockfalls (scaling, rock bolts, dowels, cable lashing, etc.), and (2) measures to control the manner in which rocks fall or to absorb energies and restrict falling rocks into roads and facilities (slope mesh, fallout areas, barriers, catch fences, etc.). Fallout area or ditch design may be performed with the aid of the detailed design char t si ncl udedi nPi er son, et al . , “ Rockf al l Cat chment Ar eaDes i gnGui de”( 2001) . If the slope is too complex to allow direct use of design charts, actual rock rolling tests or rockfall simulation analyses should be performed. In most cases, rolling rocks is not practical or possible, and computer simulation is the preferred method. The CRSP (Colorado Rockfall Simulation Program) program (Colorado DOT, et al., 2000), is widely used for this purpose. The computer program RocFall available from Rocscience Inc. (See Section 6.2.4 above) is another program with some additional capabilities. These programs may be used to aid in the design of fallout areas and the capacity and placement of barriers. Scaling, the removal of loose rock from the cut slope face, is routinely used to provide an immediate reduction in the rockfall potential; however, it is considered a temporary measure. Reinforcement or external support methods including, shotcrete, dowels, rock bolts, rock anchors, cable lashing, or concrete buttresses, can provide longer-term protection, as can various measures that intercept and control rockfalls, such as fallout areas (ditches), draped mesh, catch fence, or rockfall barrier systems. 7.

LANDSLIDES

Two geotechnical references for landslide investigations for transportation projects are ( 1)TRB Speci alRepor t247,“ Landsl i des:I nv est i gat i onandMi t i gat i on, ”and( 2)FHWA, “ Adv ancedCour seonSl opeSt abi l i t y ” . There are many technical papers regarding numerous advancements in the state-of-the-art analyses for landslides, assisting Geotechnical 02/14/2005


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Engineers to continually update their knowledge. In critical landslide mitigation applications, it may be advisable to retain a landslide expert to provide guidance to the Department or to perform the investigation and studies. Landslides can be improperly diagnosed because of inadequate geologic reconnaissance/interpretation and poorly conceived exploration/instrumentation programs. Responding to and investigating a landslide is likened to a forensic investigation. The Geotechnical Engineer is searching for clues and evidence, and needs to resolve all apparent conflicts and contradictions in the perceived causative explanation/model. Mitigation plans to stop small slides can be made through a combination of precedence, experience and judgment. An example is constructing a rock inlay to replace small slumps. More complicated and/or larger landslides generally require an extensive exploration/instrumentation program, along with expert geology and geotechnical engineering. Common mitigation measures are summarized in Figure 11-2. 8.

GEOTECHNICAL EARTHQUAKE ENGINEERING DESIGN

Earthquake engineering is a multidisciplinary design process involving the fields of geology, seismology, geotechnical engineering and structural engineering. Field mapping, aerial photograph interpretation, geophysical testing and other investigative procedures to delineate faults and fault zones are performed. Fault data is used to develop ground motion parameters, typically bedrock motions, at the ground surface (commonly referred to as the outcropping rock motion). This information could include maximum acceleration, maximum velocity, and duration of shaking. The motions could also be presented in the form of digitalized acceleration-time records of an earthquake. These first two tasks can be timeconsuming and expensive to perform for every project. Accordingly, site-specific geologic and seismic hazard evaluations are typically only performed for critical structures. For noncritical structures, ground motion parameters are usually obtained from existing regional studies and available literature. Geotechnical Engineers evaluate various potential ground shaking hazards involving soil and rock, including: 

Amplification or attenuation of bedrock motion through overlying soil deposits



Liquefaction which could cause loss of bearing pressure resistance, lateral spreading and ground settlement of loose, saturated, cohesionless soil deposits



Causing Increased lateral earth pressures on retaining structures



Causing landslides, rockfalls, and slope and embankment instability



Causing fault rupture

Bridge Engineers are primarily interested in the lateral forces applied to structural facilities, including bridges, viaducts, buildings, and retaining walls. Geotechnical Engineers provide soil and ground response parameters to the Bridge Engineer for calculation of the shear forces acting on the structures as a result of the earthquake shaking and other possible 02/14/2005


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secondary loading effects on structures, including liquefaction-induced lateral spread and settlement. Geotechnical earthquake engineering has developed significantly since the 1970s, and although research continues in this discipline, generally accepted design procedures have been established for many of the potential hazards. However, as with most areas of geotechnical practice, the Geotechnical Engineer needs to keep abreast of current research to maintain competence with general standards of practice. The Department follows AASHTO guidelines for seismic design of transportation facilities. The current AASHTO guidelines are outlined in Standard Specifications for Highway Bridges. Article 3.21 of AASHTO (2002), Division 1, states that seismic design must consider the following items: (1) the relationship of the site to active faults, (2) the seismic response of the soils at the site, and (3) the dynamic response characteristics of the structure. For bridges and roadway structures, the Geotechnical Engineer is responsible for analyzing items (1) and (2), and providing the results to the Bridge Engineer who analyzes item (3). For cuts and embankments, the Geotechnical Engineer is responsible for analyzing all three items. 8.1

Seismicity

The western portion of Nevada, known as the Nevada Seismic Zone, has experienced large earthquakes in historic times, and is considered one of the more seismically active areas in the United States. The relationship of the site to active faults is represented using peak bedrock acceleration maps. For noncritical structures, the acceleration coefficient (A) is obtained from Article 3.2 of Division IA of AASHTO, 2002. The maps of horizontal acceleration in rock, A, are based on 90 percent probability of not being exceeded in 50 years. This corresponds to an approximate 475-year return period. Article 11.3.3.8 of Department Bridge Manual (1991) specifies that the minimum expected bedrock acceleration is 0.15g. For very large or critical structures, a site-specific seismic hazard evaluation can be performed. These studies are performed on a probabilistic or deterministic basis. A probabilistic evaluation estimates the level of ground acceleration for a given return period for all potential seismic sources. A deterministic evaluation provides an estimate of the maximum ground acceleration that would be caused by each fault source or source zone. The individual fault source or source zone that results in the largest ground acceleration at the site is commonly referred to as the Maximum Credible Earthquake or MCE. According to section 3.4 of Division 1A of AASHTO, 2002, a bridge is determined to be in one of four Seismic Performance Categories (SPC), A through D, based on the Acceleration Coefficient (A) and the Importance Classification (IC). Refer to special seismic design requirements for the foundations and abutments of bridges in SPC B, C, and D. The Geotechnical Engineer may be required to perform investigations to identify potential hazards and obtain seismic design information related to: liquefaction, slope instability, fill settlement, and increased lateral earth pressure. 02/14/2005



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Seismic Response of Soils

For the design of bridges according to Section 3.5.1 of Division 1A of AASHTO, 2002, the seismic response of the soils is expressed by the Site Coefficient (S), which is in turn determined by the Soil Profile Type. The Geotechnical Engineer performs subsurface explorations, classifies the subsurface materials, and determines the Soil Profile Type. A sitespecific response may be developed by using various computer programs (SHAKE, TARA, FLAC, etc.) depending on the complexity and importance of the structure. However, sitespecific response analyses using computer programs are typically not performed, except for special cases. 8.3

Dynamic Response Characteristics of Structures

Seismic lateral forces acting on a structure are influenced by the seismic response of the soils at the site and the fundamental period of the structure. Typically, elastic seismic coefficients, as defined in Division 1A of the 1998 Commentary in AASHTO, 2002, are used to define the earthquake load to be used in the elastic analysis for seismic effects. Article 3.6 of Division 1A of AASHTO, 2002, states an alternate method that can be used is with a 5% damped, site-specific, response spectrum developed by a qualified professional. The Geotechnical Engineer may develop the site-response spectrum by using the computer program SHAKE. Earthquake time histories to be used in SHAKE should be selected to closely match the estimated ground motions for the site. The 1997 FHWA, Geotechnical Engineering, Circular No. 3, provides a summary of seismic design procedures, including selection of representative earthquake time histories. 8.4

Liquefaction

The selection of ground motion parameters for the lateral force design procedures discussed in Division 1A of AASHTO, 2002, assumes that the soil overlying bedrock is not liquefiable. If loose, saturated, cohesionless deposits are subjected to cyclic shear stresses (typically an earthquake, less commonly blasting or construction-induced vibrations), the tendency for the soil to densify will result in a temporary increase in pore water pressure. This in turn results in a decrease in effective stress and a weakening of the soil. Structures founded in liquefiable soil can lose bearing pressure resistance or skin friction, and can be subjected to increased lateral and vertical loads from lateral spreading and settlement of the liquefied deposit. Liquefaction has caused a number of bridge failures during past earthquakes. The recommended procedure to evaluate the liquefaction potential is based on the Standard Penetration Test blowcounts of soils. The liquefaction evaluation procedure is described in many standard references on geotechnical earthquake engineering, including Chapt er8ofFHWA,“ Ear t hquakeEngi neer i ng”( 1997) ,Vol . I. An example of a liquefaction ev al uat i oni si nEx ampl e5ofFHWA,“ Ear t hquakeEngi neer i ng”( 1997) ,Vol . II.

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Seismic Slope Stability

Earthquake shaking can result in failures of natural slopes and man-made embankments. The standard procedure for evaluating the stability of a nonliquefiable slope is the pseudostatic analysis, where a lateral force is applied to the center of gravity of a soil mass having a failure potential when performing a limit equilibrium analyses. The selection of shear strength in slope stability analyses involving seismic loadings should be based on shortterm undrained shear strengths. The pseudostatic procedure does not provide an estimate of potential seismic deformations. In many instances, the stability of a slope during an earthquake may drop below a factor of safety of 1 for only a brief period of time during the transient shaking. In this case, a pseudostatic analysis would indicate an unacceptable factor of safety below 1, but the actual deformation of the slope or embankment would be minimal and the overall performance acceptable. One method to estimate seismic deformations of nonliquefiable slopes is the Newmark Sliding Block Analysis. This method uses the yield acceleration of a slide mass and a seismic time history to estimate the permanent seismic deformation. This method, however, is not used on a routine basis. Refer to FHWA,“ Ear t hquakeEngi neer i ng, ”( 1997) ,andKramer “ Geot echni cal Ear t hquakeEngi neer i ng, ”(1996), for more details on the deformation analyses. The seismic slope stability and deformation analyses are not applicable to liquefiable materials. These analyses are based on the assumption that the shear strength of the soil remains relatively constant with deformation and strain. However, liquefiable soils in slopes can lose most of their shear strengths, develop into a flow failure condition, and displace considerable amounts. The mechanical/physical response of soil during flow failure is not conducive to engineering analysis at this time. One method to evaluate the potential flow failure in sloping ground is to assign liquefied residual shear strengths to the soil layers with low factors of safety against liquefaction. If the limit equilibrium slope stability analyses give low factors of safety, then flow failure should be considered a possibility at the site. Ground improvement and/or project relocation are options to consider when this occurs. 8.6

Seismic Analysis of Retaining Structures

Earthquake shaking results in increased lateral earth pressures acting on retaining structures. Types of structures needing analyses may include bridge abutments, conventional cantilever retaining walls, Mechanically Stabilized Earth (MSE) walls, tieback walls, and soil nail walls. The needed analyses involve estimating the increase in lateral earth pressures exerted on the walls by earthquakes. The Mononobe-Okabe Method is generally used for walls free to yield about their bases. A modified Mononobe-Okabe is used for walls that are not free to rotate. Refer to Standard Specifications for Highway Bridges, Articles c6.4.3, c7.4.3, and c7.4.5 of AASHTO (2002), for the seismic requirements for abutments in SPC B, C, and D, respectively, in the 1998 Commentary ofAASHTO,2002,FHWA,“ Ear t hquake 02/14/2005


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Engi neer i ng”( 1997) ,Vol . I and Kramer, “ Geot echni calEar t hquakeEngi neer i ng, ”(1996). 9.

FOUNDATIONS

Foundations must have adequate capacity to support the design load combinations and satisfy the serviceability requirements established by the Bridge Engineer. Serviceability requirements establish allowable settlement and deflections. Foundation design is generally an iterative process between the Geotechnical and Bridge Engineer. These iterations mean that the Geotechnical Engineer may have to reevaluate the design many times. Therefore, it is important to document the assumptions made during the design process and the justification for design decisions. Foundations are classified as shallow, deep, or hybrid. The most economical foundation type depends on types of subsurface soils and groundwater conditions, design loads, design scour elevations, serviceability requirements, and construction sequence. Shallow foundations consist of spread footings or mats. Deep foundations include driven piles, micropiles, and drilled shafts. Hybrid foundations are a combination of shallow and deep foundations. 9.1

Service Load vs. Load and Resistance Factor Design

Foundations are designed based on Service Load Design (SLD) or Load and Resistance Factor Design (LRFD) using the procedures outlined in the AASHTO references. The Bridge Engineer typically determines the design method. When using SLD, the Geotechnical Engineer uses actual or unfactored loads for the design provided by the Bridge Engineer. Recommended safety factors, load and resistance factors, and load combinations are outlined in AASHTO references. 9.2

Foundation Feasibility

The Geotechnical Engineer should consider several items when evaluating potential foundation systems. Cost is always a consideration. Typically, cost does not impact the choice between shallow or deep foundation systems, because in most cases, the site is either suitable for shallow foundations or it is not. Cost becomes more of a factor when comparing different types of deep foundations. Depth to suitable bearing material is the first factor to consider when choosing between shallow or deep foundations. If suitable material is at a reasonable depth, the Geotechnical Engineer should consider potential impacts of scour, groundwater, and construction sequence on shallow foundations. Scour may preclude the use of a shallow foundation if the scour level is lower than the suitable bearing material. Groundwater impacts bearing capacity and constructability. Construction sequence could impact the bearing capacity and settlements of shallow foundations. The Geotechnical Engineer should consider local practice for founding structures when choosing a foundation system. Sometimes, experience precludes a foundation type for reasons that are not readily evident. 02/14/2005


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Deep foundations can be classified as driven or drilled systems. A drilled system is typically better suited to cases where significant penetration into hard or dense material is required either to develop uplift loads or to get below the design scour depth. Driven systems are generally better suited where subsurface conditions would make drilling problematic. Conditions that make drilling difficult include encountering boulders, uniform-graded gravel, voids, and artesian groundwater. The availability of raw materials, cost of labor, and regional geology generally favor one type of deep foundation over others. It is often useful to compare different deep foundations on the basis of cost per ton of design load or per foot of installed length. There is generally enough information in recent Department bid tabulations to compare foundations on this basis. The type of foundation for all supports of a structure needs to be compatible with each other in order to minimize differential settlement between supports. Other considerations include maintaining the simplicity of structural analysis under dynamic loads, and potential structure widening in the future. If there appears to be a sound reason to use a combination of different foundation types, the Geotechnical Engineer should seek the input of the Bridge Engineer. Situations are evaluated on a case-by-case basis by the Bridge Engineer. 9.3

Spread Footings

Geotechnical Engineering, Circular No. 6,“ Shal l owFoundat i ons, ”2002,Ref er ences FHWA RD-89-185, FHWA HI-88-009, AASHTO Standard Specifications, and NHI course manual for Shallow Foundations, NHI No. 132037 (Module 7) present design methods and commentary on bearing capacity and settlement of shallow foundations. The design of shallow foundations on soils is generally controlled by allowable settlement criteria, not by shear failure. The Geotechnical Engineer should focus efforts on settlement evaluation, rather than bearing capacity for most sites. The design scour depth could make excavating to construct shallow foundations unfeasible. Groundwater depth could influence constructability as well. Groundwater flow into footing excavation can loosen potential bearing material and make forming and pouring a footing difficult. Spread footings for any structure must have a minimum of 2 feet embedment depth from bottom of the footing to the finished grade. 9.4

Foundations on Rock

AASHTO Standard Specifications, FHWA Circular No. 6, and NHI Course No. 132037 (Module 7), provide a summary of methods to calculate bearing capacity of competent as well as jointed rock. More in depth discussions are available in the References (Wylie and Canadian). The Geotechnical Engineer should determine the influence that dominant joint sets in the rock have on foundation performance. 9.5

Deep Foundations

Before planning subsurface explorations, the Geotechnical Engineer should perform preliminary calculations based on available information to estimate the depth of the required 02/14/2005


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foundation elements. Minimum exploration depths are outlined in AASHTO references. In no case should deep foundation tip elevations be deeper than the subsurface explorations. 9.5.1 Axial Capacity Both compression and uplift axial capacities should be calculated for deep foundations. References FHWA-HI-97-014 and AASHTO Standard Specifications outline design procedures for driven piles. References FHWA-IF-99-025 and AASHTO Standard Specifications for Highway Bridges describe the design procedures for drilled shafts. The Geotechnical Engineer should consider subsurface conditions and construction sequence to evaluate the potential for downdrag loads on piles. In general, downdrag is a concern whenever the ground moves downward 0.1 to 0.25 inches relative to the pile. Downdrag can occur due to settlement, shrink/swell, or liquefaction. 9.5.2 Lateral Capacity References FHWA-HI-97-014 and FHWA-IP-84-11 are helpful references for lateral load design procedures. Generally, the Geotechnical Engineer provides soil parameters to the Bridge Engineer so that LPILE program or other approved programs can be used for the lateral analysis of the foundation. The Geotechnical Engineer should consider construction methods and sequence when developing LPILE parameters. Assumed conditions should be provided to the Bridge Engineer with the parameters. 9.5.3 Seismic Analyses Seismic analysis should be performed to evaluate both axial and lateral loading conditions during and after a seismic event. The greatest influence on axial capacity is the temporary loss of skin friction during soil liquefaction and the increased downdrag force from post-liquefaction settlement. Liquefaction can also cause lateral spreading of sloping ground, which in turn increases the lateral forces acting on the pile and reduces available soil resistance to overlying inertial forces. The seismic evaluation and design of soil-pile interaction is an area of active research. 9.5.4 Liquefaction Potential and Mitigation Liquefaction potential should be evaluated per the references cited in this Chapter. Generally, if liquefiable soils are present, some means of mitigation is required to protect structure foundations. Typically, the Department policy does not require liquefaction mitigation for approach embankments. The Geotechnical Engineer should clearly explain to the design team the need of any ground improvement mitigations and any consequences if the mitigations are not implemented. For example, if liquefaction mitigation is proposed for an area around deep foundations but not under approach fills; complete reconstruction of approach fills may be required following a seismic event.

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9.5.5 Scour Considerations Typically, the Hydraulics Engineer determines the depth of scour with input from the Geotechnical Engineer. The following items are typically required to complete the scour analyses: (1) boring logs, (2) grain size analyses to characterize river bed materials, and (3) a description of the geomorphology of the site (i.e., floodplain stream, crossing of a delta). If scour has a major impact on the foundation design, the Hydraulics Engineer should be notified to consider designing some type of scour protection or revetment around deep foundations. References FHWA, Hydraulic Engineering Circular (HEC), HEC 18, HEC 20, and HEC 23, are helpful references. In some cases, it is more economical to design deep foundations for the scour case. 9.5.6 Design Phase Load Testing The decision of whether or not to conduct foundation load tests during the design phase is based on economics and the degree of uncertainty acceptable for the design. Design phase load tests should also be considered whenever loads are high and there is no redundancy in the foundation system. For medium to large projects, the cost of conducting load tests during the design phase may be offset by savings in construction. Site-specific load tests allow the Geotechnical Engineer to use lower factors of safety for design, which results in lower construction costs. There are several types of load tests, including static, dynamic, Statnamic, and Osterberg load cell tests. 9.6

Driven Piles

References FHWA-HI-97-014 and AASHTO Standard Specifications for Highway Bridges outline design procedures for driven piles. Dynamic pile driving analysis using a Pile Driving Analyzer (PDA) can be performed during design and/or construction phase. The objective of using the PDA during the design phase is to develop site-specific engineering properties in order to develop a more cost effective design with less conservative assumptions and lower factors of safety. However, the use of the PDA testing in the design phase can be more costly than during construction phase because the contractor must mobilize pile driving equipment for a relatively small amount of work. During construction, the PDA is used to confirm design assumptions. Soil setup occurs when piles are driven into saturated clays and loose to medium dense sands. Positive pore water pressures generated during pile installation result in low capacities at the end of driving. As excess pore water pressures dissipate, effective stress and pile capacity increase. PDA testing can be used to quantify setup if piles are instrumented during initial driving and on restrike. The Geotechnical Engineer can use wave equation analyses to develop driving criteria for end of driving conditions. Using criteria for end of driving conditions eliminates the need for restrikes during production.

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Drilled Shafts

Ref er ences“ Dr i l l edShafts: Const r uct i onPr ocedur esandDes i gnMet hods , ”FHWA-IF99-025 and AASHTO Standard Specifications for Highway Bridges outline design procedures for drilled shafts. FHWA provides more complete narrative and construction considerations, but design methodologies are similar. Design of drilled shafts varies from driven piles because the construction processes are different. Drilling results in lower horizontal effective stress than displacement type piles. In addition, drilling fluids and incomplete base cleaning contribute to lower unit skin friction and end bearing than driven piles. The primary advantage drilled shafts have over driven piles is their large size and resultant large capacity. Load testing can be performed during design and/or construction of drilled shafts. However, this is seldom done for Department projects. The objective of testing during the design phase is to develop a more cost effective design by using lower factors of safety. There are several methods for load testing drilled shafts. In general, static load tests are not feasible for drilled shafts due to the need of a high reaction force frame system. 9.8

Auger Cast Piles (ACP)

Design of Auger Cast Piles (ACP) is similar to drilled shafts. ACP typically has higher unit skin friction than drilled shafts. This is due to the fact that grout is injected under pressure for ACP, and sidewall asperities have a larger influence for ACP than drilled shafts because ACP has smaller diameters than drilled shafts. Local experience or load testing is generally required to choose parameters for design. 9.9

Micropiles

Micropiles are small diameter drilled piles. Reference FHWA-SA-97-070 summarizes the design methodology. Micropiles are typically used where site restrictions prohibit the use of large foundation construction equipment. Micropiles are installed by specialized drills typically used to install tiebacks. Due to their size, Micropiles have lower capacity than large deep foundation elements. Production rates are typically lower for Micropile rigs than for other types of deep foundation construction. These factors contribute to the relatively high cost of Micropiles. 10.

RETAINING WALL SELECTION AND DESIGN

There are a variety of wall types and a number of factors that control wall type selection. The Geotechnical Engineer should have an understanding of the applications of each wall type, exploration and design requirements, construction methods, and relative costs. The FHWA, Geotechnical Engineering, Circular No. 2,“ Ear t hRet ai ni ngSy st ems, ”( SA-96038), provides an overview of wall types with general information pertaining to selection criteria, and design and analysis procedures. Wall types can be classified into fill wall and cut wall applications. Examples of fill walls include standard cantilever walls, modular gravity walls (gabions, bin walls, and crib walls), 02/14/2005


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and Mechanically Stabilized Earth (MSE) walls. Cut walls include soil nail walls, cantilever soldier pile walls, and ground anchored walls (other than nail walls). Some wall types require a unique design for both internal and external stability. Other walls have standardized or proprietary designs for internal stability with external stability analyzed by the Geotechnical Engineer. Geotechnical Engineers should be able to develop their own designs as well as evaluate and review standardized and proprietary wall designs. Factor of safety recommendations for Service Load Design (SLD) of gravity and semigravity walls (standard cantilever, modular gravity, and MSE) are provided in Figure 11-3. Ref ert oAASHTO,“ St andar dSpeci f i cat i onsf orHi ghwayBr i dges, ”17t hed. ,f orLoad Factor Design (LFD) and other loading criteria. Performance factors for Load Resistance Factor Design (LRFD) are discussed in the AASHTO, LRFD Bridge Design Specifications, 2nd ed. Section 12.2 of the Department Bridge Manual (1991) states that seismic design of retaining walls must use the LFD Method, and that all other design cases should use SLD. In general, AASHTO recommended factors of safety should be used for wall designs. However, engineering judgment may allow using lower factors of safety when wall loadings are well understood, and wall costs are high. One example is a landslide stabilization wall where using AASHTO recommended factors of safety can be quite expensive. Depending on the level of understanding of slide conditions, this may merit the selection of a lower safety factor. 10.1

Standard Cantilever Walls

A concrete cantilever wall is constructed of cast-in-place reinforced concrete, consisting of a vertical stem and footing slab base connected to form the shape of an inverted T. After curing, the back of the wall is backfilled with free-draining, granular backfill. The backfill weight on the heel of the footing slab enables the structure to function as a gravity wall. General texts, such as NAVFAC, Canadian Geotechnical Manual, Terzaghi & Peck, and Peck, Hanson, & Thornburn, and AASHTO (17th ed.) provide guidelines and design charts for analysis of static conditions for standard walls. Seismic induced lateral earth pressures should be determined using the Mononobe-Okobe analysis. The FHWA, Geotechnical Engineering, Circular No. 3, provides guidance on this analysis approach. AASHTO (17th ed.) recommends using a seismic coefficient equal to one-half the acceleration coefficient (kh = 0.5A) in the Mononobe-Okobe analysis for unrestrained walls. For nonyielding walls, the seismic lateral earth pressure can be approximated by using a seismic coefficient of (kh = 1.5A) in the analysis. It should be noted that the procedure described in this reference provides the combined static and seismic loadings. It is recommended this combined loading be applied at the midheight of the wall. Section 12.2 of the Department Bridge Manual (1991) states that seismic design of retaining walls must be used in the Load Factor Design (LFD). The LFD method uses different load factors for the static and seismic forces. The Geotechnical Engineer should work closely with the Bridge Engineer to determine the appropriate earth pressure loadings for seismic conditions so that the design is performed in accordance with current Department procedures. 02/14/2005


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The Department Standard Plans include drawings of many different cantilever walls for various geometric and ground conditions. These drawings include information such as assumed surcharge forces, back slope angles, foundation capacities, seismic accelerations, and Backfill soil properties. The Geotechnical Engineer is responsible for providing all soil parameters needed to design walls that are not covered in the Department Standard Plans, as well as determining the suitability of use of the walls covered in the Department Standard Plans for the project. The Bridge Engineer performs all stability analyses. 10.2

Modular Gravity Walls

Modular gravity walls use interlocking soil or rock-filled concrete, timber, or steel modules that resist earth pressures by acting as a gravity wall. Examples include gabion walls, bin walls, concrete block walls, and crib walls. These wall types commonly use proprietary materials. Earth pressures for modular gravity walls are determined using the same procedures as for standard cantilever walls. Because many of these wall types are proprietary, it is recommended that Geotechnical Engineer susemanuf act ur er s’l i t er at ur ef ordesi gn,and check them with generic methods. Manufacturers include Maccaferri and Hilfiker (gabions), Criblock (crib walls), Contech and Double-Wal (bin walls). Seismic design of these walls is base on the Mononobe-Okobe analysis. These walls are relatively easy to construct, and have a relatively low cost. Modular gravity walls are likely to deform more than concrete cantilever walls, so the tolerable settlements of upslope structures should be considered. Department procedures recommend against use of rockery walls due to a lack of design guidance from FHWA and AASHTO. They can be used only under special circumstances (i.e., aesthetics) with approval from the Department Bridge Engineer. 10.3

Mechanically Stabilized Earth (MSE) Walls

Mechanically Stabilized Earth (MSE) walls consist of tensile reinforcements in soil backfill, with facing elements that are vertical or near vertical. The reinforced mass functions as a gravity wall. The Department has specific procedures and requirements for the design of MSE walls. The policy memorandum (dated September 27, 2002) is presented in Figure 11-1. AASHTO (17th ed.) describes the state of the practice design procedure for MSE walls. A recent, comprehensive reference on MSE wal l si s FHWA’ s manualon “ Mechanically Stabilized Earth Walls and Reinforced Soil Slopes –Design and Construction Guidelines” (FHWA-NHI-00-043). MSE walls are commonly used for medium to large wall and grade separation projects because they are often less expensive than concrete cantilever walls. Most MSE wall applications use proprietary systems where the internal design is performed by the wall vendor. The Department Research Division maintains names of approved MSE wall vendors and systems in the Qualified Products List (QPL). The Geotechnical Engineer is responsible for performing the external stability analysis 02/14/2005


ANALYSIS AND DESIGN

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in the design phase of the project, and providing the required reinforcement lengths to the Bridge Division to be included in the Construction Plans. The vendor performs the internal and external stability analyses and evaluates the adequacy of reinforcement lengths shown in the Construction Plans. The vendor submits calculations and shop drawings showing the actual reinforcement lengths to be used on the project based on the longer of needed reinforcement lengths for external or internal stability analyses. The Geotechnical Engineer reviews the submitted calculations and shop drawings for approval. 10.4

Soil Nail Walls

Soil nails are closely spaced, passive reinforcements used to strengthen existing ground. They consist of steel bars grouted into the soil connected to a temporary or permanent shotcrete facing. They are constructed in a top down manner and are used to support an excavation face. Soil nail walls are an economical alternative to ground anchored walls when installed in the appropriate soil conditions. The following are some of the items that should be taken into account when considering use of soil nail walls: 

A 6-foot high excavation face must stand unsupported for at least 48 hours. This requires some cohesion or cementation of the subject soils.



Drilling into cohesionless materials requires the use of temporary casing during drilling. This has a significant impact on construction costs.



Excavations in soft clays are unsuitable for soil nails due to the low frictional resistance of the materials.



The excavation face should be dry or dewatered to permit stability of the vertical excavation.



Proper corrosion protection is extremely important for long-term performance of a soil nail wall. The Department uses a double protection system for all soil nail walls. Typically NDOT does not use epoxy coating as a corrosion protection measure.



Soil nail walls are not recommended where the ground could deform, such as landslides.

The FHWA, Manual for Design and Construction Monitoring of Soil Nail Walls (FHWASA-96-069) is recommended for design of soil nail walls. Analysis programs such as GoldNail (available from FHWA) and Snailz (available from http://www.dot.ca.gov/hq/esc/geotech) should be used for the design. In addition to static and seismic conditions of the completed wall configuration, the stability for each stage in the construction sequence of a soil nail wall should be evaluated. The controlling condition is often a construction case. The FHWA Soil Nailing Field Inspectors Manual (FHWA-SA-93-068) provides practical information to understand construction procedures.

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11-26

Cantilevered Soldier Pile and Sheet Pile Walls

These walls consist of vertical elements that derive lateral resistance from embedment into soil below the exposed face, and support the retained soil with facing elements or the piles themselves. These walls are often used for temporary excavations to limit upslope deformations during construction. Permanent applications include short walls that are part of a taller wall section utilizing ground anchors, and where an unsupported excavation is not desired. Wall heights typically are limited to a maximum of 15 feet unless they are also supported by ground anchors. These walls do not work well when embedded in deep soft soils, where the passive resistance on the front of the wall is low. AASHTO Standard Specifications for Highway Bridges contains the relevant design charts to determine the wall loadings. Bridge Engineers determine the appropriate sizes of the structural elements based on the applied loads. 10.6

Ground Anchor Wall Systems

Ground anchored wall systems consist of ground anchors (cement-grouted, prestressed steel tendons installed in soil or rock) connected to wall elements consisting of soldier piles or concrete bearing pads. They are usually constructed in a top down manner and are most often used to support an excavation face. They can also be used for landslide stabilization. Ground anchored walls are more expensive than most traditional walls due to the need of uncommon construction equipment and skills. However, they are well suited where deformations of adjacent structures are of concern. Ground anchored walls are applicable to a wider range of materials than soil nail walls. The following are some of the items that should be taken into account when considering use of ground-anchored walls: 

Underground easements should be obtained to protect the anchors throughout their functional life.



Proper corrosion protection is essential to achieve the design life of the structure. The Department uses a double protection system for all ground anchored walls. Typically the Department does not use epoxy coating as a corrosion protection measure.



The upper level of anchors should be located and oriented below the zone normally used for buried utilities and guardrail posts.



Acceptance of ground anchors should be based on proof tests of each anchor. Sometimes preproduction tests and long-term monitoring may also be required.



Anchors bonded in clays may have long-term creep problems. Anchors in clays should be creep tested.



The contract documents should require the contractor to determine the anchor bond length necessary to resist the applied anchor force. Refer to the FHWA, Geotechnical Engineering, Circular No. 4,“ Gr oundAnchor sand

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Anchor edSy st ems” , (FHWA-IF-99-015), and the Post Tensioning Institute (PTI) publication, “ Recommendations for Prestressed Rock and Soil Anchors” , 1996. In addition to static and seismic conditions of the completed wall configuration, the stability for each stage in the construction sequence of a ground anchored wall should be evaluated. The controlling condition is often a construction case. 11.

DEWATERING

Design of dewatering systems is typically the Cont r act or ’ sr esponsi bi l i t y . The Geotechnical Engineer should have a basic understanding of the advantages and disadvantages of different dewatering systems. The Geotechnical Engineer should be able to perform calculations to establish requirements of dewatering systems. The references (Powers, and COE) provide a background and narrative for dewatering system design.

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ANALYSIS AND DESIGN 12.

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FIGURES

11-1: Policies and Procedures Memorandum STATE OF NEVADA DEPARTMENT OF TRANSPORTATION MEMORANDUM September 27, 2000 To:

See List Below

From: Parviz Noori, Assistant Chief Materials Engineer –Geotechnical Subject:

PN

Policies and Procedures Memorandum No. C028-2000-01 MSE Walls NDOT’ sa ndWa l lSuppl i e r ’ sRe s po ns i bi l i t i e s Contract Plans and Shop Drawings Standard Specifications and Special Provisions

The purpose of this memo is to help clarify responsibilities of the contractor and each NDOT Division concerning cost, analysis, details, and required information in regard to contract documents.

I. Responsibilities: A.

B.

C.

02/14/2005

The Roadway Design Division will provide (to the Geotechnical Section and the Bridge Division) alignment and profile of the wall, and cross sections at 8 meter intervals for the length of the wall. Cross sections will include elevations of top of the wall, existing (original) ground intersecting the plane of the wall, proposed ground at the exposed face at the base of the wall, bottom of the slope in front of the base (slope supporting the wall) of the wall (if applicable), and top of the slope above (slope being retained by the wall) the wall (if applicable). In addition, exact inclination angles of slopes above (retained slope) and/or below (supporting the wall) the wall (if applicable) will be provided by the Roadway Design Division. Any ditch information behind the top of the wall should also be shown. This information may be provided in tabular form or by placing these elevations on the aforementioned cross sections. Topographical information for the existing ground condition and completed condition will be provided to a distance of at least three times the wall height in front and behind the wall. NDOT is responsible for deep seated (global, rotational) external stability. The Geotechnical Section will conduct global stability analyses and provide design recommendations for wall stability. NDOT is responsible for external stability. The Geotechnical Section will conduct external stability analyses with respect to sliding, overturning, and bearing pressure failures. NDOT Geotechnical Policies and Procedures Manual

ANALYSIS AND DESIGN D.

E.

F.

G. H. I.

J.

11-29

The Geotechnical Section will design the wall with respect to external stability. Publication No. FHWA-SA-96-071 (Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines, Reprinted September 1998) and/or the latest edition of the AASHTO Standard Specifications for Highway Bridges will be used to design and determine the minimum reinforcement lengths of the wall. Typical information and details to be provided by the Geotechnical Section to the Bridge Division would include the following: 1. 300 mm wide and 150 mm thick unreinforced concrete leveling pad. 2. Exact embedment depth to top of the leveling pad for the entire length of the wall. 3. Minimum 1200 mm wide bench in front of walls placed (located) on top of slopes. 4. No steeper than 1V:2H slopes in front of or on top of walls. 5. Strength properties of soils supporting the wall (foundation soils), MSE backfill, and retained backfill. 6. Magnitude of anticipated total and differential settlement. 7. Recommended waiting period, prior to construction of barrier rails, copings, concrete anchor slabs, and roadway surface. 8. Minimum required reinforcement lengths for the entire length of the wall. 9. Surcharges. The wall supplier, based on information provided in contract documents, will check the external stability with respect to sliding, overturning, and bearing pressure to confirm NDOT’ spr opos e dmi ni mumr e i nf or c e me nt l e ng t hs . NDOT will determine the need for any changes indicated by thec ont r a c t or ’ se xt e r na ls t a bi l i t ya na l y s i s . All costs associated with changes to the wall due to external stability shall be the responsibility of NDOT. The wall supplier is responsible for internal stability. All costs associated with modifications to the overall wall geometry due to internal stability design shall be responsibility of the wall supplier. The Bridge Division will estimate the quantities and prepare the contract plans. It is NDOT policy not to allow placement of spread footings on embankment retained by MSE walls. Piles Within MSE Walls: Piles must be placed prior to the construction of the wall. Downdrag forces need to be analyzed and friction protection material such as “ Ye l l owj a c ke t ”s l e e ve sora na ppr ove de qua li fne e de dmus tbespecified in the contract documents. The soil reinforcement length and/or layout must be modified when piles are located within the wall. The wall supplier must design the reinforcement for pile locations and submit all calculations for review and approval. Bar mat systems may be cut provided at least two longitudinal bars remain connected to a transverse bar. Strap systems may be skewed up to 20 degrees from a line perpendicular to the wall face. Otherwise, bridging systems must be used.

II. Contract Plans: The Bridge Division will prepare the contract plans. Typical details to be included in the contract plans are the following:

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ANALYSIS AND DESIGN A.

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General Notes: 1.

2.

3.

Design Specifications: AASHTO Standard Specifications for Highway Bridges, (date) with interim revisions through (date), and/or Publication No. FHWA-SA-96-071 (Reprinted September 1998). Construction Specifications: NDOT Standard Specifications for Road and Bridge Construction (date) except as noted below and in the Special Provisions for the project. Loading: Live load surcharge pressure equal to 610 mm of earth (When applicable).  Seismic acceleration = (peak ground acceleration).  Use one-half of peak ground acceleration for design.

4. 5. 6. 7.

 Additional lateral load from bridge piles = (value) (When applicable). Concrete: All concrete shall be class AA (or Class A) Modified (Major) concrete with Fc’=____MPaa t28da y s . Reinforcing Steel: All reinforcing steel shall be ASTM A615 grade 410 or A706. Size of Wall Panel: Area of the MSE wall panel face shall not exceed (normally 2.8) square meters. Soil Properties: MSE wall is designed based on the following soil properties:  Mechanically stabilized earth fill:  Minimum internal angle of friction = __, minimum cohesion = __,  and minimum unit weight = _______.  Fills not meeting the above specified soil parameters should not be approved.  Foundation soils:  Internal angle of friction = ______, cohesion = _____, and unit weight = _______.  Random fills (retained fills):

8.

 Internal angle of friction = ______, cohesion = _____, and unit weight = _______. External Design Parameters:  Sliding friction factor = _________.  Allowable bearing pressure of foundation soils beneath wall = ______.

9.

02/14/2005

 Ultimate bearing pressure of foundation soils beneath wall = ______. Method of design: Specify i f“ SI MPLI FI EDMETHOD”or “ MEYERHOFMETHOD”i sus e df ort hede s i g n.


ANALYSIS AND DESIGN B.

11-31

Plan View: 1.

C.

Alignment of the wall relative to the main or major alignment with necessary stations and offsets to exposed face of wall. 2. Alignment (if applicable) of top of the slope on top of the wall (every 8 meters and at every break point) with necessary stations and offsets to exposed face of wall (this information may be provided in a table). 3. Alignment (if applicable) of top of the slope in front of the wall (every 8 meters and at every break point) with necessary stations and offsets to exposed face of wall (this information may be provided in a table). 4. Alignment (if applicable) of bottom of the slope in front of the wall (every 8 meters and at every break point) with necessary stations and offsets to exposed face of wall (this information may be provided in a table). Elevation View: 1.

Elevation at the bottom of the leveling pad, the bottom of the pad should be level (and stepped if necessary). 2. Line showing the finished grade at exposed face of the wall (finished grade must not be stepped). 3. Elevation at top of the wall every 8 meters and at every break point (this information may be provided in a table). Elevation at top of slope on top of the wall every 8 meters and at every break point (this information may be provided in a table). 4. Elevation at top of slope in front of the wall (elevation of the bench in front of the wall every 8 meters and at every break point, this information may be provided in a table). 5. Elevation at bottom of slope in front of the wall every 8 meters and at every break point (this information may be provided in a table). D. Cross sections: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 02/14/2005

Minimum soil reinforcement lengths for the entire length of the wall (this information may be provided in a table). Width and thickness of leveling pad. Minimum soil cover on top of the leveling pad. Width of the bench in front of the wall. Inclination of the slope in front of the wall (this information may be provided in a table). Inclination of the slope on top of the wall (this information may be provided in a table). Barrier rail, coping, and concrete anchor slab on top of the wall. Existing (original) ground. Limits of excavation and granular backfill. Limit of over-excavation (if applicable). Limit of MSE Backfill (reinforced soil mass). Limit of Borrow and/or Select Borrow (if applicable). NDOT Geotechnical Policies and Procedures Manual

ANALYSIS AND DESIGN

E.

11-32

13. Limit of Drain Rock (if applicable). 14. Limit of Geotextile (if applicable). Quantities: 1. 2. 3. 4. 5. 6.

F.

Area of the wall face. Volume of MSE Backfill. Volume of any Structural Excavation including any over-excavation. Volume of any Granular Backfill, Borrow, Select Borrow, or Drain Rock. Area of any Geotextile. Volume of concrete and reinforcing steel for barrier rails and concrete anchor slabs. 7. No direct payment for concrete leveling pad and reinforced concrete coping. Special Details: 1. 2. 3. 4.

Aesthetic treatments. Coping details. Connection of MSE walls to wingwalls of bridges or other retaining walls (if applicable). Details for drainage or other obstructions (if applicable).

III. Special Provisions: The Geotechnical Section will be responsible for including the following in the Special Provisions: 1. Required soil specifications such as soundness and electrochemical properties for the backfill materials. 2. Required methods of testing. 3. Any required over excavation. 4. Statements that NDOT is responsible for external stability design and Wall Supplier is responsible for checking external stability design. 5. Statements that NDOT is responsible for any cost due to required changes for the external stability design. 6. Statements that Wall Supplier (Contractor) is responsible for cost increases due to internal stability requirements. 7. Statements that Wall Supplier (Contractor) must submit 7 copies of the shop drawings and calculations. 8. Statements that shop drawings and calculations must be stamped and signed by an engineer who is a registered Professional Civil Engineer licensed to practice in the State of Nevada. 9. Statements that allow NDOT 28 working days for review and approval of shop drawings and calculations and no additional working days will be provided for submittals returned for corrections. The Bridge division will be responsible for providing the List of approved Wall Suppliers.

IV. Shop Drawings and Calculations: The Geotechnical Section will be responsible for checking and approving the following: 1. Calculations for external stability (at every 8 meters). 02/14/2005


ANALYSIS AND DESIGN

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2.

Calculations for required soil reinforcement lengths with respect to external stability. 3. Calculations for required soil reinforcement width, thickness, and lengths with respect to internal stability. 4. Soil reinforcement lengths shown on the drawings. 5. Applied bearing pressures shown on the drawings. 6. MSE Backfill materials specifications. 7. Construction methods and procedures shown on the drawings regarding geotechnical issues. 8. Corrosion protection specifications shown on the drawings. For Consultant designed projects, the Consultant will perform the above review and approval. The Geotechnical Section will perform a cursory review after the Consultant has completed their review. The Bridge Division will be responsible for checking and approving the following: 1. Wall alignment and elevations. 2. Panel design and details. 3. Coping details. 4. For Consultant designed projects, the Consultant will perform the above review and approval. The Bridge Division will perform a cursory review after the Consultant has completed their review.

V. Review & Approval Procedures for Shop Drawings and Calculations: 1. 2. 3. 4. 5.

6.

7.

02/14/2005

TheRe s i de ntEng i ne e rwi l ls e nds e ve nc opi e soft hec ont r a c t or ’ s submittal to the Bridge Division. The Bridge Division will send six copies of the submittal to the Geotechnical Section. The Geotechnical Section will contact the Resident Engineer to see if it is acceptable to contact the Wall Supplier directly. The Geotechnical Section will have twelve working days from the date of receiving the submittal to review the shop drawings and calculations. Shop drawings will have two stamps, one each from the Bridge Division and Geotechnical Section. Design calculations will have one stamp from the Geotechnical Section. For Consultant design projects, shop drawings will have three stamps (one Consultant (approval), one Geotechnical (reviewed) and one Bridge (reviewed)) and calculations will have two stamps (one Consultant (approval) and one Geotechnical (reviewed)). Prior to stamping the shop drawings and calculations, the Geotechnical Section will coordinate with the Bridge Division on the joint review. If the shop drawings and/or calculations need to be returned for corrections, one memo will be written to the Resident Engineer by the Bridge Division incorporating all needed corrections. The Geotechnical Section will send five stamped copies of the calculations and shop drawings with corrections (if any) to the Bridge Division. The Bridge Division will respond to the Resident Engineer regarding approval of the shop drawings and calculations within sixteen working NDOT Geotechnical Policies and Procedures Manual

ANALYSIS AND DESIGN

11-34

days from the date of receiving the submittal from the Resident Engineer. If you have any questions or comments regarding this matter, please call me at 888-7786. PN:pn

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ANALYSIS AND DESIGN

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11-2: List of Landslide Mitigation Methods Slide Mitigation Avoid problem

Mitigation Options Relocate facility Completely or partially remove unstable materials Install bridge

Reduce driving forces

Change line or grade Drain surface Drain subsurface Reduce weight

Increase resisting forces, apply external Use buttress and counterweight fills; toe berms force Use structural systems Install anchors Increase internal strength

Drain subsurface Use reinforced backfill Install in situ reinforcement Use biotechnical stabilization Treat chemically Use electro-osmosis Treat thermally

Note: Refer to TRB Special Report 247 (Table 17-1) for further information. 11-3: AASHTO Factors of Safety (from Standard Specifications for Highway Bridges, 17th Ed.) Analysis Condition Minimum Factor of Safety (FS) o Sliding (static) 1.5 o Sliding (seismic) 1.125 o Overturning (static) 2.0 for footings on soil 1.5 for footings on rock o Overturning (seismic) 1.5 for footings on soil 1.125 for footings on rock o Bearing Capacity (static) 3.0 (refer to shallow foundation section) o Bearing Capacity (seismic) 1.5 (refer to shallow foundation section)

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ANALYSIS AND DESIGN

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11-4: Computer Programs Vertical Static Pile Capacity S PILE

FHWA-SA-92-044

Ultimate vertical static pile capacity

PILEPMT

Texas A & M University

Ultimate vertical Load vs. depth, and Load vs. Settlement (using pressure meter data)

NEW NEG

Texas A & M University

Analysis of Piles subjected to negative skin friction

SHAFT 5.0

Ensoft, Inc., www.ensoftinc.com

A program for the study of drilled shafts under axial loads

TZ PILE

Ensoft, Inc., www.ensoftinc.com

Computes the loadsettlement relationships of vertically-loaded piles using tz cures and q-w curves

APILE

APILE Plus 3.0 for Windows, Ensoft, Inc., www.ensoftinc.com

Computes the axial capacity of driven piles as a function of depth

Group

Group 4.0 for Windows, Ensoft, Inc., www.ensoftinc.com

Pile group design program that calculates the distribution of loads to piles in a symmetrical group

FB-Pier

Florida Pier Program (FDOT, FHWA) (University of Florida)

Finite element analysis for deep foundations

Driven Piles WEAP

Gobel, G.G. & Rausche, Frank WEAP 87, Pile group design program Wave Equation Analysis of Pile Foundations, that calculates the distribution Volumes I-V, FHWA, 1987 of loads to piles in a symmetrical group

DRIVEN

FHWA-SA-98-074

02/14/2005

Finite element analysis for deep foundations


ANALYSIS AND DESIGN

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11-4: Computer Programs, contd. Lateral Loads on Piles COM624P

COM624P, Laterally Loaded Pile Analysis Program, Version 2.0, FHWA-SA-91-048, 1993,

Computes deflections and stresses for laterally loaded piles and drilled shafts

http://www.fhwa.dot.gov/bridge/software.htm

LPILE

LPILE Plus 4 for Windows

Computes deflections and stresses for laterally loaded piles and drilled shafts under lateral loads

Spread Footings CBEAR

CBEAR Users Manual, FHWA-SA-94-034, 1996, http://www.fhwa.dot.gov/bridge/software.htm

Computes ultimate bearing capacity of spread or continuous footings on layered soil profiles

Sheet Piles CWALSHT

Dawkins, William P., Users Guide: Computer Program For Design and Analysis of Sheet Pile Walls by Classical Methods, Waterways Experiment Station, 1991

Design and analysis of either anchored or cantilevered sheet pile retaining walls. Moments, shear, and deflection are shown graphically

Shoring

Civil Tech, CT-SHORING, WINDOWS 3.X, 95, NT

Excavation supporting system design and analysis

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ANALYSIS AND DESIGN

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11-4: Computer Programs, contd. Slope Stability PCSTABL

PC-STABL5M Users Manual, FHWA, 1990; PC-STABL6 Users Manual, FHWA, 1990

Calculates factor of safety against rotational, irregular, or sliding wedge failure by simplified Bishop or Janbu, or Spencer method of slices. Version 6 is used for embankments w/reinforcement by simplified Bishop method

XSTABL

Interactive Software Designs, Inc., XSTABL. An Integrated Slope Stability Analysis Program for Personal Computers Reference Manual

Program performs a two dimensional limit equilibrium analysis to compute the factor of safety for a layered slope using the modified Bishop or Janbu methods

SLOPE-W

GEO-SLOPE International, Ltd.

Program that uses limit equilibrium theory to compute the factor of safety of earth and rock slopes

1400, 633 6th Avenue SW Calgary, Alberta, Canada T2P 2Y5 http://www.geo-slope.com UTEXAS2

University of Texas

A slope stability program, which calculates the safety factor for either a prescribed shear surface or searches for the critical shear surface

Embankment Settlement EMBANK

02/14/2005

EMBANK Users Manual, FHWA-SA-92-045, Calculates compression 1993 settlement due embankment loads


ANALYSIS AND DESIGN

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11-4: Computer Programs, contd. Soil Nailing GoldNail

Golder Associates, GoldNail. A stability analysis computer program for soil nail wall design, Reference Manual Version 3.11

The program is a slip-surface, limiting-equilibrium, slopestability model based on satisfying overall limiting equilibrium (translational and rotational) of individual free bodies defined by circular slip surfaces. GoldNail can analyze slopes with and without soil nail reinforcement or structural facing

Seismic Pro Shake

EduPro Civil Systems, Inc. 5141 189th Avenue NE Sammamish, WA 98074

Shake2000

Ameritech Engineering Corvallis, OR http://www.shake2000.com

02/14/2005

The program is used to perform one-dimensional, equivalent linear ground response analyses Used for seismic analysis of soil deposits and earth structures and to provide a first approximation of the dynamic response of a site


ANALYSIS AND DESIGN

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11-4: Computer Programs, contd. Rock Slopes Rock NDOT, Geotechnical Section Database Managemint System

Contains the Rockfall Hazard Rating System information on rated slopes

Rocfall

Rocscience, Toronto, Ontario, Canada

Rockfall simulation software that provides trajectory and energy predictions for rockfalls passing up to three analysis points

CRSP

Colorado Rockfall Simulation available from Colorado DOT

RockPack III C.F. Watts & Assoc., Radford, VA

02/14/2005

Program, Rockfall simulation software that provides trajectory and energy predictions for rockfalls passing a single analysis point Rock slope stability software for the kinematic and slope stability analysis of structural discontinuity data


ANALYSIS AND DESIGN

11-41

11-4: Computer Programs, contd. MSE and Steepened Slopes MSEW

1.0 ADAMA Engineering, Inc., Mechanically Stabilized Earth Walls Software, Version 1.0

The program can be applied to walls reinforced with geogrids, geotextiles, wire mesh, or metal strips. It allows for reduction factors associated with polymeric reinforcement or for corrosion of metallic reinforcement

RSS

Reinforced Slope Stability A Microcomputer Program User ’ sManual , FHWA-SA-96-039, 1997, www.fhwa.dot.gov/bridge/software.htm

A computer program for the design and analysis of reinforced soil slopes (RSS Reinforced Slope Stability). This program analyzes and designs soil slopes strengthened with horizontal reinforcement, as well as analyzing unreinforced soil slopes. The analysis is performed using a twodimensional limit equilibrium method

ReSSA

NHI (FHWA)

Upgrade of RSS Program Other Programs

Math CAD

Mathsoft Engineering and Education 101 Main Street Cambridge, MA 02142

Alternative to Excel that accepts and displays natural mathematical notation

NOTE: Many additional programs that perform similar tasks can be obtained from the private sector. The programs listed are continually updated or revised.

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ANALYSIS AND DESIGN

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11-5: Guidelines for Geotechnical Engineering Analysis Soil Classification Unified (USCS) GW

AASHTO (Approx) A-1-a

Soil Type

GP

A-1-a

GRAVEL poorly graded

GM

A-1-b

GRAVEL well graded

GRAVEL silty GRAVEL clayey GC

A-2-6 A-2-7

SW

A-1-b

Embankment and Cut Slopes

Structure Foundations (Bridges & Retaining Walls)

Slope Stability* Analysis Stability analysis generally not required if cut or fill slope is 1½H:1V or flatter, and water table in cut slope is drawn down by underdrains. Erosion of slopes may be a problem for SW or SM soils.

Embankment Foundation Settlement Analysis Settlement analysis generally not required except possibly for SC soils.

Bearing Capacity Analysis Required for spread footings, pile, or drilled shaft foundations. Spread footings generally adequate except possibly for SC soils.

Settlement Analysis

Stability analysis is required unless nonplastic. Erosion of slopes may be a problem.

Settlement analysis required unless non-plastic.

Analysis required. Spread footings generally adequate.

Analysis required. Can use SPT values if nonplastic.

Required.

Required.

Analysis generally not needed except for SC soils or for large, heavy structures. Empirical correlations with SPT values usually used to estimate settlement.

SAND well graded SAND poorly graded

SP

Retaining Walls (Conventional, Crib, & Reinforced Soil) Lateral Earth Pressure GW, SP, SW, & SP soils generally suitable for backfill behind or in retaining or reinforced soil walls. GM, GC, SM, & SC soils generally suitable if have less than 15% fines. Lateral Earth pressure analysis required using soil angle of internal friction.

Stability Analysis All walls should be designed to provide minimum F.S.=2 against overturning, & minimum F.S.=1.5 against sliding along base. External slope stability considerations same as previously given for cut slopes & embankments.

A-3 SAND silty SM SC

ML

A-2-4 A-2-5 A-2-6 A-2-7 A-4

SAND clayey

SILT inorganic SILT Sandy

CL

Analysis required. Analysis required. Deep foundations Lab consolidation generally required test data needed to OL Required. Required. unless soil has been estimate settlement preloaded. amount & time. NOTES: These are general guidelines –Detailed slope stability analysis may not be required where past experience exists in area with similar soils and similar slope angles. This table is based on FHWA Geotechnical Checklist and Guidelines (FHWA-ED-88-053).

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A-6 Lean Clay A-4

CLAY inorganic SILT organic

These soils are not recommended for use directly behind or in retaining or rein-forced soil walls.


ANALYSIS AND DESIGN

11-43

11-5: Guidelines for Geotechnical Engineering Analysis, contd.

Embankment and Cut Slopes

Soil Classification Unified (USCS)

AASHTO (Approx)

Soil Type

Slope Stability* Analysis

Embankment Foundation Settlement Analysis

MH

A-5

SILT inorganic

Stability analysis required. Erosion of slopes may be a problem.

Required.

CH

A-7

CLAY inorganic “ f atcl ay s”

Required.

Required.

OH

A-7

CLAY organic

Required.

Required.

PT

--

PEAT muck

Required.

Required. Long-term settlement can be significant. Not required.

Rock

Fills: Analysis not required for slopes 1-1½H:1V or less. Cuts: Analysis required, but depends on spacing, orientation, and strength of discontinuities, and durability of the rock.

Structure Foundations (Bridges & Retaining Walls) Bearing Capacity Analysis

Settlement Analysis

Analysis required. Deep foundations generally required, unless soil has been preloaded.

Analysis required. Lab consolidation test data needed to estimate settlement amount and time.

Deep foundation required, unless peat excavated and replaced. Analysis required for spread footings or drilled shafts –usually empirical, related to RQD (Rock Quality Designation).

Highly compressible. Not suitable for foundation support. Analysis only required where rock is badly weathered or closely fractured (low RQD value). May require special testing, such as pressure meter.

Retaining Walls (Conventional, Crib, & Reinforced Soil) Lateral Earth Stability Analysis Pressure

These soils are not recommended for use directly behind or in retaining walls.

Lateral earth pressure analysis required using rock backfill angle of internal friction.

All walls should be designed to provide minimum F.S.=2 against overturning, & minimum F.S.=1.5 against sliding along base. External slope stability considerations same as previously given for cut slopes & embankments.

REMARKS: Soils –Temporary groundwater control may be needed for foundation excavations in GW through SM soils. Backfill specifications for reinforced soil walls using metal reinforcement should meet the following requirements to insure use of noncorrosive backfill: 1. pH range = 5-10 2. Resistivity3,000 ohm-cm 3. Chlorides 200 ppm 4. Sulfates 1,000 ppm Rock –Durability of shale (siltstone, claystone, mudstone) to be used in fills should be checked. Nondur abl eshal esshoul dbeembank edassoi l s,i . e. ,pl ac edi nmax i mum 12”l oosel i f t s& compacted with heavy sheepsfoot or grid rollers. NOTES: These are general guidelines–Detailed slope stability analysis may not be required where past experience exists in area with similar soils or rock, and gives required slope angles. This table is based on FHWA Geotechnical Checklist and Guidelines (FHWA-ED-88-053).

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ANALYSIS AND DESIGN

13.

11-44

REFERENCES

AASHTO,“ Bear i ngCapaci t yofSoi lf orSt at i cLoadonSpr eadFoot i ngs, ”AASHTO T235 AASHTO,“ Gui deSpeci f i cat i onsf orShot cr et eRepai rofHi ghwayBr i dges, ”TaskFor ce37 Report, 1998 AASHTO,“ Hi ghSt r ai nDy nami cTest i ngofPi l es, “AASHTO T298 AASHTO,“ I nSi t uI mpr ov ementTechni ques, ”TaskFor ce27Repor t ,1990 AASHTO,“ I nSi t uSoi l I mpr ov ementTechni quesTaskFor ce27Repor t , ”FHWA-SA-92-041, 1992 AASHTO,“ St andar dSpeci f i cat i onsf orHi ghwayBr i dges” ,Ar t i cl e3. 21ofDi v i si on1,2002 ASCE,“ DamageFr om Bl astVi br at i ons, ”1974 ASCE,“ Dewat er i ng:Av oi di ngI t sUnwant edSi deEf f ect s, ”I SBN0-87262-459-5, 1985 ASCE, “ Set t l ement ofShal l owFoundat i onsonCohesi onl es sSoi l s : Des i gnandPer f or manc e, ” Geotechnical Special Publication No. 5, 1986 ASTM,“ Bear i ngCapaci t yofSoi lf orSt at i cLoadonSpr eadFoot i ngs, ”ASTM D1194 ASTM,“ Hi ghSt r ai nDy nami cTest i ngofPi l es, ”ASTM D4945 ASTM,“ Lat er alLoadsonPi l es, ”ASTM D3966 ASTM,“ LowSt r ai nI nt egr i t yTest i ngofPi l es, ”ASTM D5882 ASTM,“ Nor mal i z edPenetration Resistance –Li quef act i onPot ent i al , ”ASTM D6066 ASTM,“ Pi l esUnderSt at i cAx i alCompr essi v eLoad, ”TestMet hod,ASTM D1143 ASTM,“ RockBol tAnchorPul lTest , ”ASTM D4435 ASTM,“ RockBol tLong-Ter m LoadRet ent i onTest , ”ASTM D4436 ASTM,“ Tensi l eLoadsonPi l es, ”ASTM D3966 Canadi anGeot echni calSoci et y ,“ Canadi anFoundat i onEngi neer i ngManual , ”1985 Ceder gr en,“ Seepage,Dr ai nage&Fl owNet s, ”2nded. ,Wi l ey ,1977 Chur ch,H. K. ,“ Ex cav at i onHandbook, ”McGr aw-Hill, 1981 Code of Federal Regulations,Sec t i on29,“ OSHASt andar ds” Cor psofEngi neer s,“ Desi gn,Const r uct i on,andMai nt enanceofRel i efWel l s,Techni cal Engineering and Design Guide No. 3, ”r epr i nt edbyASCE,1993 Cor psofEngi neer s,“ Desi gn,Const r uct i on,andMai nt enanceofRel i efWel l s, ”EM 1110-21914, 1992, www.usace.army.mil/inet/usace-docs/eng-manuals/em.htm

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ANALYSIS AND DESIGN

11-45

Duncan, J.M. & Buchi gnani ,A. L. ,“ An Engi neer i ng Manualf orSet t l ementSt udi es, ” Department of Civil Engineering, University of California, Berkeley, 1976 FHWA,“ Adv ancedCour seonSl opeSt abi l i t y , ”Vol s. 1 and 2, FHWA- SA-94-005 and FHWASA-94-006, 1994 FHWA,“ Br i dgeFoundat i onNeeds , ”FHWA-RD-82-050, 1982 FHWA,“ Checkl i standGui del i nesf orRev i ewofGeot echni cal Repor t sandPr el i mi nar yPl ans andSpeci f i cat i ons, ”1985 FHWA,“ Desi gnandConst r uct i onofCompact edShal eEmbankment s, ”Vol s. 1 to 5, FHWARD-75-61, FHWA-RD-75-62, FHWA-RD-77-1, FHWA-RD-78-140, and FHWA-RD-78141, 1978 FHWA,“ Desi gnandConst r uct i onofDr i v enPi l eFoundat i ons, ”Vol s. 1 and 2, FHWA-HI-97013 and FHWA-HI-97-014, 1997 FHWA,“ Desi gnandConst r uct i onofShal eEmbankment s, ”Summar y ,FHWA-TS-80-219, 1980 FHWA,“ Desi gnandConst r uct i onofSt oneCol umns, ”FHWA-RD-83-026, 1983 FHWA; “ Det er mi nat i onofPi l eDr i v abi l i t yandCapaci t yf r om Penet r at i onTes t s , ”Vol s . I through III; FHWA-RD-96-179 thru 181, 1997 FHWA;“ Dy nami cCompact i on, ”Geot echni cal Engi neer i ng,Ci r cul arNo. 1, SA-95-037, 1995 FHWA, “ Dr i l l edandGr out edMi cr opi l es: St at eof Pr ac t i c e, ”Rev i ewVol s . I. through IV.; FHWARD-96-016 thru 019, 1997 FHWA,“ Dr i l l ed and Grouted Micropiles: State-of-Pr act i ceRev i ew, ”FHWA-RD-96-019, 1997 FHWA,“ Dr i l l edShaf t sf orBr i dgeFoundat i ons, ”FHWA-RD-92-004, 1993 FHWA,“ Dr i l l edShaf t s:Const r uct i onPr ocedur esandDesi gnMet hods, ”FHWA-IF-99-025, 1999. FHWA,“ Dr i l l edShaf t s:Const r uct i onPr ocedur esandDesi gnMet hods, ”FHWA-IF-99-025, Updated 2000 FHWA,“ Ear t hRet ai ni ngSy st ems, ”Geot echni calEngi neer i ng,Ci r cul arNo. 2, SA-96-038, 1996 FHWA,“ Ear t hquakeEngi neer i ng, ”Geot echni calEngi neer i ng,Ci r cul arNo. 3, for Highways, Vol. 1 - Design Principles, and Vol. 2 - Design Examples, FHWA SA-97-076 and FHWA SA-97-077, 1997 FHWA,“ EMBANK:AMi cr ocomput erPr ogr am t oDet er mi neOne-Dimensional Compression Set t l ementDuet oEmbank mentLoads, ”FHWA-SA-92-045, 1993

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ANALYSIS AND DESIGN

11-46

FHWA,“ Ev al uat i onandI mpr ov ementofEx i st i ngBr i dgeFoundat i ons, ”FHWA-RD-83-061, 1983 FHWA,“ Ev al uat i onofSoi landRockPr oper t i es, ”Geot echni calEngi neer i ng,Ci r cul arNo. 5, FHWA-IF-02-034, 2002 FHWA,“ Ex pansi v eSoi l si nHi ghwaySubgr adesSummar y , ”FHWA-TS-80-236, 1980 FHWA, “ Geosy nt het i cDesi gnandConst r uct i onGui del i nes, ”FHWAHI -95-038, 1995 FHWA, “ Geosy nt het i cMec hani c al l ySt abi l i z edEar t hSl opesonFi r m Foundat i ons , ”FHWA-SA93-025, 1993 FHWA, Geotechnical Engineering, Circular No. 3,“ Desi gn Gui dance: Geot echni cal EarthquakeEngi neer i ngf orHi ghway s, ”Vol ume1,1997 FHWA, “ Geot echni cal Engi neer i ngNot ebook , Ac ompi l at i onof FHWAGeot ec hni c al Not ebook I ssuances”( Cur r ent l y ,t her ear e16i ssuances. Recent issuances are available at www.fhwa.dot.gov/bridge/geopub.htm) FHWA,“ Geot echni calI nst r ument at i on, ”FHWA-HI-98-034, 1998 FHWA,“ Gr oundAnchor sandAnchor edSy st ems, ”Geot echni cal Engi neer i ng, Ci r cul arNo. 4, FHWA-IF-99-015, 1999 FHWA, “ Gui deCont r ol l edBl ast i ngSpeci f i cat i on, ”Geot echni cal Adv i sor yNo. 7, Geotechnical Engineering Notebook, 1985 FHWA,“ Gui del i nesf orConePenet r at i onTestPer f or manceandDesi gn, ”FHWA-TS-78-209, 1978 FHWA,“ Gui del i nesf ort he Desi gn ofMechani cal l ySt abi l i z ed Ear t h Wal l s( I nex t ensi bl e Rei nf or cement s) , ”GT#1,FHWAGeot echni calEngi neer i ng Notebook, 1988 FHWA,“ HandbookonDesi gnofPi l esandDr i l l edShaf t sUnderLat er al Load, ”FHWA-IP-8411, 1984 FHWA,“ Hi ghwaySubdr ai nageDesi gn, ”FHWA-TS-80-224, 1980 FHWA,“ Hy dr aul i cEngi neer i ngCi r cul arNo. 18, Evaluating Scour at Bridges, 3rd ed.” ,FHWAIP-90-017, 1995 FHWA,“ Hy dr aul i cEngi neer i ngCi r cul arNo. 20,St r eam St abi l i t yatHi ghwaySt r uct ur es” , FHWA-IP-90-014, 1991 FHWA,“ Hy dr aul i c Engi neer i ng Ci r cul arNo. 23, Bridge Scour and Stream Instability Countermeasures –Experience, Selection, and Desi gnGui dance” , FHWA-HI-97-030, 1997 FHWA,“ LoadandResi st anceFact orDesi gn( LRFD)f orHi ghwayBr i dgeSubst r uct ur es, ” FHWA-HI-98-032, 1998 02/14/2005


ANALYSIS AND DESIGN

11-47

FHWA;“ LoadTr ansf erf orDr i l l edShaf t si nI nt er medi at eGeomat er i al s, ”FHWA-RD-95-172, 1996 FHWA,“ Manualf orDesi gnandConst r uct i onMoni t or i ngofSoi lNai lWal l s, ”FHWA-SA-96069, 1998 FHWA,“ Mechani cal l ySt abi l i z ed Ear t h Wal l sand Rei nf or ced Soi lSl opes–Design and Const r uct i onGui del i nes, ”FHWA-SA-96-071, 1996 FHWA,“ Mechani cal l ySt abi l i z ed Ear t h Wal l sand Rei nf or ced Soil Slopes –Design and Const r uct i onGui del i nes, ”FHWA-NHI-00-043, 2001 FHWA, “ Mi cr opi l eDesi gnandCons t r uct i onGui del i nes- I mpl ement at i onManual , ”FHWA- SA97-070, 1997 FHWA,“ Negat i v eFr i ct i onDowndr agonaPi l e, ”TS-78-210, 1978 FHWA,“ Pr ef abr i cat edVer t i calDr ai ns, ”Vol s. I to III, FHWA-RD-86-186, FHWA-RD-86-169, and FHWA-RD-86-170, 1986 FHWA, “ RSSRei nf or cedSl opeSt abi l i t y- A Microcomputer Program - Us er ' sManual , ”FHWASA-96-039, 1996 FHWA, “ Rei nf or cedSoi l St r uct ur es ” , Vol umeI , “ Desi gnandCons t r uc t i onGui del i nes , ”FHWARD-89-043, 1990 FHWA,“ RockBl ast i ngandOv er br eakCont r ol , ”Nat i onalHi ghwayI nst i t ut e,NHICour seNo. 13211, FHWA-HI-92-001, 1991 FHWA,“ RockSl opes,Tr ai ni ngCour sei nGeot echni calandFoundat i onEngi neer i ng, ”NHI Course No. 130235 –Module 5, National Highway Institute, 1998 FHWA, “ RockSl opes: Desi gn, Ex cav at i on, St abi l i z at i on, ”Tur ner -Fairbank Highway Research Center, FHWA-TS-89-045,1989 FHWA, “ Rockf al l Haz ar dMi t i gat i onMet hods, ”Par t i ci pant Wor kbook, FHWA-SA-93-085, NHI Course No. 13219, 1994 FHWA,“ Rockf al lHaz ar dRat i ngSy st em, ”Par t i ci pant ' sManual ,FHWA-SA-93-057, 1993 FHWA,“ Soi l andBaseSt abi l i z at i onandAssoci at edDr ai nageConsi der at i ons, ”Vol s. 1 and 2, FHWA-SA-93-004 and FHWA-SA-93-005, 1993 FHWA,“ Soi lNai l i ngFi el dI nspect or sManual , ”FHWA-SA-93-068, 1994 FHWA, "Soils and Foundations Workshop Reference Manual," NHI Course No. 132012, FHWA NHI-00-045, August 2000 FHWA,“ SPI LE,A Mi cr ocomput erPr ogr am f orDet er mi ni ng Ul t i mat e Ver t i calSt at i cPi l e Capaci t y , ”FHWA-SA-92-044, 1993 FHWA,“ Spr eadFoot i ngsf orHi ghwayBr i dges, ”FHWA-RD-86-185, 1986 02/14/2005


ANALYSIS AND DESIGN

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FHWA,“ Techni calGui del i nesf orEx pansi v eSoi l si nHi ghwaySubgr ades, ”Fi nalRepor t , FHWA-RD-79-51, 1980 FHWA,“ Tol er abl eMov ementCr i t er i af orHi ghwayBr i dges, ”FHWA- RD-85-107, 1985 FHWA,“ Tr ai ni ng Cour se i n Geot echni caland Foundat i on Engi neer i ng:Geot echni cal Ear t hquakeEngi neer i ng, ”Par t i ci pant ’ sManual ,andSt udentEx er ci ses, FHWA-HI-99012 and FHWA-HI-99-014, 2000. FHWA,“ Tr ai ni ng Cour se i n Geot echni caland Foundat i on Engi neer i ng:Rock Sl opes, ” Par t i ci pant ’ sManual , andSt udent Ex er ci ses, FHWA-HI-99-007 and NHI-99-036, 1999 FHWA,“ User sManual f orComput erPr ogr am CBEAR:Bear i ngCapaci t yAnal y si sofShal l ow Foundat i ons, ”FHWA-SA-94-034, 1994 FHWA,“ User ' sManualf orComputer Program DRIVEN: Ultimate Static Capacity for Driven Pi l es, ”FHWA-SA-98-074, 1998 FHWA,“ User ' sManualf orLat er al l yLoadedPi l eAnal y si sPr ogr am f ort heMi cr ocomput er , ” (COM624P) Version 2.0, FHWA-SA-91-048, 1991 Goodman,R. E. ,“ Met hods ofGeol ogi calEngi neer i ng i n Di scont i nuous Rock s , ”West Publishing Company, 1976 Hoek, E. andBr ay ,J. W. ,“ RockSl opeEngi neer i ng, ”Rev i sed3rd ed., Institution of Mining and Metallurgy, London, 1981 Hoek, E. andBr own,E. T. ,“ Under gr oundEx cav at i onsi nRock,I nst i t ut ion of Mining and Met al l ur gy , ”London,1980 I t ascaConsul t i ngGr oup,“ FLACUserManual , ”1995 Kr amer ,S. L. ,“ Geot echni calEar t hquakeEngi neer i ng, ”Pr ent i ce-Hall Inc., 1996 McVay ,M. ,Ar maghani ,B. ,andCasper ;R. ,“ Desi gnandConst r uct i onofAuger -Cast Piles in Fl or i da,Desi gnandConst r uct i onofAugerCastPi l es,andOt herFoundat i onI ssues, ” Transportation Research Record 1447, 1994 NAVFAC DM-7.1 –“ Soi lMechani cs, ”Depar t mentof the Navy, Naval Facilities Engineering Command, 1986 NAVFAC DM-7.2 –“ Foundat i onsandEar t hSt r uct ur es, ”Depar t mentof the Navy, Naval Facilities Engineering Command, 1986 NCEERWor kshops,“ Li quef act i onResi st anceofSoi l s:Summar yRepor t , ”1996 NCEER/ NSF,“ Wor kshopsonEv al uat i onofLi quef act i onResi st anceofSoi l s, ”1998 NCHRP ( Br i aud,etal . ) ,“ Downdr agOnUncoat edandBi t umen-Coat edPi l es, ”Resear ch Report 393, 1994 NCHRP,“ Shal l owFoundat i onsf orHi ghwaySt r uct ur es, ”Sy nt hesi s107,1983 02/14/2005


ANALYSIS AND DESIGN

11-49

NCHRP,“ St at i candDy nami cLat er alLoadi ngofPi l eGr oups, ”NCHRPRepor t461,2000 NCHRP, “ Tr eat mentofPr obl em Foundat i onsf orHi ghwayEmbankment s, ”Sy nt hesi s147, 1989 Or egonDOT,“ Rockf al l Cat chmentAr eaDesi gnGui de, ”Resear chPr oj ectSPR-3(032), 2002 Or egonDOT,“ TheNat ur eofRockf al l AsTheBasi sf oraNewFal l outAr eaDesi gnCr i t er i af or 0. 25: 1Sl opes, ”Resear chRepor tNo. FHWA-OR-GT-95-05, 1994 Peck,R. B. ,Hanson,W. E. ,andThor nbur n,T. H. ,“ Foundat i onEngi neer i ng, ”2nded. ,Wi l ey , 1974 Pi er son,L. A. ,Gul l i x son,C. F. ,andChassi e,R. G. ,“ Rockf al l Cat chmentAr eaDesi gnGui de, ” Oregon DOT and FHWA Final Report SPR-3(032), FHWA-OR-RD-01-04, 2001 PostTens i oni ngI nst i t ut e( PTI ) ,“ Recommendat i onsf orPr est r essedRockandSoi l Anchor s, ” 1996 Power s,J. P. ,“ Const r uct i onDewat er i ng:AGui det oTheor yandPr act i ce, ”Wi l ey ,1981 Schmertmann, J.H., “ Gui del i nesf orUsei nt heSoi l sI nv est i gat i onandDesi gnofFoundat i ons f orBr i dge St r uct ur es i nt he St at e ofFl or i da, ”Resear ch Repor t121-A, Florida Department of Transportation, 1967 Seed,H. B. ,andI dr i ss,I . M. ,“ Si mpl i f i edPr ocedur ef orEv al uat i ngSoi l Li quef act i onPot ent i al , ” Journal Soil Mechanics and Foundations Division, ASCE, 97:SM9, pp 1249 - 1273, September 1971 SHAKE, “ AComput erPr ogr am f orConduct i ngEqui v al ent Li nearSei s mi cRes pons eAnal y s es ofHor i z ont al l yLay er edSoi lDeposi t s, ”User ’ sManual, Modified by I.M. Idriss and J.I. Sun, 1991 Ter z aghi ,K. ,andPeck,R. B. ,“ Soi l Mechani csi nEngi neer i ngPr act i ce, ”2nded. ,Wi l ey ,1967 TRB,“ Desi gnofPi l eFoundat i ons, ”NCHRPSy nt hesi sofHi ghwayPr act i ce42,1977 TRB,“ Landsl i des:I nv est i gat i onandMi t i gat i on, ”Speci alRepor t247,1996 USCor psofEngi neer s,“ Desi gn,Const r uct i on,andMai nt enanceofRel i efWel l s,Techni cal Engineering and Design Guide No. 3, ”r epr i nt edbyASCE,1993 USFor est Ser v i ce, “ Sl opeSt abi l i t yRef er enc eGui def orNat i onal For es t si nt heUni t edSt at es , ” Vols. I to III, EM-7170-13, August 1994 Wy l i e,D. C. ,“ Foundat i onsonRock, ”2nded. ,E&FNSpon,1999 Youd,T. L. ,Hansen,C. M. ,andBar t l et t ,S. F. ,“ Rev i sedLi nearRegr essi onEquat i onsf or Prediction of Lateral Spread Displacement, Journal of Geotechnical and Geoenv i r onment alEngi neer i ng, ”December2002 YoudandI dr i ss,andASCE,“ Geot echni cal andGeoenv i r onment al Engi neer i ng, ”Apr i l ,2001 02/14/2005


ANALYSIS AND DESIGN

11-50

Youd, T. L. , andI dr i ss, I . M. , “ Li quef act i onResi st anceofSoi l s: Summar yRepor t f r om t he 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soi l s, ”Jour nalofGeot echni calandGeoenv i r onment alEngi neer i ng,ASCE,pp297312, April 2001

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CHAPTER 12 PRESENTATION OF GEOTECHNICAL INFORMATION

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PRESENTATION OF GEOTECHNICAL INFORMATION

12-i

TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

INTRODUCTION ......................................................................................................... 1 GEOTECHNICAL REPORT ORGANIZATION ............................................................ 1 TITLE PAGE................................................................................................................ 4 TABLE OF CONTENTS .............................................................................................. 5 EXECUTIVE SUMMARY ............................................................................................. 5 INTRODUCTION ......................................................................................................... 5 PROJECT DESCRIPTION .......................................................................................... 5 GEOLOGIC CONDITIONS AND SEISMICITY ............................................................ 5 FIELD INVESTIGATIONS ........................................................................................... 6 LABORATORY ANALYSES ........................................................................................ 6 DISCUSSION .............................................................................................................. 6 CALCULATIONS ......................................................................................................... 6 ANALYSES.................................................................................................................. 6 RECOMMENDATIONS ............................................................................................... 7 REFERENCES ............................................................................................................ 9 FIGURES..................................................................................................................... 9 SUBSURFACE EXPLORATIONS DATA..................................................................... 9 LABORATORY TESTS RESULTS .............................................................................. 9 IN SITU TESTS RESULTS.......................................................................................... 9 INSTRUMENTATION RESULTS................................................................................. 9 REFERENCES .......................................................................................................... 10

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PRESENTATION OF GEOTECHNICAL INFORMATION 1.

12-1

INTRODUCTION

Upon completion of the geotechnical investigation and analysis, the information and findings must be compiled in a standard report format. The report serves as the permanent record of all geotechnical data known to be pertinent to the project and is referred to throughout the design, construction, and service life of the project. The data and recommendations are typically compiled in a Geotechnical Report. The intent of the Geotechnical Report is to present the data collected in a clear manner, to draw conclusions from the data, and to make recommendations for the geotechnical aspects of the project. The primary clients that use the report are roadway designers, Bridge Engineers, construction personnel, and contractors. The Geotechnical Report is a professional document, and must be prepared under the direction of a registered professional engineer. When Consultants pr epar er epor t s,t heConsul t ant ’ sr ecommendat i onsmustber ev i ewed,document edand retained by the Geotechnical Engineer assigned to the project. All final reports, calculations, boring logs, details, etc. must be submitted to the Department on Compact Disks (CD) in addi t i ont opapercopi es.Al l bor i ngl ogsmust bepr epar edusi ngt he“ gI NT”sof t war epr ogr am wi t hpr i nt out si nt heDepar t ment ’ sf or mat .TheDepar t ment ’ sf i nal deci si onont heuseoft he Consul t ant ’ sr ecommendat i ons should be documented (i.e., in a memorandum to the Project Manager in charge of the project). This Chapter describes the format for presentation of geotechnical data. General outlines of the topics to be discussed in the Geotechnical Report are presented. 2.

GEOTECHNICAL REPORT ORGANIZATION

The Geotechnical Report contains factual data, interpretations, engineering studies and analyses, and recommendations for design and construction. The report should be formatted to present information using a standardized approach, so that users are able to locate information readily and consistently. The format and contents of the Geotechnical Report are somewhat dependent on the type of project. The general outline for a Geotechnical Report is as follows:  Title Page  Table of Contents  Executive Summary (optional)  Introduction o General o Scope o Other reports and investigations  Project Description  Geologic Conditions and Seismicity o Local Geology o Faulting and Seismicity

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PRESENTATION OF GEOTECHNICAL INFORMATION   





 





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Field Investigations (summary, with details in Appendices A, B, D, and E) Laboratory Analyses (summary, with details in Appendix C) Discussion (with supporting figures in Appendix A) o Anticipated Subsurface Conditions (soil, rock, groundwater) o Geologic Hazards o General Site Evaluation Summary of Engineering Analyses and Calculations (typically a summary will suffice in a main section of the Geotechnical Report, and the detailed documentation of analyses and calculation could be in an appendix or as a separate report.) Recommendations o Site Grading and Earthwork  Use of Materials  Embankments  Cut Slopes  Drainage o Rock Slopes (slope angles, stabilization, rockfall mitigation) o Foundations  Spread Footings  Driven Piles  Drilled Shafts  Micropiles o Retaining Walls o Construction Specifications o Recommended Construction Observations, Testing and Instrumentation o Closure References Appendix A: Figures o Site Location Map o Soil Boring Location Map o Geologic Mapping o Supporting Photographs of Site Conditions o Interpreted Geologic Cross-Sections o Recommended Design Details Appendix B: Subsurface Explorations Data o Boring Log Key o Boring Logs o Test Pit Logs o Geophysical Data Appendix C: Laboratory Test Results o Test Result Summary Sheets

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 

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o Particle Size Distribution Report Sheets (gradation curves) o Consolidation/Hydrocollapse Test Report Sheets and/or Summary Table o Triaxial Test Results Sheets and/or Summary Table o Direct Shear Test Report Sheets and/or Summary Table o Chemical Analysis Results Sheets and/or Summary Table Appendix D: In Situ Test Results Appendix E: Instrumentation Results

Much less commonly, a Geotechnical Baseline Report may be required, particularly in conjunction with solicitations for Design-Build projects. The Geotechnical Baseline Report outline is similar to the above outline, except that it is strictly a factual report, and no analyses or design recommendations are presented. Geotechnical Reports should be prepared using a formal technical report writing style. The reports are read by various parties within the Depar t mentandbyt heDepar t ment ’ sagent s( Consul t ant s,cont r actors, attorneys, etc). In litigation matters, the Geotechnical Report could be read by opposing legal counsel looking for weaknesses, misstatements, errors, omissions, evidence of substandard work or implied conditions. Internal report reviews are criti calt ov er i f yt hatr epor t smeett heDepar t ment ’ s standards before the reports are distributed. Reports and report drafts are discoverable in legal proceedings, and can be used by opposing counsel in an attempt to cast doubt on the competency of the Depart ment ’ sGeot echni calEngi neer . The Geotechnical Report typically is used by the Department as the basis for resolving contractor claims of changed conditions. The Geotechnical Report should divulge all subsurface information used for design. The report writers and reviewers should be aware that the information contained in the report is typically used by contractors to prepare their bids. Since some words and phrases can have double meanings, it is important, to avoid the use of incomplete, ambiguous, and subjective statements. Reports should be reviewed specifically for such content and the questionable words and phrases replaced with clearer terms. Geotechnical interpretations are needed to describe and justify the assumptions made in areas where conditions are unknown. Unnecessary interpretations and statements or overly optimistic statements should be avoided. Guidance for checking the completeness of Geotechnical Reports is provided in the FHWA publ i cat i on “ Checkl i stand Gui del i nes f orRev i ew ofGeotechnical Reports and Pr el i mi nar yPl ansandSpeci f i cat i ons”( 1985) .Checkl i st sar epr ov i dedf orv ar i oust y pesof geotechnical investigations and construction elements, in the following categories:  Site investigation information  Shallow foundations  Pile foundations  Drilled shaft foundations  Retaining walls  Bridge approach embankments over soft ground

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Centerline cuts and embankments Landslide corrections Material sites PS&E review checklist Minimum geotechnical engineering analyses required for embankments, cut slopes, structure foundations, and retaining walls Guideline minimum boring, sampling, and testing criteria

In addition, recent FHWA technical publications for different types of geotechnical construction (such as soil nailing and ground anchors) provide guidance on documentation relevant to those areas. Analyses and computations should be checked by an independent Geotechnical Engineer following appropriate QA/QC procedures. Reviews should utilize the gui del i nesi nFHWApubl i cat i on“ Checkl i st andGuidelines for Review of Geotechnical Reports andPr el i mi nar yPl ansandSpeci f i cat i ons”( 1985) ,aswel l ast hi sManual ,andFHWAdesi gn reference manuals. To maximize the benefits of the geotechnical investigation, the Geotechnical Engineer should interact with the project design and construction engineers throughout the duration of the project. The geotechnical input should be considered and incorporated into the project as the design is developed. If the project design is altered as project development advances, the geotechnical recommendations may have to be modified from those presented in the Geotechnical Report. When the project approaches the final design stage, the Geotechnical Engineer should determine if an additional or a final Geotechnical Report should be prepared to reflect modified assumptions and recommendations incorporated in the final design plans.      

The following offices should be provided copies of Geotechnical Reports, as applicable: Project Manager District Engineer Construction Engineer Structural Design Division Roadway Design Division FWHA Project Engineer (for Federally funded projects)

In addition to writing the report, the Geotechnical Engineer should review all phases of the plans and specifications to ensure that the geotechnical recommendations have been cor r ect l yi ncor por at ed. The Depar t ment“ St andar d Speci f i cat i onsf orRoad and Br i dge Const r uct i on”andPul l Sheet speci f i cat i onsshoul dnot bechangedf orpr oj ec t sex c ept wi t ht he approval of the Assistant Materials Engineer. 3.

TITLE PAGE

The title page should include the formal name of the project, the project identification number, the county, the date the report was finalized, and the names with titles of report

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preparers and their signatures (which includes the author, the reviewer, and approval by the overseeing engineer). 4.

TABLE OF CONTENTS

The table of contents should list the report sections and subsections, followed by appendices. A list of tables and figures should be included. A table of contents is not necessary for a short report or technical memorandum. 5.

EXECUTIVE SUMMARY

The Executive Summary may be desirable for larger reports to help provide the most important findings and recommendations in a short and simple manner. An Executive Summary is not necessary for a short report or technical memorandum. 6.

INTRODUCTION

This section introduces the scope of work as it relates to the general project description (a more detailed project description is provided in the next report section). A list of previous reports and investigations that are relevant to the current project and site should be identified in this introductory section. 7.

PROJECT DESCRIPTION

This section describes the elements of the project and the geotechnical-related items. Provide a list of project information that was received during the course of the investigation (alignment, foundation layout, 30% plans, scour estimate, etc.). The details should include the various grading requirements and structure needs. Project constraints should be identified. Design loads and seismic criteria should be addressed. Provide a description of width, composition, and condition of existing roadway. Provide the estimated depths of scour used (typically determined by the Hydraulics Engineer), if applicable. A vicinity map is useful to show the general location of the project. 8.

GEOLOGIC CONDITIONS AND SEISMICITY

This section describes the known and published geology of the site and vicinity, as well as the regional and local seismicity. Provide a description of significant geologic and topographic features of the site. The principal geologic formations are described, along with their soil and rock characteristics. The general thicknesses (and contact elevations) of the principal geologic units should be described based on available information. Describe both natural and man-made features that are of construction importance or need to be protected. Include pertinent geologic mapping. Identify the closest relevant faults and areas of seismic activity, along with the published expected peak horizontal ground acceleration (as stated in r el i abl egeol ogi cpubl i cat i onsandt heAASHTO“ St andar dSpeci f i cat i onsf orHi ghwayBr i dges Desi gnManual ” ) .

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FIELD INVESTIGATIONS

This section presents an overview of the exploration program. Information presented here should include geologic reconnaissance work, the method of subsurface explorations, in situ testing, and instrumentation. The sampling methods should be briefly described. Each boring and test pit should be identified and labeled, along with its depth and purpose. Provide a sentence referencing the exploration logs, in situ test results, and instrumentation results in the appendices. 10.

LABORATORY ANALYSES

List the types of tests performed and summarize the results, leaving the details in the appendix. Briefly describe key findings from the laboratory tests. Provide a sentence referencing the laboratory test results in the appendix. 11.

DISCUSSION

The subsurface conditions should be described along the route of the project. This might require splitting the discussion into sections along the alignment. Describe the engineering characteristics and anticipated behavior of each soil and rock unit. Identify potentially difficult or problematic conditions. Describe any precedent information such as past slope performance or instabilities and ground settlement evidence. The groundwater regimes throughout the project should be described. Describe any potential geologic hazards, such as unstable slopes and rockfall hazards. 12.

CALCULATIONS

A complete set of the analysis computations should be adequately documented and saved in a separate file or report. All calculations by Consultants are reviewed by the Geotechnical Engineer. The Geotechnical Engineer reviews and makes recommendations back to the Consultants to be incorporated into the calculations. Consultants remain responsible for the accuracy and completeness of all deliverables. 13.

ANALYSES

Provide an overview of the geotechnical engineering analyses and studies performed. Describe the purpose of each set of analyses, and provide the assumptions used, the corresponding results, and impact on the project. Details should be included in an appendix, if necessary. When applicable, analyses for alternate foundations including spread footings, driven piles and drilled shafts should be provided for all structures. A description of the analyses performed and an explanation of why specific foundation alternatives were eliminated should be included.

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RECOMMENDATIONS

The Geotechnical Engineer must provide recommendations for all earthwork, rock slopes, retaining walls, foundations and geotechnical problems. The excavated materials must be described in terms of their behavior and its suitability for use as Borrow material. Address how the materials satisfy Department standards for Borrow materials. Unsuitable materials must be addressed and their locations identified. If groundwater or seepage could impact the project, describe any recommended drainage systems and their locations. Estimate earthwork shrink/swell factors to allow for computation of earthwork quantities. Provide recommendations for embankment construction, including methods to ensure slope stability and manage settlement. Estimate the magnitude and rate of settlement. Evaluate possible alternatives if magnitude or time required for settlement is excessive, and recommend treatment based on economic analysis, time and environmental constraints. When addressing stability, describe the factor of safety criteria and the level achieved with the recommended approach. Evaluate possible treatment alternatives if the factor of safety is too low. Provide recommendations for any ground improvement. Reinforced slopes, if to be used, should be detailed for design. Landslide mitigation measures require detailed design recommendations. Provide rock slope recommendations including the design of slopes (appropriate cut slope angles) and fallout area dimensions. The potential for rockfall should be described and any recommended mitigations should be detailed. Foundation recommendations should be provided for all structures including bridges, soundwalls, earth retaining walls, channels, box culverts and poles. Address the use of both shallow and deep foundations and describe advantages and disadvantages for each. Provide detailed recommendations for preferred foundation types. For shallow foundations, provide the recommended elevations of bottom of footings and the allowable soil pressures based on settlements and bearing capacities. Describe suitable pile types and reasons for design selections and exclusions. Provide plots of soil resistance for selected pile size alternates. Pl ot sshoul dbedev el opedi ndi cat i ngbot hDav i s s on’ sc ur v eandul t i mat es oi l r es i s t anc ev er s us elevation, and should show end bearing and skin friction as well as total resistance. Depth of scour should be accounted for on each plot. Separate pile analyses for recommended pile sizes are to be performed for each boring. A corresponding pile capacity curve for each analysis should be provided. When more than one boring is drilled at a pile group location or when it is appropriate to generalize the soil strata, one design analysis is performed for each pile size. Recommendations for piles include:  Lateral capacity  Vertical (axial) capacity  Seismic criteria and design parameters  Minimum pile length or tip elevation (related to axial capacity)  Minimum pile spacing

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Estimated pile settlement or pile group settlement Effects of scour, down drag, and lateral squeeze, if applicable. Pile cap depths or elevations Maximum driving resistance to be encountered in reaching the estimated bearing elevation including the estimated amounts of scour used in the capacity analysis Recommended locations of test piles and pile installation criteria for dynamic monitoring Selection of load test types, locations and depths, where applicable

Recommend which retaining wall types are appropriate for the project. Provide detailed recommendations for design of the preferred wall type(s). Provide loads and factored soil resistance with respect to sliding and overturning for walls other than cantilever walls included i nt heDepar t ment“ St andar dPl ansf orRoadandBr i dgeConst r uct i on” ,andaddr essov er al l stability of walls. Include any requirements for tiebacks, geotextiles, reinforcing materials, etc. I ncl udeMSEr ei nf or cementl engt hsandl ocat i onsi fl engt hsv ar y .SeeNDOT,“ Br i dgeDesi gn andPr ocedur esManual ”f ordet ai l s. Describe the effect of roadway construction (vibratory rollers, utility excavations, settlements, etc.) on surrounding structures and any possible impacts they may have on the use of the structures during construction. Structures in close proximity to construction activities must be evaluated for potential damages caused by these activities. When warranted, recommendations such as time restraints on certain operations, underpinning, and monitoring need to be provided to reduce the damaging effects of the construction. Where there is a potential impact on existing buildi ngsi nt hesur r oundi ngar ea, i ncl udet hes t r uc t ur e’ s address, type of construction, the estimated vibration level that may cause damage, the usage (storage building, hospital, etc.), what the potential problem may be and what actions should be taken to minimize the impact in the report. TheDepar t ment ’ s“ St andar dSpec i f i c at i onsf orRoadandBr i dgeCons t r uc t i on”mus t be utilized wherever possible for simplicity and contractor familiarity. Provide specifications and details where the Standard Specifications do not apply or do not address the planned const r uct i onoper at i onf ort hepr oj ec t .Ther ei snoneedt or epeatt heDepar t ment ’ sSt andar d Specifications in the Geotechnical Report. Provide recommendations for geotechnical testing, observations, and/or instrumentation, depending on the needs of the project and the relative complexity or criticality of the work to be performed. Describe the benefit of performing the testing and instrumentation, and the possible consequences if they are not performed or if the instruments are accidentally damaged. List the tests and instruments to be used and their planned locations. Comment son const r uct i oni ssuesar e hel pf ult o bot ht he Depar t ment ’ sResi dent Engineer and the contractor. Unless otherwise specified by the Department, provide information about anticipated water, soil, and rock conditions that might affect construction operations, sequences, and methods. These conditions might include soft foundation soils, quick soils, extremely weathered or fractured rock, massive rock, high moisture contents,

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presence of subsurface boulders, buried drainage systems, and/or springs that could interfere with construction. Identify design features that were specifically included to address geotechnical problems during construction. Discuss the design features and possible consequences of not implementing these features. Identify restrictions, such as not being allowed to place fill or temporary stockpiles in sensitive or unstable areas, and provide information on temporary cut slopes. 15.

REFERENCES Cite the references used in the geotechnical evaluations and analyses.

16.

FIGURES



Figures are typically presented in Appendix A. The main figures should include: Topographic site plan, usually with a vicinity map Boring location map Geologic mapping Supporting photographs of site conditions Geologic cross-sections and typical sections along the alignment, if approved by the Principal Geotechnical Engineer Recommended design details

17.

SUBSURFACE EXPLORATIONS DATA

    

The details of the exploration methods are in the main body of the Geotechnical Report and do not need to be repeated in the appendices. On large projects, a Summary Table with borings listed in numerical order and their corresponding stationing locations may be included to allow the reader to find boring locations and numbers readily. Subsurface exploration data including Boring Logs, Test Pit Logs, and/or Geophysical plots are typically presented in Appendix B. A key to Boring Logs needs to be included. 18.

LABORATORY TESTS RESULTS

A Summary Table of laboratory test results and detailed graphs of results of tests such as consolidation, shear strength, triaxial, and gradation are typically presented in Appendix C. 19.

IN SITU TESTS RESULTS

Details of any in situ testing (other than SPT) and corresponding test data and results are typically presented in Appendix D. 20.

INSTRUMENTATION RESULTS

Details of the instrumentation installations and the monitoring program are typically presented in Appendix E. The results of the monitoring program are typically included.

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REFERENCES

AASHTO,“ ManualonSubsur f aceI nv est i gat i ons, ”1988 AASHTO,“ St andar dSpeci f i cat i onsf orHi ghwayBr i dgeDesi gnManual ” FHWA,“ Checkl i standGui del i nesf orRev i ewofGeot echni cal Repor t sandPr el i mi nar yPl ans and Specifications,”FHWA-PD-97-002, 1985 FHWA, Engineering Notebook Issuance GT-15, “ Geot echni cal Di f f er i ngSi t eCondi t i ons , ”May 1996 FHWA, “ Soils and Foundations Workshop Reference Manual,”NHI Course No. 132012, FHWA NHI-00-045, August 2000 NDOT,“ Br i dgeDesi gnandPr ocedur esManual ,St r uct ur alDi v i si on” NDOT,“ St andar dSpeci f i cat i onsf orRoadandBr i dgeConst r uct i on”

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CHAPTER 13 CONSTRUCTION PHASE

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CONSTRUCTION PHASE

1. 2. 3. 4. 5. 6. 7. 8. 9. 9.1 9.1.1. 9.1.2. 9.1.3. 9.1.4. 9.2 9.2.1. 9.2.2. 9.2.3. 9.3 9.3.1. 9.3.2. 9.3.3. 9.3.4. 10. 10.1 10.2 10.3 11. 12. 13. 14. 15. 16.

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TABLE OF CONTENTS PURPOSE ............................................................................................................ 1 INTRODUCTION .................................................................................................. 1 EARTHWORK ...................................................................................................... 1 GROUND IMPROVEMENT .................................................................................. 2 GEOSYNTHETICS............................................................................................... 2 ROCK SLOPES.................................................................................................... 2 EXCAVATION SHORING, COFFERDAMS AND DEWATERING ......................... 3 SPREAD FOOTINGS ........................................................................................... 3 DEEP FOUNDATIONS ......................................................................................... 3 Driven Piles .......................................................................................................... 3 Dynamic Driving Analysis ..................................................................................... 4 Construction Inspection ........................................................................................ 4 Pile Driving Analyzer............................................................................................. 4 Pile Integrity Testing ............................................................................................. 4 Drilled Shafts ........................................................................................................ 5 Construction Inspection ........................................................................................ 5 Shaft Inspection Device (SID) .............................................................................. 5 Shaft Integrity Testing........................................................................................... 6 Load Tests............................................................................................................ 6 Static Load Tests.................................................................................................. 7 Dynamic Load Tests............................................................................................. 7 Statnamic Load Tests........................................................................................... 7 Osterberg Load Tests........................................................................................... 8 RETAINING STRUCTURES ................................................................................ 8 MSE Walls and Reinforced Soil Slopes ............................................................... 8 Ground Anchors ................................................................................................... 8 Soil Nail Walls ...................................................................................................... 9 LANDSLIDE MITIGATION.................................................................................... 9 FIELD INSTRUMENTATION MONITORING...................................................... 10 TROUBLESHOOTING ....................................................................................... 10 RECORDS / DOCUMENTATION ....................................................................... 10 SPECIFICATIONS AND STANDARDS............................................................... 11 FIGURES ........................................................................................................... 12 13-1: Statnamic Axial Load Test (1 of 2) ............................................................ 12 13-1: Statnamic Axial Load Test (2 OF 2) .......................................................... 12 13-2: Osterberg Load Cells (1 of 4) ................................................................... 13 13-2: Osterberg Load Cells (2 of 4) ................................................................... 13 13-2: Osterberg Load Cells (3 of 4) ................................................................... 14 13-2: Osterberg Load Cells (4 of 4) ................................................................... 14 REFERENCES ................................................................................................... 15 NDOT Geotechnical Policies and Procedures Manual

CONSTRUCTION PHASE 1.

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PURPOSE

Geotechnical Engineers are involved in the construction phase of projects. The Geotechnical Engineers should visit the site to observe any encountered problems firsthand. It is important to document observations made during the visit. 2.

INTRODUCTION

During construction, in situ materials and construction methods may require inspection to assure compliance with the design assumptions and the project specifications. The i nspect i ont asks, dependi ngont heRes i dent Engi neer ’ sr eques t , mayi nc l udes ubgr adeand/ or embankment compaction control, assurance of proper backfilling techniques around structural elements; typical footings, drilled shafts, piles, and ground anchor installations. The Resident Engineer (Inspectors) need to be provided with geotechnical information and written guidelines to perform their tasks effectively. Existing structures that are potentially sensitive to vibrations or movement should be monitored, including preconstruction and postconstruction surveys of the structures. Mitigating action may be necessary to reduce the impact of construction induced ground movements. It may also be desirable to monitor groundwater level changes, settlement, heave, and/or lateral displacement of the structures. 3.

EARTHWORK

Inspectors perform day-to-day inspection for earthwork projects. Typical earthwork inspection requires only nominal involvement from the Geotechnical Engineer during construction. However, if special considerations must be addressed during construction, Resident Engineers and their Inspectors should be advised prior to the start of construction. They should also be made aware that it is important to notify the Geotechnical Engineer if “ changedcondi t i ons”and/ orsi gni f i c ant gr oundwat erf l ow/ spr i ngsar eenc ount er ed. I ngener al , the Geotechnical Engineer should not assume that Inspectors will initiate contact, and should maintain communication with Inspectors if certain work items require input or support from the Geotechnical Engineers. Inspectors typically require construction support from the Geotechnical Engineer regarding works such as:  Excavation of poor foundation soils  Staged embankment placement over soft foundations  Settlement monitoring and mitigation methods  Cement and lime stabilization  Use of degradable rock materials  Cutting slopes  Drainage systems installation beneath fills

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GROUND IMPROVEMENT

Geotechnical Engineers provide specifications for ground improvement techniques in the design stages of projects. Projects involving ground improvement measures (such as excavation, surcharging, wick drains, stone columns, dynamic compaction, or grouting) typically require the Geotechnical Engineer to provide day-to-day support to the Inspector at the early stages of ground improvement work. Once design assumptions are confirmed and the ground improvement contractor has established a routine, the Geotechnical Engineer may decrease involvement to regular review of daily inspection reports and occasional site visits. During each site visit, the Geotechnical Engineer should confirm that ground improvement activities are conducted as directed, based on evaluations of obtained technical data. The site visit is an opportunity to verify any ground variation from the anticipated subsurface conditions. If variations exist, the need to modify ground improvement operations to suit the different subsurface conditions should be evaluated. 5.

GEOSYNTHETICS

Geotechnical Engineers provide specifications for geosynthetic material requirements and installation methods in design stages of projects. Geosynthetic applications include subgrade separation, construction platform, erosion control, drainage filter, embankment reinforcement, pavement reinforcement, MSE wall reinforcement, and impermeable barriers. Inspectors typically perform routine inspection of common geosynthetics, checking certifications and ordering any tests required by the specifications. Any specific concerns regarding geosynthetic material property values or installation should be discussed with the Inspector. 6.

ROCK SLOPES

Geotechnical Engineers meet with Inspectors and contractors at the sites to review the rockwork objectives before construction of projects commences. The Geotechnical Engineer shoul dassi sti nr ev i ewi ngt hecont r act or ’ sbl ast i ngsubmi t t al s,andobser v i ng/ ev al uat i ngt est blasts, if applicable. Previously undisclosed rock slope problems could occur during construction, for which the Geotechnical Engineer should perform an additional investigation. Typically, a three-dimensional evaluation of rock structure and problem conditions is needed. Typically, as construction proceeds, slope conditions and the need for special measures, such as rock bolts can change due to blasting or scaling operations. The Geotechnical Engineer should routinely evaluate slopes during construction and be prepared to modify the mitigation measures as necessary. Because rockfall mitigation measures are rarely applied, construction personnel generally have little experience with them. The Geotechnical Engineer should provide on-site support for specialty work items such as slope scaling, slope screening, rock bolting, block underpinning, cable lashing, barrier systems installation, and shotcrete placement.

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EXCAVATION SHORING, COFFERDAMS AND DEWATERING

Temporary shoring, cofferdams, and dewatering are typically the responsibility of the contractor. Shoring requirements ar especi f i edi n“ Occupat i onal Saf et yandHeal t hStandards f ort heConst r uct i onI ndust r y , ”29CFRPar t26,pr omul gat edbyt heOccupat i onal Saf et yand Health Administration (OSHA), U.S. Department of Labor. Bridge and Geotechnical Engineers review shop drawings and calculations. The Geotechnical Engineer may be asked to assist the Inspector when the shoring system is complex and critical facilities are located nearby. Dewatering may be necessary with excavation for bridge foundations and retaining walls, to prevent base heave, subgrade softening, and flow of soil from the side slopes. Instrumentation might be required in critical shoring and dewatering applications. 8.

SPREAD FOOTINGS

Geotechnical Engineers are not typically involved in the inspection of shallow foundations during construction. Footing pad preparation inspection is straightforward when standard specifications are used and Inspectors have adequate training and support. Special situations may require the involvement of the Geotechnical Engineer where soil conditions are poor (weak foundations) and/or where the applied bearing pressures are high (heavy loads). In these cases, the Geotechnical Engineer should discuss the design intent and anticipated subsurface conditions with Inspectors prior to construction. If foundation soil conditions in the field are different from those shown on Plans and/or the Geotechnical Report, the Resident Engineer typically informs the Geotechnical Engineer of the change so that appropriate modifications can be implemented (ref ert o FHWA,“ Shal l ow Foundat i ons, ” Geotechnical Engineering Circular No. 6, 2002). 9.

DEEP FOUNDATIONS

Geotechnical Engineers remain involved with deep foundation projects during const r uct i on.Ani ni t i alt aski st or ev i ew t hecont r act or ’ spr oposedconst r uct i onappr oach including evaluating items such as the adequacy of pile hammers or drilling equipment. Site visits are often required to assist the Inspector and to look for unusual or changed site conditions. The Geotechnical Engineer should regularly contact the Inspector to follow progress, and to review and file pile installation records. Deep foundation systems can be classified as driven (displacement) or drilled (replacement). 9.1

Driven Piles

The Geotechnical Engineer should be familiar with the recommended construction inspection procedures outlined in the following FHWA publications:  Performance of Pile Driving Systems –I nspect or ’ sManual  Design and Construction of Driven Pile Foundations  Static Testing of Deep Foundations

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9.1.1. Dynamic Driving Analysis Geotechnical Engineers perform dynamic pile driving analyses during the design phase of projects to evaluate pile types, driving stresses, and drivability with different size hammers. These analyses are performed using wave equation software such as WEAP. The contractor proposes use of a hammer type for driving of the piles. The Geotechnical Engineer reviews the cont r act or ’ ssubmi t t alandev al uat est hepr oposedpi l e/ hammersy st em t ocal cul at edr i v i ng stresses and the driving criteria that corresponds to the resistance loads. The Geotechnical Engineerper f or msawav eequat i onanal y si sbasedont hecont r act or ’ ssubmi t t al t ov er i f yt he adequacy of the proposed equipment and methods. The Geotechnical Engineer provides driving criteria to the Resident Engineer. 9.1.2. Construction Inspection Geotechnical Engineers work with Resident Engineers to verify that equipment used at the sites matches the equipment proposed by the contractors. This involves inspecting hammer models and serial numbers. Hammer cushions are difficult to observe without disassembling the helmet; however it is important to verify that the cushion material and t hi cknessmat cht hecont r act or ’ ss ubmi t t al .TheGeot ec hni c al Engi neers houl dr ef ert oSection 508,“ Dr i v en Pi l es, ”oft he Depar t mentSt andar d Speci f i cat i ons f orRoad and Br i dge Construction as a guide when involved with construction of driven piles. 9.1.3. Pile Driving Analyzer Using a Pile Driving Analyzer (PDA) involves attaching strain gauges and accelerometers to a pile prior to being driven into the ground. Data collected by the instruments as the pile being driven are processed by the PDA unit to calculate the following:  Pile load capacity  Driving stresses  Energy transferred from hammer to pile Signal irregularities that may result from pile damage can be detected by obtained data. Data from the PDA can be further processed using the CAPWAP program to determine sitespecific soil engineering properties to be used in wave equation analyses. The PDA is used during construction to confirm design assumptions. If PDA measurements taken during construction indicate differing site conditions than assumed in the design, there is the potential for costly redesign efforts and contractor change orders. 9.1.4. Pile Integrity Testing Geotechnical Engineers could be involved in evaluating questionable piles during construction. The use of low strain, impact, nondestructive testing has become common to assess damage in driven piles. It can also be used to determine the actual length of piles supporting existing structures. One instrument used for this testing is the Pile Integrity Tester (PIT). When using the PIT, the top of the pile is struck with a hammer and the signal reflection is measured at the top of the pile. The signal reflects when there is a change in impedance in 02/14/2005


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the pile section. If the signal comes back too quickly, there may be damage to the pile. The PIT can be particularly useful in evaluating the length of foundations for older structures without as-built drawings. The main advantage of using the PIT device is low cost. The main disadvantage is the test results are very subjective and limited to cases where the top of the pile is accessible for testing. The use of high strain, impact, nondestructive testing is preferable to using the PIT if pile-driving equipment is available. This testing involves instrumenting a pile with a PDA and restriking it with the pile hammer. 9.2 Drilled Shafts Geotechnical Engineers should be familiar with the recommended construction inspection procedures outlined in the following FHWA publications:  Static Testing of Deep Foundations  Drilled Shafts: Construction Procedures and Design Methods 9.2.1. Construction Inspection The quality of a drilled shaft installation is dependent on the construction procedures. Geot echni calEngi neer sshoul dr ef ert oSect i on509,“ Dr i l l edShaf t s, ”oft heDepartment Standard Specifications for Road and Bridge Construction as a guide when involved with construction of drilled shafts. The Geotechnical Engineer evaluates t hecont r ac t or ’ sproposed construction methods before equipment are mobilized to the site. During the review, the Geotechnical Engineer considers how the construction procedures affect the engineering properties such as unit end bearing and unit skin friction. The Geotechnical Engineer should arrange to be on site early in the construction phase so that any installation techniques that adversely affect the performance of the shaft are eliminated. Geotechnical Engineers should contact Inspectors to ensure that they understand the construction processes and know when in the construction process problems typically occur. Different techniques are used to properly construct and maintain the integrity of the shaf topeni ngpr i ort opl acementoft heconcr et e.Fort hewetmet hod,mi ner alor“ pol y mer sl ur r y ” , i fal l owed, is used to maintain a positive head inside the open shaft in order to keep the hole open. In order to ensure that the slurry meets the requirements to perform properly, the following control tests shall be performed: density, viscosity, sand content, and pH. For drilled shafts socketed into rock, it is important to evaluate the quality of the rock at the base of the socket. In order to evaluate the quality of the rock directly below the shaft excavation, rock cores may be taken once the shaft design depth is reached. The coring method must be approved, and should be able to provide core samples from 4 to 6 inches in diameter and allow the cored material to be removed in an undisturbed state. (Refer to ASTM D 2113 and ASTM D 5079.) 9.2.2. Shaft Inspection Device (SID) The SID is used to inspect the bottom cleanliness of excavated drill holes prior to placement of concrete. The SID uses a high-resolution camera mounted in a watertight 02/14/2005


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chamber. The inspection bell is lowered from a service platform to the bottom of the shaft, and the operator can view the bottom via the camera. The bell is fitted with a depth gauge to indicate the thickness of debris on the shaft bottom. The SID also has the capability to sample soils along sidewalls of shaft excavations in order to evaluate the buildup of slurry. 9.2.3. Shaft Integrity Testing Various test methods are available to assess the quality of the in-place deep foundation element. These quality assurance tests need to be performed by qualified personnel, and the results need to be analyzed and interpreted by experienced engineers in order to provide meaningful results. Pile Integrity Testing can be used to detect anomalies, such as necking or voids in some drilled shafts. However, since drilled shaft foundations carry such high loads, it is common to perform high-resolution integrity testing on every shaft. Crosshole Sonic Logging (CSL) is a method commonly used to evaluate the integrity of a completed shaft. The test involves lowering probes to the bottoms of water-filled access steel or PVC tubes. Measurements are made of different properties of compression waves emitted from a source probe in one tube and detected by a receiver probe in another tube (at the same elevation). The probes are pulled back to the surface, and this procedure is repeated at various depths to obtain a profile of the entire depth of the shaft. Potential defects are indicated by delays in the signal arrival time and lower energies at a given test depth. Since access tubes are needed for this test, the design and arrangement of the reinforcement must take the total number and location of these tubes into account. Typically, CSL for drilled shafts is performed by a consultant through an agreement with the Department. If problems are revealed by CSL, the contractor may be required or choose to core the shaft to evaluate the severity of the defect. Revealed problem areas may be repaired using pressure-grouting techniques. Drilled shafts are typically designed with a minimum diameter of three feet, and have the following number of CSL tubes: Drilled Shaft Diameter (feet) Number of CSL Tubes

9.3

3 2

3.5 4 5 6 3 3 4 5

7 6

8 9 7 8

10 11 12 9 10 11

Load Tests

Geotechnical Engineers can use load tests during design phases of projects to develop a more cost-effective foundation, or during construction to verify design assumptions. Traditionally, load tests have only been required for complex or high capacity deep foundations. A few years ago at the Department when load tests were required, Geotechnical Engineers typically relied on static load tests. Currently, conducting static load tests for projects are not common. The primary reason static load tests are not used frequently is the high cost to conduct the test.

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The objectives of load tests are to verify that actual piles or shafts response to loading is in agreement with the anticipated response, and to ensure that the actual ultimate capacities are not less than the calculated ultimate capacities. Geotechnical Engineers should be involved in the load tests and the interpretation of test results. Designs should be modified as necessary based on the results of load tests. 9.3.1. Static Load Tests There are three types of commonly used static load tests: axial compression (refer to ASTM D 1143), axial tension (refer to ASTM D 3689), and lateral load (refer to ASTM D 3966). In each case, the test typically consists of a jack/load cell system to apply loads against a reaction frame and a dial gauge set up to measure displacements. The Department has a set of equipment for conducting low capacity axial compression tests, which includes a small jack (approximately 100 tons capacity), a pump, dial gauges and a generator. The contractor pr ov i dest her equi r edl oadf r amesy st em. TheGeot echni cal Engi neerr ev i ewst hec ont r ac t or ’ s proposed reaction system for approval. 9.3.2. Dynamic Load Tests High strain dynamic testing can be performed to confirm the foundation capacity, determine site-specific soil engineering properties, and to evaluate potential damage. Dynamic testing is performed using a PDA. Dynamic testing can be performed before construction as part of a test pile program or during construction to confirm design assumptions (refer to ASTM D 4945) .Dy nami cl oadt est i ngi susedonmostoft heDepar t ment ’ spr oj ect sandi s performed by specialty engineering Consultants under contract with the contractor or agreement with the Department. Geotechnical Engineers are involved in the planning and evaluation of test data. 9.3.3. Statnamic Load Tests Statnamic load tests are used to load high capacity foundations using relatively small reaction masses. Reaction piles needed for static load testing are not required for Statnamic testing. In a Statnamic test, solid fuel is burned in a pressure chamber located between the foundation element and reaction masses. As pressure builds in the pressure chamber, equal and opposite forces are exerted on the foundation and reaction masses. Loading increases to a maximum before unloading by controlled venting of exhaust gasses. Loads and deflections are measured by load cells and laser levels, respectively. A typical Statnamic test with a duration less than 1 second will yield 2,000 or more pairs of load versus deflection data. Statnamic tests are capable of applying axial or lateral loads up to 3,400 tons (see Figures 13-1). The load application is between a static load and a dynamic load. Computer software calculates damping and inertial effects to yield a static-equivalent load versus deflection plot. The software also calculates particle velocity and acceleration. All results are calculated and available immediately on site.

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Statnamic tests can be performed on single or group foundation elements on land and over water. Tests can be performed on drilled shafts, driven piles, and shallow foundations. 9.3.4. Osterberg Load Tests Osterberg load tests are often a cost-effective alternative to static load tests. The Osterberg Load Cell, also referred to as an O-cell, is most commonly used in conjunction with drilled shafts; however, they can also be used with driven piles. For drilled shafts, they can be placed anywhere within the shaft (see Figures 13-2). Multiple cells can be used to obtain strength information for an isolated strata of interest. For driven piles, the unit consists of a sacrificial jacking unit placed on the bottom of the pile. In all applications, the cell expands to apply equal loads to the portions of the foundation element above and below the cell. During an Osterberg load test, deflections of the top and bottom plate of the cell are measur edusi ng“ t el l t al es. ”Def l ec t ion at the top of the pile is measured using dial gauges. Load is determined by the pressure applied to a calibrated Osterberg cell. The maximum load achievable in Osterberg load tests is limited by one of three factors: the capacity of the foundation element below the cell, the capacity of the foundation element above the cell, or the capacity of the Osterberg cell. Currently there is no ASTM standard on this type of testing. See the FHWA manual on the Osterberg Cell for guidance on conducting the test and interpreting the data. 10.

RETAINING STRUCTURES

The Geotechnical Engineer is involved in project performance with structures, especially when the performance depends on sensitive design assumptions. 10.1 MSE Walls and Reinforced Soil Slopes Typically, retaining wall vendors perform the detailed internal design for MSE systems. Geotechnical Engineers review calculations and shop drawings submitted by wall vendors for external and internal stabilities as described in the policies and procedures memorandum No. CD28-2000-02. When requested, Geotechnical Engineers assist Inspectors to verify that engineering properties used by wall vendors match the actual field conditions, and that compaction techniques and efforts being employed are appropriate and adequate. MSE wall requirements are specified in Section 640 of the Standard Specifications for Road and Bridge Construction. Techniques for construction of Reinforced Soil Slopes (RSS) are similar to MSE walls. For a discussion on construction inspection, refer to the FHWAmanualon“ Ear t hRet ai ni ng Sy st ems, ”Geot echni calEngi neer i ngCi r cul arNo.7,I F-02-054, (2002). 10.2

Ground Anchors

Geotechnical Engineers review ground anchor calculations and shop drawings submitted by contractors. When the project is designed by a Consultant, the Geotechnical Engineer should be thoroughly familiar with the design to perform the review. Ground anchor 02/14/2005


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load tests are conducted by contractors and evaluated by Inspectors. Geotechnical Engineers may be requested to assist with these evaluations. This involvement would typically be reduced once contractors have established procedures that meet the design requirements and Inspectors become more experienced. Geotechnical Engineers work with Inspectors to maintain well-documented written records ofcont r act or s’oper at i onsandi nst al l at i ondet ai l s, especially in dealing with potential construction claims. Geotechnical Engineers should be familiar with construction methods and load testing procedures described in Sections 643 and 660, of the Department, Standard Specifications of Road and Bridge Construction, which are included as Pull Sheets at this time. There are three types of anchor tests. A proof test consists of loading an anchor in increasing increments to the maximum test load. The maximum test load is held for a limited duration to check for creep deformation. A performance test is similar to a proof test except the anchor is unloaded after each load increment until the maximum test load is obtained. An extended creep test consists of a performance test with a creep testing duration of 1 to 8 hours. The Geotechnical Engineer reviews all test results for approval. A detailed discussion of load testing for post-tensioned gr ound anchor si sav ai l abl ei nt he FHWA manualon “ Gr ound Anchor sand Anchored Sy st ems, ”Geot echni calEngi neer i ngCi r cul arNo,4,FHWA-IF-99-105, (1999). 10.3 Soil Nail Walls Geotechnical Engineers review calculations and shop drawings for approval, submitted by contractors. Soil nail construction specifications are covered in Sections 643 and 660 of the Department, Standard Specifications of Road and Bridge Construction, which is included as Pull Sheets at this time. Soil nail load tests are conducted by contractors and evaluated by Inspectors. Typically, the Geotechnical Engineer is involved in the early stage of soil nail installation and his/her involvement is reduced once the contractor has established a procedure that meets the design requirements and the Inspector is experienced enough to perform the inspection independently. Geotechnical Engineers should be familiar with construction methods and load testing procedures as well as the design intent of the soil nails. Soil nail testing typically consists of one or two verification tests performed prior to production work, and proof testing performed on 5% of the production nails. Proof and verification tests are loaded to 150% and 200% of the design nail load, respectively. Creep tests are performed as part of the verification or proof tests to determine the long-term load holding characteristics. A comprehensive discussion on soil nail construction is included in t heFHWA,“ Soi l Nai l i ngFi el dI nspect or ’ sManual , ”FHWASA-93-068,( 1993) ,and“ Soi lNai lWal lManual , ”Geot echni calEngi neer i ngCi r cul arNo.7, FHWA-SA-96-069. 11.

LANDSLIDE MITIGATION

Landslide mitigation projects are typically complex. Ref ert o TRB,“ Landsl i de I nv est i gat i onandMi t i gat i on”f orc ons t r uc t i ongui del i nes . Des i gnsar eal way sbas edonal i mi t ed number of subsurface explorations and numerous assumptions regarding subsurface 02/14/2005


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conditions between borings, and, therefore, geotechnical involvement is required through construction. It is important for the Geotechnical Engineer to regularly visit the site to observe subsurface soil and groundwater conditions. In order to maintain slope stability, a staged construction approach is often used to limit the amount of excavation that is allowed at any one time (to minimize the loss of ground support). Geotechnical Engineers must clearly communicate these requirements to Inspectors. The Geotechnical Engineer should review the design and any submitted shop drawings and construction methods/procedures before commencement of work; evaluating the relative levels of stability for various work phases of the project. In addition, once construction begins, the Geotechnical Engineer should anticipate differing site conditions that could require field adjustments. This situation is not uncommon, and therefore, a plan should be prepared in advance to address potential changed conditions scenarios in the event they occur. 12.

FIELD INSTRUMENTATION MONITORING

Field instrumentation could be used during and after construction to verify that actual field conditions are in agreement with the assumptions made for the design, or to monitor performance of the facility and/or changes in the field. Instrumentation can serve as an early warning of potential problems, and should be monitored according to the schedule developed by the Geotechnical Engineer. Immediate data reduction and evaluation is typically required. Problems identified by instrumentation often require immediate construction response and/or mitigation efforts. 13.

TROUBLESHOOTING

No matter how carefully projects are investigated and designed, the possibility exists for unforeseen problems to arise during construction or afterwards. Geotechnical Engineers should be prepared to investigate when such problems occur, and recommend design changes or changes in construction techniques to suit the conditions, while minimizing construction delays. If it is determined that the cause of a problem has a geotechnical basis, the Geotechnical Engineer should recommend remedial actions that will eliminate, or at least minimize, potential consequences. At times, a quick evaluation followed by emergency-level recommendations may be necessary to keep an emerging issue from becoming a major construction and safety problem. 14.

RECORDS / DOCUMENTATION

Valuable geotechnical information is gained from all construction projects. Therefore, it is important to document this information for future applications. This data is often helpful during the design of other projects under similar conditions, and often is valuable in defending the Department from construction claims. Problems similar to those encountered in construction of completed projects can possibly be avoided in the future when the Geotechnical Engineer has detailed records of the problems and events.

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Complete records of the geotechnical aspects of the construction and maintenance phases of a project should be kept. Any specialized construction procedures or design changes should be noted. Special Provisions should be modified and improved, based on experiences gained from past projects. Construction and maintenance problems and their solutions should be described in detail. It is valuable to document observations made during each site visit. Documentation should include written descriptions of problem soil and rock conditions, as well as photographs. All photographs should be date stamped and cataloged in a permanent record. Di gi t al phot ogr aphsneedt obekeptont heGeot echni cal Engi neer ’ sDeskTopcomput erwi t h backupcopi esont hedat aser v er ,onhar dcopi es,andonCD’ si nt hepr oj ectf i l e. If appropriate, the Geotechnical Engineer should take cross-section measurements of problem areas. Cross-sections in conjunction with station and offset limits help quantify problem areas. Measurements should always be tied to a relatively permanent benchmark, or reference point. A benchmark may consist of a survey stake that has known coordinates (identifiable on a site map) or an identifiable point on a nearby structure indicated on the plans. Additional information, such as elevations, may occasionally be obtained from benchmarks placed by other organizations (USGS, etc.) if the elevation is stamped on the benchmark. These measurements could be valuable when negotiating potential contractor claims. 15.

SPECIFICATIONS AND STANDARDS TEST Statnamic Load Test Osterberg Load Test Viscosity of Slurry pH of Slurry Standard Test Method for Piles Under Static Axial Compressive Load Standard Test Method for Individual Piles Under Static Axial Tensile Load Standard Test Method for Piles Under Lateral Loads Standard Test Method for Density of Bentonitic Slurries Standard Test Method for Sand Content by Volume of Bentonitic Slurries Standard Test Method for High-Strain Dynamic Testing of Piles Standard Practices for Preserving and Transporting Rock Core Samples Standard Test Method for Low Strain Integrity Testing of Piles

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ASTM D 1143

AASHTO -

D 3689

-

D 3966 D 4380 D 4381

-

D 4945

T 298

D 5079

-

D 5882

-



13-12

FIGURES

13-1: Statnamic Axial Load Test (1 of 2)

13-1: Statnamic Axial Load Test (2 OF 2)

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13-2: Osterberg Load Cells (1 of 4)


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13-15

REFERENCES

AASHTO,“ I nspect or s’Gui def orShot cr et eRepai rofBr i dges, ”TaskFor ce37Repor t ,1999 ADSC,“ Dr i l l edShaf tI nspect or ’ sManual , ”1989 ASCE,“ Damagef r om Bl astVi br at i ons, ”1974 FHWA, COM624P –“ Lat er al l yLoadedPi l eAnal y si sPr ogr am f ort heMi cr ocomput erVer si on 2. 0, ”FHWA-SA-91-048, 1991 FHWA,“ Desi gnandConst r uct i onofDr i v enPi l eFoundat i ons, ”FHWA-HI-97-014, 1997 FHWA,“ Desi gnandConst r uct i onofSt oneCol umns, ”FHWA-RD-83-026, 1983 FHWA, “ Dr i l l edShaf t : Cons t r uc t i onPr oc edur esandDes i gnMet hods , ”FHWA-IF-99-025, 1999 FHWA,“ Ear t hRet ai ni ngSy st ems, ”Geot echni cal Engi neer i ngCi r cul arNo.2,FHWA-SA-96038, 1997 FHWA, “ Ex t r apol at i onofPile Capacity from Non-Fai l edLoadTes t s , ”FHWA-RD-99-170, 1999 FHWA,“ Geosy nt het i cDesi gnandConst r uct i onGui del i nes, ”FHWA-HI-95-038, 1995 FHWA,“ Geot echni calI nst r ument at i on, ”FHWA-HI-98-034, 1998 FHWA,“ Gr oundAnchor sandAnchor edSy st ems, ”Geotechnical Engineering Circular No. 4, FHWA-IF-99-015, 1999 FHWA,“ Gr oundI mpr ov ementTec hni calSummar i es, ”Vols. 1 and 2, FHWA-SA-98-086R FHWA,“ Hi ghwayandSl opeMai nt enanceandSl i deRest or at i onWor kshopManual , ”FHWART-88-042, 1988 FHWA,“ Manualf orDesi gnandConst r uct i onMoni t or i ngofSoi lNai lWal l s, ”FHWA-SA-96069, 1998 FHWA,“ Manual onDesi gnandConst r uct i onofDr i v enPi l eFoundat i ons, ”FHWA-HI- 97-013 and 14, 1996 FHWA,“ Mechani cal l ySt abi l i z ed Ear t h Wal l sand Rei nf or ced Soi lSl opes–Design and Construct i on, ”FHWA-SA-96-071, 1996 FHWA,“ Mi cr opi l eDesi gnandConst r uct i onGui del i nes, ”FHWA-SA-97-070, 2000 FHWA,“ Per manentGr oundAnchor s, ”FHWA-DP-68-1R, 1988 FHWA,“ RockBl ast i ngandOv er br eakCont r ol , ”FHWA-HI-92-001, 1991 FHWA,“ Rockf al lHaz ar dMi t i gat i on Methods –Par t i ci pant ’ sWor kbook, ”SA-93-085, NHI Course #13219, 1994 FHWA,“ Rockf al lHaz ar dRat i ngSy st em,Par t i ci pant ’ sManual , ”FHWA-SA-93-057, 1993 FHWA,“ Shal l owFoundat i ons, ”Geot echni calEngi neer i ngCi r cul arNo.6,FHWA-IF-02-054, 2002 FHWA,“ Soi l Nai l Wal l Manual , ”Geot echni cal Engi neer i ngCi r cul arNo.7,FHWA-SA-96-069 FHWA,“ Soi lNai lWal l sGeot echni calEngi neer i ngCi r cul arNo.7, ”I F-02-054, 2002 FHWA,“ Soi lNai l i ngFi el dI nspect or ’ sManual , ”FHWA-SA-93-068, 1993. FHWA,“ Soi l sand Foundat i onsWor kshop Ref er ence Manual , ”FHWA-NHI-00-045, NHI Course #132012, 2000 FHWA,“ St at i cTest i ngofDeepFoundat i ons, ”FHWA-SA-91-042, 1991 FHWA,“ TheOst er ber gCel l f orLoadTest i ngDr i l l edShaf t sandDr i v enPi l es, ”FHWA-SA-94035, 1995 02/14/2005


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FHWA,“ ThePer f or manceof Pile Driving Systems –I nspect or ’ sManual , ”FHWA-RD-86-160, 1986 FHWA, “ TheTex asQui ck-Load Method for Foundation Load Testing - Us er sManual , ”FHWAIP-77-8, 1976 Gobl e, G. G. andRausche, Fr ank, GRLWEAP, “ Wav eEquat i onAnal y s i sof Pi l eFoundat i ons , ” GRL & Associates, Inc., 1991 Keene,“ SandDr ai nConst r uct i onI nspect i onManual , ”FHWAHi ghwayFocus,Vol ume10, Number 3, 1978 NDOT,“ St andar dSpeci f i cat i onsf orRoadandBr i dgeConst r uct i on, ”Sect i on640 NDOT,“ St andar dSpeci f i cat i onsf orRoadandBr i dgeConst r uct i on, ”Sect i on643 NDOT,“ St andar dSpeci f i cat i onsf orRoadandBr i dgeConst r uct i on, ”Sect i on660 OSHA,“ CodeofFeder alRegul at i ons, ”Sect i on29,OSHASt andar ds Pi l eDy nami cs,I nc. ,“ Pi l eDr i v i ngAnal y z erManual , ”PAK,Cl ev el and,Ohi o,1997 TRB, Dunni cl i f f ,John,“ Geot echni calI nst r ument at i on f orMoni t or i ngFi el d Per f or mance, ” NCHRP Synthesis 89, 1993 TRB,“ Gui det oEar t hwor kConst r uct i on:St at eoft heAr tRepor t , ”TRBRepor tNo.8,I SBN0309-04957-1, 1990. TRB,“ Landsl i des:I nv est i gat i onandMi t i gat i on,Speci alRepor t247, ”I SBN 0-309-06151-2, 1996

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CHAPTER 14 MAINTENANCE PHASE

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14-i

TABLE OF CONTENTS 1. 2. 3. 4. 5. 6. 7. 8.

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PURPOSE ......................................................................................................... 1 INTRODUCTION ............................................................................................... 1 RESPONDING TO MAINTENANCE REQUESTS AND EMERGENCIES ......... 1 RESEARCHING HISTORIC DATA.................................................................... 2 MONITORING GEOTECHNICAL PERFORMANCE ......................................... 3 ROCKFALL HAZARD RATINGS OF HIGHWAY SLOPES................................ 3 MITIGATION OF SLOPE FAILURES AND LANDSLIDES................................. 4 REFERENCES .................................................................................................. 5


MAINTENANCE PHASE

1.

14-1

PURPOSE

Maintenance staff may contact Geotechnical Engineers regarding specific problems and when in need of immediate assistance. Monitoring of problem conditions may include field evaluations, documentation, and instrumentation. Recommendations should be provided when problem conditions are significant or when Maintenance staff has plans to make repairs. 2.

INTRODUCTION

Typically, potential maintenance problems include roadway settlement/distortion, swelling ground, slope erosion, slope failures, rock slope degradation, rockfall hazards, and groundwater seepage. In addition, damage could occur to constructed items such as subdrains, horizontal drains, ground anchors, and wall systems. Earthquakes, heavy precipitation, fires and floods are causes of hazards and damage to facilities. Man-made hazards include vehicular damage to walls and foundations and geotechnical instrumentation. Some existing constructed items may need occasional maintenance, such as flushing and surging horizontal drains and unplugging subdrain discharge pipes. When requested, Geotechnical Engineers should visit the site to observe and document the occurring problems. By evaluating the problem areas, Geotechnical Engineers may decide to monitor the problems, recommend interim mitigation measures (within available Maintenance budget), or recommend a standard stabilization method (which could require new project funding and placement on the State Transportation Improvement Plan). The involved District Engineer evaluates the options. 3.

RESPONDING TO MAINTENANCE REQUESTS AND EMERGENCIES

Generally, it is more cost effective to respond to maintenance requests than to emergencies. Working with Maintenance staff to investigate problem areas before they become emergencies assists to identify the cause of the problem and plan for an appropriate repair. Geologic conditions can result in hazardous conditions at or near roadways. However, impending geologic hazards could be difficult to identify by Maintenance staff. Geotechnical Engineers should evaluate the geologic conditions and potential hazards and provide recommendations regarding the relative risks that road users may face, as well as Maintenance staff that may be working in close proximity. In performing the site evaluation, Geotechnical Engineers are cautioned to follow safety practices for their own protection as well as others involved. (Refer to Department guidelines and OSHA.) In geotechnical site problems, typically Geotechnical Engineers are requested to assess potential hazards and risks. In situations that could imperil the public, warnings may need to be provided and local road users and property owners notified. In extremely 02/14/2005


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hazardous situations, road closure may be required. In responding to such public safety issues, consult with the Principal Geotechnical Engineer, and the area Maintenance Foreman or Supervisor. Depending on the maintenance cost of a problem and the availability of funds, Geotechnical Engineers may be asked to recommend interim solutions or“ band-ai d” mitigations rather than more permanent solutions. When responding to maintenance emergencies, a rapid response is often necessary to ensure public safety and maintain the integrity of the roadway. As maintenance repairs proceed, on site inspection and assistance should be provided to identify differing conditions and make field adjustments as required. Innovative and experimental mitigations may be appropriate, especially if they fit within budget constraints. Removal of slide debris from a roadway or ditch is often done to restore road service, but could cause additional slope distress and failures. Short-term options to a variety of maintenance problems could include surface water control/diversion, draining of trapped water, slope modifications (flatter slopes or benched slopes), rock inlays, berms, horizontal drains, dewatering wells, fabric walls and gabion walls (MSE), soldier pile and sheetpile walls, pin piles, pavement patching, bio-remediation (seeding, willow wattles, etc.), interim buttresses, injection or jet-grouting, scaling, preliminary rock bolts/bars and beams to pin rock that is on the verge of toppling, and unloading a slope to slow slide movements until a permanent solution is constructed. Sometimes these solutions are implemented without complete engineering analyses in order to provide a rapid response; however, Geotechnical Engineers must explain the uncertainties and risks to the decision-makers and follow through with thorough analyses to determine whether the implemented measures are adequate and whether additional or different measures would need to be included. Sometimes the interim solutions are implemented to address immediate concerns, and are followed later by permanent solutions if greater funding becomes available and Plans can be prepared. Frequently, interim repairs are relied upon much longer than initially intended. Therefore, before recommending an interim or experimental solution, Geotechnical Engineers should consider the drawbacks related to the measure becoming permanent. Geotechnical Engineers should document and keep records of events regarding maintenance issues. With adequate risk/consequence evaluations, the Maintenance Division will be in a position to consider the relative advantages of each option when making decisions on how to proceed. In order to secure funding, for a maintenance project, typically, justification for need of mitigation is required. Larger projects typically need to be submitted for construction consideration. 4.

RESEARCHING HISTORIC DATA

Although timeliness is important, Geotechnical Engineers should use available resources as time permits to identify the true cause of problems. Geotechnical Engineers should ask Maintenance staff for their experience in the area, consult geology publications, 02/14/2005


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and examine air photos (stereo pairs), research Department files for historic data, hazards, and prior projects. Geotechnical Engineers should review any available relevant Geotechnical Reports, instrumentation memorandums/data, and any notes to see if any unknown or unanticipated conditions were encountered or any unusual methods were used in construction of the facility. Information sources and suggestions are described in the referenced manuals for various types of hazards. When responding to a rockfall hazard, Geotechnical Engineers should ask Maintenance staff how often rockfall events occur, where it comes to rest, how much material is typical for a single event, and whether it is comprised of individual blocks or a volume of numerous pieces. Occasionally Geotechnical Engineers are involved in evaluating existing structure foundations for new loading conditions. These typically occur as part of a seismic or scour vulnerability assessment. An important part of the assessment is the type, depth, and condition of the structure foundation. The sources for this information may be as-built drawings, construction records, and Plans for the structure. 5.

MONITORING GEOTECHNICAL PERFORMANCE

By regularly monitoring problem areas, Geotechnical Engineers can often reduce the uncertainties involved in the design of mitigation measures and permanent stabilizations. Instrumentation could be as complicated as extensometers and slope inclinometers or as simple as survey points. Regardless of the complexity of the monitoring program, Geotechnical Engineers should place and secure instruments as needed to survive for the duration of the intended monitoring period. For example, placing PK nails in pavement as survey points would not be a good choice where snow is plowed or pavement repairs may occur during the monitoring period. Existing structures that are potentially sensitive to vibrations or movement should be monitored. It may also be desirable to monitor groundwater level changes, settlement, heave, and/or lateral displacement of the roadway and structures. 6.

ROCKFALL HAZARD RATINGS OF HIGHWAY SLOPES

Rockfall potential is inherent along roadways in mountainous terrain. Rockfall originates from both natural and man-made slopes because of geologic processes. The Rockfall Hazard Rating System (RHRS) is a rock slope management tool for quantifying the potential hazard a rock slope poses to users. The Department has implemented the RHRS. The RHRS database is valuable to the Department because, when fully implemented and maintained, it contains historical slope performance and quantifies the rockfall potential to provide a rational basis for determining project priorities. 

The six steps in the RHRS process are summarized below: Slope Inventory (creating a geographic database of rockfall locations)

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14-4

Preliminary Rating (grouping the rockfall sites into three more manageably sized categories: A, B, and C) Detailed Rating (numerically prioritizing the identified rockfall sites from the least to the most hazardous) Preliminary Design and Cost Estimate (adding remediation information to the rockfall database) Project Identification and Development (advancing rockfall correction projects to construction) Annual Review and Update (maintaining the rockfall database)

Det ai l soft heRHRS andt hepr ocedur esi nv ol v edar edescr i bedi nt he“ FHWA Rockf al lHaz ar dRat i ngSy st em Par t i ci pant ’ sManual ” ,FHWA-SA-93-057, 1993. 7.

MITIGATION OF SLOPE FAILURES AND LANDSLIDES

Mitigation of slope failures and landslides that are not part of design and construction contracts are often managed differently due to smaller funding sources and emergency response timeframe. Feasible solutions might not be able to fully stabilize the problem, but can be planned to reduce risk and maintenance. A source of guidance for maintenancelevel slides is FHWA publication “ Highway and Slope Maintenance and Slide Restoration Wor kshopManual , ”FHWART-88-042, 1988.

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REFERENCES

AASHTO, “ I nspect or s’ Gui def orShot cr et eRepai rofBr i dges, ”TaskFor ce37Repor t , 1999. FHWA,“ Ear t hRet ai ni ngSy st ems, ”Geot echni cal Ci r cul arNo.2,FHWA-SA-96-038, 1997. FHWA,“ Geosy nt het i cDesi gnandConst r uct i onGui del i nes, ”FHWA-HI-95-038, 1995. FHWA,“ Geot echni calI nst r ument at i on, ”FHWA-HI-98-034, 1998. FHWA,“ Gr oundAnchor sandAnchor edSy st ems, ”Geot echni cal Ci r cul arNo.4,FHWA-IF99-015, 1999. FHWA, “ Hi ghwayandSl opeMai nt enanc eandSl i deRes t or at i onWor k s hopManual , ”FHWART-88-042, 1988. FHWA,“ Mechani cal l ySt abi l i z edEar t hWal l sandRei nf or cedSoi lSl opes–Design and Const r uct i on, ”FHWA-SA-96-071, 1996. FHWA,“ Rockf al l Haz ar dMi t i gat i onMet hods–Par t i ci pant ’ sNot ebook, ”FHWA-SA-93-085, 1993. FHWA,“ Rockf al lHaz ar dRat i ngSy st em,Par t i ci pant ’ sManual , ”FHWA-SA-93-057, 1993. FHWA,“ Soi l sandFoundat i onsWor kshopRef er enceManual , ”NHICour seNo.132012, FHWA NHI-00-045, August 2000 OSHA, “ CodeofFeder alRegul at i ons, ”Sect i on29,OSHASt andar ds. TRB, Dunnicliff, John,“ Geot echni calI nst r ument at i onf orMoni t or i ngFi el dPer f or mance, ” NCHRP Synthesis 89, Transportation Research Board, 1993. TRB,“ Landsl i des:I nv est i gat i onandMi t i gat i on, ”Speci al Repor t247,I SBN0-309-06151-2, 1996.

02/14/2005


GLOSSARY

G-1

ACCELEROMETERS –An electronic measuring device that is attached to a structural member to measure and record accelerations, typically used with Pile Driving Analyzer to measure the stress wave induced by pile driving equipment. ALLUVIUM –Unconsolidated and poorly sorted sediments deposited by a river or stream. The deposited sediments typically range from silt to gravel-size but can include boulders. The size of the material deposited is dependent on the speed at which the water is flowing. The more rapidly the water is flowing the larger the material transported. ASSIGNED SHIFT–The hours and times the employee is regularly scheduled to work. AUGER –A screw-like boring tool used to explore relatively unconsolidated near-surface materials. BECKER PENETRATION TEST (BPT) – A test used to investigate coarse-grained materials (gravel, cobbles) using an instrumented steel pipe pile. BEDDING –Distinct layers of sediment or rock that may differ in a variety of ways from adjacent layers. Bedding typically applies to sedimentary and pyroclastic rocks. BORROS ANCHOR–A three-pronged mechanical anchor lowered into a borehole used to secure the base of a settlement or heave monitoring instrument in soft soils. BORROW –Material that is excavated on the project site or supplied by a Contractor for earthwork or other construction applications. CDL –Commer ci alDr i v er ’ sLi cense CABLE LASHING –The use of anchored and tensioned cables to provide support for an isolated potentially unstable rock. CALIFORNIA BEARING RATIO (CBR) –A simple penetration test developed to evaluate the strength of road subgrades. In this test a plunger of standard area penetrates a soil sample. The force required to cause the penetration is plotted against measured penetration to determine the CBR value. CANTILEVERED WALL –The most common type of conventional reinforced concrete wall, where the wall stem is attached to a spread footing (or pile cap). CEMENTATION –Bonding of grains by secondary minerals (e.g., calcite or iron oxide) or degradation products (e.g., clay). Typically causes an increase in dry strength. COLLUVIUM–Soil transported and deposited downslope by gravity, typically by landslides, soil slumps, debris flows, downhill creep, etc. The material is generally poorly sorted and tends to form hummocky terrain. COLORADO ROCKFALL SIMULATION PROGRAM (CRSP) –A computer program used to simulate rockfall events and provide information on rockfall trajectories and energies. CONE PENETROMETER TEST (CPT) –An in situ test that produces a plot of resistance with depth used to interpret the profile of subsurface materials.

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NDOT Geotechnical Policies and Procedures

GLOSSARY

G-2

CONSULTANT –A firm, or professional, that has an expertise in specific disciplines that can contract with the Department to perform services on behalf of the State. CONTROLLED BLASTING –The use of closely spaced and lightly loaded blast holes to produce a relatively undamaged, stable cut slope. CORE RECOVERY –An index of rock quality calculated by the ratio of the length of core recovered (rock/soil extracted in the core barrel) to the total core run length reported as a percentage. Core recovery depends on drilling technique and speed, and equipment quality, as well as rock characteristics and condition. COUNTERBERM –A fill embankment placed at the toe of a marginally stable slope to improve overall stability. CONSOLIDATED-UNDRAINED (CU) TEST –A flexible triaxial shear strength test used to determine total or effective stress strength parameters. The specimen is consolidated before shearing and is not allowed to drain during the test. CREEP TESTS (SOIL NAILS AND ANCHORS) –Determines the long-term performance characteristics of either soil nails or ground anchors, usually requires 1-8 hours to perform. CROSSHOLE SONIC LOGGING –Method used to determine the integrity of drilled shafts and slurry walls by use of down-hole measurements. DEGREE OF INDURATION –A qualitative measurement of the hardening of a rock or rock material by heat, pressure, or the introduction of cementing material, esp. the process by which relatively consolidated rock is made harder or more compact. It can also indicate the formation of hardpan by chemical action on a soil horizon. DEGREE OF WEATHERING – A measurement of rock weathering based on an established scale (see Table 9-18) used as a descriptor of rock and an indicator of rock quality and strength. Weathering is the destructive process by which earthy and rocky materials are changed in color, texture, composition, firmness or form by exposure to atmospheric agent sneart heEar t h’ ss ur f ace.I tcanl eadt ot hecompl et edi si nt egr at i onand chemical decomposition of rock. DEWATERING –The art of drawing down groundwater levels to enable construction and improve slope stability. DILATANCY –A qualitative descriptor of the movement of water in soil voids caused by shearing or shaking; used as a soil characteristic in visual classification. DISPERSION –The characteristic occurrence and amount of settlement or suspension of a soil in water that can be used for visual classification. For example, clay remain suspended in the water longer than silt or sand, which tends to settle faster leaving the water less opaque or clear. DRILLED SHAFTS –Deep reinforced concrete foundations constructed in a drilled hole to a desired bearing level. The shaft borings are typically cased.

02/14/2005


GLOSSARY

G-3

DRY STRENGTH –A soil characteristic quantified by the pressure required to crush a dried lump of soil. This characteristic may be used as part of a visual soil description. DUTY STATION –Theempl oy ee’ sassi gnedwor kl ocat i on. DYNAMIC COMPACTION –A method of ground improvement that densifies subsurface soils by dropping a heavy mass on the ground surface in a grid pattern. DYNAMIC DRIVING ANALYSIS (WEAP) –Pile analysis performed before pile driving to determine a suitable pile type, such as steel or concrete, and to evaluate the proposed driving system. DYNAMIC PILE TEST –Test performed while driving piles to evaluate the performance of the pile driving system, calculate pile installation stresses, determine pile integrity, and estimate static pile capacity. EA –Engineering Authorization EEO –Equal Employment Opportunity EMBANKMENT EARTH PRESSURE CELLS –Devices installed within embankments to determine the magnitude and direction of total stress. ENTRY PERMITS –Formal permission documents to access private property. EXTENSOMETER – Small diameter steel rods used to measure relative displacements/deformations within a soil or rock mass. A typical extensometer consists of a reference head at the collar of a drill hole, and one or more in-hole steel rods attached to anchors at known depths within the ground. EXTRUDED POLYSTYRENE (EPS) –A very low density (2 lbs/cu. ft.) material, used in lightweight fill applications. FACTOR OF SAFETY (FS) –The ratio of resisting to driving forces used to quantify the margin of stability for various design applications, such as foundations, slope stability, retaining walls, etc. FAULTS –A break in the continuity of materials, where displacement has occurred. The presence of gouge (pulverized rock), bedding offset, and/or slickensided surfaces (commonly with mineral or clay coating) may be indicators of fault movement. FILL –Soil or rock that has been added or placed at a location by human activity. FMLA –Family Medical Leave Act FOLIATION – A descriptive term common to metamorphic rocks for the structural or textural appearance of the rock due to flattening or aligning of the constituent minerals. GEOTECHNICAL PROJECT FILE –File containing the complete Geotechnical history of a project SPECIFIC GRAVITY OF SOILS (GS) –Ther at i oofamat er i al ’ sdensi t yt ot hedensi t yof water.

02/14/2005


GLOSSARY

G-4

GRAVITY WALL –A wall that relies on mass for stability such as a bin, crib, or mass concrete wall. GROUND ACCELERATION – A material property used for seismic analysis that is dependent on the earthquake recurrence interval and site conditions. GROUND ANCHORS – Retaining wall support system consisting of anchors (steel tendons, rods, etc.) placed in holes that penetrate competent geologic strata. The anchors are grouted in place and then tensioned to the prescribed design load. HORIZONTAL DRAINS –Drilled holes used to reduce groundwater pressures in soil or rock slopes, or landslides. HYDRAULIC FRACTURING TEST (HF) –A test used to directly measure the in situ lateral stress state (Ko) in rock formations. IGNEOUS ROCKS –Intrusive or extrusive rocks formed from cooled and solidified magma or lava. Common igneous rock types include: granite, basalt, diorite, andesite, rhyolite, and gabbro. INCLINOMETER –Instruments used to monitor lateral movements below ground. This instrument consists of four elements: 1) casing with internal guide grooves, 2) sensor (a probe with wheels that fit the grooves in the casing), 3) control cable (signal wire and depth measurement), and 4) a readout device (indicator). The change in casing profile over time is used to determine the depth and rate of movement at the failure surface in a landslide. INFILLING –The material separating the adjacent sides of a discontinuity in rock. INTERCEPTOR DRAINS –Ditches or trench drains installed to collect surface water/runoff, shallow groundwater, and/or springs in order to reduce infiltration into cut slopes or other marginally stable areas. IOWA STEPPED BLADE TEST (ISB) –A direct measure of the in situ lateral stress state (Ko) in soils. JACK/LOAD CELL SYSTEM – Static pile load testing equipment used to apply compressive load to the pile and measure movements. JET GROUTING –Method of ground stabilization that injects cement and water and mixes t hem wi t hi nsi t us oi lt ocr eat eanet wor kofst r engt hened“ s oi l -cementcol umns. ” JOINT ROUGHNESS COEFFICIENT (JRC) – The surface shape along a rock discontinuity. The JRC can be visually approximated by comparing joint surfaces with reference charts. JOINT –A rock discontinuity where no displacement has occurred, often caused by tensile stresses associated with rock cooling, removal of adjacent rock, or tectonic movements. A repetitive pattern of more or less parallel joints is called a joint set. KINEMATIC ANALYSIS – Evaluation of the capability of a rock block bounded by discontinuities and a slope face to fail out of the slope without reference to forces involved.

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GLOSSARY

G-5

LARGE PENETRATION TEST (LPT) –A modification of the Standard Penetration Test, which uses a larger diameter sampler for use in gravelly soils. LIQUID LIMIT (LL) –The moisture content of a soil at the boundary between the liquid and plastic states. Used in the classification of soils and the determination of the plasticity index. LIQUEFACTION –A problem condition that develops when pore water pressures are suddenly increased to the extent that the effective shear strength approaches 0 and the soil turns fluid. LOAD AND RESISTANCE FACTOR DESIGN (LRFD) –A design approach for structures in which failure and serviceability conditions can be evaluated, considering the uncertainties associated with loads and material resistances. LOAD CELL – A transducer that converts force into a measurable electrical output. Although there are many varieties of load cells, strain gage based load cells are the most commonly used type. MECHANICALLY STABILIZED EARTH WALL (MSE WALL) –Gravity fill wall reinforced with horizontal steel strips, geogrids, wire mesh, geosynthetic fabric or other material. Many patented systems and a variety of facing options are available. METAMORPHIC ROCK –A rock formed from igneous, sedimentary or other metamorphic rocks by intense heat and pressure. Common metamorphic rock types include: slate, schist, gneiss, quartzite, and marble. MODULAR GRAVITY WALLS –Interlocking concrete, steel, or wood modules such as gabions, bin walls, crib walls, concrete blocks, etc. MSDS –Material Safety Data Sheets NDOT –Nevada Department of Transportation NON DESTRUCTIVE TECHNIQUES (NDT) –Measurement of in-place pile properties or drilled shaft condition without damaging the member. NDT methods include geophysical surveys, transient shock excitation, ground penetrating radar and cross-hole sonic logging. NRS –Nevada Revised Statute OBSERVATION WELL –A casing (commonly PVC) installed in borehole, which is slotted or perforated in the depth range desired for groundwater measurement. Ideally, the water level in the casing represents the average head of water acting on the perforated zone. OBSERVATIONAL METHOD –The use of geotechnical observations and instrumentation during construction to adjust designs to fit field conditions.

02/14/2005


GLOSSARY

G-6

ON-CALL AGREEMENT – A general agreement between the Department and a Consultant that is executed periodically, normally every two years, for a specific discipline of work. It does not contain any details about particular project work assignments, but does include all necessary terms and conditions to bind the parties into a contractual relationship. The agreement can be utilized by issuing a Task Order when the service of a Consultant is needed. ON-CALL CONSULTANT –A Consultant under contract to NDOT that can be issued Task Orders to provide specific work. OPEN WORK GRAVEL –A processed, poorly-graded, coarse gravel used for drainage applications. OSHA –Occupational Health and Safety Act. OSTERBERG LOAD TEST –Jacking unit attached to the bottom of a pile or placed at the base of a drilled shaft that applies pressure to measure foundation resistance. PEAK GROUND ANCHOR –Method to develop forces necessary to stabilize structures and landslides. Anchors can include helix, bar or strand types. PERS –Publ i cEmpl oy ee’ sRet i r ementSy st em. PIEZOCONE PENETROMETER TEST (PQS) –The use of a Cone Penetrometer with a piezometer at the tip to measure pore pressures generated during the test and to determine the rate of pore pressure dissipation during consolidation. PIEZOMETER –Instrument used to measure groundwater pressure (pore pressure) at the elevation of the sensor. PILE DRIVING ANALYZER (PDA) –System used to perform computations to analyze the response of a pile to driving equipment, driving stresses, pile integrity and the pile capacity. PILE INTEGRITY TESTER (PIT) – An NDT test that uses a hammer and recording instrument to measure signal response of the pile to a low energy source (hammer). PILE LOAD TEST –Tests in which either a tensile or compressive load is applied to determine load/deflection relationships and to evaluate pile capacity. PILES –Deep foundations that are either drilled or driven into place. Many types of displacement and non-displacement piles exist, typically made of steel or concrete. PLASTICITY INDEX (PI) –A quantitative or qualitative property of a soil that describes its response to changes in moisture content to create a soft and pliable consistency. Used for identification and classification of soil. PLASTIC LIMIT (PL) –The moisture content at the boundary between the plastic and semi-solid states. Used in the classification of soils and the determination of the plasticity index.

02/14/2005


GLOSSARY

G-7

POOR MAN’ SI NCLI NOMETER –A means of determining the approximate depth to the slide failure surface by lowering a length of steel rod on a cable into a simple small diameter plastic pipe (similar to an observation well). Distortion and bending of the pipe caused by ground movements prevents the steel rod from passing. PRECOMPRESSION –A ground improvement method used to compress the foundation soil before constructing sensitive structures and pavements on soft ground. Precompression in fine-grained soils can be accelerated by using vertical drainage systems, such as sand or wick drains. PRELOADING –See Surcharging. PRESSUREMETER (PMT) –An in situ test used to measure the stress/strain properties of soils by inflating a probe lowered into a borehole. The PMT provides a much more direct measurements of soil compressibility and lateral stresses than other test methods such as SPT or CPT. PROOF TESTS (SOIL NAILS AND ANCHORS) – Test of soil nail or ground anchor capacity by incrementally loading to 125% - 150% of the design load. PUSHED-IN SPADE CELLS –A device used to directly measure the in situ lateral stress state (Ko) in soils. QTEST (UNCONSOLIDATED-UNDRAINED, UU) – Triaxial shear strength test used primarily in the calculation of immediate embankment stability during short-term (quick-loading) conditions. During the test, the specimen is not permitted to change its initial water content before or during shear. The results are total stress strength parameters. RTEST (CONSOLIDATED-UNDRAINED, CU) –A flexible triaxial shear strength test used to determine either total or effective stress strength parameters. In this test, the specimen is allowed to consolidate before shearing, but during shear the sample is not allowed to drain, maintaining the consolidated water content. R-VALUE –A test used to determine subgrade strength and the ability of the soil to resist lateral deformations when a vertical load is acted upon it. REINFORCED SOIL SLOPES (RSS) – Embankments constructed with metal or geosynthetic reinforcements to allow construction of steeper side slopes or to improve slope stability. RELICT ROCK STRUCTURE – Describes decomposed rock or residual soil that still reveals the original texture of the crystals of the parent rock. RESILIENT MODULUS (MR) –A test used to measure stress-deformation relationships of subgrade materials. RIGHT OF ENTRY –Permission to enter privately owned property.

02/14/2005


GLOSSARY

G-8

ROCK BOLTS –Tensioned steel bars installed in drilled holes to support isolated rock blocks on a slope. Anchorage can be achieved by either mechanical or grouting methods. ROCK BUTTRESS –The placement of a rock fill at the toe of a soil or rock slope to improve stability. It is a measure commonly used to mitigate an existing landslide. ROCK DOWELS –Untensioned steel bars used to add support to isolated rock blocks on a slope. The term also refers to short steel shear pins grouted into drilled holes at the leading edge of a rock slab to prevent sliding. ROCKFALL HAZARD RATING SYSTEM (RHRS) –A technique for managing rock slopes and quantifying the rockfall hazard adjacent to highways. The system provides a proactive, rational way to prioritize spending of construction funds to mitigate rockfall hazards. ROCK INLAY –Slope protection blanket, usually 2 to 10 feet thick, placed against an overexcavated portion of a slope to replace weak surface soil. ROCK QUALITY DESIGNATION (RQD) –An index of rock fracturing based on the number and frequency of fractures in core samples recovered while drilling. The RQD is used for rock classification and characterization. ROCK SLOPE FALLOUT/CATCHMENT AREA –An area located at the base of a rock slope designed to capture and restrict rockfalls from reaching the roadway or other facility. ROTARY DRILLING –The chief method of drilling deep wells. A drill bit grinds a hole in the rock. Lubrication and cooling are provided by continuously circulating water or drilling mud, which brings the well cuttings to the surface. SAND DRAINS –A method to accelerate settlement by increasing the rate of drainage in fine-grained, compressible strata by shortening the drainage path to a much more permeable, small diameter column of sand. SCALING – Removal of loose rock from slopes using either manual or mechanical methods. SCOUR –Erosion of river or stream bed or bank sediments that could undermine nearby foundations. A significant concern for bridge applications. SEDIMENTARY ROCKS –Rock formed by cementation or by pressure from overlying sediments. Common sedimentary rock types include: conglomerate, breccia, sandstone, siltstone, claystone, shale, limestone, chalk, and dolomite. SEISMIC REFRACTION – A noninvasive subsurface exploration technique used to interpret the layering of subsurface materials, which relies on the travel times of the seismic waves as they pass through materials of increasing seismic velocity with depth. SENSITIVITY –Sensitivity refers to the significant loss of strength when a fine-grained soil is remolded.

02/14/2005


GLOSSARY

G-9

SERVICE LOAD DESIGN (SLD) – Foundation design that uses factor of safety met hodol ogy appl i ed t o ul t i mat e bear i ng capaci t i es t o det er mi ne “ al l owabl e bear i ng pr essur es . ”Al sor ef er r edt oast heAl l owabl eSt r essDesi gnmet hod( ASD) . SETTLEMENT PLATE – A simple platform and riser pipe that is placed within the embankment. The top of the pipe is surveyed at various times during embankment construction to determine the magnitude and time-rate of settlement. SHAFT INSPECTION DEVICE (SID) –Sampling method (with camera) used to inspect the bottom and side-walls of drilled shafts to evaluate the base and sidewall condition. SHEAR KEY – A mitigation method for improving the shear resistance in landslides, retaining walls and embankments. SHEAR PLANE INDICATOR –A shear plane indicator consists of a plastic pipe installed in abor ehol e,si mi l art oanobs er v at i onwel l .Al soSee“ PoorMan’ s”I nc l i nomet er . SHEET PILE WALL –A wall formed with a continuous and interlocked line of steel sheet piles that behave in a cantilevered manner. Tie-back anchors are sometimes added if the wall height creates high structural moments in the sheets. SHELBY TUBE –A thin-walled, push-tube sampler used to obtain undisturbed samples of cohesive soils. SHOTCRETE –The high-pressure application of concrete onto a soil or rock surface to prevent erosion, sloughing, and raveling. SHRINK/SWELL –The change (percent decrease or increase) in volume that occurs when excavated earth materials are placed in a compacted or uncompacted embankment. Rock materials tend to swell; soil materials tend to shrink. SHRINKAGE LIMIT (SL) –A test performed on clay soils suspected of having swell potential . The t estdet er mi nest he l i mi t sofa soi l ’ st endencyt ol ose vol ume dur i ng decreases in moisture content. SLICKENSIDES –A discontinuity between adjacent rock blocks that appears polished or glossy, sometimes with linear markings showing evidence of the orientation of past movement. Not all slickensides are caused by faulting. Slickensides can be caused by deformation (i.e., folds, flows) or landsliding. SLOPE MESH –Steel mesh (gabion or chain link) anchored at the crest of a slope that drapes down the face of the slope to control the descent of rockfall. SOIL NAIL WALL – Soil cut slope retaining system consisting of steel bars/tendons installed in drilled holes and grouted in-place. Earth pressure near the face is transferred to soil nails by a reinforced shotcrete facing. The final wall facing may consist of shotcrete or concrete panels (precast or cast-in-place). SPACING – The distance between individual joints or beds. Care must be taken to distinguish between joints and mechanical breaks that are caused by handling or drilling.

02/14/2005


GLOSSARY

G-10

SPLIT-SPOON SAMPLER –A thick-walled, divided tube sampler used to obtain disturbed soil samples and penetration rates during the Standard Penetration Test (SPT). STANDARD PENETRATION TEST (SPT) –A standardized soil sampling procedure in which a 140-pound hammer is dropped 30 inches to drive a two-inch split-spoon sampler 18 inches. The number of blows (blow count) required to drive the sampler through the last 12 inches is correlated with the soil conditions. STATNAMIC LOAD TEST –A test that uses pressure created by burned fuel to apply either horizontal or vertical load to a pile or drilled shaft. STONE COLUMNS – A ground improvement method that displaces and densifies subsurface soil through vibration and replacement of displaced soil with free-draining crushed stone. Installation increases overall shear strength and accelerates consolidation. STRAIN GAUGES – Electronic measuring device attached to a structural element to measure small compressive or tensile deformations over a set distance. Results are used to calculate percent strain. STRATIFICATION – The layering of rock units evidenced by changes in texture, composition, age, fossil content or unique forms. STRUCTURAL DISCONTINUITIES –Natural breaks within a rock mass such as joints, bedding, faults, fractures or foliations. SUBDRAINAGE – A technique used below pavements or embankments to remove groundwater. SURCHARGING –Placement of a temporary fill or other weight to accelerate settlement prior to constructing a permanent facility, such as pavements or bridge abutments. SURVEY HUBS –Stakes that are positioned in critical areas to monitor relative ground surface movements using standard survey techniques. T.P. –Transportation Policy. TASK ORDERS –A document used to specifically describe all items of work agreed upon between the Department and a Consultant for a particular project. Task Orders are numbered and are sub parts of an On-Cal lagr eement .Anex ampl ewoul dbe“ TaskOr der Number 5 of On-Call Agreement Number P063-07-089. ” TELLTALE STAKES – St akes i ns t al l ed al ong a “ l i ne-of-si ght ”used t o make v i sual evaluations of ground surface movements. TEMPORARY DUTY STATION – A work location to which an employee is formally transferred, in writing, for a period of time in excess of two weeks. TERRACE DEPOSIT –Alluvial deposits found along the margin or above the level of a stream channel marking a former water level. They are commonly composed of higher energy deposits such as sand and gravel.

02/14/2005


GLOSSARY

G-11

TEST PITS –A pit dug with a shovel or backhoe to obtain bulk samples and to identify the types and sequence of near surface materials. THERMISTOR – Measures ambient or ground temperature using a calibrated gauge consisting of two wires made of different materials that exhibit a predictable contraction or expansion in response to a change in temperature. TILTMETER –Tiltmeters use a server-accelerometer to measure the rotation of a surface point on a critical slope or structure. The data is transferred to a readout device via a control cable. TIME DOMAIN REFLECTOMETRY (TDR) –A device used to determine the depth of a landslide that relies on changes in electrical properties of a coaxial cable caused by thinning/stretching at the failure surface as landslide movements proceed. TOTAL STRESS CELLS (TSC) –A device used to directly measure the in situ lateral stress state (Ko) in soils. TOUGHNESS –A qualitative measurement used as a descriptor of a soil based on the way a soil lump or ball breaks when in a moist state. TRAVEL STATUS –Tempor ar yas si gnmentawayf r om t heempl oy ee’ sdut yst at i on,whi ch does not require written transfer. TREMIE TUBE –During the backfilling process, grout can be delivered to the bottom of a borehole through a tube to prevent contamination, caving or bridging. TRENCH DRAINS –A method of subdrainage to intercept, collect and remove shallow groundwater. UNCONSOLIDATED-UNDRAINED (UU) – Triaxial shear strength test result used primarily in the calculation of immediate embankment stability during short-term (quick-loading) conditions. In this test, the specimen is not permitted to change its initial water content before or during shear. UNDERDRAIN BLANKET –A method to reduce the potential for groundwater to affect an embankment by placing a free-draining rock layer on the foundation soil prior to placing fill. VALUE ENGINEERING (VE) –An engineering process to re-examine project development and decisions to evaluate if more efficient or less costly solutions could be incorporated. VECTOR SUMS –Used to determine the overall direction of movement. VERIFICATION TESTS –Performance test used to verify that constructed elements (such as soil nails) meet design specifications. Generally sacrificial elements are loaded to 200% of the design load.

02/14/2005


GLOSSARY

G-12

VIBRATING-WIRE PIEZOMETER OR STRAIN GAUGE –Electronic gauges that utilize the frequency of a wire connected to a flexible diaphragm to measure strain or pressure. The key principle is that the natural frequency of a vibrating wire constrained at both ends varies with the square root of the tension in the wire. Changes in the tension of the wire indicate corresponding changes in strain or pressure of the attached structural member. VIBRATION MONITORING – Ground vibrations are monitored with an instrument containing an oscillographic recording system, capable of measuring vertical, longitudinal and transverse components of motion with respect to the source of vibration motion. Commonly used in blasting or pile driving operations. VIBROFLOATATION –A method of ground improvement that creates a vertical hole for incorporating sand backfill (using a vibrating probe) to create denser conditions. WEEP HOLES –Drain holes formed in cut slopes, walls or shotcreted surfaces to relieve the buildup of groundwater pressure. WICK DRAINS – Geosynthetic fabric and plastic core drains inserted into the soil to increase subsurface soil drainage. Used to accelerate settlement to shorten construction time. They are an alternative to sand drains.

02/14/2005


Geo_ppm - Nevada Dot

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