INDUSTRY PRACTICE STANDARDS AND A ND DFI PRACTICE GUIDELINES FOR STRUCTURAL SLURRY WALLS
First Edition Copyright 2005
Prepared Pre pared by by
DEEP FOUNDATIONS INSTITUTE
INDUST INDUSTR RY PRACTICE STA STA NDARDS AND A ND DFI PRACTICE GUIDELINES FOR STRUCTURAL SLURR LURRY WALLS ALL S
First Edition
DFI – Deep Foundations Institute 326 326 Lafayett e Avenue Hawtho Hawt horn rn e, NJ 07506 07506 USA www.dfi.org
May 10, 2005
BY DFI SLURR SLURRY Y WALL /TRENC /TRENCH H COMMIT COMMITTEE TEE
Copyright 2005 Al l Right Rig ht s Reserved Reser ved This book or any part thereof must not be reproduced in any form without the written permission permission of the publisher. publisher. Printed in USA USA
PREFACE
This publication of the Deep Foundations Institute (DFI) is intended to provide the industry with model practice guidelines for design and construction of structural slurry walls. It does not represent a design document, nor does it provide a pre-engineered slurry wall specification; rather, it is a composite of the opinions of practicing engineers, construction experts and the DFI Slurry Wall/Trench Committee. This publication is intended to provide an understanding of standard slurry wall practices in the U.S. heavy construction industry. Industry practice standards and DFI practice guidelines are intended to highlight major considerations in selecting structural slurry wall elements for temporary and permanent use as foundation elements. Since the application of slurry wall elements in tunnels, bridges, buildings, dams, marine construction, etc. is so diverse, a single publication cannot cover all the conditions and codes governing its specifications and usage. It remains the primary responsibility of experienced professionals to provide the appropriate contract documents and use their own judgment in each instance. The Committee does not anticipate that this publication will cover every project circumstance nor will it replace the importance of local experience. There are numerous factors that need to be considered on a project-by-project basis by experienced engineering and construction personnel . Among them are the actual design parameters, site conditions, subsurface characteristics, groundwater conditions, structure water tightness, site accessibility, available equipment, desired work practices, etc. These factors are discussed and guidelines are provided in this document. The history of slurry wall construction will provide some insight into the development of the process used in the United States and worldwide. The names of many individuals and corporations who contributed to the development of slurry wall construction have been omitted from this publication in the interest of brevity. Information obtained from references is cited in the references in Part V by [reference number]. Figures referenced in the text material are included in Part IV. Additional resource literature is listed in the bibliography in Part V. English customary units of measurement are used through this publication; metric conversions in scientific units (SI) and customary kilogram units are listed in Part IV. Users of this publication are encouraged to contact DFI with questions and comments. This and other DFI publications are available from: The Deep Foundations Institute 326 Lafayette Avenue Hawthorne, NJ 07506 Tel: (973) 423-4030 Fax: (973 423-4031 Email: dfih
[email protected] i
DEEP FOUNDATIONS INSTITUTE SLURRY WALL/TRENCH COMMITTEE MEMBERS Chairman
Poletto, Raymond J., P.E.
Mueser Rutledge Consulting Engineers
Members
Bonita, John Ph.D, P.E.
Weidlinger Associates, Inc.
Bruce, Donald A. Ph. D, P.E.
Geosystems, L.P.
Cardoza, Edmund J. Jr.,
Private Consultant
D’Argenzio, Domenic, P.E.
Mueser Rutledge Consulting Engineers
Hosseini, Mamoud, P.E.
Clark Construction Company
Jacobsen, Edward, P.E.
Case Foundation Company
Lager, David E.
NETCO Inc.
Nicholson, Peter J., P.E.
Nicholson Consulting Company
Paniagua Z., Walter I.
Pilotec Cimentaciones Profundas
Ressi di Cervia, Arturo, L., Ph.D
Treviicos Corporation
Schmednecht, Fred C.
Slurry Systems Inc.
Schranz, Gernot
Liebherr Werk Nenzing Gesmbh
Tamaro, George J., P.E.
Mueser Rutledge Consulting Engineers
Former Contribut ing Committee Member
Pearlman, Seth, L., P.E.
DGI-Menard, Inc.
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NOMENCLATURE USED IN SLURRY WALL CONSTRUCTION
Illust ration 1: Standard Terms
RELATED TERMS AND CONSTRUCTION METHODS
The term “Slurry Wall” is commonly used in the United States and refers to the construction of concrete elements using a slurry fluid to support the sidewalls of the excavation before the slurry is replaced with tremie concrete and other structural elements. The terms “Diaphragm Wall” and “Milan Wall” are used elsewhere and refer to the final constructed foundation element. Cutoff Walls and Slurry Trenches are constructed similarly to structural slurry walls using a variety of backfill materials, but their purpose is to provide either a water cutoff, environmental barrier or collection system related to groundwater control or environmental mitigation and are not the subject of this publication. DEFINITION OF A SLURRY WALL AND OTHER STANDARD TERMINOLOGY (See Illus trati on 1)
A “Slurry Wall” is a structural foundation element constructed below ground using a controlled slurry fluid, consisting of a colloidal suspension of either bentonite, pulverized clays or polymer thoroughly mixed with water, to support the side walls of an excavation, that is later backfilled with tremie concrete, which may be reinforced with a steel cage, steel tendons or wires, steel beams or a precast panel. In practice, the controlled slurry fluid level in the trench is kept near the ground surface and several feet above the ground water level. A guide wall is placed on each side of the wall alignment to pro-
ii i
vide vertical and horizontal alignment control for the excavation and subsequent support of the tremie equipment and reinforcing elements to be placed in the excavated unit. The slurry wall is constructed in discrete units, called “panels,” which are usually joined at their ends formed by keyed joints from an extracted end stop shape, or can be prepared by milling along a vertical plane at the cast end of the panel. Steel beams are often used as joints or connectors between panels. Panel dimensions in plan commonly range between 2 ft. and 5 ft. in width and between 7 ft. and 25 ft. in length. Panels are excavated in one or more passes with overlapping of excavating buckets or drilling machines depending on soil/rock conditions and the geometry of the slurry wall system. Additional definitions of standard slurry wall construction and equipment terms are provided in Part III.
HISTORY OF SLURRY WALL CONSTRUCTION
The origin of the use of colloidal clay slurries to stabilize the sidewalls and bottom of an excavated trench may be traced to the earliest known methods of sinking deep wells by the Chinese in the Third Century B.C. They learned that the efficiency of their tools in rock was improved by the addition of water; formations were softened and cuttings were more easily removed with bailing tools. This practice of pouring water into drilled holes continued through the middle of the Nineteenth Century when fluid flushing and rotary drilling systems were developed in France. By the end of the century, the sealing and stabilizing characteristics of clay and water slurry were identified and put to use in the developing oil industry in the United States. In the first thirty years of the Twentieth Century, the properties of drilling fluids became more and more important as well depths exceeded one mile. Between 1926 and 1929, bentonite was first used as a suspending and gelling agent for drilling muds. The use of slurry to support the sidewalls and bottom of excavated trenches followed directly from bored pile experience in Europe. Early applications with slurry walls experimented by using various concrete and plastic concrete materials to form barriers, called cutoffs, to seal water infiltration through various soil layers. The interlocking of bored piles to form continuous walls (1930 through 1950, in Italy and France) marked the next logical step in the development of slurry wall technology [1]. By 1950, Italian contractors developed methods of excavating elongated panels using percussion drilling equipment and a stabilizing slurry. The technique was patented and the first cutoff walls were installed at the Santa Maria Dam near Venafro, Italy.
iv
During the next decades, primarily Italian and French construction firms and manufacturers developed a variety of equipment for the installation of slurry walls, using the “joined panel” technique. The equipment developed for slurry walls included: mechanical cable-activated and Kelly-guided clamshell buckets, hydraulic activated clamshells, reverse circulation methods with drilling tools, percussion chisels, churn drills, bentonite slurry mixing and cleaning units, tremie concreting equipment, jointing systems and devices for monitoring the effectiveness of the technique. Developments in Italy and France quickly spread to the East and West in the form of license agreements and exportation of equipment and expertise. Today, contractors continue to evolve the techniques of the industry and modern hydraulic milling or “hydromill” excavators are the current behemoths (monster machines) used in slurry wall construction. The continuous trenching method of slurry cutoff wall construction developed in the United States in parallel with the European panel wall approach. In the mid 1940’s, chain-bucket dredgers and dragline machines were busy along the Mississippi River and on the West Coast excavating long, continuous, slurry supported trenches, which were backfilled with clay to form cutoff walls to protect adjacent land and structures from inundation. The improvements in excavating equipment (deep digging hydraulic excavators) and backfill mix design (well graded materials with a significant fraction of plastic fine grained soils) during the last five decades, have lead to the use of the soil backfilled, continuously excavated slurry trenches, as the most technically effective and most cost efficient method of seepage control and waste containment in the United States. Slurry wall panel type construction is utilized all over the world in construction of large underground structures. The most dramatic applications and severe tests of the method have been on dam rehabilitation projects in North America, where panel walls were carried to depths in excess of 400 feet to a stricter tolerance than previous construction practice had achieved. The success of these projects must be attributed to the ingenuity of engineers, contractors, equipment manufacturers and slurry experts of today and yesterday. The first structural slurry wall construction was used in the United States in 1962 on a tunnel project located in Brooklyn, New York City, for a 25 ft. diameter access shaft beneath the East River [2]. It was constructed to a depth of almost 80 ft. (See Photo 1).
v
Courtesy of Rodio
Photo 1: First U. S. Structural Slurry Wall project in Brooklyn, NY. Used Rotary Reverse Circulation Drill to form c ircular panels.
Shortly thereafter, several building and subway projects in Boston and San Francisco used the slurry wall method to construct foundations for these structures. After these projects started, a slurry wall was constructed in 1966-1968 on a monumental scale ($10 million) for the basement retaining walls of the World Trade Center (See Photo 2). Following these trail blazing projects, over 280 additional slurry wall projects have been completed in the United States. A total of more than 18 million square feet of structural slurry wall has been installed in the U.S. during the last four decades. The largest single use of slurry wall construction on a single U.S. project is the Central Artery Tunnel Project in Boston for the Massachusetts Turnpike Authority from 1993 to 2004 (See Photo 3). More than 6 miles or 2,900,000 square feet of structural slurry wall panels have been constructed on this project, costing more than one third of a billion U.S. dollars.
Courtesy of G. Tamaro, Mueser Rutledge Consulting Engineers
Photo 2: World Trade Center’s sl urr y wall and excavation phase in 1969. vi
Information has been gathered on 361 completed projects in the United States, Canada, Caribbean areas and Mexico. These projects are cataloged in Part VI, Project List. These projects are alphabetically listed by the above locations. Many slurry wall projects are concentrated in the District of Columbia, Boston and New York City and are grouped together. Some projects (e.g. subway sections) are similar in nature and are also combined into a single group. Six types of project information (slurry wall thickness and depth, type of wall and excavation support, project size, description and year constructed) are included as the basic data in the summary of structural slurry wall applications.
Courtesy of Big Dig, Central Artery Tunnel Project
Photo3: Bauer low-headroom hydromi ll wo rking on Boston’s Central Artery Tunnel Project.
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TABLE OF CONTENTS Page
Preface.........................................................................................................i DFI Slurry Wall/Trench Committee Members .............................................ii Nomenclature Used in Slurry Wall Construction ........................................iii Related Terms and Construction Methods .................................................iii Definition of a Slurry Wall and other Standard Terminology ......................iii History of Slurry Wall Construction ............................................................iv Tables of Contents....................................................................................viii
PART I
INDUSTRY PRACTICE STANDARDS
1. Classification of Slurry Wall Panels......................................................1 2. Typical Sizes of Slurry Wall Panels ......................................................5 3. Panel Depths ........................................................................................6 4. Equipment.............................................................................................6 5. Slurry Fluids........................................................................................16 6. Phases of Panel Construction ............................................................18 7.
Inspection, Records and Final Condition Observations ....................18
Figures referenced in Part I and Part II are sho wn in Part IV.
viii
TABLE OF CONTENTS
(continued)
Page PART II
DFI PRACTICE GUIDELINES
1.
Scope ...............................................................................................21
2.
Contractor Qualifications ..................................................................21
3.
Subsurface Investigation ..................................................................21
4.
Design and Site Considerations .......................................................23
5.
Materials...........................................................................................25
6.
Slurry Fluids .....................................................................................27
7.
General Submittal Requirements .....................................................27
8.
Preparation for Excavation ...............................................................28
9.
Excavation........................................................................................29
10. Reinforcement Placement ................................................................31 11. Concrete Placement .........................................................................32 12. Tolerances ........................................................................................34 13. Differing Site Conditions ...................................................................34 14. Completion of the Work....................................................................35 15. Water Tightness Criteria ...................................................................35 16. Compensation ..................................................................................37
PART III
DEFINITIONS ...................................................................38-48
ix
TABLE OF CONTENTS
(continued)
Page PART IV
FIGURES ..............................................................................49
Figure 1 - Classification of Panels .....................................................50 Figure 2 - Slurry Wall Panel Configurations.......................................51 Figure 3 - Types of Panel Joints ........................................................52 Figure 4 - Types of Clamshell Buckets ..............................................53 Figure 5 - Slurry Excavation Operations ............................................54 Figure 6 - Cleanup with Sand Separating Unit ..................................55 Figure 7 - Phases of Slurry Wall Construction ...................................56 Figure 8 - Slurry Wall Inspection Report Form...................................57 Figure 9 - Slurry Fluid Test Report Form ...........................................58 Figure 10 - Tremie Concrete Inspection Report Form .......................59 Figure 11 - Major Types of Slurry Wall Construction and Applications...............................................................60 Figure 12- Typical Guide Wall Construction.......................................61 Figure 13- Guide Wall Constructed in a Prepared Trench.................62 Figure 14- Slurry Wall Tolerances ......................................................63
PART V
ADDITIONAL INFORMATION
References................................................................................................64 Bibliography ..............................................................................................65 Metric Conversion Table ...........................................................................69
PART VI
PROJECT LIST
Slurry Wall List Parameters ......................................................................70 Slurry Wall Projects in North America .................................................71-92
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PART I 1.
INDUSTRY PRACTICE STANDARDS
CLASSIFICATION OF SLURRY WALL PANELS
There are many ways to classify structural slurry wall elements, but the DFI committee chooses to limit these descriptions to three functional requirements, namely: design function, plan configuration and type of panel reinforcement. (See Figure 1 in Part IV for panel classification). Slurry walls can function as: 1. Curvilinear or linear elements for temporary and/or permanent structures to resist lateral forces transferred from the ground, water, earthquakes and various surcharge loads. 2. Load bearing elements in various plan shapes to resist vertical forces. 3. Combination Elements to resist combined forces under conditions 1 and/or 2. For example, elliptical shafts with various openings for tunnels and conduits have been commonly used for deep excavations. Slurry walls can be constructed in any plan configuration, solely limited by the dimensions of the excavation equipment, the type of geology and the practical imagination of the engineer and contractor (See Figure 2 in Part IV). Slurry walls can be reinforced by the addition of the following structural elements: 1. 2. 3. 4.
Reinforcing steel bars or fiber reinforcing - (Conventional Concrete Panel). Structural steel beams - (Soldier Pile and Tremie Concrete Panel). Prestressing steel elements - (Precast Concrete Panel). Tensioned steel prestressing bars, wire strand or wire elements - (Posttensioned Concrete Panel).
All structural slurry walls use structural concrete comprised of Portland cement, occasionally fly ash, fine and coarse aggregates, water and concrete additives that is usually specified in the range of 3000 psi to 5000 psi compressive strength at 28 days. Slurry wall panels with various reinforcements are illustrated in Figure 1 in Part IV and are commonly used in United States construction practice. In a conventional panel, an end stop shape is usually placed to form the joint between adjacent panels. In some cases, joints can be cut at the end of the panel by using a rotary grinding or milling tool (hydromill). An unreinforced concrete panel with formed joints was originally used for water cut-off walls and sometimes without joints for load bearing elements. Circular shafts and elliptical shaped cofferdams are examples of slurry wall applications that have achieved excellent results when properly designed and have allowed the construction of structures without bracing or obstructing any of the work during the 1
excavation of areas, to 250 feet in diameter and 80 feet in depth. Other slurry wall systems may use different types of joints, which are described, in later sections depending on their special applications in deep foundations. When used as part of an earth support system or permanent foundation wall, a reinforced panel resists the bending moments and shears caused by vertical and lateral loads and is supported by steel, concrete or timber bracing, soil or rock tiebacks or anchors and/or the floor systems of a structure. A reinforced panel can include a variety of inserts, such as: plates, keys, dowels or sleeves attached to the reinforcing cage and is often used as the permanent foundation wall for buildings and underground structures (See Photo 4).
Photo 4: Reinforcing cage with tieback sleeves and floor keys for conventional panel construction in Washington DC.
Another type of reinforced panel is a Soldier Pile and Tremie Concrete Panel, called “SPTC” panel. This type of panel has special applications in “open cut” and “cut and cover” construction where narrow, long and deep excavations are temporarily supported laterally with pipe or beam struts. The “cut and cover” SPTC wall was installed in San Francisco in 1967 for the construction of the Powell St. subway station of the BART transit system. This panel wall Courtesy of The Architect of U.S. Capitol can be constructed by two alternative methods: pre-drilling and setting beams (soldier piles) at 6 to 8 foot spacing in advance of the panel excavation or setting beams within an excavated, slurry filled trench. The steel beams can act as vertical reinforcing and panel joints. Concrete is tremied between the beams to form a watertight wall system depending on the quality of the panel installation. If large beam spacing is used, then a reinforcing cage is installed between the beams to serve as “concrete lagging”. Counterfort and corner panels are special T-shaped and L-shaped panels used for retaining walls and corners of walls. The counterfort panel is highly adapted to serve as a cantilever wall without bracing or as a thin wall with light reinforcing that can span large distances with a minimum number of lateral supports. Both of these types of conventional concrete panels are constructed as a monolithic tremie concrete pour with a single cage to accommodate the plan layout of the walls. 2
Courtesy of TREVIICOS Corp.
Photo 5: Precast wall panel installation on railroad construction in Massachusetts.
Precast concrete panels are used where a finished wall with a uniform or architectural textured face is desired. A precast panel is inserted into an oversized trench containing a cement-bentonite (C-B) slurry (See Photo 5). The C-B grout sets shortly after the panel is aligned vertically and horizontally. In the precast concrete panel system, a vertical rubber waterstop, usually a patented system, and C-B grout are installed within the panel joint. These materials seal the panel joints and form a watertight system. Sometimes, an excavation for a precast panel is made under bentonite slurry. A precast panel is then suspended within the excavated panel and the panel is grouted at the bottom to serve as the bearing support for the panel and as replacement of some of the slurry. Later, the space between the trench sidewalls and the concrete may be backfilled with cement bentonite or other self-hardening cementitious materials.
Precast concrete panels were initially used in France in the early 1970’s, and are less commonly used in the United States, except where appropriately skilled labor and large pre-casting facilities are available. The disadvantage of this system is the inherent difficulty of installing sequential panels in urban sites, especially where utilities cross the wall alignment. In these cases, the excavation is stopped and the utilities are relocated before the next panel excavation can resume. It is difficult to install a precast panel element perfectly within the gap left to allow for a later utility relocation, and as a result the watertight joint connection between panels may be compromised. Patented post-tensioned panel systems were developed during the 1970’s in Italy and Great Britain. A post-tensioned panel is constructed in the same manner as a conventional reinforced concrete panel. However, draped posttensioning tendon ducts are substituted for heavier reinforcing bars (See Photo 6).
3
The strands are pulled within the tendon ducts after the concrete sets and then the steel wire strands are posttensioned and grouted. This system reduces the quantities of concrete and steel needed and permits relatively large distances between brace levels, thereby minimizing the number of braces. Post-tensioned panels have structural bending resistance equivalent to counterfort (T-shaped) panels. This type of panel is difficult to utilize with multiple brace and floor levels because tendons can best be placed for only one or two levels of support. Load Bearing Elements are usually reinforced with structural elements Courtesy of TREVIICOS Corp. within the panels in various planimetric shapes. Round, single or multiple Photo 6: Reinforcing cage with posttensioned strands for panel in Boston bucket excavations can be used to cre- Central Artery pr oject. ate I, T, X, H, L, C or Y panel shapes (See Figure 2 in Part IV). Their primary function is to support large vertical loads and other applied forces [3]. Structural beams and/or other structural elements can be installed within the panel to connect to the structural framing system, particularly where top-down or up-down construction methods are used in a project. This type of panel can be easily integrated into a monolithic structure by doweling into subsequent construction. Concrete columns or mat foundations can be directly cast onto the load-bearing element after unsuitable concrete is removed from the top of the element. A load bearing element obtains its load capacity from either direct end bearing on the underlying soil strata and bedrock, through friction/adhesion along the embedded depth of the element or through a combination of end bearing and friction/adhesion. Joints between panels are illustrated in Figure 3 in Part IV. The early practice with conventional panels was to use pipes to form round joints or “end stop” panel joints. Later, structural beams were used in the United States with Soldier Beam and Concrete Lagging Panels. Finally, welded structural steel shapes and built-up members are also used as panel joints, and are easier to remove by using either the crane’s lifting line or by the closing and opening of a collar extraction device operated by a hydraulic power unit after tremie concrete is placed in the panel. The optional waterstop within a panel joint has been rarely used in United States practice because of difficulty in execution. The construction practice of installing waterstops within panel joints is usually more costly than sealing joints with grout materials.
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2.
TYPICAL SIZES OF SLURRY WALL PANELS
Panel dimensions and configurations are usually controlled by the technical elements of the design and the size of the equipment that is available to the contractor performing the work. It is obvious that the panel thickness and length can be no thinner or shorter than the width and the length of the excavation bucket. Short panel lengths, usually in the range of 6 to 7 feet, should be used at areas of unstable soils or where very high surcharge loads result from adjacant structures. Longer panels, ranging to 30 feet in length, can be used in stable soils and favorable site conditions. Panel lengths can vary anywhere from 6 feet to 30 feet; however, many panel sizes are dictated by the location of internal bracing, tieback spacing, interior column layout and locations of adjacent footings. Walls are commonly 24, 30, 32, 36 and 48 inches (2.0, 2.5, 2.67, 3.0 and 4.0 feet) thick. Thicker walls are available if required for bending and shear resistance or if required to support high vertical loads. Thinner walls are sometimes used for special conditions, which is discussed in Section 4 of Part I. Typical slurry wall panel dimensions and other conditions affecting their selection are indicated in Table 1.
TABLE 1 - TYPICAL SLURRY WALL PANEL DIMENSIONS Panel Width or Wall Thickness (Note 1)
Panel Length Size limitations are dictated by commercially available equipment and site geological conditions; ground stability, water levels, and proximity to adjacent structures. Consult an experienced specialty contractor and geotechnical engineer for their recommendations. Conventional Concrete Panels
Soldier Pile & Lagging
Counterfort, T-Panel
Corner, L-Panel
Precast Concrete Panel
Posttensioned Panel
Load Bearing Element
18”-21”
Note 2
Note 2
Note 2
Note 2
6’ to 8’
Note 2
Note 2
24”
7’ to 25’
6’ to 10’
10’ x 10’
14’ to 25’
6’ to 8’
12’ to 20’
7’ to 25’
30”
7’ to 25’
6’ to 10’
12’ x 12’
14’ to 25’
6’
12 to 20’
7’ to 25’
32”
7’ to 25’
6’ to 10’
12’ x 12’
14’ to 25’
6’
12’ to 20’
7’ to 25’
36”
7’ to 20’
6’ to 10’
12’ x 12’
14’ to 25’
6’
12’ to 20’
7’ to 25’
40”
7’ to 20’
6’ to 10’
12’ x 12’
14’ to 20’
Note 3
Note 2
7’ to 20’
48”
7’ to 16’
Note 4
Note 2
14’ to 16’
Note 3
Note 2
7’ to 20’
60”
7’ to 12’
Note 4
Note 2
14’ to 16’
Note 3
Note 2
7’ to 16’
Table 1 Notes:
1. Panels of 12” to 14” thickness have been constructed outside the U.S. with special hydraulically operated clamshell rigs. 2. Only used under special conditions. 3. Length and width of precast panels are dictated by shipping and handling limitations. 4. Special built-up member sizes are required for walls that are more than 40” thick. 5
3.
PANEL DEPTHS
A. For Excavation in Relatively Uniform Types of Soil. 1. By conventional light duty, cable-hung clamshell bucket, telescoping Kelly-mounted bucket or drilling machine, depths of approximately 100 ft. can be excavated. Special telescoping Kelly-bars may reach depths of 165 ft. [4]. Panel depths may reach 300 ft. using cable-hung, heavy duty clamshell buckets. 2. The industry standard for out of plumbness tolerance is one percent of the depth of the panel excavation. For panel depths in excess of 100 ft. verticality control is critical for connecting ends of adjacent panels and tighter tolerances may be required.
B. For Excavation in Layered Soils Mixed with Cobbles, Boulders and Rock. 1. Panel depths are generally limited to less than 100 ft. using lightduty clamshell buckets and percussion, auger or star drills into granular soils or soft rock. 2. Panel depths are generally limited to less than 150 ft. using heavy-duty clamshell and rotary or percussion drilling equipment in medium to hard rock. 3. Panel depths are generally limited to 300 ft. for excavation and drilling with special equipment and excavating with heavy duty clamshell buckets and chisels. 4. Panel depths as reported by manufacturers’ literature could be constructed to 500 ft using hydromills. However, the operation of this equipment in very dense soils or hard rock can limit the panel depths because the vertical alignment and the twist must be controlled to properly connect the adjacent panels. 4.
EQUIPMENT
A. Panel Excavation For the past 50 years, the main excavation tools have been cable-suspended (wire-rope) or Kelly- guided clamshell buckets and percussion chisels. Either crawler cranes or specialty tripod controls clamshell buckets or quadruped rigs with a winch system. Commonly used in the industry are several styles of mechanical, cable-hung clamshell buckets and their physical characteristics are shown in Table 2. Tripod rigs were originally used in some projects where limited space was available for excavation equipment. Rotary drilling techniques were developed in the 1950’s through the 1970’s and used in Japan and Europe throughout this period. 6
TABLE 2 - CHARACTERISTICS OF MECHANICAL (WIRE-ROPE) CLAMSHELL BUCKETS
Nominal Bucket Width or Wall Thickness
Bucket Bite Lengths
Bucket Height with Closed Jaws
Bucket Weight
(inches)
(ft)
(ft)
(ft)
(tons)
18-21
1.7
6.0 to 9.2
12.3 to 13.5
8 – 10
24
2.0
7.0 to 13.8
13.8 to 14.7
10 – 13
30
2.5
7.8 to 13.8
20.5 to 23.9
11 – 14
32
2.7
7.8 to 11.3
20.5 to 23.9
12 – 15
36
3.0
7.8 to 13.3
20.5 to 21.5
13 – 16
40
3.3
10.0 to 11.3
21.0 to 22.9
14 - 19
48
4.0
10.0 to 14.0
23.0 to 25.6
15 – 22
60
5.0
10.5 to 14.0
24.0 to 26.0
19 – 28
Table 2 Notes:
1. Typical sizes available from manufacturers and specialty contractors. 2. Mechanical buckets are generally heavier and have a smaller bite and height than hydraulic buckets. 3. Buckets are available with curved or rectangular jaws. 4. Special bucket sizes can be fabricated for special projects and low headroom. (Consult manufacturers and specialty contractors.) 1. Clamshell Buckets The first slurry wall clamshell buckets were free-hanging, two cable buckets operated by two drum winches on tripod rigs or a crane. Buckets are usually controlled by a crane operator and may have either round jaws or rectangular jaws. Excavation with round end buckets facilitates the placement of conventional stop end pipe joints. Rectangular jaws are more appropriate when flat stop end joints or beams are used to form the ends of panels (see Figures 3 and 4 in Part IV). The jaws can be fitted with different teeth as needed. Most buckets work with 3 teeth on one side and 2 on the other for up to 40 inch thick walls; 4 teeth on one side and 3 on the other are used for thicker walls. For a free-hanging excavation bucket, a guiding system is needed to minimize the rotation caused by the lifting and closing cables of the bucket. To ensure a vertical excavation, the bucket is equipped with a top guide that is of the same width as the jaws (see Photo 7). The guide also assists in maintaining vertical alignment and adds weight, which improves the 7
bucket capability to penetrate denser soils. Operator skill has an important role in the control of the mechanical clamshell bucket and keeping it vertical during excavation. Swinging the bucket 180 degrees on the cable regularly during excavation helps to minimize the twist or corkscrew deviations frequently encountered in penetrating denser soils or weathered rock. Clamshell buckets can be manipulated by adjusting the crane’s lifting cables with one left twist and one right twist to avoid the bucket to drift to one side. The bucket may be turned at the side of the trench after each cycle of excavation. Modern winches in crawler cranes allow the operator to rotate the bucket smoothly around the vertical axis. This operation also improves the verticality of the wall. Photo 7: Mechanical clamshell bucket.
Excavating buckets can also be attached to a Kelly-bar (See Figures 4 and 5 in Part IV). The Kelly can be tubular, telescopic, or a large beam. The mechanism is operated from a standard crawler crane by means of a specially designed attachment consisting of a Kelly-bar and a Kelly-guide. The use of the Kelly-bar ensures control for the insertion and removal of the bucket between and away from the guide walls, thus increasing the Courtesy of Liebherr Nenzing Gesmbh productivity in the excavation cycle. In addition, the weight of the Kelly helps the excavating bucket penetrate into the soil. One of the drawbacks of the Kelly equipment is that for difficult soil conditions, it is necessary to also use percussion tools to remove cobbles or boulders and/or to remove weak rock. In those conditions another excavating rig is usually provided to employ percussion tools. A Kelly-guided or a free-hanging bucket can also be hydraulically operated. This type of bucket has jaws which can be opened and closed either by two hydraulic cylinders, one to each jaw, (see Photo 8), or by a single, larger hydraulic cylinder operating both jaws. The hydraulic lines are automatically synchronized with single or dual spoil feeds on the Kelly and
8
Photo 8: Kelly-bar guided clamshell bucket used in Washington DC.
Courtesy of Nicholson Construction Corp.
powered by the crane’s power or auxiliary hydraulic power pack. In the last couple of years clamshell bucket sizes have increased in weight and size. Bucket widths of 48 inches, weighing about 28 tons empty and 36 feet high, are in current use in Europe for better production and better verticality. These buckets have interchangeable sets of jaws and an upper bucket body to suit the range of needed panel widths. Unlike U.S. practice, some European contractors elected to not use guide walls, but rely on the crane’s controls having gyroscopes and inclinometers to guide the clamshell equipment and to indicate the depth of excavation and the twist of the bucket. Special buckets and crane rigs working up to 16 feet high clearance and tight quarters have been adapted for specific job conditions and panel configurations (See Photo 9). Three-jawed buckets have been used for constructing T-shaped panels. Buckets can have side cutters added to increase the panel thickness if needed for special conditions. The cost of this modification is usually greater than the cost of using the next available size bucket. Buckets and rigs need to be modified where excavation is limited in low-head room conditions, generally less than 20 feet. Slurry wall buckets are usually fabricated mechanically simple for maintenance and adequately strong to stand up to adverse digging conditions. Some manufacturers install special seals on bucket sheaves to provide lubrication for long term usage. Buckets need to be of sturdy construction in order to be able to act as an opened jaw chisel in dense soil. Buckets are commonly equipped with different types of teeth to facilitate digging in variable soil conditions that may contain cobbles, boulders, and widely varying depths and quality and conditions of rock. The industry opinion is that clamshell buckets provide more flexibility and adapt more easily for operating in difficult soil conditions than drilling machines. The standard tolerance for verticality can be improved to 0.5% with special clamshell 9
bucket handling techniques. This improvement will affect operations by slowing down the excavation rate for soil containing cobbles and boulders. Photo 9: Mini-excavator rig working on building site in Mexico City
Courtesy of Pilotec Cimentaciones Profundas
2. Percussion Equipment When the material to be excavated contains cobbles or boulders or is bedrock, the panel excavation is advanced using percussion tools. Beam sections or multiple steel plates can be welded together (four to six starshaped chisel) and hardened at the tip to serve as a heavy percussion tool (see Photo 10). The chisel can vary from 10 feet to 25 feet long and weigh 5 tons to 15 tons. The chisel is raised and dropped by a cable on a crane or by a percussion type rig. When panels are socketed into hard rock, a percussion rig with a reverse circulation system is usually employed to pulverize and remove rock material. Photo 10: Percussion chisel with 6 hardened bits for rock excavation.
Courtesy of Mueser Rutledge Consulting Engineers
10
3. Drilling and Milling Machines Rock can also be removed using a rig with multiple rotating drill heads or roller bits, and reverse circulation of slurry. The reverse circulation method is used to lift slurry through the hollow drill stem, removing soil and cuttings to a disposal location. Direct suction or an airlift can be used to lift the slurry and pulverized materials at the bottom of the drill head. The soil cuttings and the slurry are separated over a vibrating screen and/or desanding unit. The drilling fluid is returned to the panel through the rig’s supply line or discharged directly to the trench. An early rotary drilling machine with reverse circulation is shown in Photo 1 in the introduction section on page vi. In the early 1950’s, European contractors used drilling machines when the light clamshell buckets available could not remove the soil or when the excavation had to be carried to depths considerably greater than 100 ft. As larger crawler cranes and buckets became available in the 1960’s, the reverse circulation drilling method became less economical to utilize on ordinary slurry wall projects, except for dams where vertical alignment and drift of slurry wall elements had to be controlled within strict tolerances. An improvement to this method occurred in Japan in the 1970’s when a special multiple head drilling technique was developed. The rig used submersible drills suspended by a cable rig traveling on a rail system. The multiple drill bits had a suction pump to continuously remove the cuttings. One of the disadvantages of this system of excavation was the inability to remove large cobbles, boulders or rock fragments through the 6-inch diameter suction hoses. In the 1970’s and 1980’s, European equipment manufacturers and contractors improved the reverse circulation drilling method by manufacturing trench cutter (hydromill) machines. See typical hydromill tool and rig in Illustration 2. It is possible to excavate trenches for slurry walls with a hydromill at a greater rate than with clamshell bucket rigs, but usually a vertical excavation down to 30 to 50 ft is needed to operate the intake pump at the bottom of the cutters.
11
Illust ration 2: Model FD 32 Casagrande Hydr omil l [5]. See Table 3 for labeled dimensi ons.
The general characteristics of commonly used hydromills are given in Table 3 below. A crawler crane supports and controls this equipment which consists of a steel frame with a dredge-type mud pump and two hydraulic drives and cutter wheels mounted on a horizontal axis attached to its base frame (See Illustration 2 and Photo 11). The drives rotate the dual wheels in opposite directions. The cutter wheels, commonly equipped with tungsten carbon tipped teeth, continuously loosen and break up soil and rock material and mix it with slurry. Removable cutting teeth, button-type or wedge-type, are usually welded on multiple fins that are diagonally mounted on the wheels. These teeth are capable of cutting soft to medium rock up to 10,000 to 15,000 psi compression strength. The cost of replacing carbide or diamond bit teeth and equipment downtime are usually considered in contractor’s costs and selection of either vertical rotary or hydromill drilling machines. 12
Table 3 - Characteristics of Hydromills [5] Manufacturer Model No.
Cutter Width “ a” (ft)
Cutter Length “ l” (lf)
Cutter Disk Speed (rpm)
Discharge Pumping Rate (yd 3/min.)
Max. Excavation Depth (ft)
Tool Height “ hd” (lf)
Cutter Weight (tons)
Bauer Series BC
2.0 to 6.0
9.2, 10.5
30 to 52
27 to 55
0 to 25
5 to 11
215
Bauer MBC 30
2.0 to 5.0
9.2
16.4
20 to 25
0 to 30
7
175
Bauer CBC 33
2.0 to 6.0
9.2
33 to 55
22 to 38
0 to 30
7
330
Casagrande K2
2.0 to 3.3
8.2
40
19
0 to 27
10
330
Casagrande K3L
2.0 to 4.0
10.3
47
32
0 to 31
10
400 to 500
Casagrande K3C low headroom
2.2 to 4.0
10.3
40
19
0 to 31
10
230
Casagrande FD 25
2.0 to 3.3
8.2
32
19 to 30
0. to 27
7
165
Casagrande FD 32
3.0 to 6.0
10.5
50
44
0 to 19
11
200
Soletanche Hydrofraise HF 4000
2.0 to 4.7
9.2
50
25
-
10
400 to 500
Soletanche Hydrofraise HF 12000
4.7
9.2
50
60
-
10
400 to 500
Soletanche Hydrofraise HFA-4RCII
2.5 to 4.0
9.2
40
18
-
-
300
Rodio Urbana low headroom
2.0 to 4.0
7.9, 9.2
20
20
-
-
115
Rodio Latina low headroom
2.0 to 4.0
7.9, 9.2
16.4
20
-
-
145
The soil and rock cuttings are pumped through the rig’s discharge hose to a slurry treatment plant for separation and return of clean slurry to the panel. See Illustration 3 for the typical schematic diagram of the operation of a hydromill system. During the hydromill excavation process, the spoil-laden slurry can be pumped usually up to 1500 ft to the plant. This distance can be increased with the addition of in-line booster pumps. A high capacity plant can treat 500 to 1500 yd 3 per hour of slurry and separate solids through a series of vibratory screens and cyclones down to a coarse silt size. Fines can be further removed from the slurry with special centrifuges in a separate cycle. Slurry storage tanks at the treatment plant need to have at least twice the volume of the panels to be excavated.
13
Illustration 3: Hydromill Operations
Guidance systems attached to the hydromill machine permit modest steering of the cutters. The verticality of hydromill excavation is monitored with special inclinometers mounted on the cutter frame and connected to a readout device and recorder inside the crane operator’s cab. The operator can make adjustments to correct lateral drift and longitudinal plan deviations by varying the relative speed of the cutters and moving the interior shield connected to each side of the main frame of the cutter assembly. Hydromill machines are usually capable of achieving a vertical tolerance in the range of 0.2% to 0.5% in the longitudinal and lateral direction in most soil conditions without cobbles and boulders. The opinion of the industry is that soils mixed with cobbles and boulders are the most difficult to excavate with the hydromill equipment and require more stringent verticality control to achieve design tolerances. This tolerance is more difficult to achieve when variable weathered rock or rock with closely jointed or fractured zones are encountered. Hydromill equipment is also fabricated for working in 16 feet or less headroom conditions as seen in Photo 3 on page vii and Photo 12. For limiting disruption to traffic and area occupants, the desander, slurry treatment and slurry mixing operations can be set-up fairly distant from the excavation of the panel.
14
Photo 11: Hydromill (trench cutter) for construction of slurr y walls.
Courtesy of Big Dig, Central Artery Tunnel Project
Photo 12: Low headroom hydromill trench cutter working Boston. Courtesy of TREVIICOS Corp.
B. Slurry Mixing and Desanding 1. Proper mixing of bentonite is needed to produce effective dispersion and uniformity of the bentonite. Colloidal mixers produce the best possible mixing. Sometimes flash mixers are used. Careful control and testing of the bentonite slurry must be maintained throughout the duration of the panel excavation and prior to concrete operations. Sprinkling or pouring dry bentonite into the trench and relying on the excavation tool to mix the bentonite will result in lumpy slurry with variable viscosity and filtration properties usually falling outside of desired limits. 2. Bentonite slurries are circulated through a desanding or de-silting device prior to the placement of concrete in the panel and/or prior to storage or re-use. Used bentonite slurry is pumped onto a vibrating
15
screen sand separator unit that allows the screened slurry to pass into a collection tank (See Figure 6 in Part IV). The collected slurry is then pumped through a cyclone device to spin the fine sand from the slurry and sometimes through a de-silting unit, and then returned to the excavated panel or a storage tank. U.S. contractors often provide their own custom designed units, although high efficiency units are commercially available throughout the United States and worldwide. 3. Polymer slurries are also used in slurry wall construction and are mixed in accordance with the manufacturer’s recommendations. A conventional mud mixer is generally used to recirculate the slurry suspension prior to its use. Polymer slurries are not desanded since sand does not stay in suspension during trench excavation, but falls to the bottom of the panel. Use of modern desanding/desilting equipment enhances the recycling of the polymer slurry and minimizes the time needed for sand to settle to the bottom of the excavation. 4. The cleaning of the bottom of the excavation supported by polymer slurry is dependent on the soil conditions, depth and tools used in excavation. Mud or sludge may be present at the bottom of the excavation. Generally, a smooth blade excavation bucket is used to remove the finer materials that settle and an airlift or a submersible pump is used to extract the mud or sludge.
5.
SL URRY FL UIDS
A. Bentonite slurry is the most common water based slurry used in the industry. Bentonite slurry is the simplest to mix and maintain and is sufficiently versatile for use in most geologic formations and ground water conditions. Bentonite slurry is prepared by mixing about 6 percent of bentonite (clay mineral montmorillonite) by weight with potable water. The resulting slurry has a viscosity greater than water, possesses the ability to suspend relatively coarse and heavy particles, and tends to form a thin, low permeable filter cake on the sidewalls of the excavated trench. Sufficient viscosity and gel strength are important characteristics to transport excavated material to a suitable screening system. The sand percentage and specific gravity of the slurry are controlled to maintain the stability of the excavation and to allow proper tremie concrete placement. Bentonite slurry can be modified using peptizing agents and/or organic additives. Bentonite should comply with the American Petroleum Institute (API) Specification 13A. Information on the chemistry and mechanism of slurry wall fluid support of the trench and filter cake development is found in the references in Part IV.
16
B. Polymer slurries have been developed recently and perform well for most slurry wall operations. Polymer slurries are becoming increasingly more common in slurry wall construction because of ease of disposal and the tendency of suspended soil particles to settle out in the panel due to the absence of gel strength. Polymer slurries reduce the amount of contaminated concrete at the slurry-concrete interface and result in less entrapped material at the end stop joint between panels. Because of its low unit weight relative to bentonite slurry, the controlled use of polymer slurry is more critical at locations where there is a high water table, loose soils and where groundwater chemistry is uncertain. Some polymer slurries are composed of natural polymers (guar bean and cellulose materials) and degrade naturally within a short time. Other polymers are complex chemical elements (vinyl and synthetic bio-polymers) that are manufactured specially for slurry wall construction. Polymer slurry can be treated with special agents to degrade the slurry back to properties similar to water for disposal to sewer systems, if permitted. C. Bentonite and polymer slurries are sometimes used together in blended slurry to produce less viscous slurry. This procedure enhances the stability of the excavation since fines are present to effectively seal porous soil formations although almost no filter cake is formed. The bentonite and water are typically mixed and hydrated before the polymer slurry is added. Ratios of blended slurry mixtures vary according to site-specific demands such as geology and water chemistry. D. Understanding the chemistry and source of mixing water is an important factor in controlling the properties of the slurry. Brackish and seawater are usually avoided. Potable water supply with limited chlorine is more commonly used. Water softeners are sometimes added to potable water sources to limit high acid concentrations and to bring the water pH to 9.
17
6.
PHASES OF PANEL CONSTRUCTION
A. The phases of panel construction differ with the type of wall and the type of slurry fluid selected. Except for precast walls, panels are generally constructed in an alternating panel sequence (See lower sketch in Figure 7 in Part IV) in the following steps: 1. 2. 3. 4. 5. 6. 7.
Excavate under slurry fluids, Clean the excavated panel, and test the slurry, Install end stops or structural shapes, Clean end stops of secondary and consecutive panels, Place reinforcing cages, if required, Install tremie concrete and remove end stops, Stress post-tensioning elements, if utilized.
B. For precast concrete panels, the following sequence is usually employed, that follows a primary and consecutive sequence (See upper sketch in Figure 7 in Part IV): 1. Excavate under cement bentonite slurry, or with a slurry fluid, 2. When slurry fluid is used, it is replaced by a cement slurry. Grout may be placed at the bottom of the excavation, if required by design to support the precast panel and applied loads, 3. Clean ends of previously installed precast panels, 4 Install the precast panel. Waterstops can be installed in groves at ends of panels and grouted to form a barrier to prevent water ingress through the panel joint. 5. Remove temporary panel holding devices and clean or trim the top of the wall. 6. Install waterstops, if provided, and grout panel joints.
7. INSPECTION, RECORDS AND FINAL CONDITION OBSERVATIONS
A. Inspection The project owner should contract with a qualified inspector and/or geotechnical engineer, to inspect the slurry wall installation. The inspector should have ACI training in concrete testing and reinforcing placement. See ACI Manual of Concrete Inspection, SP-2 for inspector’s duties, records and reports. The inspector should also have knowledge of slurry testing procedures and adequate geotechnical experience to properly identify the soil types and rock formations encountered during panel excavation. The contractor should cooperate with the inspector in the performance of his quality assurance duties. The presence of the inspector shall in no way relieve the contractor of his obligation to perform the slurry wall installation in accordance with the project’s drawings and specifications and with good construction practice. 18
B. Records Accurate detailed records of slurry mixing and its properties in the excavated panel, materials encountered during excavation, slurry preparation and mixing, concrete placement and reinforcing cage fabrication or beam installation are essential. The contractor shall keep independent records of these operations. The contractor should be fully responsible for quality control of the slurry wall operations. The inspector shall verify that the contractor is maintaining independent records. The inspector and contractor should review and reconcile their records to minimize conflicts. The inspector should keep project report forms and verify that the work is proceeding as required by the contract documents following good construction practices. Sample forms for recording the inspector’s observations are included as Figures 8, 9 and 10 in Part IV and are described below. The inspector’s records should include the following general information on each of the slurry wall panel inspection reports: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
Name of contractor Location on job site Date of excavation and completion of guidewalls Panel identification number Date that panel approval was given Method of panel construction (conventional, SPTC, precast, etc.) Buckets, machines and tools that are employed Weather conditions Plan and as-built panel dimensions Ground elevation at guide wall or reference point Plan and as-built elevation of top of panel Plan and as-built elevation of the bottom of the panel Major soil strata encountered, and their elevations Time and date of beginning and ending of panel excavation Elevation at which ground water encountered, if any Time and date of sampling of subgrade and slurry for sand content and density Time and date of cleaning of joints of secondary and consecutive panels, if any Time and date of beginning and ending tremie concrete placement Slurry property test data Time and date of beginning of reinforcing cage or beam installation Concrete slump, pour levels and truck quantities during tremie operations Identification of concrete samples within panel Any unusual occurrences 19
C. Final Condition Observations 1. When the wall is exposed during general excavation, the inspector should check the wall against specified tolerances (See Figure 14 in Part IV). After the wall is exposed and the wall is cleaned, soil and weak concrete should be removed and protrusions beyond the permitted tolerance should be removed. 2. Keys and inserts should be exposed and prepared for subsequent use in the final structure. 3. The inspector should check all panel joints or defects to evaluate whether they are watertight and will not “blow” at a later stage of construction. Leaks at inserts or through vertical joints must be sealed. Defective joints or cracks should be chipped out, cleaned and packed with rapid setting cement grout mixes. Occasionally, it is also necessary to inject chemical or cement grout into the soil directly behind the wall at the location of the leak, or to grout the panel joint directly. 4. Leaks should be sealed with chemicals or cement grout after the release of the bracing and tieback system supporting the slurry wall. A suitable non-shrink mortar patch and reinforcing should be installed over any abandoned openings or plates in the wall.
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PART II 1.0
DFI PRACTICE GUIDELINES
SCOPE
1.1
These guidelines have been prepared for use in the design and installation of temporary and permanent structural slurry walls using bentonite, mineral clay or polymer slurry trenching methods. These guidelines represent good construction practice in slurry wall construction in the United States.
1.2
Various types of structural slurry walls can be used for temporary and permanent structures as well as foundation elements. See Figure 11 in Part IV for major applications of slurry wall in foundation and marine construction. Selection of wall type and reinforcing depends on the temporary and permanent forces and conditions relevant to the design.
1.3
Slurry walls are the best solution when all of their properties are considered in the design of the structure, namely; when they provide lateral and vertical support, water cut-off and can eliminate underpinning of adjacent structures.
2.0
CONTRACTOR QUALIFICATIONS
2.1
Slurry walls should only be constructed by companies employing personnel experienced in methods comparable to the specified work.
2.2
Experience should be relevant to anticipated subsurface materials, groundwater conditions, panel sizes, and special techniques required for slurry fluids and excavation tools.
2.3
The contractor should demonstrate to the satisfaction of the owner’s representative the availability and dependability of equipment and techniques to be used on the project.
3.0
SUBSURFACE INVESTIGATION
3.1
A thorough geotechnical investigation of the site should be performed prior to the start of design.
3.2
Adequate geologic information should be obtained for design and construction purposes. The exploratory information may consist of the following; borings with “disturbed” or “undisturbed” methods, representative soil samples and their descriptions, Standard Penetration
21
(Resistance) Tests (SPT), laboratory tests with grain size distribution and Atterberg limits, moisture content and density tests, rock core samples and recovered core barrel piece lengths expressed in percentage of the total core run (RQD) and rock core hardness and strength, descriptions of rock weathering pattern, orientation of bedding planes, joints, fractures, solution channels insoluble rocks such as limestone and inclusions. These tests need not be performed for every project. Information should be sufficiently detailed to delineate obstructions and variations in soil and rock material properties. 3.3
A geotechnical report should be provided to the contractor during the bidding period. The three most typically used geotechnical report formats [6] are as follows: • •
•
Geotechnical data report (GDR): A compilation of facts, such as boring logs and laboratory tests, excluding any interpretations. Geotechnical interpretive report (GIR): The geotechnical engineer’s interpretation of the data, including profiles of regional geology and interpretation of site-specific data that may help predict what is likely to be found underground. Geotechnical baseline report (GBR), sometimes referred to as a geotechnical design summary report (GDSR): The design engineer’s interpretation of the anticipated geological conditions and the expected behavior of the ground during construction This report establishes “baselines,” quantified measures of estimated ground behavior parameters. Such baselines permit bidders to formulate bids on certain ground conditions, with the understanding that if the actual ground conditions are more or less adverse than the baseline, the owner will consider modification to the contract under the differing site condition (DSC) clause.
3.4
Soil and rock samples collected during subsurface explorations should be preserved at natural moisture content and arranged so that they can be readily examined. The samples should be kept at some central location, such as the owner’s office.
3.5
Groundwater levels should be measured and recorded in borings and piezometers that may indicate whether natural or artesian water levels are present at the project site.
3.6
It is recommended that the owner employ and pay for all geotechnical services required. A conflict of interest could occur if these services are provided and paid for by the contractor.
22
3.7
The contractor should notify the owner if in his opinion the available geotechnical information is inadequate to bid and to plan the work.
3.8
The contractor may perform additional soils exploration to improve his knowledge of site soil and rock conditions, if permitted by the owner.
4.0
DESIGN AND SITE CONSIDERATIONS
4.1
There is no single code in the United States that fully applies to slurry wall applications. The designer must therefore select the most applicable codes and standards, such as American Concrete Institute, American Institute of Steel Construction, The American Association of State Highway and Transportation Officials and American Railroad Engineering Association, ASCE Design Loads on Structures During Construction, local building codes and project standards. Many of these codes do not deal with specific regulations for temporary structures. For this reason, the designer should provide the proper guidelines for the contractors upon which to base their bids.
4.2
All design should be performed by qualified licensed professional engineers utilizing contemporary design procedures that are in accordance with good engineering practice. See Bibliography in Part V for commonly used design references.
4.3
Existing utilities and structures should be indicated in contract documents and verified. The presence of pre-existing structures or abandoned utilities should be also identified. Groundwater monitoring is strongly advised during and after slurry wall construction and general site excavation.
4.4
The design should consider all loads on the wall due to at-rest, active and passive soil pressures, water and seismic loads and their effect on soil strength, surcharge effects, loads resulting from connection to a structure, effects of wall movements during and after construction, soil mass effecting the global stability of the wall, as well as the effects of wall support systems such as struts or tiebacks. All design loads and load combinations should be clearly identified in the computations.
4.5
Adequate safety factors should be provided considering the nature of the load, its duration and the effect of the load on the temporary and permanent performance of the wall. Reductions in safety factor may be applied to temporary walls, to combinations of transient loads [dead load + live load + wind], to loads of infrequent occurrence [flood or earthquake] in combination with service loads. Safety factors and load factors should not be compounded, that is, applied to the loads, 23
then to the structural design of the wall using already factored loads and then to the support system using already factored wall loads. Safety and load factors should consider the variability of geotechnical design parameters, which affect the wall design and support systems. 4.6
When Allowable, Load Factor and Ultimate Design Methods are used, the design should take into account the effects of incompatibility of the methods, particularly with regard to analysis and the use of safety and load factors. Increases in the basic allowable stresses should be applied to bending members and secondary compression members such as walers. Estimates for deflections of walls should consider possible uncracked or cracked section properties that result during staged excavation and should be based on non-factored loads. Increases in allowable stresses should not be applied to compression members such as struts.
4.7
Structural design of the wall should be in accordance with all current editions of national and local building codes and relevant sections of the American Concrete Institute, the American Institute of Steel Construction, the American Association of State Highway and Transportation Officials and American Railroad Engineering Association codes.
4.8
Effects of in-plane and normal loads should be considered in the design of the wall. The combined effect of these loads should not exceed code limits.
4.9
The design layout of slurry wall panels may affect adjacent structures or utilities. The design shall indicate that special excavation procedures, tools, reduced panel lengths, underpinning, grouting or ground treatment may be required to protect or limit wall movement near these structures or utilities.
4.10
The design should account for residual stresses resulting from temporary stages of construction and their effect on the serviceability and long-term performance of the wall.
4.11
Compatibility of wall movements should be considered when selecting wall support systems, wall reinforcement and panel jointing methods.
4.12
Specially designed details should be provided where loads are to be transferred across joints.
24
4.13
Construction documents, whether prepared by the consulting engineer or the contractor, should clearly define the scope of the work; indicating, where relevant, the thickness of the wall; panel lengths; the location of the wall in plan; dimensions or elevations of the top and bottom of the wall; size, position and length of reinforcement; position of all keys and inserts and location and magnitude of temporary support loads.
4.14
Specified wall tolerances, finishes and reinforcing cover should consider site geology (i.e. boulders and cobbles) and exposed depths of walls. See Section 12.0, for tolerances commonly used in the U.S.
4.15
Wall monitoring and instrumentation should be utilized to verify wall design parameters and to record performance of wall systems. During general site excavation, wall and bracing systems, as well as expected and critical structures adjacent to the site should be carefully monitored and the parties responsible for design and construction should review and respond to discrepancies in performance.
5.0
MATERIALS
5.1
Concrete should meet the specified minimum compressive strength (f’c) at 28 days, usually between 3000 psi and 5000 psi, at a slump ranging between 7 and 9 inches. Approved plasticizing agents, fly ash and/or air entrainment may be used to improve the workability of the mix. Water to cementitious materials ratio should not exceed 0.6. Normal low range plasticizers are recommended for producing workable concrete mixes. The use of super-plasticizers in concrete mixes is discouraged because of the short time of extended slump workability due to temperature changes between the times of concrete placement and when the superplasticizer is added to the mix plant. For water containment structures or special wall exposures, the water cement ratio can be adjusted to the standards of the applicable codes or standards of good practice only if the workability of the mix is not affected.
5.2
The aggregates used in the mix should be limited to 3/4-inch to 1-inch size, well graded, durable and inert, with hard rounded gravel and a sandier mix preferred.
5.3
Concrete should be proportioned, mixed and placed in accordance with ACI and other relevant codes and recommendations.
5.4
Steel reinforcement should consist of new deformed billet steel bars conforming to the requirements of ASTM A615, Grades 60 and 75 or rolled steel shapes conforming to the requirements of ASTM Grade A36 (currently not being rolled but may be available), or ASTM A-572, A-588 or A-992, Grades 50 and 60 or equivalent metric standards. 25
5.5
Reinforcing steel cages should be detailed as simple as possible. Multi-layers of bars on faces of cages, complicated bends, splices, cutoffs and grade and size changes should be avoided. Cages should be securely tied with wire. Welding of interconnecting bars or attachments should be discouraged. The steel cages shall be rigid enough for lifting during construction and may require additional reinforcing steel beyond that required for design.
5.6
Inserts and keys for walls and floors and grout pipes for post grouting should be accurately located and tied to the cage. Any pipes or tubes for geotechnical instrumentation should be attached per manufacturer’s recommendations. Adequate room for placement of tremie pipes and minimum clear spacing of adjacent bars to facilitate concrete placement must be considered in the design and reinforcing cage fabrication. Special threaded bars or crimped bar block-outs should be considered for more densely packed reinforcing cages. In corrosive conditions, epoxy coated or galvanized reinforcing bars should be considered.
5.7
Provision should be made for field alteration of cages if variations in panel dimensions are anticipated. Suitable spacers or rollers should be attached to the cage to maintain the required concrete cover. Round concrete blocks on steel bar axles, spacers that do not scrape or dig into soil faces or non-metallic devices are recommended.
5.8
Bentonite and other mineral clays should conform to the requirements of American Petroleum Institute (API) 13A. Chemically treated bentonites may be required to counter the effects of contaminated soil or ground water. Chemical additives should not be applied to bentonite slurry at the trench. Chemical additives may be added at the mixing plant under controlled conditions and to meet clearly defined objectives.
5.9
Polymer slurries used for trenching can be specially treated organic materials or chemical compounds. The specific conditions of the soil and groundwater regime should be considered with highly acidic and alkaline conditions avoided. Special slurry handling and disposal procedures should be considered and monitored for the duration of the wall construction.
5.10
Water used in the preparation of bentonite slurry should be neutral, clean, fresh, and free from oil, alkali, organic matter or other deleterious matter. Monitoring of the groundwater and its chemistry is usually performed when aggressive soil conditions or contaminated ground water or fluids are found.
26
6.0
SLURRY FLUIDS
6.1
Freshly mixed bentonite should have a minimum unit weight of 64 pounds per cubic foot (pcf), measured using the mud balance, minimum viscosity of 32 seconds, measured using the Marsh Funnel; filtrate loss of less than 25 cc using the standard filter press; and pH between 7 and 11.5. More viscous slurries or plugging agents may be required where high slurry losses are expected.
6.2
In typical wall installations, bentonite slurry properties are adjusted to have a maximum unit weight of 70 pcf, maximum viscosity of 50 seconds, maximum sand content of 5 percent prior to placement of concrete, all measured 2 feet above the bottom of the panel excavation. When conditions for conventional work are affected, e.g. panel depth is significantly deep and/or the volume and rate of the tremie concrete placement are not sufficient to displace the bentonite slurry, the sand content of the slurry can be reduced to about 1% to 2% to improve the horizontal flow of concrete throughout the panel. Similarly, if the panel is designed for load bearing in soil or rock, the sand content should be at the lower level and then tested at closer intervals along the length of the panel.
6.3
Polymer slurries should exhibit a maximum unit weight of 64 pcf, viscosity of 40 to 90 seconds, and maximum sand content of 1%, measured 6 inches above the bottom of the panel.
6.4
Slurry liquid should be carefully controlled and its properties tested by a slurry specialist or qualified engineer throughout the duration of the work.
7.0
GENERA L SUB MITTA L REQUIREMENTS
7.1
Shop drawings should be submitted showing guide walls, panel layout, dimensions and numbering scheme, sequence of panel installation, end stop detail, protection of structures and utilities, reinforcing steel details, location and detail of all inserts and keys or any other embedded item.
7.2
A statement should be submitted indicating methods of monitoring adjacent structures, trench stability, plumbness and deviation, including corrective measures, if necessary.
7.3
Time schedule, equipment schedule and list of specialized personnel should be submitted.
7.4
Detailed description of contractor’s quality control program should be submitted. 27
7.5
Bentonite, mineral clay and polymer slurry mix and manufacturer’s test reports for material to be supplied should be submitted.
7.6
Concrete mix design should be submitted including name of supplier, proportions, gradation, and test results of ingredients. Laboratory trial mixes are recommended, except where local practice has developed significant experience with available standard mixes.
7.7
Engineering calculations, drawings and details of contractors’ designed portions of the work should be prepared by a licensed professional engineer experienced in the relevant design and construction. Engineering calculations may be required to evaluate the effect of staged construction, construction induced loads; and contractor or field changes affecting the design of the temporary lateral support system.
7.8
Resumes of experienced personnel should be submitted as required, including information on each type of wall project, employer, supervisory duties held and/or field duties performed, and years of experience.
7.9
Contractor’s slurry wall project summaries should be submitted as required, including project name, owner, engineer, contact person, dates and descriptions of walls completed, and a list of projects performed as joint ventures.
7.10
Equipment summaries should be submitted as required, including available mechanical or hydraulic bucket sizes, drills, chisels, operating cranes, slurry storage facilities, mixing and distribution systems and concreting equipment.
8.0
PREPARATION FOR EXCAVATION
8.1
Utilities and structures in the vicinity of the wall should be located, protected, maintained and restored. The surface of adjacent structures should be covered and protected from the spillage of soil, bentonite or concrete. All utilities and man-made obstructions within the alignment of the slurry wall should be removed or capped or relocated as required. Utility information should be checked with local authorities and utility companies. Test pits and careful pre-trench work should be performed where accurate records are not available.
8.2
Install continuous, reinforced concrete guide walls to the line and grade of the finished wall providing sufficient clearance between guide walls to permit passage of the excavation tool. See Figure 12 in Part IV for typical guide wall construction details. Provide temporary 28
guide wall bracing to maintain correct position and clearance during excavation. The guide walls should be carried down to the level of the lowest adjacent utility or structure. The location of panel joints should be clearly marked on the guide walls. 8.3
Top of guide walls should be set a minimum 5 feet above the highest anticipated natural groundwater level. A stockpile of material should be provided to backfill the excavation in the event of flooding or an unanticipated rise in the groundwater level.
8.4
Guide walls should be founded on suitable soil for bearing purposes. In some circumstances, the bearing layer may not be suitable for the support of the guide walls. Some contractors prefer to prepare a lean concrete fill as the founding subgrade for the guide walls (See Figure 13 in Part IV). Note: Information obtained from references [7, 8, 9 and 10] has been used extensively in Sections 9.0 through 15.0.
9.0
EXCAVATION
9.1
Excavation equipment contractor should be provided that is capable of removing all soil, fill and rock materials encountered within the alignment of the wall. Man-made obstructions are typically removed in the pre-trenching process prior to constructing the guide walls. Clamming, drilling, scraping and grinding methods may be employed subject to environmental constraints such as spillages, excess noise and vibration.
9.2
Excavation should be conducted in a continuous manner to the required lines and grades with a minimum of two unexcavated panels, usually a minimum of 30 to 40 feet, or one concreted panel usually 15 to 20 feet separating any open panels. Excavation should not be performed adjacent to concrete placed within the preceding 24 hours, except where necessary to remove stuck stop end devices.
9.3
Sufficient survey control should be provided to assure that the panel excavation conforms to the required alignment and tolerances for verticality and position. The contractor should measure verticality and horizontal position at regular intervals approximately 15 to 20 feet apart. Wires connected to the teeth or side lugs of the clamshell buckets or built-in slope inclinometers within specially fabricated buckets tied to the operator’s controls can be used to judge the clamshell bucket’s position, referenced to the guide walls. Also, electronic readout and control devices in the crane’s cab can be used to determine the correct alignment and prevent “corkscrewing” as the excavation 29
proceeds downward. More precise measurements, using sonic devices or spiders, can provide a profile of the faces of the panel after the excavation is completed. These measurements can verify the minimum wall thickness and clearance to install reinforcing, beams and end stops. In deep excavations, verticality is critical to the effective connection of adjacent panels. In thin wall applications with deep panels, the verticality tolerance of the excavation may be restricted to 0.5 percent or less depending on design requirements. 9.4 9.4
Wall all emb embed edme ment nt (“so (“sock cket et”) ”) in suit suitab able le bear bearin ing g soi soill or or roc rock k sho shoul uld d be be verified in the presence of the inspector. Soil or rock samples may be required at closer intervals where change of geotechnical formations, anomalies or large boulders is encountered to verify that proper sockets are achieved. All sockets should be verified and the bottom of the panel thoroughly leveled and cleaned prior to placement of reinforcing and concrete. The use of toothless buckets, specially designed pumps and airlifts are generally used for cleaning sockets.
9.5 9.5
Pane Panell dep depth ths s sho shoul uld d be be mea measu sure red d at at the the star startt of of eac each h day day to chec check k if if cave-ins occurred overnight. Final panel depths should be verified at short spacing along the bottom of the panels to ensure that structural elements will be installed properly. The inspector should verify the bottom of the panel by using a weighted line or rod to ensure that no sand residue or rock fragments is at the bottom of the panel.
9.6 9.6
Bent Benton onit ite e slu slurr rry y sho shoul uld d be be pro provi vide ded d in in a cont contin inuo uous us mann manner er in orde order r to assure that the excavated trench is always full to within 2 feet of the top of the guide walls. A sufficient sufficient supply supply of bentonite slurry slurry or backfill should be maintained to assure trench stability in the event of unanticipated losses of slurry. Bentonite slurry should be constantly monitored to assure that the slurry conforms to specification requirements and will perform its intended function and excavation does not result in danger to adjacent structures and utilities.
9.7 9.7
Fres Fresh h min miner eral al slur slurri ries es shou should ld be mixe mixed d with with suit suitab able le col collo loid idal al mix mixer ers. s. Water for mineral slurries shall be potable and free of deleterious chemical substances, which can affect the slurry properties. Slurries should be stored in lined ponds or storage tanks to permit proper hydration. The contractor should establish a quality control laboratory on site to perform periodic testing to assure the slurry is suitable for its intended purpose.
9.8 9.8
Fres Freshl hly y sto store red d slu slurr rrie ies s sho shoul uld d be be tes teste ted d for for densi density ty,, vis viscos cosit ity y, fil filtr trat atio ion n and pH. The slurry in the excavated panels should be tested daily for specific gravity, viscosity and, near the bottom of the panel, for sand content. See Figure 9 in Part IV for a typical Slurry Fluid Test Report Form. 30
9.9 9.9
Prop Proper er clea cleani ning ng of the the slu slurr rry y in in non non-c -con onta tami mina nate ted d gro groun und d wil willl per permi mitt multiple re-uses. Contaminated ground, calcium from tremie concrete operations, or poor cleaning can affect the slurry properties, requiring the early disposal of slurry. The contractor should carefully control, monitor and isolate the slurry from multiple uses in various panels.
9.10 9.10
A slurr slurry y sam sampl plin ing g too tooll wit with h a spec specia iall bot botto tom m ent entry ry only only flap flap shoul should d be be used to take slurry samples from the bottom and mid-height of the excavation at any time to ensure that accumulated materials or sludge like material does not affect the excavation and tremie concrete operations.
9.1 9.11
Poly Polyme merr slur slurry ry shoul should d be main mainta tain ined ed and and mon monit itor ored ed in a cont continu inuou ous s manner similar to bentonite slurry, except that filter cake will not develop on the trench walls. The collection of solids at the bottom of the panel should be made with a toothless clamshell bucket. Chemical treatment may be needed for special polymer slurries.
9.12 9.12
Exca Excava vatio tion n spo spoils ils and waste waste bent benton onite ite shou should ld be be disp dispos osed ed of of in an environmentally sound manner.
10.0
REINFORCEMENT PLAC PLACE EMENT
10.1 10.1
The The slur slurry ry flu fluid id sho shoul uld d be teste tested, d, mod modif ifie ied d and and clea cleane ned d as neces necessa sary ry and the bottom and sides of the panel should be measured and cleaned prior to the placement of stop end devices and the reinforcement. Reinforcement (steel rebar cages and/or structural beams) should be placed as soon as possible after cleaning of bottom of the panel, or not more than 3 hours after testing of the slurry fluid flu id for sand content and sedimentation.
10.2 10.2
End End sto stop p dev device ices s in in pri prima mary ry and and cons consec ecut utiv ive e pan panel els s sho shoul uld d be be securely fastened in position and the cage, beam, and panel dimensions verified prior to lifting and installing the cage. All loose rust, oil or other deleterious material should be removed from the reinforcement.
10.3 10.3
Stru Struct ctur ural al bea beams ms and and rei reinf nfor orci cing ng bar bar cag cages es,, if req requi uire red, d, are are usu usual ally ly fabricated on site, on the ground for installation within the panel. The cage is fabricated by connecting individual bars with tie wire, chairs and spacers. Blocks, rollers or other devices dev ices are added to provide the concrete cover as needed. The location of the tremie pipe(s) should be considered and rebar placed clear of the tremie pipe locations. Welding of rebar is usually discouraged. Beams are usually fabricat-
31
ed and stiffened by frames located within the panel. The frames should permit the free flow of the tremie concrete, but still maintain the position of the vertical beams. The beams are inserted into the panel and the cage is then hung from the guide g uide walls. The contractor should provide additional stiffening elements within the panel for lifting the cage upright and tying block outs, instrumentation attachments, floor and wall keys, tieback trumpets and bearing plates, etc. 10.4 10.4
Suff Suffic icien ientt sling slings, s, lin lines es and and equ equipm ipmen entt shou should ld be be prov provide ided d to prev preven entt permanent distortion of the cage. The cage should be supported from the guide walls in correct position and 6 inches clear of the bottom. Local trimming, cutting, narrowing and other modification of the cage, which may be required to accommodate misalignment of the excavation, should not be done without the approval of the engineer. Repositioning or retying of loose bars, inserts, keys and other devices may be required during lowering of the reinforcement.
11.0
CONCRETE PLA CEMENT
11.1 1.1
Prio Priorr to conc concre reti ting ng the the pre previ viou ous s cast cast joi joint nt of of seco second ndar ary y and and cons consecu ecu-tive panels should be scarified and carefully cleaned. Concrete should be placed shortly after testing for sand content and within 3 hours of placement of the reinforcement or 24 hours after cleaning the excavation. If a delay occurs, then slurry should be retested to meet the test limits or the slurry replaced. Once started, concrete placement should proceed continuously until uncontaminated concrete has reached the required top of wall elevation. Detailed records of the quantity, quality and rise of concrete in the panel should be maintained. Adequate equipment should be provided to assure an uninterrupted supply and placement of concrete, even in the event of equipment breakdown.
11.2 1.2
The The cont contra ract ctor or sho shoul uld d ensur ensure e that that the the ris rise e of the the con concr cret ete e is fai fairl rly y uniuniform along the top of the rising concrete and that blockage of the tremie pipe does not occur. occur. See Figure 10 in Part IV for a typical Tremie Concrete Inspection Report Form. Concrete shall be placed by tremie methods in such a manner that the concrete displaces the slurry progressively from the bottom and rises uniformly to the surface, such that intermixing of the concrete and slurry will not occur. occur. If a “go-devil” or plug is provided to minimize the initial mixing of concrete and slurry, care should be taken that it not be entrapped in the concrete or otherwise cause a defect in the concrete.
11.3 1.3
The The cont contra racto ctorr shou should ld cont contro roll conc concre rete te plac placem emen entt by tru truck ck del deliv iver erie ies, s, pumping and by more careful control using two tremie pipes for standard panels, except SPTC panels (See Photo 13). For SPTC panels, 32
a tremie pipe should be provided for each beam element where multiple soldier piles are used to form a panel. The use of the “go devil” or starter plug, is usually not employed with tremie concrete placement. The contractor should revise his procedures if cold joints develop or if intermixing of concrete and slurry occurs. The use of a superplasticizer in concrete mixes has potential problems, limiting the period of desired slump and concrete placement within the tremie pipes. This placement should be carefully monitored and controlled. Concrete mixes furnished by suppliers should be suitable for the contractor’s placement methods. The contractor is responsible for any defects within the panel that may occur during concrete placement. 11.4
The tremie pipe should be 8 to 10 inches in diameter and shall be embedded a minimum of 5 feet and a maximum of 15 feet into fresh concrete. Surging of the pipe may be required during placement. Care should be taken to assure that the pipe is always embedded in fresh concrete and that loss of the tremie seal does not occur and result in a cold joint.
11.5
Where two tremie pipes are used, care should be taken to assure that both pipes are always of equal length, that a sufficient number of trucks is always available to charge both tremie hoppers uniformly and that the concrete level at each pipe is essentially level. The use of more than two tremie pipes should be discouraged for standard panels, except SPTC panels. Photo 13: Tremie con crete placement operations in Washington DC.
Courtesy of the Architect of U.S. Capitol
11.6
End stop devices should be withdrawn in a smooth and continuous operation after the initial set of the concrete. The contractor and the inspector should determine the suitable rate of withdrawal by checking set times of sequential batches of concrete selected from delivery trucks. In some instances when using laterally extractable end stops, the end stop removal sequence may be different.
33
11.7
Extra concrete cylinders may be taken during placement so that unusual conditions or suspected samples with low strength concrete breaks could be checked at a later time. Concrete cylinders should be protected from freezing and from vibration during their transport to the lab.
11.8
Concrete strength, if disputed, can be verified by coring and testing concrete from the wall at a later time.
12.0
TOLERANCES
12.1
Panel joints should be within 6 inches of the correct position and within 1% of vertical if not specified otherwise.
12.2
The overall out-of-plumb tolerance of the reinforcing cage and attached assemblies perpendicular to the plane of the wall should not exceed 1% of the depth of the wall at the depth measured and 3 inches in any direction in the plane of the wall. See Figure 14 in Part IV for standard tolerances. More rigorous verticality requirements of up to 0.5% may be required to assure proper overlap of panels in deep walls. The use of clamshell buckets or hydromill excavators in variable soil or rock conditions should be properly controlled to meet such stringent tolerance. In rare instances for dam construction, verticality has been controlled with special equipment to 0.2% verticality.
12.3
The minimum concrete cover should be 3 inches. An additional tolerance of 3 inches beyond the minimum concrete cover should be limited to areas not critical at the exposed surface of the wall.
12.4
Construction accuracy and wall finishes depend on site soils, equipment used and the skill of the contractor. Tolerances may be relaxed or walls set farther from neat lines where walls are constructed through loose, bouldery soils or fills consisting of piling, timbers, demolition or other loose debris, or where walls are temporary and are sufficiently clear of permanent construction.
13.0
13.1
DIFFERING SITE CONDITIONS
In the absence of a contract clause for differing site or changed conditions, the following procedures are recommended when conditions are encountered in the performance of the work which differs from those indicated by contract documents (including the geotechnical report) or ordinarily recognized as inherent in work as described in the contract.
34
13.2
A written notice to the appropriate owner’s representative should be given promptly when encountering these conditions.
13.3
An equitable adjustment and time extension notice should be discussed with all parties to cover the resulting extra unanticipated scope, change in schedule and associated costs.
14.0
COMPLETION OF THE WORK
14.1
All loose bentonite, soil and laitance should be removed from the top and face of the wall. Top of wall shall be trimmed to finished elevations. Embedded water stops at the top of walls are usually difficult to execute and are not recommended. Keyways for extension of the wall should be carefully cut into sound concrete and waterstops properly installed.
14.2
All leaks should be sealed or patched in order to provide for the required “watertight wall”.
14.3
Misalignments, bulges, protrusions and cavities should be brought into conformance with the required tolerances and should be repaired.
14.4
All existing structures and utilities should be restored to their preconstruction condition.
14.5
Collect and secure all construction records relating to bentonite slurry quality, excavation, reinforcement, concreting and repairs.
14.6
Contaminated and excess bentonite slurry and excavation spoil should be removed to an offsite location in a safe, lawful manner. Onsite disposal may be permitted upon receipt of relevant owner or local authority approvals.
15.0
WATER TIGHTNESS CRITERIA
15.1
There has been continuing improvement in the quality of slurry wall construction, however, there is a common misconception amongst specialist contractors, owners, designers and project managers as to the degree of watertightness that can be expected. The construction industry and interested parties acknowledge the difficulty of producing slurry walls that don’t leak, or have minimal seepage, however, there is no industry wide acceptance criterion for the water tightness of slurry wall systems. Project documents usually require that the slurry wall system not leak, show running water and/or contain material inclu35
sions or defects in panels and joints. Clearly, the specialist contractor should address these problems if they occur. Running water on the surface of the wall, at joints or at inserts in a panel, is not acceptable, however, a slurry wall may exhibit patches of moisture, [like beads of sweat] and still be considered “impermeable” or “watertight”. 15.2
The watertight quality of slurry walls can be affected by cracks and movement at panel joints that form due to structural deflections and/or differences between panel support conditions, by floor openings, embedded tieback anchors and internal waling within the slurry wall. Even fairly thick concrete slurry walls allow some transmission of water, although the amount of water is relatively low in shallow aquifers and low permeability soil conditions. A simple calculation using Darcy’s Law of water passing through a 2-foot thick, fairly dense and homogeneous concrete wall with a 30 foot head of water would indicate a flow of 0.5 gallons per 10,000 sq. ft. of wall per 24 hours.
15.3
There is no standard industry criterion on how to minimize moisture and dampness in underground structures. Some building basements, parking structures, mechanical and electrical rooms, subways and other tunnels can sometimes tolerate moisture or dampness. Sensitive below grade uses, such as habitable spaces, medical, food, and computer or document storage do not permit dampness or moisture and exceptionally dry environments are desired. It is questionable whether or not it is necessary to have the highest degree of water tightness specified for all slurry wall structures.
15.4
If required for the proper functioning of the underground space for the service conditions, there are six ways to achieve the highest possible level of water tightness. They include: 1. Watertight concrete construction relying on well thought out designs and the highest quality of slurry wall construction. 2. Sealing all panel joints and fixing faulty construction adequately after temporary bracing has been removed, and the slurry wall and structure has stabilized. 3. The use of liner walls cast against the slurry wall. 4. Cavity wall construction with provisions for drainage, sumps and ventilation. 5. The application of interior waterproofing using membranes or spray on waterproofing applied after the walls have been repaired and sealed. 6. The use of water stops cast into the panel joints and other connections exposed to water.
36
15.5
While it can be debated as to the need for the use of the above methods, there is no straightforward way to estimate the quantity of water, dampness or moisture that is acceptable. The design and expected slurry wall water tightness should be carefully planned and presented in the contract documents so as to avoid construction disputes and litigation.
16.0
COMPENSATION
16.1
Payment is usually made on a unit price basis, as measured by square feet of vertical wall face. This measurement should include the actual area between the top of (sound) wall and the bottom of wall indicated on the drawings, or as directed by the engineer. Plan measurement should be made along the centerline of the wall. Measurement of the bottom of the wall depths is made by (rigid) rods or sounding devices at 2 feet intervals. No payment should be made for walls installed beyond these limits. Payment usually includes all compensation for furnishing materials, labor, equipment, tools and incidentals required to complete the work. The contract price should also include all panel excavation, watertight joints, reinforcing steel bars, supply of embedded items, tremie concrete, guide wall construction and removal, supply, handling and disposal of slurry fluids, hauling of excavation materials, trimming of the top of the wall, removal of unsound concrete, removal of bulges or projections, and sealing or grouting of the wall for watertightness.
16.2
Payment for the slurry wall should be made against pay units established in the contract. Separate pay units may be established for removal of rock, boulders or obstructions, concrete overruns, slurry losses, reinforcing steel, inserts or embedded items, guide wall installation and slurry disposal. Absent such provision, no separate payment should be made.
16.3
As much as ten percent of the slurry wall contract price is often retained until the wall is fully exposed and found to be in conformance with contract requirements. Unexposed slurry cutoff walls may have another criteria for retaining payment (e.g. measurement of specific performance provisions, permeability or movement) as required by project provisions.
16.4
Confirmatory soil borings or rock cores, when required by the contract, should be paid on a unit price basis per linear foot and unit price for each soil sample or rock core drilled.
37
PART III
DEFINITIONS
A ACI: American Concrete Institute. Airl ift : Device for lifting slurry, suspended solids and drill cuttings from the bot-
tom of a bentonite or polymer slurry filled trench. Usually, compressed air is introduced into the slurry at the bottom of the trench using a small pipe inside of a larger pipe. This upward flow tends to lift material from the bottom of the trench. API: American Petroleum Institute API Spec. 13A : API Specification for Oil Well Drilling-Fluid Materials. API Spec. 13B : API Recommended Practice, Standard Procedure for Testing
Drilling Fluids. ASTM: American Society for Testing and Materials. Auger Dr ill : Helical device used to scrape, grind and/or dig into soil and rock.
B Barrette: See Load-Bearing Element. Bentonite: Montmorillonite clay containing sodium cations formed primarily
by in-place alteration of silicate rocks of volcanic origin. Bentonite Slurry : Mixture of bentonite and water. Berm : Sloping surface of soil providing lateral support to wall. Blockout : Device to form recess in wall. Bond : Adhesion of concrete to reinforcing steel. Brace: Linear structural element used to provide lateral support to the wall,
positioned perpendicular or at an angle to the wall. Brace Plate: Steel plate embedded in wall to receive brace and transfer load
from wall to brace.
38
C Cable-hung Clamshell Bucket : Excavation bucket operated by cables. Cage: Network of interconnected reinforcing steel bars. Cake: See Filter Cake. cc: Cubic centimeter. Metric unit of volume. Cement Bentonite: Low strength mixture of cement, bentonite and water,
which hardens with time. Cement Grout : High strength mixture of cement and water, which hardens
with time. Chisel : Heavy steel tool used to soften or fracture rock or obstructions. Clamshell Bucket : A mechanical bucket operated by two cables from a crane
or rig. In some cases hydraulic cylinders may be used on other types of buckets. Spoil is removed from the bucket by swinging it to one side of the trench and releasing the closing lines of the bucket. Chemical Grout : Mixture of chemical compounds, which become more vis-
cous and/or harden with time. Churn Drill : Fixed boom-drilling machine, which raises and drops a chisel
used for rock excavation. Closed Specification : Specification, which describes the end product and
how it is to be achieved. Usually, used for permanent walls. Cofferdam : Excavation support system. Usually, used to inhibit the entry of
water. Cold Joi nt : Discontinuity in concrete caused by a disruption in the placement
of tremie concrete. Concrete Cover : Distance from closest reinforcing bar surface to the face of
the wall surface. Consecuti ve Panel : Panel cast with one end against a previously cast panel. Corner Panel : Panel, not linear in plan, used to accomplish change in direc-
tion of wall.
39
Conventional Panel : Panel cast with one or two end stops, except for SPTC
and precast panels. Cutoff Wall : Non-structural wall used to inhibit the movement of water. Cyclone: Centrifugal device used to remove fine soil particles suspended in
bentonite slurry.
D Desander : Device used to remove sand and silt particles suspended in ben-
tonite slurry. Desig n Drawin g : Drawing prepared to show intent of the work. Drawing is not
sufficiently detailed to permit construction. Diaphragm Wall : See Slurry Wall. Direct Circulation Drill : Hollow stem chisel with provision for application of
bentonite slurry under pressure at the head of the drill in order to remove drill cuttings. Dowel : Reinforcing steel bar projecting from the top or face of the wall intend-
ed for connection of reinforcement or concrete at a later time. Drainage Chase: Space provided between slurry wall and interior finish wall
for collection of seepage from slurry wall.
E End Pipe: See End Stop. End Stop : Round pipe or shaped device placed at ends of panel excavation
prior to placement of concrete and withdrawn from excavation after concrete has set, providing smooth surface at ends of panel. End Stop Extractor : Device to withdraw end stop after concrete has
achieved initial set.
40
F Filter Cake: Thin layer of hydrated bentonite gel, which forms on the soil face
of the excavation. Filter Press : Device used to measure the filtration and filter cake develop-
ment of bentonite slurry. Filtrate Loss : Water loss from bentonite slurry applied under pressure against
a filter. Flocculation : Condition where dispersed clay particles form agglomerates or
clumps.
G Go Devil : Device placed in tremie pipe prior to placement of concrete into
pipe. Device is intended to prevent concrete from mixing with bentonite slurry during initial placement of concrete. Grab : See Clamshell bucket. Grout : A mixture of cement and water or sand and chemicals, used for filling
voids. It is typically made for pumping under pressure. Gel : Semi-rigid colloidal suspension of a solid in a liquid. Guide Walls: Shallow concrete walls placed on either side of the alignment of
the slurry wall to provide vertical and horizontal alignment control for the excavation and subsequent support of the reinforcing steel cage and/or other elements to be placed in the trench.
H Hydraulic Clamshell Bucket : Excavation bucket operated hydraulically. Hydromill Excavator : Reverse circulation drilling/grinding machine operated
by hydraulic drives to rotate cutter wheels on a horizontal axis. The spoil is removed by a submersible pump within the framework of the machine. Hydrofraise: See Hydromill Excavator
41
I Insert: Any device intended to be permanently embedded in the wall. Instrumentation: Any device intended to measure the performance of the
wall. Internal Waler : Reinforcing steel embedded in the wall to provide bending
resistance between points of lateral support.
J Joint : Discontinuity between panels usually formed by end stops or embed-
ded structural shapes.
K Kelly-Bar: Vertical shaft used to transfer torque from a power unit to a rotary
type drill, or to raise and lower a clamshell bucket. Key : A recess in the wall intended to receive a wall or floor slab.
L Laitance: Contaminated concrete which forms at the top of the tremie con-
crete as a result of the mixing of concrete and the bentonite slurry. Lean Concrete: Low strength concrete usually intended as backfill in situa-
tions where the material will be subsequently removed. Lifting Sling : Cable device used to lift reinforcing steel cages with minimal
distortion. Liner Wall : Interior finish wall placed in contact with or separated from the
slurry wall. Load Bearing Element: Element constructed in various plan configurations
and intended to primarily carry vertical loads.
42
M Man-made Obstruction : Any below ground man-made object, such as con-
crete, timber, building rubble, abandoned utilities, which cannot be easily removed by clamshell bucket. It requires removal by chiseling, grappling or the use of special mechanical devices. Marsh Cone: See Marsh Funnel. Marsh Funnel : Cone shaped funnel used to indirectly measure bentonite slur-
ry viscosity by measuring the time of passage of a quart of slurry through a specified opening size. Milan Method : See Top Down Method. Milling Machine : A reverse circulation, rotating, grinding device used to exca-
vate hard ground or soft rock. See Hydromill Excavator. Mixing Plant : Combination of mechanical devices used to mix, store, clean
and/or distribute bentonite slurry. Montmorillonite: A principal clay mineral group. A hydrous aluminum silicate
characterized by a crystalline structure of layers or thin sheets. This is the main ingredient of bentonite clay. Mud Balance: Scale device used to measure unit weight, specific gravity or
density of slurry.
O Over-break : The difference between the actual amount of concrete placed
and the neat theoretical volume. Usually expressed as a percentage. Over-pour : The extra amount of concrete placed in a panel beyond the theo-
retical panel volume.
P Panel : Section of a slurry wall that is concreted as a single unit. The panel
may be linear, T-shaped, L-shaped, or other plan configuration. pcf: Pounds per square foot. Imperial unit of pressure.
43
Pipe Sleeve: Insert in wall intended to permit the passage of a pipe through
the wall. Pipe Extractor : See End Stop Extractor. pH : Measure of the alkalinity or acidity of a liquid using a numeric scale set
with 7.0 as neutral, less than 7.0 indicating acidity and greater than 7.0 indicating alkalinity. Plastic Concrete: Concrete consisting of cement, bentonite, aggregates,
additives and water intended to provide minimal strength, a low modulus of elasticity and high strain prior to failure. Pony Beam : Short waler beam placed across a panel joint intended to sup-
port two panels from one point of lateral support. Porcupine Plate: Steel plate provided with numerous steel studs, straps or
bars welded to the plate intended to be embedded in the wall to provide shear or tensile capacity to a connection to the wall. Post-tensioned Wall : Wall, which derives its primary strength by the applica-
tion of longitudinal compression force by tensioning high strength strands embedded in the wall after the concrete hardens. Precast Wall : Wall constructed by insertion and positioning of precast con-
crete panels into a self-hardening slurry. Preload : Application to the wall of all or part of a predetermined brace or
anchor support load. Pre-stress : See Preload. Primary Panel : Panel constructed with end forming devices at both ends. ps i : Pounds per square inch. Imperial unit of pressure.
R Raker : Sloping brace, which provides lateral support to a wall by transferring
forces against a footing or other structural element within the excavation. Reinforced Concrete Wall : Wall whose primary strength is derived from a
reinforcing steel cage.
44
Reinforcement : Addition of steel to the concrete to provide tensile or bending
strength. Reverse Circulation : Method of removing excavation spoil by airlift or pump
and pipe. Reverse Circulation Drill : Hollow stem chisel with provision to draw ben-
tonite slurry and drill cuttings up the stem during drilling. Rotary Drill : Rotary grinding and cutting device primarily used to fracture or
soften rock.
S Sand Cone: Calibrated device used to measure percentage of sand by vol-
ume suspended in slurry. Sand Content : Percentage of sand by volume suspended in a slurry fluid. Secondary Panel : Panel cast against previously concreted panels. Shoulder Pipe: See End Pipe. Shop Drawing : Detailed drawing expanding on information shown on design
drawing. Work can be constructed from this drawing. Shotcrete: mixture of cement, aggregates, additives and water applied under
pressure by a spray technique. Slope Indic ator Tube: Pipe device installed vertically in the wall or adjacent
ground used to guide a slope-measuring device (inclinometer), which measures wall or ground movement. Slump : Measure of workability of fresh concrete. Slurry : A mixture of water and clay (bentonite or mineral clay) or polymer in
colloidal suspension. Slurry Specialist : Individual trained and experienced in the mixing, cleaning
and use of bentonite slurries as well as all operations necessary to properly construct a slurry wall. Slurry Trench: An excavation filled with bentonite slurry. Also, a trench back-
filled with blended “impervious” soils or cement bentonite.
45
Slurry Wall : Concrete wall constructed below ground using slurry to support
the sidewalls of the excavation. Socket: Embedment of the wall into a bearing and/or impervious strata. Soldier Beam: A steel beam or pile section installed vertically into the wall to
act as an end stop device or structural reinforcing for a panel. Also, called a “Soldier Pile”. Soldier Beam and Tremie Concrete Panel: A type of reinforced panel with
beam sections installed vertically into the wall. Also, called “SPTC” type of wall panel. Spacer : Device attached to the face of the cage to position the cage in the
excavation and provide the required concrete cover. Specifi c Gravity : Ratio of weight of a unit volume of bentonite slurry to a unit
volume of water. Stabili zing Fluid : Slurry used to support the sidewalls of a slurry trench exca-
vation. Starter Walls : See Guide Walls. Steel Beam and Concrete Lagging Wall : Wall whose primary strength is
derived from vertical steel beams at ends of panel, which serve as stop ends and waterstops. Also, called SPTC panel wall. Stop End Joint : See End Pipe. Strut: See Brace.
T Temporary Wall : Wall used primarily to provide soil and water retention dur-
ing construction and not utilized in the permanent construction. Thixotropy: The property exhibited by a slurry gel that becomes viscous
when undisturbed and loses viscosity when stirred or agitated. Tieback : Anchor used to lateral support for a slurry wall panel. Tieback Sleeve: See Tieback Trumpet.
46
Tieback Trumpet : Device cast into the wall intended to permit the installation
of a tieback through the wall and the transfer of the tieback load to the wall. Tolerance: Allowed variation from the design location of the wall. Top-down Method : Method of constructing a structure from grade downward,
constructing the roof and/or floor slabs of the structure in stages with excavation proceeding below the slabs. The slabs provide both temporary and permanent lateral support of the wall. Tremie Concrete : Concrete placed by the tremie method. Tremi e Method : Utilizes the displacement of a fluid by placement of concrete
through one or more supply pipes, which is kept immersed in fresh concrete so that the rising concrete from the bottom displaces the fluid without washing out the cement content. Tremie Pipe: Pipe through which tremie concrete is lowered to the bottom of
the slurry filled panel. Tremie Plug : Device placed at the bottom of the tremie pipe intended to min-
imize mixing of the concrete and slurry at the start of the concrete operation. Trench Cutter : See Hydromill Excavator.
U Under the Roof method : See Top-down Method. Updown Method: Use of the top-down method to excavate the basement
while simultaneously constructing the superstructure.
V Viscosity: Measure of shear strength of a liquid.
47
W Wale: Structural member installed at the face of the wall to transfer loads from
the wall to braces. Water to Cementi tious Materials Ratio : The ratio of the weight of mix water
to the weight of cementitious elements (cement and fly ash). Watertight Wall: Wall exhibiting a surface free of running water. Patches of
moisture or beads of water [like beads of sweat] may be evident, but free flowing water is not present throughout the wall surface.
48
PART IV
FIGURES
Figure 1 - Classification of Panels ..........................................................50 Figure 2 - Slurry Wall Panel Configurations ...........................................51 Figure 3 - Types of Panel Joints.............................................................52 Figure 4 - Types of Clamshell Buckets ...................................................53 Figure 5 - Slurry Excavation Operations.................................................54 Figure 6 - Cleanup with Sand Separating Unit .......................................55 Figure 7 - Phases of Slurry Wall Construction........................................56 Figure 8 - Slurry Wall Inspection Report Form .......................................57 Figure 9 - Slurry Fluid Test Report Form ................................................58 Figure 10 - Tremie Concrete Inspection Report Form............................59 Figure 11 - Major Types of Slurry Wall Construction and Applications...60 Figure 12 - Typical Guide Wall Construction ..........................................61 Figure 13 - Guide Wall Constructed in a Prepared Trench ....................62 Figure 14 - Slurry Wall Tolerances..........................................................63
49
Figure 1: Classif ication of Panels 50
Figure 2: Slurry Wall Panel Configurations 51
Figure 3: Types of Panel Joints 52
Figure 4: Types of Clamshell Buckets 53
Figure 5: Slurry Excavation Operations 54
Figure 6: Cleanup with Sand Separating Unit 55
Figure 7: Phases of Slurry Wall Construc tion 56
Figure 8: Slurry Wall Inspection Report Form 57
Figure 9: Slurry Fluid Test Report Form 58
Figure 10: Tremie Concrete Inspecti on Report Form 59
Figure 11: Major Types of Slurry Wall Construc tion and Applications 60
Figure 12: Typical Guide Wall Construction 61
Figure 13: Guide Wall Cons tru cted i n a Prepared Trench 62
Figure 14: Slurr y Wall Tolerances 63
PART V
ADDITIONAL INFORMATION
REFERENCES
1. Ressi di Cervia, A.L.,“History of Slurry Wall Construction ”, Slurry Walls: Design, Construction and Quality Control, STP 1129, American Society for Testing and Materials, Philadelphia, PA (1992). 2. Rodio-Italy, Company publication on geotechnical work experience, AGV-Vicenza-Mondado Group, Italy (October 1986). 3. Tamaro, G.J.,”Load Bearing Elements Constructed Using Bentonite Slurry Techniques”, Notes of the Met Section ASCE Seminar, Foundation Problems in the New York Metropolitan Area (Nov. 3-4, 1987). 4. Hooks, J. M. et al, “ A Report on the Design and Construction of Diaphragm Walls in Western Europe” , Federal Highway Administration, Washington D.C. (December 1980). 5. Sociedad Mexicana de Mecanica de Suelos, A.C., “Capitulo 3 - Muros Milan,” Manual de Construccion Geotecnia I, Mexico D.F. (2002). 6. Edgerton, W. W., “Site Investigations: a Guide,” Civil Engineering Magazine, Reston, VA (June 1998). 7. Tamaro, G.J. and Poletto, R.J., “Slurry Walls- Construction Quality Control”, Slurry Walls: Design, Construction and Quality Control, ASTM STP 1129, American Society for Testing and Materials, Philadelphia, PA (1992). 8. Rosenvinge, IV, T. and Tamaro, G. J., “Chapter 9: Caissons and Slurry Wall Construction”, Field Inspection Handbook”, ed. D.S. Brock, et al, 2nd ed., McGraw-Hill, New York (1995). 9. Poletto, R. J. and Good, D. R., “Slurry Walls and Slurry TrenchesConstruction Quality Control” , International Containment Technology Conference Proceedings, FL (Feb. 9-12, 1997). 10. Puller, M. “The Waterproofness of Structural Diaphragm Walls,” Proc. Institute of Civil Engineers - Geotechnical Engineering, Great Britain (Jan. 1994).
64
BIBLIOGRAPHY
1. American Petroleum Institute, “Recommended Practice-Standard Procedure for Field Testing Oil-Based Drilling Fluids” , API 13B-2, Washington DC (1990). 2. American Petroleum Institute, “Specification for Drilling-Fluid Materials”, API Specification 13, Washington DC (1990). 3. ASCE, “Slurry Wall Construction for BART Subway Stations ”, Preprints of the ASCE National Meeting on Structural Engineering, Pittsburgh, PA (1968). 4. ASCE, “Design and Performance of Earth Retaining Structures”, Special Publication 25, Proceedings of an ASCE Conference, Cornell University, Ithaca, NY (June 1990). 5. Becker, J.M. and Haley, M.X., “Up/Down Construction”, Design and Performance of Earth Retaining Structures , Proceedings of Geotechnical Engineering Division, Cornell University, Ithaca, NY (1990). 6. Braun, W.M., “Post-Tensioned Diaphragm Walls in Italy” , Concrete Construction, New York (April 1972). 7. Boyes, R.G.H. “Structural and Cut-Off Diaphragm Walls ,” Wiley, New York (1975). 8. British Standards Institute, “Execution of Special Geotechnical WorkDiaphragm Walls”, Document 94/106168, London (1994). 9. Canadian Geotechnical Society, “Canadian Foundation Engineering Manual”, 2nd ed., Ottawa (1985). 10. Catalano, N., et al. “Post-Tensioned Diaphragm Wall T-Panel for Large Unbraced Excavation Spans ,” Proceedings of the 19th Annual Conference and Meeting of the Deep Foundation Institute, Boston, MA (October 3-5, 1994). 11. Clough, G.W., Performance of Tied-back Walls, “Proceedings of the ASCE Specialty Conference on Performance of Earth and Earth Supported Structures”, Vol. 3, Lafayette, IN (1972). 12. Clough, G.W., “Proceedings of the Short Course – Seminar on Analysis and Design of Building Foundation”, Deep Excavations and Retaining Structures, Bethlehem, PA (1975).
65
13. Clough, G.W. and Schmidt, B., “Design and Performance of Excavation and Tunnels in Soft Clay”, Soft Clay Engineering, Elsevier Scientific Publishing Co., Amsterdam (1981). 14. Clough, G.W. and Buchignani A.L., “Slurry Walls in the San Francisco Bay Area”, ASCE reprint (1981). 15. Cunningham, J.A. and Fernandez, J.I., “Performance of Two Slurry Wall Systems in Chicago”, Proceedings of the Specialty Conference on the Performance of Earth and Earth Supported Structures, ASCE (1972). 16. Federal Highway Administration, “Proceedings from the Symposium on Design and Construction of Slurry Walls as Part of Permanent Structures,” Washington DC (March 1980). 17. Gill, S. A. “ Applications of Slurry Walls in Civil Engineering Projects”, ASCE Convention Preprint 3355, Chicago, IL (October 1978). 18. Goldberg, A.T., Jaworski, W., E. and Gordon M.D., Federal Highway Administration Reports FHWA RD-75-128, FHWA-RD-75-129, FHWARD-75-130, National Technical Information Service (1976). 19. Huder, J., “Stability of Bentonite Slurry Trenches with Some Experience in Swiss Practice”, Proceedings of the Fifth European Conference on Soil Mechanics and Foundation Engineering, Vol. 1, Madrid (1972). 20. Institute of Civil Engineers, “Diaphragm Walls and Anchorages ,” Proceedings of the 1974 Conference of the Institution of Civil Engineers, London (1975). 21. Institute of Civil Engineers, “A Review of Diaphragm Walls, A Discussion of Diaphragm Walls and Anchorages,” Institution of Civil Engineers, London (1977). 22. Kapp, M.S., “Slurry Trench Construction for Basement Wall of World Trade Center”, Civil Engineering, ASCE (1969). 23. Kerr, W. and Tamaro, G.J., “Diaphragm Walls – Update on Design and Performance”, Earth Retaining Structures (1988). 24. Kirmani M. and Highfill, S., “Design and Construction of the Circular Cofferdam for Ventilation Building No. 6 at the Ted Williams Tunnel ,” Civil Engineering Practice, (Spring-Summer 1996). 25. Konstantakos, D.C., “Measured Performance of Slurry Walls”, M.S. Thesis, Department of Civil and Environmental Engineering, MIT, Cambridge, MA (2000). 66
26. Konstantakos, D.C., Whittle A.J., et al, “Control of Ground Movements for a Multi-level Anchored, Diaphragm Wall during Excavation, ” Proceedings of the 5th Int. Conference on Case Histories in New York Geotechnical Engineering, (2004). 27. Lambe, T.W., “Predicted Performance of Braced Excavations”, Proceedings of the ASCE Specialty Conference on Performance of Earth and Earth Supported Structures , Vol. 3, Lafayette, IN (1972). 28. Littlejohn, G.S. and MacFarlane, I.M., “Case History of Multi-tied Diaphragm Walls”, Proceedings of the Conference on Diaphragm Walls and Anchorages, London (1975). 29. Millet, R.A. and Perez, J.Y., “Current USA Practice Slurry Wall Specifications”, Journal of the Geotechnical Engineering Division, ASCE Vol. 107, (Aug. 1981). 30. NAVFAC, “Design Manual 7.1 – Soil Mechanics”, Department of Navy, Naval Facilities Engineering Command, Washington, DC (1982). 31. NAVFAC, “Design Manual 7.2 – Foundation and Earth Structures”, Department of Navy, Naval Facilities Engineering Command, Washington, DC (1982). 32. O’Rourke, T.D., “Ground Movements Caused by Braced Excavations”, Journal of Geotechnical Engineering, ASCE Vol. 107 (1981). 33. Paniagua Espinosa, W., Paniagua, Zavala, W.I. and Valle, J.A., “Construction of Precast Walls in the Tramo Cola –Garibald Line 8 of the Metro”, 2nd Symposium of Construction, SMMS, Mexico (1994). 34. Poletto, R.J., “Slurry Wall Design,” University of Wisconsin-Milwaukee Seminar on Slurry Walls and Slurry Trenches, Arlington, VA (1999). 35. Rosenberg, P., St. Arnaud, G., et al, “Design, Construction and Performance of a Slurry Trench Wall next to Foundation”, Canadian Geotechnical Journal, Vol. 14 (1977). 36. Santarelli, G. and Ratay R.T., “Handbook of Temporary Structures in Construction ”, Chapter 9, 2nd ed., McGraw-Hill, New York (1996). 37. Saxena, S.K., “Measured Performances of a Rigid Concrete Wall at the World Trade Center”, Proceedings Conference on Diaphragm Walls and Anchorages, Institution of Civil Engineers, London (1974).
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38. Sen. K. K., Alostaz, Y., et al, “Support of Deep Excavation in Soft Clay: A Case History Study, ” Proceedings 5th Int. Conference on Case Histories in Geot. Engr., New York (2004). 39. Tallard G., “New Trenching Method Using Synthetic Bio-Polymers”, Slurry Walls: Design, Construction and Quality Control, STP 1129, American Society for Testing and Materials, Philadelphia, PA (1992). 40. Tamaro, G.J. and Gould, J.P., “Analysis and Design of Cast In-situ Walls”, Retaining Structures, Institution of Civil Engineers, London (1993). 41. Tamaro, G.J., “Slurry Wall Design and Construction”, Design and Performance of Earth Retaining Structures, ASCE Conference, Cornell University, Ithaca, NY (1990). 42. Tamaro, G.J., “Recovery Efforts at the World Trade Center Bathtub”, Proceedings of the 9th Int. Conference on Piling and Deep Foundations, Nice, France (2002). 43. Winter, E.W., Nordmark, T.S. and Tallard, G., “ Slurry Wall Performance Adjacent to Historic Church”, Slurry Walls: Design, Construction and Quality Control, STP 1129, American Society for Testing and Materials, Philadelphia, PA (1992). 44. Xanthakos, P., “Slurry Walls”, 1st Ed., McGraw-Hill, New York (1979). 45. Xanthakos, P., “Slurry Walls as Structure Systems” , 2nd ed., McGrawHill, New York (1994).
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METRIC CONVERSION TABLE
69
PART VI PROJECT LIST Slurry Wall Project List Parameters Locations:
North America only, separate groups by: 50 US States, Boston, New York City and Washington DC Method/Type:
SW SPTC PT PRE LBE TB TD SH
-
Conventional panel walls constructed with end stop joints Beam Wall systems with concrete considered as lagging Post-tensioned Walls Precast Walls Load Bearing Elements or Barrettes Anchored Walls with soil or rock tiebacks. Top-down method of construction used Shaft Construction used
Year:
Date of start of slurry wall construction Width:
Maximum panel depth, in feet Depth:
Maximum panel depth, in feet Area:
Plan length multiplied by wall depth, in square feet Description:
Brief description of project or significant feature of construction, e.g. excavation support wall, permanent wall, shaft wall, etc.
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
