1726-2017

AS 1726:2017

Accessed by MONASH UNIVERSITY LIBRARY on 23 May 2017 (Document currency not guaranteed when printed)

AS 1726:2017

Geotechnical site investigations

This Australian Standard® was prepared by Committee CE-015, Site Investigations. It was approved on behalf of the Council of Standards Australia on 7 April 2017. This Standard was published on 2 May 2017.

The following are represented on Committee CE-015:


          

Australasian Tunnelling Society Australian Drilling Industry Association Australian Geomechanics Society Austroads Cement Concrete and Aggregates Association Consult Australia CSIRO International Association of Hydrogeologists Australia New Zealand Geotechnical Society University of Newcastle University of Wollongong

This Standard was issued in draft form for comment as DR2 AS 1726:2016. Standards Australia wishes to acknowledge the participation of the expert individuals that contributed to the development of this Standard through their representation on the Committee and through the public comment period.

Keeping Standards up-to-date Australian Standards® are living documents that reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments that may have been published since the Standard was published. Detailed information about Australian Standards, drafts, amendments and new projects can be found by visiting www.standards.org.au Standards Australia welcomes suggestions for improvements, and encourages readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at [email protected], or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.

AS 1726:2017

Australian Standard®


Geotechnical site investigations

Originated as AS 1726—1978. Previous edition 1993. Fourth edition AS 1726:2017.

COPYRIGHT © Standards Australia Limited All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher, unless otherwise permitted under the Copyright Act 1968. Published by SAI Global Limited under licence from Standards Australia Limited, GPO Box 476, Sydney, NSW 2001, Australia ISBN 978 1 76035 743 6

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PREFACE This Standard was prepared by the members of the joint Standards Australia/Standards New Zealand Committee CE-015, Site Investigations, to supersede AS 1726—1993. After consultation with stakeholders in both countries, Standards Australia and Standards New Zealand decided to develop this Standard as an Australian Standard only, at this time, rather than a joint Australian/New Zealand Standard. This document may become a joint stand in future revisions. The objective of this Standard is to establish the requirements for the execution of effective geotechnical site investigations and to provide a standardized system for the description and classification of soils and rocks. It addresses spatial and physical characteristics of soil, rock and groundwater, but does not cover the chemical, biological or other environmental aspects of the investigation of contaminated ground. Commentary on the changes from the 1993 edition is set out in Appendix F. Statements expressed in mandatory terms in Notes to Tables are deemed to be requirements of this Standard. Figures provided in this Standard are informative.


The term ‘informative’ has also been used in this Standard to define the application of the appendices to which it applies. An ‘informative’ appendix is only for information and guidance.

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CONTENTS Page 1

SCOPE ........................................................................................................................ 4

2

EXCLUSIONS ............................................................................................................ 4

3

NORMATIVE REFERENCES ................................................................................... 4

4

DEFINITIONS ............................................................................................................ 4

5

OVERVIEW OF GEOTECHNICAL SITE INVESTIGATIONS ................................ 7 5.1 Process .................................................................................................................. 7 5.2 Geotechnical model ............................................................................................... 9 5.3 Execution of geotechnical site investigation ........................................................ 10 5.4 Initial assessment of site conditions..................................................................... 11 5.5 Fieldwork ............................................................................................................ 11 5.6 Reporting and interpretation ................................................................................ 14 5.7 Review of geotechnical site investigation ............................................................ 15


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SOIL, ROCK AND GROUNDWATER .................................................................... 16 6.1 Soil description and classification ....................................................................... 16 6.2 Rock identification, description and classification............................................... 36 6.3 Surface water and groundwater observations....................................................... 58 6.4 Gases ................................................................................................................... 58

APPENDICES A GEOTECHNICAL SITE INVESTIGATION TECHNIQUES ................................... 59 B LABORATORY EXAMINATION AND TESTING ................................................. 61 C GROUNDWATER CONSIDERATIONS .................................................................. 64 D PROBLEMATIC MATERIALS ................................................................................ 66 E SYMBOLS ................................................................................................................ 69 F COMMENTARY ....................................................................................................... 72 BIBLIOGRAPHY ..................................................................................................................... 74

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STANDARDS AUSTRALIA Australian Standard Geotechnical site investigations 1 SCOPE This Standard specifies requirements for the execution of geotechnical site investigations and provides a standardized system for the identification, description and classification of soils and rocks. This Standard applies to geotechnical site investigation of natural or filled ground for— (a)

new construction;

(b)

maintenance of existing facilities;

(c)

the evaluation of post construction performance;

(d)

the assessment of failure; and

(e)

broad geotechnical studies.


NOTE: Commentary on the changes from the 1993 edition is set out in Appendix F.

2 EXCLUSIONS This Standard does not cover the following: (a)

The application of geotechnical site investigation outcomes for geotechnical design.

(b)

The chemical, biological or environmental aspects of the investigation of contaminated ground.

3 NORMATIVE REFERENCES The following normative documents are referenced in this Standard: NOTE: Documents referenced for informative purposes are listed in the Bibliography.

AS 4133 Methods of testing rocks for engineering purposes 4133.4.1 Method 4.1: Rock strength tests—Determination of point load strength index 4133.4.2.1 Method 4.2.1: Rock strength tests—Determination of uniaxial compressive strength of 50 MPa and greater 4 DEFINITIONS For the purpose of this Standard, the definitions below apply. 4.1 Acid sulfate soil Naturally occurring soils, sediments or organic substrates (e.g. peat) that contain sulfide minerals (predominantly pyrite) or their oxidation products. In an undisturbed state where soil is saturated, acid sulfate soils are generally benign. However, if the soils are excavated or exposed to air by a lowering of the groundwater level, the sulfides react with oxygen to form sulfuric acid. NOTE: Refer to Appendix D.

4.2 Carbonate rock A rock containing more than 50% by weight of carbonate compounds (such as calcium carbonate).  Standards Australia

www.standards.org.au

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4.3 Carbonate soil A soil containing more than 50% by weight of carbonate compounds (such as calcium carbonate). 4.4 Cemented soil A soil bound with a cementing substance, such that if remoulded and recompacted to its original density and moisture content, exhibits a significantly lower strength than in its undisturbed condition. 4.5 Classification A system which places a material into one of a limited number of groups on the basis of a defined characteristic or set of characteristics. For example, a soil classification may be based on the grading and plasticity of disturbed samples. 4.6 Cohesive and non-cohesive soils Soils are conveniently divided into two groups based on the ability of a soil mass to hold together. Those capable of holding together are termed ‘cohesive’ and those having no ability, or strength, to hold together by themselves at very low applied total stress levels are termed ‘non-cohesive’.


4.7 Competent person A person who has, through a combination of training, education and experience, acquired knowledge and skills enabling that person to correctly perform a specified task. 4.8 Consistency The ability of the soil, at specific moisture contents, to resist mechanical stress or manipulation (remoulding). 4.9 Contamination The condition of land or water where any chemical substance or waste has been added as a direct or indirect result of human activity above background level and represents, or potentially represents, an adverse health or environmental impact. Contamination may have an impact on human health during construction or the service life of a structure erected on the site or may have detrimental effects on the environment. NOTE: While this Standard does not address investigation of the presence of contamination or management of such contamination, the possibility of the presence of contamination should be considered during the planning and conduct of geotechnical site investigations.

4.10 Controlled fill Any fill for which engineering properties are controlled during placement. Sometimes referred to as structural or engineered fill. 4.11 Description, soil or rock A statement of the physical characteristics of a sample of soil or rock. 4.12 Desk study A study to collate and review the existing information relevant to the site. 4.13 Dispersive soils Those soils, which by nature of their mineralogy and pore water chemistry, are susceptible to separation in water of individual clay particles. NOTE: Refer to Appendix D.


 Standards Australia

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4.14 Duricrust A cemented zone occurring in weathered rock or soil formed by the mobilization and deposition of minerals. 4.15 Engineered fill Refer to ‘Controlled fill’. 4.16 Fill A volume of material that has been placed by anthropogenic processes. 4.17 Geotechnical Pertaining to the nature, condition and physical properties of the earth’s crust (whether soil or rock and including water and gases therein), which affect its engineering performance. 4.18 Geotechnical model The interpretation of ground conditions in a form useful for engineering design or assessment. It may contain a surface and subsurface model detailing the geological and engineering characteristics of the various materials and groundwater. 4.19 Geotechnical site investigation The process of assessing and evaluating the geotechnical characteristics of a site. Accessed by MONASH UNIVERSITY LIBRARY on 23 May 2017 (Document currency not guaranteed when printed)

4.20 Groundwater Water located beneath the earth’s surface in pore spaces, fractures and voids in soil and rock. 4.21 In situ In the place and condition in which it exists naturally. 4.22 Liquid limit (wL) Moisture content at which the soil passes from the plastic to the liquid state as determined by the liquid limit test. 4.23 May Indicates that a statement is an option. 4.24 Monitoring Recording observations and/or measurements over a period of time. 4.25 Mottled Having areas of two or more colours or shades in a spotted or blotched, irregular configuration. 4.26 Plastic limit (wP) Moisture content at which the soil becomes too dry to be in a plastic condition as determined by the plastic limit test. 4.27 Plasticity index (IP) Numerical difference between the liquid limit and the plastic limit of a soil. 4.28 Project The wider project for which a geotechnical site investigation is carried out. 4.29 Shall Indicates that a statement is mandatory.  Standards Australia


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4.30 Should Indicates that a statement is a recommendation. 4.31 Soil Particulate materials that occur in the ground and can be disaggregated or remoulded by hand in air or water without prior soaking. 4.32 Rock Any aggregate of minerals and/or organic materials that cannot be disaggregated by hand in air or water without prior soaking. 4.33 Uncontrolled fill Materials that have been deposited by anthropogenic processes, which do not meet the definition of ‘controlled fill’. 4.34 Undisturbed sample A term applied to samples obtained using techniques designed to minimize changes in the properties of the sample. 5 OVERVIEW OF GEOTECHNICAL SITE INVESTIGATIONS


5.1 Process 5.1.1 General The delivery of geotechnical site investigations should follow an iterative process in which the outcomes of the investigations are reviewed against the purpose for which the investigation is being carried out and further investigations are planned as required. This process is illustrated in Figure 1. Quality assurance and work health and safety programs should be in place during this entire process.



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D efin e t h e pur p o se of t h e inve st i g at i o n an d i d e nt i f y t h e s c o p e an d o bj e c t i ve s

A s s e m b l e i nfor m at i o n r e l at i n g to t h e proj e c t

D eve l o p t h e G e ot e c hni c al M o d e l b a se d o n g e o l o g i c al c o n c e pt s, g e ote c h ni c al infor m at i o n an d proje c t infor m at i o n an d ant i c i pate w hat m i g ht b e e n c o u ntere d o n s i te

Plan t h e inve st i g at i o n to ad d r e s s t h e o bj e c t i ve s

Refine the G e ot e c hni c al M o d e l a n d rev i ew t h e inve st i g at i o n outc o m e s ag ain st t h e s c o p e an d o bj e c t i ve s

H ave t h e o bj e c t i ve s b e e n m et an d t h e s c o p e ac hi eve d?

No

Ye s


Carr y out the g e ote c hni c al i nve s t i g at i o n

R ev i s e o bj e c t i ve s and /or s c o p e and /or investigation methods

C o n clu d e inve s t ig a t ion

FIGURE 1 GEOTECHNICAL INVESTIGATION—OVERVIEW

5.1.2 Project description Geotechnical site investigations are usually carried out in service of a wider activity, such as land development, infrastructure, mining, or assessment of landslide risk. This wider activity is usually referred to as ‘the project’. The entire area that could affect the project or be affected by the project is referred to as ‘the project area’ and the immediate area of the project itself is referred to as ‘the site’. A description of the project, the project area and the site shall be provided.



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5.1.3 Purpose of investigation The general purpose of the geotechnical site investigation and its specific investigation objectives within the context of the project shall be clearly defined and documented to the satisfaction of all parties involved. 5.1.4 Scope of work The proposed scope of work shall reflect the investigation objectives and shall be clearly documented. 5.1.5 Staging Geotechnical site investigations are usually carried out in stages, with the number of stages dependent upon the geotechnical complexity of the site. A program of staged investigation should be developed to implement the selected investigation activities. This program should recognize that, during the investigation, conditions may be revealed which were not anticipated or which trigger a need for review of the remainder of the program. For larger or more complex investigations it may be appropriate to include one or more reporting and review stages in order to refine or revise the latter stages of the investigation.


The stages may include the following: (a)

Literature review.

(b)

Site walkover.

(c)

Field investigation staged in order to retrieve data most economically (e.g. carry out cone penetrometer testing first before deciding where to position boreholes with in situ testing and sampling).

(d)

Review after each stage to assess the need to carry out further stages.

(e)

Laboratory testing, staged and optimized for the development of geotechnical design parameters and the soil-groundwater chemistry (e.g. testing to identify acid sulfate soils).

Investigations should be executed in such a way that adequate data are obtained to refine the geotechnical model at the end of each stage, to allow advancement of wider studies or to guide subsequent investigations. Each stage may involve interpretation, analysis and reporting. 5.2 Geotechnical model A geotechnical model shall be developed for every geotechnical site investigation. The level of refinement and model detail will depend on the complexity of the project. In its most basic form the geotechnical model may consist of a simple description of the local geology derived from existing data together with some of the engineering characteristics of the project area. More usually, the geotechnical model would include a geological map and cross-section depicting the strata likely to be encountered and information on the engineering characteristics of the soils and rocks and the groundwater levels. On some large projects, a more sophisticated geotechnical model, based on a large data set and presented as a 3D visualization, may be developed to present the interaction between a large complex structure and a variable soil/rock/groundwater system. The geotechnical model should be based on factors such as the following: (a)

The nature of the project.

(b)

The regional geological and hydrogeological setting.

(c)

The stratigraphic succession, including the presence of significant aquifers.



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(d)

Expected groundwater levels.

(e)

The geological structure.

(f)

Geomorphology and surface processes.

(g)

Engineering properties of the soils and rocks encountered.

The geotechnical model shall provide a consistent explanation of the concepts, observations and interpretations associated with the geology, geomorphology, hydrogeology, hydrology and engineering characteristics of the project area that are relevant to the project. The geotechnical model should be used to communicate geotechnical information about the site to all interested parties involved in the project. This information may include: (i)

Past and present surface processes/activities.

(ii)

Types of soil or rock units and their distribution.

(iii) Groundwater levels and groundwater flow directions. (iv)

Preliminary geotechnical characteristics of soil and rock units.

(v)

The types of geological structure and their orientation.

(vi)

Seismic risk.


(vii) Potential occurrence of contaminated ground or groundwater that might be hazardous to people, the environment or the durability of construction materials. (viii) Potential occurrence of hazardous gases. 5.3 Execution of geotechnical site investigation 5.3.1 Health and safety Relevant work health and safety legislation applies to all geotechnical site investigations. Site-specific risk assessment and work method statements should be established. All significant risks associated with the geotechnical site investigation should be assessed, and control measures implemented. 5.3.2 Competency All personnel involved in geotechnical site investigations shall have geotechnical experience, training and qualifications appropriate for their role in the investigation. 5.3.3 Literature review A literature review shall be carried out as part of the geotechnical site investigation. This review should include the assembly of reports, maps and other information pertaining to the site. In selecting relevant information, the site should be considered in terms of its position in the overall landscape and the broader geological setting, prior to the investigation focusing exclusively on the immediate area of the site. Information that can be used to gain an understanding of the site prior to fieldwork includes, but is not limited to, the following: (a)

Geological maps and memoirs of the site.

(b)

Existing geotechnical site investigation reports for the site or nearby sites.

(c)

Topographic or bathymetric information.

(d)

Maps or photographs, which may show topographic features such as swamps or creek lines that have been subsequently obscured by human activities.

(e)

Aerial photographs (vertical and oblique).

(f)

Large scale geological maps.



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(g)

Geohazard maps.

(h)

Published soils maps.

(i)

Acid sulfate soil risk maps.

(j)

Maps of vegetation.

(k)

Previous local and anecdotal experience from the area.

(l)

Historical records such as newspaper articles.

(m)

Mine working maps.

(n)

Construction records for the site or nearby projects.

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5.4 Initial assessment of site conditions


An initial assessment shall be made of the conditions in the area to be investigated, which could be expected to influence the investigation. This may be drawn from site reconnaissance, earlier studies, experience, background reports and published information. This assessment of site conditions influencing the design of the field investigation should include, but not be limited to— (a)

accessibility;

(b)

hazards to health, safety and environment;

(c)

proposed geotechnical model;

(d)

structures or services which could affect or be affected by the investigation;

(e)

groundwater conditions;

(f)

geographical, geomorphological and geological features;

(g)

seismic setting;

(h)

potential for encountering contamination and hazardous gases; and

(i)

regulatory approvals required.

The initial assessment of the site should include an appraisal of the area and volume of ground that would affect or be affected by the project. 5.5 Fieldwork 5.5.1 General Fieldwork should typically include the following: (a)

Mapping of the topography, geology, geomorphology and other relevant features.

(b)

Logging of cuttings or other exposures.

(c)

A program of sub-surface works (such as boreholes, test pits and probe tests such as cone penetration tests).

(d)

Measurements, e.g. recording of groundwater levels and in situ testing.

(e)

Collection of soil, rock and groundwater samples for subsequent testing.

Fieldwork may also involve use of indirect methods, e.g. seismic or resistivity surveys and use of satellite and airborne sensing. All observation locations (especially pits, boreholes and probe tests) shall be surveyed to the required level of accuracy.



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5.5.2 Selection of investigation methods The methods to be used for investigation should be selected taking account of— (a)

objectives of the investigation;

(b)

site conditions;

(c)

available equipment;

(d)

cost and time constraints;

(e)

health, safety and environmental considerations; and

(f)

regulatory requirements.

NOTES: 1 A list of some of the available field investigation methods is provided in Appendix A. Laboratory studies may also be required to measure the properties of materials. 2 A list of some of the available laboratory investigation methods is provided in Appendix B. 3 Notes on groundwater considerations are provided in Appendix C.

5.5.3 Data collection and record keeping


Results from routine field tasks shall be recorded in the field (either electronically or on paper). In addition to the results of the field task, records should reference the project, the date, the location and the person carrying out the work. The records of the results of fieldwork and laboratory testing should be maintained in a form suitable for archival and information transfer. Ideally, this should be in a digital form consistent with standards expected by the client and other professionals contributing to the project. 5.5.4 Sample handling and management 5.5.4.1 Soil Geotechnical site investigation often involves taking soil samples, which may be either disturbed or undisturbed. Project specific procedures for sample handling and labelling, transport and storage, and chain of custody, shall be developed in order to reduce deterioration in sample quality and the potential for errors. All samples shall be clearly labelled and logged with a unique reference number immediately after being taken. Samples suspected of contamination shall be identified on the label. Samples taken for geotechnical purposes should be maintained in a temperature range to avoid freezing or heat damage and wide temperature variations. As soon as practicable after sampling, samples should be stored in airtight bags or containers. Where the intention is to limit disturbance, samples should be coated with wax (preferably microcrystalline) or retained in sealed sample tubes in order to reduce moisture changes during transit to the laboratory. Excess moisture associated with sample collection, such as from drilling fluids, should be removed prior to storage. Soil should be removed from the ends of tube samples to a depth of about 25 mm, and the air gap filled by custom made plugs or molten wax, followed by end caps and adhesive tape. Undisturbed block samples should be cut and trimmed by hand and wrapped in cloth and coated with molten wax. At least three layers of cloth and wax should be applied on each surface. The sealed sample should then be placed into a wooden box with the air gap between the box and sample, filled with packing material. Sample tubes containing soft soil should be transported and stored in a vertical orientation to reduce the potential for sample disturbance, and rough handling should be avoided.



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Samples taken for the purpose of testing of the soil chemistry (such as for acid sulfate soil analysis) require special handling, and should be managed in accordance with regulatory guidelines pertaining to the relevant state or territory. 5.5.4.2 Rock Project-specific procedures for core handling and labelling, transport and storage, and chain of custody shall be developed in order to reduce deterioration in core quality and the potential for errors. The same storage temperature control criteria used for soil should be adopted for rock. Measures should be taken to mitigate moisture loss of rock core while working with it in the field. Rock core shall be placed as soon as practicable into a core box in order of increasing depth, left to right, and top to bottom. The core box shall be uniquely identified and labelled with borehole number and core run depths. In order to provide a permanent visual record, all rock core shall be photographed moist under uniform lighting conditions as soon as practicable after placement in core boxes, and prior to sampling or disturbance during logging. Each photograph should include a reference colour chart.


When core is prone to degradation on drying, the core should be wrapped in plastic film after field logging to reduce changes in moisture content. When core is fragile and may break up in the core box, it should be placed into PVC splits located within the core box. When rock core specimens are sub-sampled from the core tray for laboratory testing, a process for sample handling and management should be developed to reduce the likelihood of damage of the samples during handling and transport. Intervals of core loss or where core is extracted for testing should be marked as such, and in-filled with polystyrene or similar. Where core is observed to have degraded during handling or storage, this shall be noted on logs. 5.5.4.3 Groundwater Groundwater samples may contain dissolved or suspended materials. The method of collection, storage and treatment of samples can affect the results obtained from subsequent laboratory testing. The field procedure used to collect samples shall be recorded and reported, indicating— (a)

time of sampling;

(b)

purging prior to sample collection;

(c)

whether field filtering of the groundwater sample was carried out and if so, the type of filter;

(d)

preservation methods employed after sampling and prior to delivery to a laboratory for testing; and

(e)

quality control and assurance methods employed.

5.5.4.4 Identification and labelling of samples Sample identification shall be shown on sample bags, labels or tags and shall be secure and legible. Where bottles or containers are used to store samples, the identification should be placed on the vessel and also on the lid or cap as required. Each sample retained during the geotechnical site investigation shall be labelled, including a unique identifier. The following details should be included: (a)

Project or job number.

(b)

Date sampled.

(c)

Test pit, borehole, or hand auger hole number.



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(d)

Sample location and depth.

(e)

Sample reference number.

(f)

Any other relevant information such as requirements for special handling.

Samples suspected of containing hazardous materials should be labelled and packaged such that those handling the samples from accidental exposure are protected. 5.5.4.5 Storage of samples Prior to and during testing, samples should be stored in designated areas within the laboratory. Samples should be stored in a manner that provides protection from damage, corrosion or contamination that may invalidate test results. All samples should be stored away from direct sunlight and rain. Careless handling of undisturbed samples after they have been received by the laboratory may cause disturbance that could influence test results, potentially leading to serious design and construction consequences. All tube or block samples should therefore be handled by a competent person and stored in an upright position until required for testing, and in a location where they are not likely to be knocked over or dropped.


The potential for disturbance, moisture migration and corrosion within tube samples increases with time. It is therefore important that samples are prepared and tested in a timely manner. When samples are tested more than 30 days after their retrieval, this should be noted on the laboratory data and test results sheet. 5.6 Reporting and interpretation 5.6.1 General A report (or reports) shall be produced that presents the information obtained from the geotechnical site investigations. The report content may include— (a)

factual information and observations;

(b)

interpretations; and

(c)

opinions.

The type of report is dependent on the requirements of the project objectives and shall be as agreed during the planning stage. The various types of geotechnical engineering reports are further explained in Clauses 5.6.2 and 5.6.3. NOTE: A list of graphical symbols that may be useful for reporting purposes is contained in Appendix E.

5.6.2 Geotechnical data report This report documents the procedures employed and the data collected, and despite the fact that soil and rock logging has an interpretive nature attached to it, a geotechnical data report is considered predominantly factual and may also be referred to as a factual report. A geotechnical data report should include but may not be limited to the following information: (a)

Objectives and agreed scope.

(b)

Location and description of the project site and its history.

(c)

Plan showing investigation locations.

(d)

Description of the regional and local geology.

(e)

Records of fieldwork, including methods and results.

(f)

Laboratory testing and summary of results.



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5.6.3 Geotechnical interpretive report Interpretation is a continuous process, which should begin in the preliminary stages of data collection and should proceed as information from the ground investigation becomes available. The interpretive report should include but is not limited to the following components: (a)

Reference to the data upon which the interpretation has been made.

(b)

An interpretation of the site geology and the development of the geotechnical model.

(c)

A summary of the geotechnical properties of the ground applicable to the project.

(d)

An engineering interpretation of the implications of the ground conditions for the project.

(e)

An assessment of potential geotechnical risks to the project.

(f)

Recommendations for further work, if relevant.


In developing geotechnical interpretive reports, there are important aspects to be mindful of, which include the following: (i)

The nature and constraints of the project and proposed development These define how and where structures or facilities will interact with the ground, including the type, degree and period of loading and any site constraints. Possible impacts on the nearby built or natural environment and potential future uses of the site should be considered.

(ii)

The nature and limitations of the geotechnical model The geotechnical model is an interpretation that will change both during the course of the investigations and the development of the overall project, as more information becomes available. Reporting of the geotechnical model should clearly indicate the information on which it is based, the varying reliability of the interpretation and the process whereby an acceptable level of reliability will be achieved.

(iii) The nature and limitation of data Consistency and reliability of data assessed (previous work may have been done by different consultants standards of work and assumptions). Cross-checking and verification to practicable should be undertaken. The limitations of the data collected investigation program should be highlighted.

should be to varying the degree during the

A geotechnical interpretive report may also contain expressions of professional opinion. A professional opinion is dependent on conclusions derived from consideration of relevant available facts, interpretations and analysis and judgement. Since the process involves interpretation and judgement, opinions of professionals may differ, although substantial agreement is expected. 5.7 Review of geotechnical site investigation On completion of a geotechnical site investigation, the findings of the investigation should be reviewed against the objectives of the investigation. Where critical objectives are not adequately achieved, the consequence of this inadequacy should be considered, the risks to the project assessed and recommendations for further investigation developed. Geotechnical project risks identified in the geotechnical interpretive report may be mitigated by review of geotechnical conditions exposed during construction or by monitoring of performance (such as ground movement monitoring or groundwater level monitoring). Recommendations for such review and monitoring should form part of the geotechnical interpretive report. This may include the recommendation for development of a formal risk assessment and risk management plan.



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6 SOIL, ROCK AND GROUNDWATER 6.1 Soil description and classification 6.1.1 General The classification system adopted in this Standard differs in a number of important respects from the Unified Soil Classification System (USCS) and AS 1726—1993 and may result in some soils being named and classified differently from USCS and AS 1726—1993. A major difference is the criteria used to distinguish between coarse and fine-grained soils. A behavioural approach has been adopted in this Standard when identifying, naming and classifying soil. However, the boundary defining the change in behaviour between coarse and fine-grained soils is not a precise one. Nevertheless, this boundary has been defined in Clause 6.1.4.2, Table 1 and Figure 2. 6.1.2 Basic approach Description of soil is the process of identifying its components and assessing their relative proportions and behavioural characteristics, observing the condition and structure of the soil and interpreting its origin. Classification of soils involves allocating the soil into different soil groups on the basis of different observable characteristics.


Soil description and classification requires, as a minimum, the identification of the engineering characteristics and properties of the soil through a visual and tactile assessment. Observation and identification of a soil should be carried out in a series of logical steps where the components of the soil are considered and assessed individually. The visual–tactile assessment process may be augmented by laboratory testing. Where laboratory tests are carried out subsequent to visual–tactile assessment, and where these indicate that the visual–tactile assessment was inaccurate, logs and other records of the assessment shall be adjusted if required, and any adjustments made to the logs and other records shall be documented. Soils may be disturbed or undisturbed but if the soil is disturbed there are limits to what can be described. The approach described in this Standard is equally applicable to both natural and artificial soil materials. Although systematic description of the soil composition must be completed before classification can occur, the soil group is usually reported at the beginning of the full description and classification. 6.1.3 Systematic description A soil description should be presented as a series or list of specific terms, separated by semi-colons, generally without these being formed into sentences. A systematic and standardized order of description shall be used. When it is possible, the following characteristics shall be described: (a)

Composition of soil (disturbed or undisturbed state) The description shall include the following: (i)

Soil name (use BLOCK LETTERS).

(ii)

Plasticity, behavioural or particle characteristics of the primary soil component.

(iii) Colour of the soil. (iv)

Secondary soil components’ name(s), estimated proportion(s), plasticity, behavioural or particle characteristics, colour.

(v)

Minor soil component’s name, estimated proportion, behavioural or particle characteristics, colour and, where practical, its plasticity.

The presence of FILL and TOPSOIL shall be indicated at the beginning of the description using BLOCK LETTERS.  Standards Australia


17

(b)

AS 1726:2017

Condition of soil The description shall include the following: (i)

Moisture condition (disturbed or undisturbed state).

(ii)

Consistency of fine-grained soils (undisturbed state only).

(iii) Relative density of coarse-grained soils (determined by in situ tests). (c)

Structure of soil In the undisturbed state, the description shall include the following: (i)

Zoning.

(ii)

Defects.

(iii) Cementing. (d)

Origin of soil.

(e)

Additional observations.

NOTE: The order of descriptions given above is recommended.

6.1.4 Composition of soils 6.1.4.1 General Observations of the primary, secondary and minor soil components are used to construct the soil name, which describes the composition of the soil.


6.1.4.2 Soil components Soils are composed of solid particles, water and gas, sometimes with the inclusion of organic substances. Soil particles are differentiated on the basis of size, according to the definitions in Table 1. TABLE 1 PARTICLE SIZE DEFINITIONS Fraction Oversize

Components

Subdivision

BOULDERS

>200

COBBLES Coarse grained soil

GRAVEL

SAND

Fine grained soil

SILT CLAY

Size* mm

63–200 Coarse

19–63

Medium

6.7–19

Fine

2.36–6.7

Coarse

0.6–2.36

Medium

0.21–0.6

Fine

0.075–0.21 0.002–0.075 <0.002

* These sizes correspond approximately to standard sieve sizes.



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18

As differentiation of grain sizes of fine particles between clay and silt is difficult, and as the grain size of fine particles is less important than their engineering behaviour, the sizes in Table 1 for silts and clays are taken as indicative only, and instead, fine soils shall be described as silts or clays on the basis of their behaviour as assessed by visual tactile techniques. Additional guidance for field assessment of fine grained soils is provided in Tables 7 and 8. Soils that contain a significant organic content or a significant carbonate content shall be identified. 6.1.4.3 Identification of components


The field process for identifying soil primary components is summarized in Figure 2.



19

AS 1726:2017

Can any of t h e m ater i al b e d i s ag gre g ate d by han d in water to par t i c l e s s m all er t h a n c o b b l e s ize (< 6 3 m m)? YES

NO

Use s o il d e s c r i pt i ve ter m s for t h e m ater i al l e s s t han 6 3 m m i n s ize

D e s c r i b e p ar t i c l e s l ar g er t h a n g r ave l s (>6 3 m m) a s c o b b l e s / b o ul d er s or u s e r o c k d e s c r i pt i o n ter m s a s a p pro pr i ate

D o e s t h e s o il reac t (fiz z) w it h d ilute hydro c hl or i c ac i d? YES

NO

Cal c are o u s o r c ar b o n ate s o il ad d t h e a p pro pr i ate prefix fro m Ta b l e 5


D o v i s i b l e s o i l p ar t i c l e s (s a n d an d gr ave l) d o m inate — m ake u p m ore t han 6 5% of t h e s o il? YES

NO

C oar se gr ain e d s o il: a m ix ture of s an d an d gr ave l

Fine grained soil

D o e s t h e s o i l h ave a s p o n g y fe e l or fi brou s tex ture, w it h s i g n i f i c ant v i s i b l e o r g an i c m at ter an d an or g ani c o d our ? YES

I s t h e s o i l d ar k c o l o ure d, w i t h an or g ani c o d o ur an d s o m e v i s i b l e o r g a n i c m at ter ?

Is more than 50% of the coarse gr ain e d s o il gr ave l > 2 m m?

YES

NO

NO

NO

YES Organic soil ad d t h e prefix “ O r g ani c ” to t h e s o il nam e

D o e s t h e fin e gr ain e d s o il b e have like a s ilt — i s t h e s o i l d i l at a nt ?

GR AVEL

SAN D

PE AT

YES

NO

SILT

CL AY

NOTES: 1 Gravel, sand, silt and clay are the major components of a soil. They are defined in Table 1. 2 Assessment of component proportions is by dry mass. 3 Dilatancy is assessed on the reaction of wet soil to shaking. Table 7 provides a method of assessment of dilatancy as well as other diagnostic characteristics of silt and clay.

FIGURE 2 PROCESS FOR THE FIELD IDENTIFICATION OF SOIL PRIMARY COMPONENTS www.standards.org.au


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6.1.4.4 Soil name The soil name shall be based on the identified components of a soil and their behavioural characteristics. The components of a soil are assessed to be primary, secondary, or minor, on the basis of their significance for the probable engineering characteristics of the soil at any particular moisture content. The primary component of a soil is that component which dominates its engineering behaviour. A secondary component of a soil is any component of a soil which is not the primary component, but which is significant to the engineering properties of the soil. A minor component is present in the soil but is not significant to its engineering properties. 6.1.4.5 Assessment of primary component In the field, the size of grains in the coarse fraction is assessed from a representative portion of the soil, from which any boulders and cobbles have been removed. It may be helpful to examine the soil under air-dried and/or submerged conditions in order to achieve a clear separation between the coarse and fine fractions. In the laboratory, coarse and fine fractions can be separated by wet sieve analysis.


The primary component is chosen to reflect whether the soil is either fundamentally fine or coarse grained. This assessment is made according to whether the total dry mass of coarse fractions exceeds 65% (a coarse soil) or the total dry mass of fine fractions exceeds 35% (a fine soil). If it is a coarse grained soil, the relative proportions of the sand and gravel can be estimated or measured and the primary component identified as SAND if sand exceeds gravel, or GRAVEL if gravel exceeds sand. If it is identified as a fine grained soil, the behaviour shall be assessed to decide if the soil behaves as a silt or a clay and this will indicate primary component and soil name. Where assessed by visual tactile techniques (refer to Tables 7 and 8), a silt is indicated by low dry strength, low wet toughness and dilatancy, whereas a clay is indicated by high dry strength, high wet toughness and plasticity. Where assessed by laboratory testing, clay plots above the A-line and silt below the A-line on the Casagrande chart (refer to Clause 6.1.6 and Figure 5). In borderline cases, the terms silty CLAY or clayey SILT may be used at the discretion of the classifier, noting that there is no specifically defined criterion for their use, and that these descriptions imply only that the materials are borderline between behaving as silts or clays. The presence of cobbles and boulders shall be specifically noted by beginning the description with ‘MIXTURE OF SOIL AND COBBLES/BOULDERS’ with the word order indicating the dominant proportion first and the proportions of cobbles and or boulders described together with an indication of whether they are supported by a matrix of soil or supported by themselves. The remaining soil shall then be described. 6.1.4.6 Assessment of secondary and minor components Any accessory soil components (i.e. those other than the primary component) are deemed to be either secondary or minor components, on the basis of their type and their amount, as determined by their presence on a percentage dry mass basis, according to Table 2. A visual aid to assessing the proportions of coarse particles is provided in Figure 3.



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AS 1726:2017

TABLE 2 DESCRIPTIVE TERMS FOR ACCESSORY (SECONDARY AND MINOR) SOIL COMPONENTS In coarse grained soils Designation of components

% Fines 5

Minor

Terminology

Add ‘trace clay/silt’ to description, as applicable

>5, 12 Add ‘with clay/silt’ to description, as applicable


Secondary

>12

Prefix soil name as ‘silty’ or ‘clayey’, as applicable

5%

% Accessory coarse fraction

In fine grained soils

Terminology

15

Add ‘trace sand/gravel’ to description, as applicable

>15, 30

Add ‘with sand/gravel’ to description, as applicable

>30

12%

Prefix soil name with ‘sandy’ or ‘gravelly’, as applicable

% Sand/ gravel 15

Terminology

Use ‘trace’

>15, 30 Add ‘with sand/gravel’ to description, as applicable >30

Prefix soil name with ‘sandy’ or ‘gravelly’, as applicable

3 5%

FIGURE 3 DIAGRAM OF VARIOUS PERCENTAGES OF GRAINS

6.1.4.7 Assignment of a name The name of a soil is made up of the primary and secondary components. The primary component is included as a noun, written in BLOCK LETTERS on logs, qualified by the secondary components (if present), included as adjectives. Minor fractions are not included in the name, but are included in the description using phrases which include the words ‘trace’ or ‘with’, according to their relative importance, as indicated in Table 2. As an example, consider a soil with 30% plastic fines and 70% coarse fractions, which comprise 10% gravel and 60% sand. The soil is coarse and sand is the primary component. Gravel is a minor component and does not appear in the name. The plastic fines exceed 12% and are a secondary component, so ‘clayey’ is added as an adjective to the word ‘sand’. Hence it would be named ‘Clayey SAND’.



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22

6.1.4.8 Peat soils Organic content of soils can have a significant effect on their geotechnical properties. Colour and odour are the key properties for field identification of organic soils. Organic soils are usually either dark grey or black. Fresh, moist organic soils generally have a mouldy odour which can be intensified by heating. Putrefying, rotten organic components in soil can be recognized by their odour typical of hydrogen sulfide, which can be intensified by pouring dilute hydrochloric acid on the sample. Dry inorganic clays have an earthy odour after being moistened. Organic soils should be named with ‘Organic’ preceding the primary soil name. For example, ‘Organic CLAY’ or ‘Organic SILT’. Peat can be identified in the field by its spongy feel and fibrous texture. Where laboratory tests are available, organic soils and peat may be identified using Table 3. Table 4 provides terms that may be used to describe the degree of decomposition of Peat. TABLE 3 IDENTIFICATION OF ORGANIC SOILS USING LABORATORY TESTS Material

Organic content – % of dry mass

Inorganic soil

<2


Organic soil

2 to 25

Peat

>25

TABLE 4 DESCRIPTIVE TERMS FOR THE DEGREE OF DECOMPOSITION OF PEAT Term Fibrous

Decomposition Little or none

Remains

Squeeze

Clearly recognizable

Only water No solids

Pseudo-fibrous Moderate

Mixture of fibres and amorphous paste

Turbid water <50% solids

Amorphous

Not recognizable

Paste >50% solids

Full

6.1.4.9 Carbonate soils The carbonate content of soils can have a significant effect on their geotechnical properties as soil particles composed of calcium carbonate can have high porosity and low crushing strengths. The carbonate content should be assessed by the application of droplets of dilute hydrochloric acid (10% HCl, see Note to Table 5). Table 5 gives an approximate carbonate content based on the reaction to acid, and provides descriptive terms for carbonate content.



23

AS 1726:2017

TABLE 5 ASSESSMENT OF CARBONATE CONTENT Term

Reaction to acid

Approximate carbonate content

Non-calcareous

HCl produces no effervescence

Negligible

Calcareous

HCl produces weak or sporadic effervescence

<50%

Carbonate

HCl produces clear sustained effervescence

>50%

NOTE: 10% hydrochloric acid is made by taking 10 mL of concentrated HCl acid solution (36% HCl) and making it up to 100 mL. This gives 3.6% HCl by mass which is about 1.2 molar.

6.1.4.10 Plasticity and behaviour (fine grained soils) When laboratory tests are available, clay and silt, both alone and in mixtures with coarser material, shall be described according to their plasticity as defined in Table 6. TABLE 6 DESCRIPTIVE TERMS FOR PLASTICITY Accessed by MONASH UNIVERSITY LIBRARY on 23 May 2017 (Document currency not guaranteed when printed)

Descriptive term Non-plastic Low plasticity Medium plasticity High plasticity

Range of liquid limit for silt

Range of liquid limit for clay

Not applicable

Not applicable

50

35

Not applicable

>35 and 50

>50

>50

When laboratory tests are not available, plasticity and soil behaviour are assessed in the field using the visual–tactile techniques described in Table 7. These procedures are to be performed on particles less than 0.2 mm in size. For field classification purposes, screening is not intended, simply remove by hand the coarse particles that interfere with the tests. Table 8 gives a guide to typical soil names and plasticity characteristics.




FIELD ASSESSMENT OF FINE GRAINED SOILS Dry strength Mould a pat of soil to the consistency of putty, adding water if necessary. Allow the pat to dry completely by oven, sun or air drying, and then test its strength by breaking and crumbling between the fingers. This strength is a measure of the character and quantity of the colloidal fraction contained in the soil. The dry strength increases with increasing plasticity. High dry strength is characteristic for clays of the CH group. A typical inorganic silt possesses only very low dry strength. Silty fine sands and silts have about the same dry strength, but can be distinguished by feel when powdering the dried specimen. Fine sand feels gritty whereas a typical silt has the smooth feel of flour.

Dilatancy (reaction to shaking)

Toughness (consistency near plastic limit) 3.

Mould a pat of soil to the consistency of putty. If too dry, add water, and if sticky, the specimen should be spread out in a thin layer and allowed to lose some moisture by evaporation. Then, roll a thread of the soil by hand on a smooth surface or between the palms until it is about 3 mm in diameter. The thread is then folded and re-rolled repeatedly. During this manipulation the moisture content is gradually reduced, the specimen stiffens, finally loses its plasticity, and crumbles. When the thread crumbles, the pieces should be lumped together with a kneading action. The plastic limit has been reached, when the soil crumbles at about 3 mm thickness. The tougher the thread near the plastic limit and the stiffer the lump when it finally crumbles, the more potent is the colloidal clay fraction in the soil. Weakness of the thread at the plastic limit and rapid loss of coherence of the lump below the plastic limit indicate either inorganic clay of low plasticity, or materials such as kaolintype clays and organic clays which plot below the A-line. Highly organic clays have a very weak and spongy feel at the plastic limit.

Criteria for describing dilatancy

Criteria for describing toughness

Criteria for describing dry strength


None

The dry specimen crumbles into powder with mere pressure of handling.

None

No visible change in the specimen.

Low

The dry specimen crumbles into powder with some finger pressure.

Slow

Medium

The dry specimen breaks into pieces or crumbles with considerable finger pressure.

Water appears slowly on the surface of the specimen during shaking and does not disappear or disappears slowly upon squeezing.

High

The dry specimen cannot be broken with finger pressure. Specimen will break into pieces between thumb and a hard surface.

Very High

The dry specimen cannot be broken between the thumb and a hard surface.

Rapid

Water appears quickly on the surface of the specimen during shaking and disappears quickly upon squeezing.

Low

Only slight pressure is required to roll the thread near the plastic limit. The thread and the lump are weak and soft.

Medium

Medium pressure is required to roll the thread to near the plastic limit. The thread and the lump have medium stiffness.

High

Considerable pressure is required to roll the thread to near the plastic limit. The thread and the lump have very high stiffness.

24

Prepare a pat of moist soil with a volume of about 10 cm Add enough water, if necessary, to make the soil soft but not sticky. Shake the pat horizontally in the palm of the hand, striking vigorously against the other hand several times. A positive reaction consists of the appearance of water on the surface of the pat which changes to a livery consistency and becomes glossy. When the sample is squeezed between the fingers, the water and gloss disappear from the surface. The pat stiffens, and finally it cracks or crumbles. The rapidity of appearance of water during shaking and its disappearance during squeezing assist in identifying the character of the fines in the soil. Very fine clean sands give the quickest and most distinct reaction whereas a plastic clay has no reaction. Inorganic silt, such as a typical rock flour, shows a relatively rapid reaction.

AS 1726:2017


TABLE 7

25

AS 1726:2017

TABLE 8 IDENTIFICATION OF FINE GRAINED SOILS BY VISUAL—TACTILE METHODS Soil description

Identification of inorganic fine-grained soils Dry strength

Dilatancy

Toughness and plasticity

None to low

Slow to rapid

Low or thread cannot be formed

Clayey SILT—Clay/silt mixtures of low plasticity

Low to medium

None to slow

Low to medium

Silty CLAY—Silt/clay mixtures of medium plasticity

Medium to high

None to slow

Medium

High to very high

None

High

SILT

High plasticity CLAY

6.1.4.11 Particle characteristics (coarse grained soil) Particle size shall be reported in millimetres or by use of the subdivisions in Table 1.


The spread of sizes represented should be described using one of the following terms (refer to Table 9): (a)

‘Well graded’—having good representation of all particle sizes from the largest to the smallest.

(b)

‘Poorly graded’—with one or more intermediate sizes poorly represented.

(c)

‘Gap graded’—with one or more intermediate sizes absent.

(d)

‘Uniform’—essentially of one size.

The assignment of one of the above terms may be made solely on the basis of visual–tactile examination, or on the basis of laboratory measurements. Where laboratory data are available, a well graded soil is one for which the coefficient of uniformity Cu > 4 and the coefficient of curvature 1 < Cc < 3. Otherwise, the soil is poorly graded. These coefficients

D  D where D10 , D30 and D60 are those grain sizes for are given by Cu  60 and Cc  30 D10 D60 D10 which 10%, 30% and 60% of the soil grains are smaller. 2

Where significant, particle shape should be reported as follows: (i)

Equi-dimensional particles: ‘rounded’, ‘sub-rounded’, ‘sub-angular’, or ‘angular’, as shown in Figure 4.

(ii)

Essentially two-dimensional particles with the third dimension small by comparison: ‘flaky’ or ‘platy’.

(iii) Essentially one-dimensional particles with the other two dimensions small by comparison: ‘elongated’. Where significant, particle composition should be described using the rock or mineral name (e.g. quartz sand or carbonate sand).



AS 1726:2017

26

Rounded

A n g u l ar

Sub-rounded

Su b - a n g u l ar

FIGURE 4 PARTICLE SHAPES


6.1.5 Colour The colour of a soil shall be described in the moist condition, using simple terms such as black, white, grey, red, brown, orange, yellow, purple, green, blue, etc. These may be modified as necessary, e.g. by ‘pale’, ‘dark’, or ‘mottled’. Borderline colours may be described as a combination of these colours, e.g. red-brown. Where a soil colour consists of a primary colour with a secondary mottling it shall be described as follows: (Primary colour) mottled (secondary colour), e.g. grey mottled red-brown clay. Where a soil consists of two colours present in roughly equal proportions the colour shall be described as mottled (first colour) and (second colour), e.g. mottled brown and red-brown. A mixture of distinct colours may be described as, for example, mottled red/grey. 6.1.6 Soil classification Soil classification can occur after the soil composition has been described. Soils shall be classified into one of a number of soil groups designated by a two character group symbol. Classification is based on the grading of the coarse particles, and the behaviour and plasticity of the fraction of the material passing the 0.425 mm sieve. This may be assessed by visual–tactile methods or from laboratory tests. Where the classification derived from laboratory tests conflicts with that derived from visual–tactile methods the conflict shall be reported and some or all of the visual–tactile classifications may be modified and, where modified, this shall be documented. The group symbol classifications are given in Tables 9 and 10. Soils are classified to reflect their primary component and significant secondary components. The first classification symbol shall be G, S, M, or C, where the primary components are gravel, sand, silt or clay, respectively. For soils classified as coarse grained soils (S or G), the second symbol reflects either the grading of the coarse fraction, or the presence of clay or silt fines. For soils classified as fine soils (C, M or O), the second symbol reflects the plasticity of the sub 0.425 mm portion of the soil. In cases where laboratory measurements of the Atterberg limits are available, Figure 5 should be used to assist in classifying the fine grained soil.  Standards Australia


27

AS 1726:2017

TABLE 9 CLASSIFICATION OF COARSE GRAINED SOILS Major divisions


Coarse grained soil (more than 65% of soil excluding oversize fraction is greater than 0.075 mm)

GRAVEL (more than half of coarse fraction is larger than 2.36 mm)

SAND (more than half of coarse fraction is smaller than 2.36 mm)

Group symbol

Typical names

Field classification of sand and gravel

Laboratory classification

GW

Gravel and gravel-sand mixtures, little or no fines

Wide range in grain 5% fines size and substantial amounts of all intermediate sizes, not enough fines to bind coarse grains, no dry strength

GP

Gravel and gravel-sand mixtures, little or no fines, uniform gravels

Predominantly one size or range of sizes with some intermediate sizes missing, not enough fines to bind coarse grains, no dry strength

GM

Gravel-silt mixtures and gravel-sand-silt mixtures

‘Dirty’ materials with 12% fines, Fines behave excess of non-plastic fines are as silt fines, zero to medium silty dry strength

GC

Gravel-clay mixtures and gravel-sand-clay mixtures

‘Dirty’ materials with 12% fines, Fines behave excess of plastic fines are as clay fines, medium to high clayey dry strength

SW

Sand and gravel-sand mixtures, little or no fines

Wide range in grain 5% fines size and substantial amounts of all intermediate sizes, not enough fines to bind coarse grains, no dry strength

SP

Sand and gravel-sand mixtures, little or no fines

Predominantly one size or range of sizes with some intermediate sizes missing, not enough fines to bind coarse grains, no dry strength

SM

Sand-silt mixtures

‘Dirty’ materials with 12% fines, excess of non-plastic fines are fines, zero to medium silty dry strength

SC

Sand-clay mixtures

‘Dirty’ materials with 12% fines, excess of plastic fines are fines, medium to high clayey dry strength

5% fines

5% fines

Cu > 4 1 < Cc < 3

Fails to comply with above

Cu > 6 1 < Cc < 3

Fails to comply with above

NA

NOTE: Where the grading is determined from laboratory tests, it is defined by coefficients of curvature C c and uniformity C u derived from the particle size distribution curve, as specified in Clause 6.1.4.11.

For fines contents between 5% and 12%, the soil shall be given a dual classification comprising the two group symbols separated by a dash, e.g. for a gravel with between 5% and 12% silt fines, the classification is GP-GM. Soils that are dominated by boulders, cobbles or peat (Pt) are described separately and are not classified. www.standards.org.au


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TABLE 10 CLASSIFICATION OF FINE GRAINED SOILS

Major divisions

Fine grained soils (more than 35% of soil excluding oversize fraction is less than 0.075 mm)

SILT and CLAY (low to medium plasticity, %)

Group symbol


Highly organic soil


Typical names

Dry strength

Dilatancy

Laboratory classification

Toughness % < 0.075 mm

ML

Inorganic silt and very fine sand, rock flour, silty or clayey fine sand or silt with low plasticity

None to low

Slow to rapid

Low

Below A line

CL, CI

Inorganic clay of low to medium plasticity, gravelly clay, sandy clay

Medium to high

None to slow

Medium

Above A line

Organic silt

Low to medium

Slow

Low

Below A line

Inorganic silt

Low to medium

None to slow

Low to medium

Below A line

OL SILT and CLAY (high plasticity)

Field classification of silt and clay

MH CH

Inorganic clay of high plasticity

High to very high

None

High

Above A line

OH

Organic clay of medium to high plasticity, organic silt

Medium to high

None to very slow

Low to medium

Below A line

—

—

—

—

Pt

Peat, highly organic soil


29

AS 1726:2017

60

e ) lin - 8 L e (W th 9 0. = U

50

PL ASTICIT Y IN DE X I P, %

IP 40

t

he

CH or O H

IP

=

0.

e 0) lin -2 L (W 73 A

30 CI or OI 20

M H or O H CL or O L

10 CL - M L

M L or O L 0 10

0

20

30

40

50

60

70

80

90

10 0

LIQ UID LIMIT W L , %


NOTE: The U line is an approximate upper bound for most natural soils. Data which plot above the U line may represent unusual/problem soil behaviour, or unreliable data and should be considered carefully.

FIGURE 5 MODIFIED CASAGRANDE CHART FOR CLASSIFYING SILTS AND CLAYS ACCORDING TO THEIR BEHAVIOUR

6.1.7 Condition of soil The condition of a soil shall be described. The following terms are used to describe the soil condition: (a)

Moisture condition Where the moisture condition of a coarse grained soil is estimated in the field it should be described by the appearance and feel of the soil using one of the following terms: (i)

Dry (D)

– Non-cohesive and free-running.

(ii) Moist (M) – Soil feels cool, darkened in colour. – Soil tends to stick together. (iii) Wet (W)

– Soil feels cool, darkened in colour. – Soil tends to stick together, free water forms when handling.

The moisture condition of fine grained soils shall be described based on a judgement of the soil’s moisture condition relative to the plastic limit (or liquid limit for soils with high moisture contents), as follows: (A)

‘Moist, dry of plastic limit’ (hard and friable or powdery) (or ‘w < PL’).

(B)

‘Moist, near plastic limit’ (soils can be moulded at a moisture content approximately equal to the plastic limit) (or ‘w ≈ PL’).

(C)

‘Moist, wet of plastic limit’ (soils usually weakened and free water forms on hands when handling) (or ‘w > PL’).

(D)

‘Wet, near liquid limit’ (or ‘w ≈ LL’).

(E)

‘Wet, wet of liquid limit’; (or ‘w > LL’).



AS 1726:2017

(b)

30

Consistency The consistency of cohesive soils describes the ease with which the soil can be remoulded. Consistency shall be described using the terms in Table 11. Cohesive soils include fine-grained soils, and coarse grained soils with sufficient fine-grained components to induce cohesive behaviour. In the field, the consistency of the soil may be assessed either by tactile means, or by measuring the undrained shear strength by mechanical testing (refer to Table 11). Mechanical determination methods should be carried out in accordance with AS 1289 series. Methods not covered by AS 1289 may also be used provided the method is suitably calibrated. Values of undrained shear strength assessed by field tests for classification purposes may not necessarily be appropriate for use in design. TABLE 11 CONSISTENCY TERMS FOR COHESIVE SOILS Field guide to consistency

Indicative undrained shear strength kPa

Very Soft (VS)

Exudes between the fingers when squeezed in hand

12

Soft (S)

Can be moulded by light finger pressure

>12 and 25

Firm (F)

Can be moulded by strong finger pressure

>25 and 50

Stiff (St)

Cannot be moulded by fingers

>50 and 100

Very Stiff (VSt)

Can be indented by thumb nail

>100 and 200

Hard (H)

Can be indented with difficulty by thumb nail

Friable (Fr)

Can be easily crumbled or broken into small pieces by hand


Consistency

>200 —

NOTE: Consistency is affected by the moisture content of the soil at the time of measurement.

(c)

Relative density of non-cohesive, coarse grained soils The density of non-cohesive soils is described in terms of density index, as defined in AS 1289.5.6.1. The relative density of coarse grained soils is inherently difficult to assess by visual or tactile means and these techniques should not be used. Relative density assessment should be carried out using a combination of penetration test procedures (standard penetration test, dynamic penetrometer or static cone penetration test, as specified in AS 1289, Methods 6.3.1, 6.3.2, 6.3.3 or 6.5.1) in conjunction with well-established correlations. Alternatively, in situ density tests may be conducted in association with minimum and maximum density tests performed in the laboratory. Table 12 lists descriptive terms applicable to these soils.



31

AS 1726:2017

TABLE 12 RELATIVE DENSITY OF NON-COHESIVE SOILS Term Very Loose (VL)

Density index % 15

Loose (L)

>15 and 35

Medium Dense (MD)

>35 and 65

Dense (D)

>65 and 85

Very Dense (VD)

>85

NOTE: The moisture content may influence the inferred relative density.


(d)

Cementation Soils or defects within soils may be cemented together by various substances. The following terms should be used to describe cemented soils: (i)

‘Weakly cemented’—the soil may be easily disaggregated by hand in air or water.

(ii)

‘Moderately cemented’—effort is required to disaggregate the soil by hand in air or water.

Where consistent cementation throughout a soil mass is identified as a duricrust, it shall be described in accordance with Clause 6.2 and Table 18. The nature of the cementing agent shall be identified if possible from its appearance, strength, and reaction to acid. 6.1.8 Mass properties of soil If present, the structure of the soil shall be described. The following terms should be used. If alternative descriptions are used, the terms shall be defined: (a)

Zoning Soil in situ or in samples may consist of separate zones differing in colour, grain size or other properties. The patterns of these zones shall be described using the following terms: (i)

‘Layer’, i.e. the zone is continuous across the exposure or sample.

(ii)

‘Lens’, i.e. a discontinuous layer of different material, with lenticular shape.

(iii) ‘Pocket’, i.e. an irregular inclusion of different material. The thickness, orientation and any distinguishing features of the zones shall be described. The boundaries between zones shall be described as gradational or distinct. ‘Interbedded’ or ‘interlaminated’, shall be used if layers of alternating soil types are too thin to describe individually. NOTE: The maximum/mean/minimum thickness of the beds/laminations should be given.

(b)

Defects Defects in soil shall be described using the terms defined in Table 13. NOTE: The approximate dimensions, orientation and spacing of defects should be given.

(c)

Mixed soils ‘Intermixed’ may be used to describe two or more soil types arranged in an irregular manner.



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TABLE 13 SOIL DEFECT TYPES


Term

Definition

Parting

A surface or crack across which the soil has little or no tensile strength. Parallel or sub parallel to layering (e.g. bedding). May be open or closed.

Fissure

A surface or crack across which the soil has little or no tensile strength but which is not parallel or sub parallel to layering. May be open or closed. May include desiccation cracks.

Sheared seam

Zone in clayey soil with roughly parallel near planar, curved or undulating boundaries containing closely spaced, smooth or slickensided, curved intersecting fissures which divide the mass into lenticular or wedge shaped blocks.

Sheared surface

A near planar, curved or undulating smooth, polished or slickensided surface in clayey soil. The polished or slickensided surface indicates that movement (in many cases very little) has occurred along the defect.

Softened zone

A zone in clayey soil, usually adjacent to a defect in which the soil has higher moisture content than elsewhere.

Diagram

S of te n e d zo n e

Tube

Tubular cavity. May occur singly or as one of a large number of separate or interconnected tubes. Walls often coated with clay or strengthened by denser packing of grains. May contain organic matter. Origins include root holes, animal burrows, tunnel erosion.

Tube cast

An infilled tube. The infill may be uncemented or weakly cemented soil or have rock properties.

Infilled seam

Sheet or wall like body of soil substance or mass with roughly planar to irregular near parallel boundaries which cuts through a soil mass. Formed by infilling of open defects.

NOTE: Where practical, the surface of the defects shall be described in terms of shape (planar, stepped, curved, irregular), surface roughness (rough, smooth, polished, slickensided), and coating.

6.1.9 Soil origin The geological origin of the soil shall be interpreted and recorded. Where there is doubt, the terms ‘possibly’ or ‘probably’ shall be used. Soil origin cannot generally be deduced on the basis of material appearance and properties alone; it requires further geological evidence and broader field observation. The geological origin of a soil may be interpreted from an assessment of the geological and geomorphological setting in which it occurs. Soil deposits can be formed in situ from the weathering of parent materials, or formed from the accumulation of soil materials formed elsewhere and transported to their present location. Transported soils may include both natural and anthropogenic materials.



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Useful descriptors of soil origin may include, but are not limited to, the following: (a)

Residual soil Formed directly from in situ weathering of geological formations. These soils no longer retain any visible structure or fabric of the parent soil or rock material.

(b)

Extremely weathered material Formed directly from in situ weathering of geological formations. Although this material is of soil strength it retains the structure and/or fabric of the parent rock material.

(c)

Alluvial soil Deposited by streams and rivers.

(d)

Estuarine soil Deposited in coastal estuaries, and including sediments carried by inflowing rivers and streams, and tidal currents.

(e)

Marine soil Deposited in a marine environment.

(f)

Lacustrine soil Deposited in freshwater lakes.

(g)

Aeolian soil Carried and deposited by wind.

(h)

Colluvial soil Soil and rock debris transported down slopes by gravity, with or without the assistance of flowing water and generally deposited in gullies or at the base of slopes. Colluvium is often used to refer to thicker deposits such as those formed from landslides, whereas the term ‘slopewash’ may be used for thinner and more widespread deposits that accumulate gradually over longer geological timeframes.

(i)

Topsoil Mantle of surface and/or near-surface soil often but not always defined by high levels of organic material, both dead and living. Remnant topsoils are topsoils that have subsequently been buried by other transported soils. Roots of trees may extend significantly into otherwise unaltered soil and the presence of roots is not a sufficient reason for describing a material as topsoil. ‘TOPSOIL’ should be emphasized by the use of BLOCK LETTERS.

(j)

Fill Any material which has been placed by anthropogenic processes described in detail in Clause 6.1.1. ‘FILL’ should be emphasized on logs by the use of BLOCK LETTERS.

Soils should be assigned to a stratigraphic unit. Where there is doubt, the terms ‘possibly’ or ‘probably’ shall be used. 6.1.10 Additional observations Where significant these shall be recorded. Examples include changes in colour over time, odour, hydrocarbon or other contamination, the presence of burrowing animals and delineation of soil horizons. Where there is some doubt as to the representativeness or quality of a sample, this shall be stated. If this affects the overall description, this shall again be reflected in the overall description. If the material is assessed to be not representative, terms such as ‘poor recovery’, ‘non-intact’, ‘recovered as’ or ‘probably’ shall be applied. 6.1.11 Description of fills 6.1.11.1 General Where fill is present, the thickness and composition shall be recorded. The fact that soils have been deposited on a site by other than natural mechanisms may have significant geotechnical and environmental implications. The material shall be identified clearly in the field log as fill, and then described in sufficient detail to record the nature and extent of the particular materials that are present. When describing fill, the word ‘FILL’ shall precede the soil name.



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Significant fill materials that may be encountered and should be noted during an investigation are given in Table 14, although this list is not exhaustive. Typical characteristics of fill include— (a)

unusually variable range of colours;

(b)

very distinct changes in soil profile;

(c)

presence of foreign objects such as glass, plastic, slag;

(d)

buried organic matter in some instances; and

(e)

‘cloddiness’ of clay soil indicating previous disturbance by excavation.

Fill placed in accordance with AS 3798 or other controlled method, as demonstrated by construction documentation, may be considered as controlled fill. The presence of controlled fill should be included under ‘additional observations’ (refer to Clause 6.1.10). Fill for which no construction documentation is available shall be considered uncontrolled fill. Wherever possible, descriptions of uncontrolled fill shall follow the system used for other soils as described in Clause 6.1.


6.1.11.2 Detailed descriptions A list of the main components of uncontrolled fill shall be made in order of decreasing importance. For solid objects, the composition and size shall be given either in millimetres (or metres for larger objects) or using standard soil particle sizes, e.g. ‘15% cobble to boulder sized blocks of reinforced concrete’. For hollow objects, state whether they are empty (and potentially compressible), infilled or crushed. Any putrescible materials shall also be explicitly noted. Additional comment, regarding the structure of the material shall be given. Examples include the following: (a)

The presence of voids.

(b)

If waste is contained in drums or bags.

(c)

If there are discrete layers of materials.

(d)

Any items which could indicate the age of the uncontrolled fill should be identified, such as dates on newspapers, distinctive bottles, or ‘best before’ dates on food and drink packaging.

The terms in Table 14 may be useful in describing organic and artificial materials.



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TABLE 14 DESCRIPTIVE TERMS FOR FILL MATERIALS Generalized terms Organic matter

Typical descriptions Fibrous peat Charcoal Wood fragments Roots (greater than 2 mm diameter) Root fibres (less than 2 mm diameter) Night soil Putrescible waste

Artificial materials

Oil, bitumen Masonry Concrete rubble Fibrous plaster, plasterboard Timber pieces, wood shavings, sawdust Iron filings, drums, steel bars, steel scrap


Bottles, broken glass Leather Slag Chitter, ash, tailings Asbestos, fibre cement Rubber tyres

6.1.12 Problematic soils Some of the more common characteristics of problematic soil include— (a)

volumetric change;

(b)

loss of strength; and

(c)

corrosive potential.

NOTE: Further information about the behaviour of selected problematic soil types is provided in Appendix D.

6.1.13 Examples of soil description and classification To illustrate the application of the provisions of Clause 6.1, the following examples are provided: (a)

For a red-brown, basaltic soil with desiccation cracks, which is assessed as comprising 20% fine to medium, sub-rounded gravel in a very stiff, moist, medium plasticity clayey matrix, an appropriate description would be: CI CLAY with gravel, red-brown, medium plasticity, very stiff; gravel 20%, fine to medium, sub-rounded; moist, with desiccation cracks; residual.

(b)

For a ‘dirty’, grey, medium grained sand encountered on a tidal flat in the Fullerton Cove area, assessed to have <5% silt fines, wet, and found to be medium dense as assessed by dynamic penetrometer, an appropriate description would be: SP SAND, trace silt, grey, medium grained; medium dense; dry; marine; Tomago Sand Beds.



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6.2 Rock identification, description and classification 6.2.1 Basic concepts Rock description and classification shall distinguish between: (a)

Rock material The intact rock that is bounded by defects.

(b)

Defect A discontinuity, fracture, break or void in the material or materials across which there is little or no tensile strength.

(c)

Structure The nature and configuration of the different defects within the rock mass and their relationship to each other.

(d)

Rock mass The entirety of the system formed by all of the rock material and all of the defects that are present.

Rock mass behaviour is generally controlled by the nature and configuration of defects and describing the type, character and distribution of defects is an essential part of the description of many rock masses. Rock mass behaviour may also be related to the nature and scale of the project elements. 6.2.2 Overview The following characteristics shall be described: NOTE: Characteristics should be reported in the order given below. Accessed by MONASH UNIVERSITY LIBRARY on 23 May 2017 (Document currency not guaranteed when printed)

(a)

Description of rock material: (i)

Rock NAME (BLOCK letters).

(ii)

Grain size and type.

(iii) Colour. (iv)

Fabric and texture.

(v)

Inclusions or minor components.

(vi)

Moisture content.

(vii) Durability. (b)

Classification of the rock material condition: (i)

Strength.

(ii)

Weathering and/or alteration.

(c)

Description of defects.

(d)

Interpreted stratigraphic unit.

(e)

Geological structure.

The following characteristic may also be described: (i)

Parameters related to core drilling.

(ii)

Classification of the rock mass: (A)

Rock mass weathering.

(B)

Duricrust development.

(C)

Rock mass characterization.



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6.2.3 Description of rock material 6.2.3.1 Rock name


Simple rock names should be used to provide a reasonable engineering description rather than a precise geological classification. The rock name should be chosen by considering the nature and shape of the grains or crystals, the texture and fabric of the rock material, the geological structure and setting, information from the geological map of the area and the following guidelines: (a)

Sedimentary rocks are deposited in beds, have grains that are cemented together and which are often rounded and there may be interbedded combinations of different sediment types, different beds and bedding partings and sedimentary structures such as cross bedding. They often have significant porosity. A guide to the naming of sedimentary rocks for engineering purposes is provided in Table 15.

(b)

Igneous rocks are formed from molten rock and have a crystalline texture, i.e. interlocking crystals. Most igneous rocks are massive, however a few exhibit flow banding. They typically have low porosity, unless they contain bubbles. A guide to the naming of igneous rocks for engineering purposes is provided in Table 16.

(c)

Metamorphic rocks are formed when rocks are subject to heat and/or pressure and commonly have a directional fabric (a foliation which may be specifically a cleavage and/or a schistosity) although some are massive. They typically have low porosity and may have a crystalline texture. A guide to the naming of metamorphic rocks for engineering purposes is provided in Table 17.

(d)

Duricrust rocks are formed as part of a weathering profile and show evidence of having been cemented in situ. The cementation is often irregular and exhibits replacement textures. A guide to the naming of duricrust rocks for engineering purposes is provided in Table 18.

If a rock type cannot be identified, the material should be given a distinctive interim name until an observation by a more experienced observer or a petrographic assessment is available. Engineering properties should not be inferred directly from the rock names in Tables 15 to 18 but the use of a particular name does indicate a likely range of characteristics. The rock names given in this Standard are sufficient to describe most of the rocks that are likely to be encountered. However, they are provided as a guide only, and other names may be used where available information or local knowledge can be used to justify a more appropriate name. If alternative rock names to those provided in Tables 15 to 18 are used, then the geological characteristics of the rocks shall be briefly summarized in the report.



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TABLE 15 GUIDE TO THE NAMING OF SEDIMENTARY ROCKS At least 90% of rock is carbonate (Note 3)

Grain size mm

>2

Deposited rock type

Low porosity, indurated

CONGLOMERATE (larger rounded grains in a finer matrix) BRECCIA (angular or irregular rock fragments in a finer matrix)

LIMESTONE or DOLOMITE (Note 4) 0.06–2 0.002–0.06

Porous, core can be broken by hand

Ejected from a volcano

CALCIRUDITE AGGLOMERATE (rounded grains in a finer matrix or VOLCANIC BRECCIA (angular fragments in a finer matrix)

SANDSTONE (Notes 1,2)

CALCARENITE TUFF

MUDSTONE (Note 5)

SILTSTONE (Note 5)

CALCISILTITE

silt and clay

mostly silt

Fine grained CALCILUTITE TUFF

<0.002

CLAYSTONE (Note 6) mostly clay


NOTES: 1

Other commonly used terms for SANDSTONE are GREYWACKE (consisting mainly of rock fragments), ARKOSE (consisting mainly of feldspar) and QUARTZOSE SANDSTONE (quartz grains and siliceous cement). In some cases the proportions of the different grains in the sandstone may be estimated.

2

Sandstones may be described as fine, medium or coarse when their grains are identified as comprising fine, medium or coarse sand, respectively.

3

Where carbonate content is 50–90% the names provided should be used preceded by the word IMPURE.

4

LIMESTONE (predominantly calcium carbonate – CaCO 3 ) should be distinguished from DOLOMITE (predominantly calcium magnesium carbonate – CaMgCO3 ) where possible.

5

SHALE is a fissile mudstone with preferential weakness parallel to bedding.

6

Rocks displaying alternating fine inter-laminations of different grainsize (e.g. SILTSTONE/CLAYSTONE or SILTSTONE/FINE SANDSTONE) may be referred to as LAMINITE.

7

BRECCIA is any sedimentary rock composed of angular fragments in a finer matrix.

8

COAL is a mostly organic rock that consists of indurated accumulations of plant debris.

9

The term carbonaceous may be added to the names in the table where a rock is assessed to contain a significant carbon content.

10 EVAPORITES are rocks that consist mainly of salts such as halite, anhydrite or gypsum. 11 FLINT and CHERT are amorphous or cryptocrystalline quartz, from any origin. 12 Cements may be, for example, siliceous, calcareous, limonitic, carbonaceous, argillaceous (clay), or zeolite and where identified this should be noted. 13 The depositional origin of the sediment may be indicated by prefixes such as aeolian, glacial, or marine.



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TABLE 16 GUIDE TO THE NAMING OF IGNEOUS ROCKS Massive crystalline

Grain size mm

Much quartz, pale (felsic)

Coarse (>2) Medium (0.06–2) Fine (<0.06)

Little quartz, dark (mafic)

GRANITE

DIORITE

GABBRO

MICROGRANITE

MICRODIORITE

DOLERITE

RHYOLITE

ANDESITE

BASALT

NOTES: 1

PEGMATITE is an igneous rock consisting of large crystals often forming a dyke or vein.

2

OBSIDIAN and VOLCANIC GLASS are rocks that have cooled too quickly for crystals to develop and consequently have an amorphous (glassy) texture.

3

APLITE may occur as light coloured veins of quartz and feldspar in other igneous rocks.

4

PORPHYRY is an igneous rock consisting of large crystals in a much finer matrix.

TABLE 17 GUIDE TO THE NAMING OF METAMORPHIC ROCKS


Grain size mm

Foliated

Non-foliated

Coarse (>2)

GNEISS—well developed but often widely spaced foliation sometimes with schistose bands

Medium (0.06–2)

SCHIST—well developed foliation with much mica, QUARTZITE—fused quartz grains some micas larger than 2 mm SERPENTINITE—usually a grey and green rock formed by the PHYLLITE—slightly undulose foliation sometimes alteration of mafic igneous rocks spotted. HORNFELS—usually a fine SLATE—well developed planar cleavage grained rock formed by thermal metamorphism

Fine (<0.06)

MARBLE—crystalline calcium carbonate

NOTE: Foliated metamorphic rocks normally form by regional metamorphism and non-foliated metamorphic rocks form by contact or thermal metamorphism.

TABLE 18 GUIDE TO THE NAMING OF DURICRUST ROCKS Dominant cementing mineralogy Iron oxides and hydroxides

Silica

Calcium carbonate

Gypsum

FERRICRETE

SILCRETE

CALCRETE

GYPCRETE

NOTES:


1

Refer to rock mass grades in Table 25, Clause 6.2.10.2 for a classification of duricrusts.

2

Field differentiation of LIMESTONE and CALCRETE should be based on observation of textures, fabric and defects with LIMESTONE being dominated by sedimentary features and CALCRETE being dominated by replacement features.


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6.2.3.2 Grain size and type In sedimentary rocks with predominantly sand sized grains, the following terms should be used to describe the dominant or average grain size: (a)

Coarse grained—mainly 0.6 mm to 2 mm.

(b)

Medium grained—mainly 0.2 mm to 0.6 mm.

(c)

Fine grained—mainly 0.06 mm (just visible) to 0.2 mm.

In igneous and metamorphic rock types, where significant, the following terms should be used to describe the dominant or average grain size and/or the grain size may be recorded in millimetres: (i)

Coarse grained—mainly greater than 2 mm.

(ii)

Medium grained—mainly 0.06 mm to 2 mm.

(iii) Fine grained—mainly less than 0.06 mm (just visible). If readily identifiable, the minerals should be described. 6.2.3.3 Colour


The colour of a rock shall be described in the moist condition, using simple terms such as black, white, grey, red, brown, orange, yellow, purple, green, blue, etc. These may be modified as necessary, e.g. by ‘pale’, ‘dark’ or ‘mottled’. Borderline colours may be described as a combination of these colours. 6.2.3.4 Texture and fabric The texture of a rock describes the arrangement of, or the relationship between, the grains and/or crystals that make up the rock. Terms such as porphyritic (larger crystals— phenocrysts—set in a finer groundmass), crystalline (consisting of interlocking crystals having a distinctive colour and habit), amorphous (having no definite crystalline structure), glassy (looking like manufactured glass) should be used to describe the texture where it is significant. A rock possesses a fabric where the arrangement of grains shows an alignment, a preferred orientation or a layering that is visible at the scale of outcrop or core. Where a fabric is visible it shall be described. The following are common terms for describing the type of fabric in the rock material, but other terms may be used: (a)

(b)

(c)

Sedimentary rocks: (i)

Bedding Layering produced by changes in sedimentation, which may be defined by grain size, colour, or other features.

(ii)

Lamination Similar to bedding but developed in layer thicknesses of less than 20 mm.

Metamorphic rocks: (i)

Foliation The parallel arrangement of minerals due to metamorphic processes.

(ii)

Cleavage A type of foliation developed in fine grained metamorphic rocks such as slates.

Igneous rocks—Flow banding A layering produced during flow of a partially solidified igneous rock that causes crystals to become oriented. Sometimes called a trachytic fabric.



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AS 1726:2017

The most important observation to make is the effect that the fabric has on rock strength. That is, does the fabric have no significant effect on the strength, which is therefore isotropic, or does the fabric cause the strength to be anisotropic, which means that the rock will have different strengths in different directions. The visual appearance of the rock is not necessarily a good indicator of the influence of any fabric on strength and the rock should be broken to establish the influence of the fabric. The degree of development of the fabric shall be described using the following terms: (i)

Indistinct fabric There is little effect on strength properties.

(ii)

Distinct fabric The rock may break more easily parallel to the fabric. NOTE: Where ‘fabric’ is any appropriate geological term for the relevant rock type such as those described above.

The orientation and thickness of the layers defining the fabric shall be described directly, e.g. distinct bedding dipping at 30°, 30 mm to 100 mm thick. 6.2.3.5 Features, inclusions and minor components


Features, inclusions and minor components within the rock material shall be described where those features could be significant, i.e. the features could influence engineering behaviour. Examples of features which could be significant under certain circumstances include— (a)

gas bubbles (vesicles if empty; amygdules or amygdales if mineralized) in igneous rocks;

(b)

veins of quartz, calcite or other minerals;

(c)

pyrite crystals and nodules or bands of ironstone or carbonate;

(d)

cross-stratification in sandstone; and

(e)

clast or matrix support in conglomerates and breccia.

The general proportions and dimensions of features and inclusions should be described directly, e.g. ‘about 30% vesicles from 2 mm to 5 mm in size’. 6.2.3.6 Moisture content Where significant, this shall be described by the feel and appearance of the rock using one of the following terms: (a)

Dry Looks and feels dry.

(b)

Moist Feels cool, darkened in colour, but no water is visible on the surface.

(c)

Wet Feels cool, darkened in colour, water film or droplets visible on the surface.

The moisture content of rock cored with water may not be representative of its in situ condition, i.e. the moisture content may be higher due to the drilling water coming in contact with the core. 6.2.3.7 Durability If the rock material shows any tendency to develop cracks, break into smaller pieces or disintegrate in air or in contact with water, or if there is any other evidence that the rock material may not have adequate durability, this shall be noted and described. 6.2.4 Classification of rock material condition 6.2.4.1 Rock material strength The strength of the rock material shall be classified using Table 19. It should be based on the uniaxial compressive strength (UCS). The UCS for classification purposes should be based on specimens tested at close to their in situ moisture content. Where strength is measured at another moisture condition, this shall be clearly stated. www.standards.org.au


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Where it is not practical to conduct UCS tests, or adequate UCS test data are not available, classification of strength may be made on the basis of the point load strength index (Is(50)) measured on specimens close to their in situ moisture condition. Table 19 implies a correlation between Is(50) and UCS that should be used for classification, unless a correlation is or has been developed for specific rock types at the location of the investigation. Established and documented correlations between UCS and Is(50) may also be used for classification purposes. If point load strength tests are used to assess the strength of rock with a distinct fabric, the strength perpendicular to the planar anisotropy shall be used for classification purposes and the strength anisotropy index (Ia(50)) shall be reported where possible. For preliminary field classification, or where testing is not practical, the field assessment of strength in Table 19 provides guidance on methods and interpretation of results, which may be adopted for strength classification.


Any correlation implied in Table 19 shall not be relied upon for design purposes without supporting evidence.



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TABLE 19 ROCK MATERIAL STRENGTH CLASSIFICATION

Term


Very Low Strength

Uniaxial Guide to strength compressive Point load strength strength Abbreviation index I s(50) (see Note 1 Field assessment (see Note 3) and Note 2) MPa MPa VL

0.6 to 2

0.03 to 0.1

Material crumbles under firm blows with sharp end of pick; can be peeled with knife; too hard to cut a triaxial sample by hand. Pieces up to 30 mm thick can be broken by finger pressure.

Low Strength

L

2 to 6

0.1 to 0.3

Easily scored with a knife; indentations 1 mm to 3 mm show in the specimen with firm blows of the pick point; has dull sound under hammer. A piece of core 150 mm long by 50 mm diameter may be broken by hand. Sharp edges of core may be friable and break during handling.

Medium Strength

M

6 to 20

0.3 to 1

Readily scored with a knife; a piece of core 150 mm long by 50 mm diameter can be broken by hand with difficulty.

High Strength

H

20 to 60

1 to 3

A piece of core 150 mm long by 50 mm diameter cannot be broken by hand but can be broken by a pick with a single firm blow; rock rings under hammer.

Very High Strength

VH

60 to 200

3 to 10

Hand specimen breaks with pick after more than one blow; rock rings under hammer.

Extremely High Strength

EH

more than 200

more than 10

Specimen requires many blows with geological pick to break through intact material; rock rings under hammer.

NOTES: 1

Material with strength less than ‘Very Low’ shall be described using soil characteristics. The presence of an original rock structure, fabric or texture should be noted, if relevant.

2

The method for measuring the uniaxial compressive strength shall be in accordance with AS 4133.4.2.1.

3

The method for measuring the point load strength index shall be in accordance with AS 4133.4.1.

6.2.4.2 Degree of weathering The process of weathering involves physical and chemical changes to the rock in response to the changes in pressure, temperature, moisture and chemical environments that result from being exposed at the earth’s surface. The degree of weathering of the rock material shall be classified. The terms in Table 20 should be used. If an alternative rock material weathering classification scheme is used, it shall be documented. This approach is typically used when logging rock cores. Where it is useful to describe the degree of weathering of the rock mass, rather than just the weathering of the rock material, e.g. when logging outcrops or excavations, the classification system provided in Table 24 may be used.



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TABLE 20 CLASSIFICATION OF MATERIAL WEATHERING Term

Abbreviation

Definition

Residual Soil (Note 1)

RS

Material is weathered to such an extent that it has soil properties. Mass structure and material texture and fabric of original rock are no longer visible, but the soil has not been significantly transported.

Extremely Weathered (Note 1)

XW

Material is weathered to such an extent that it has soil properties. Mass structure and material texture and fabric of original rock are still visible.

Highly Weathered (Note 2)

HW Distinctly Weathered (Note 2)


Moderately Weathered (Note 2)

DW

The whole of the rock material is discoloured, usually by iron staining or bleaching to the extent that the colour of the original rock is not recognizable. Rock strength is significantly changed by weathering. Some primary minerals have weathered to clay minerals. Porosity may be increased by leaching, or may be decreased due to deposition of weathering products in pores. The whole of the rock material is discoloured, usually by iron staining or bleaching to the extent that the colour of the original rock is not recognizable, but shows little or no change of strength from fresh rock.

MW

Slightly Weathered

SW

Rock is partially discoloured with staining or bleaching along joints but shows little or no change of strength from fresh rock.

Fresh

FR

Rock shows no sign of decomposition of individual minerals or colour changes.

NOTES: 1

The term ‘Extremely Weathered rock’ is misleading as the material has soil properties. The word ‘rock’ should be replaced with the name of the original rock in lower case or the word ‘material’, e.g. Extremely Weathered granite or Extremely Weathered material. Residual Soil and Extremely Weathered material should be described using soil descriptive terms.

2

Where it is not practicable to distinguish between ‘Highly Weathered’ and ‘Moderately Weathered’ rock the term ‘Distinctly Weathered’ may be used. ‘Distinctly Weathered’ is defined as follows: ‘Rock strength usually changed by weathering. The rock may be highly discoloured, usually by iron staining. Porosity may be increased by leaching, or may be decreased due to deposition of weathering products in pores’. There is some change in rock strength.

6.2.4.3 Degree of alteration (alteration intensity) Where physical and chemical changes of the rock material are caused by hot gases or liquids at depth the process is called alteration. The distinction between weathered material and altered material is important because they are likely to have different distribution patterns. For example, unlike weathered material, altered material may occur at any depth and show no relationship to topography. When altered materials are recognized, the terms presented on Table 21 should be used. If alternative rock material alteration classification schemes are used, they shall be documented.



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TABLE 21 CLASSIFICATION OF MATERIAL ALTERATION Term

Abbreviation

Extremely Altered

Material is altered to such an extent that it has soil properties. Mass structure and material texture and fabric of original rock are still visible.

XA

Highly Altered (Note 2)

HA Distinctly Altered (Note 2)

Moderately Altered (Note 2)

Slightly altered

Definition

DA

The whole of the rock material is discoloured, usually by staining or bleaching to the extent that the colour of the original rock is not recognizable. Rock strength is changed by alteration. Some primary minerals are altered to clay minerals. Porosity may be increased by leaching, or may be decreased due to precipitation of secondary minerals in pores. The whole of the rock material is discoloured, usually by staining or bleaching to the extent that the colour of the original rock is not recognizable but shows little or no change of strength from fresh rock.

MA

SA

Rock is slightly discoloured but shows little or no change of strength from fresh rock.


NOTES: 1

The term ‘Extremely Altered rock’ is misleading as the material has soil properties. The word ‘rock’ should be replaced with the name of the original rock or the word ‘material’, e.g. Extremely Altered basalt or Extremely Altered material. Extremely Altered material should be described using soil descriptive terms.

2

Where it is not practicable to distinguish between ‘Highly Altered’ and ‘Moderately Altered’ rock the term ‘Distinctly Altered’ may be used. ‘Distinctly Altered’ is defined as follows: ‘Rock strength usually changed by alteration. The rock may be highly discoloured, usually by staining or bleaching. Porosity may be increased by leaching, or may be decreased due to precipitation of secondary minerals in pores’. There is some change of rock strength.

6.2.5 Description of defects 6.2.5.1 Generalized versus detailed defect description The degree of defect description required shall be evaluated to suit project requirements. For some projects it will be unnecessary to describe each individual defect in a rock mass. Where multiple similar defects are present which are too numerous to log individually, generalized descriptions should be used. The part of the rock mass to which this applies shall be delineated. Generalized examples are as follows: (a)

‘Most defects between depth x and y are bedding partings.’

(b)

‘Joint spacing is typically 100 mm to 300 mm and most joint traces less than 1 m.’

(c)

‘Joints irregular, surfaces rough and stained with limonite.’

Attention shall be paid to recognizing and describing individually all defects judged to be particularly significant. For example, the following defects might be judged as significant: (i)

In-filled seams on a dam abutment.

(ii)

Open, limonite stained joints near a pressure tunnel.

(iii) Crushed seams in an apparently unstable slope. Regardless of whether specific defect descriptions are provided, a general description outlining the number of defect sets within the rock mass and their broad characteristics shall be provided where it is possible to do so.



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6.2.5.2 Defect type The type of defect should be described using the terms defined in Table 22. If alternative defect description schemes are used they shall be documented. Most defect types can be identified and described at all scales of observation, although depending on their thickness, identification of seams and sheared zones may not be practical where there is limited opportunity to observe the entire feature. Recognizing the origin of defects is extremely important in developing an understanding of the geology and predicting engineering properties and behaviour for a rock mass. If it is not possible to interpret the origin of a seam (i.e. whether it is an extremely weathered seam or an infilled seam), it shall be described as a soil seam with soil properties, e.g. 30 mm bed of weakly cemented sand. Healed defects are those of any type outlined in Table 22 that have been re-cemented by minerals such as chlorite or calcite. Healed defects generally possess some tensile strength across the defect surface, but the re-cemented strength is less than that of the rock material. Healed defects should be described using the same terms including the term ‘healed’ preceding the defect type; e.g. ‘healed joints’.


Where incipient fractures are observed, they should be described using the relevant rock texture and fabric terms (see Clause 6.2.3.4).



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TABLE 22 ROCK DEFECT TYPES


Type

Sub-type

Definition

Parting

A surface or crack across which the rock has little or no tensile strength. Parallel or sub-parallel to layering (e.g. bedding) or a planar anisotropy in the rock material (e.g. cleavage). May be open or closed.

Joint

A surface or crack with no apparent shear displacement and across which the rock has little or no tensile strength, but which is not parallel or subparallel to layering or to planar anisotropy in the rock material. May be open or closed.

Sheared Surface (refer to Note)

A near planar, curved or undulating surface which is usually smooth, polished or slickensided and which shows evidence of shear displacement.

Sheared Zone (refer to Note)

Zone of rock material with roughly parallel near planar, curved or undulating boundaries cut by closely spaced joints, sheared surfaces or other defects. Some of the defects are usually curved and intersect to divide the mass into lenticular or wedge-shaped blocks.

Seams

Sheared Seam (refer to Note)

Seam of soil material with roughly parallel almost planar boundaries, composed of soil materials with roughly parallel near planar, curved or undulating boundaries cut by closely spaced joints, sheared surfaces or other defects. Some of the defects are usually curved and intersect to divide the mass into lenticular or wedge-shaped blocks.

Crushed Seam (refer to Note)

Seam of soil material with roughly parallel almost planar boundaries, composed of disoriented, usually angular fragments of the host rock material which may be more weathered than the host rock. The seam has soil properties.

Infilled Seam

Seam of soil material usually with distinct roughly parallel boundaries formed by the migration of soil into an open cavity or joint, infilled seams less than 1 mm thick may be described as a veneer or coating on a joint surface.

Extremely Weathered Seam

Seam of soil material, often with gradational boundaries. Formed by weathering of the rock material in place.

Diagram

Seam

NOTE: Sheared surfaces, sheared zones, sheared seams and crushed seams are generally faults in geological terms.

6.2.5.3 Defect orientation The maximum dip of the mean plane of the defect from the horizontal should be measured and should be expressed in degrees as a two-digit number, e.g. 50°. The azimuth of the dip (dip direction) should be measured in degrees counted clockwise from true north and expressed as a three-digit number, e.g. 240°. The dip and dip direction should be recorded in that order, with the two digit and three digit numbers separated by a slash, e.g. 50/240. If alternative measurements are made, such as dip and strike or dip direction relative to magnetic north this shall be documented. The relationship between dip, strike and dip direction is given in Figure 6.



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N B 350

20 40

N 60 β 270

W

E

80 90

α A

240

S


20 0

13 0

18 0

This Figure has been reproduced with modification from Figure 1, Clause 4.3.3.2, ISO 14689-1 Geotechnical investigation and testing—Identification and classification of rock— Part 1: Identification and description. Copyright for this figure remains with ISO. LEGEND: A Dip direction B Strike (= dip direction 90)  Dip (dip angle) = 50°  Dip direction (dip azimuth) = 240° Plane of discontinuity = 50/240

FIGURE 6 DIAGRAM SHOWING DEFECT ORIENTATION MEASUREMENTS

In vertical boreholes the dip is generally measured relative to the horizontal plane. If the borehole is inclined the dip is generally measured relative to the core axis as it simplifies the assessment of the possible defect orientation. Where the core has been drilled and defect orientation has been carried out by the use of a core orientation device, e.g. a downhole camera or other suitable instrument, measurement of the defect orientation angles should be carried out and recorded in a form suited to the particular device being employed. 6.2.5.4 Defect roughness and shape The characteristics of the defect surface that can be described are dependent on the scale of observation as follows: (a)

Small scale (10–100 mm) Surface roughness and shape with some limitation on the latter due to the small scale.

(b)

Medium scale (100–1000 mm) Surface roughness and shape.

(c)

Large scale (>1000 mm) Surface roughness, shape and waviness.



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Although the surface roughness of defects can be described at all scales of observation, the overall shape of the defect surface can usually be observed only at medium and large scale. For example, a defect which appears planar in a 50 mm diameter drill core may be described as curved, undulating or stepped when observed in outcrop where more of the defect is visible. The roughness and shape of defects combine to have a significant effect on their shear strength, which is also affected by large scale features. Where it is necessary to assess the shear strength of a defect, observations should be made at multiple scales. Measurements should be taken as outlined by the following: (i)


(ii)

Surface roughness At all scales of observation the defect surface roughness shall be described using the following terms: (A)

Very rough Many large surface irregularities (amplitude generally more than 1 mm). Feels like, or coarser than very coarse sand paper.

(B)

Rough Many small surface irregularities (amplitude generally less than 1 mm). Feels like fine to coarse sand paper.

(C)

Smooth Smooth to touch. Few or no surface irregularities.

(D)

Polished Shiny smooth surface.

(E)

Slickensided Grooved or striated surface, usually polished.

Surface shape At the medium scale of observation, description of the roughness of the surface shall be enhanced by description of the shape of the defect surface using the following terms, as illustrated in Figure 7: (A)

Planar The defect does not vary in orientation.

(B)

Curved The defect has a gradual change in orientation.

(C)

Undulating The defect has a wavy surface.

(D)

Stepped The defect has one or more well defined steps.

(E)

Irregular The defect has many sharp changes of orientation.

NOTE: Measurements should be made of the height of steps or irregularities, and the amplitude and wavelength of undulations. Figure 8 shows a generalized guide to measurements at medium scale, which may also be applied to the large scale of observation.

Alternatively, the surface roughness may be characterized by the joint roughness coefficient (JRC) using the profiles provided in Figure 9. (iii) Waviness Where large scale observations are possible, further measurement of the parameters defining defect waviness shall be made. NOTE: See Figure 10. ‘i’ is the angle of the asperities relative to the overall dip angle of the structure. This can be used in conjunction with the angle of friction of the rock surface to assess the shear strength along the defect.



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Pl anar

Cur ve d


U n d u l at i n g

S te p p e d

Irre g ul ar

10 0 m m

FIGURE 7 DEFECT SHAPES ILLUSTRATED AT MEDIUM SCALE



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S tr ai g ht e d g e Wave l e n g t h — m m

As per it y am plitud e — mm

Le n g t h over profil e — m or m m a s a p p li c a b l e

FIGURE 8 MEDIUM TO LARGE SCALE MEASUREMENT OF DEFECT SHAPE


Typic al roughness profiles for JRC range: 1

0 –2

2

2– 4

3

4–6

4

6–8

5

8 –10

6

10 –12

7

12 –14

8

14 –16

9

16 –18

10

18 – 20

0

5

10 cm

S c al e

This figure is based on: Barton, N and Choubey, V. The Shear Strength of Rock Joints in Theory and Practice. Rock Mechanics. Vol. 10 (1977), pp. 1–54. With permission of Springer. FIGURE 9 ROUGHNESS PROFILES AND CORRESPONDING RANGE OF JRC VALUES ASSOCIATED WITH EACH ONE www.standards.org.au


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“ i ” an g l e

“ i ” an g l e O ver all d i p of str u c ture

1–10 m

FIGURE 10 LARGE SCALE MEASUREMENTS OF DEFECT WAVINESS


6.2.5.5 Defect coatings and composition of seams Many defects have a surface coating which could affect their shear strength. Description of coating is generally possible for all scales of observation. Coatings shall be described using the following terms: (a)

Clean No visible coating.

(b)

Stained No visible coating but surfaces are discoloured.

(c)

Veneer A visible coating of soil or mineral, too thin to measure; may be patchy.

(d)

Coating A visible coating up to 1 mm thick. Thicker soil material shall be described using defect terms (e.g. infilled seam). Thicker rock strength material shall be described as a vein.

Where possible the mineralogy of the coating shall be identified. The composition of seams shall be described using soil description terms as given in Clause 6.1. 6.2.5.6 Defect spacing, length, openness and thickness Spacing, aperture (openness) and seam thickness and composition shall be described directly in millimetres and metres. In general descriptions, half order of magnitude categories are often useful, e.g. joint spacing typically 100 mm to 300 mm, sheared zones 1 m to 3 m thick. Depending on project requirements and the scale of observation, spacing may be described as the mean spacing within a set of defects, or as the spacing between all defects within the rock mass. Where spacing is measured within a specific set of defects, measurements shall be made perpendicular to the defect set. Defect spacing and length (sometimes called persistence), shall be described directly in millimetres and metres. Where significant, the nature of the defect end condition (i.e. termination) should be recorded in the context of the scale of the exposure. Each end of a defect may— (a)

start and/or end outside the extent of the exposure;

(b)

terminate within rock material; or

(c)

terminate at an intersecting defect set.



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6.2.5.7 Block shape Where it is considered significant, block shape should be described using the terms given in Table 23. TABLE 23 BLOCK SHAPE TERMS* Term

Figure

Description

Irregular discontinuities without arrangement into distinct sets, and of small persistence.

Polyhedral blocks

1 1

1

One dominant set of parallel discontinuities (1), for example bedding planes, with other noncontinuous joints; thickness of blocks much less than length or width.


Tabular blocks

1

Prismatic blocks

Two dominant sets of discontinuities (1 and 2), approximately orthogonal and parallel, with a third irregular set; thickness of blocks much less than length or width.

1 2

1

3

2

Equidimensional blocks

Three dominant sets of discontinuities (1, 2 and 3), approximately orthogonal, with occasional irregular joints, giving equidimensional blocks.

1 1

3

2

1

3

3

1

2 2

Rhomboidal blocks 2

Three (or more) dominant, mutually oblique, sets of joints (1, 2 and 3) giving oblique-shaped, equidimensional blocks.

1 3

5 1

Columnar blocks

2 3 4

Several, usually more than three sets of continuous, parallel joints (1, 2, 3, 4, 5) usually crossed by irregular joints; lengths much greater than other dimensions.

* This table has been reproduced from Table 10, ISO 14689-1 Geotechnical investigation and testing— Identification and classification of rock—Part 1: Identification and description. Copyright for these figures remain with ISO.



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6.2.6 Stratigraphic unit Rocks should be assigned to a stratigraphic unit. Where there is doubt, the terms ‘possibly’ or ‘probably’ shall be used. 6.2.7 Geological structure After describing the rock material and the defects and observing exposures and/or excavations and/or cores the geological structure of the rock mass should be interpreted and documented. This may include the preparation of borehole logs, maps, sections and/or stereographic projection of defect information to assess the type and distribution of strata, the defect sets and their orientation and the presence of any structures such as dipping strata, folds, faults, and features such as unconformities and weathering profiles. 6.2.8 Examples of rock description and classification


To illustrate the application of the provisions of Clause 6.2, the following examples are provided: (a)

ANDESITE, grey-blue, Very High Strength, Slightly Weathered, joint spacing 300 to 3000 mm, vertical columnar joints, sub-horizontal joints with about 5 to 10 m persistence and Extremely Weathered Seams (50 mm of Clayey Sand), columnar joints planar and rough. Triassic Mount Byron Volcanics.

(b)

SANDSTONE, grey, Medium Strength, Slightly Weathered, bedding and joint spacing 20 to 100 mm; interbedded with MUDSTONE, grey green, Very Low Strength, Distinctly Weathered, laminations spaced 10–20 mm. Ordovician Eildon Formation.

6.2.9 Parameters related to core drilling 6.2.9.1 General There are a number of parameters that may be measured during core drilling (of both soil and rock), and which may provide useful investigation data. The measurements that define these parameters should be taken during the drilling process, when drill core is relatively undamaged. 6.2.9.2 Total core recovery Total core recovery (TCR) is defined as:

TCR 

Length of core recovered  100% Length of core run

Depth intervals where core is not recovered should be designated ‘No Core’ on drilling records and logs. Where there is doubt about the specific depth interval over which core was not recovered, usual practice is to assign the ‘No Core’ zone to the end of the core run. 6.2.9.3 Defect spacing or fracture index The frequency of defects within drill core should be measured as either— (a)

the spacing between successive defects, or the mean spacing for relatively broken core; or

(b)

the ‘Fracture Index’, which is the number of defects per metre of core.

Under some circumstances it may be useful and practical to record the spacing between defects within specific defect sets. 6.2.9.4 Rock quality designation A measure of defect spacing in drill core is rock quality designation (RQD). NOTE: This measurement was originally developed by Deere et al. (1989) (refer to Bibliography).  Standards Australia


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AS 1726:2017

RQD is expressed as:

RQD =

 Length of sound core pieces  100 mm in length  100% Length of core run

Only core lengths of rock strength material delineated by natural defects shall be measured. If the core is broken by handling or by the drilling process, the broken pieces shall be fitted together and counted as one piece. Figure 13 shows the measuring process used to calculate RQD. Length measurements shall be taken along the central axis of the core.

L = 25 0 m m


RQD =

25 0 + 19 0 + 20 0 × 10 0% 120 0

L = 0 E x tremely weat hered d o e s n ot m e et s o u n d n e s s r e q u ire m e nt

L = 0 c e ntre lin e p i e c e s < 10 0 m m and ex tremely weat h ere d

L = 19 0 m m

C o r e r u n tot a l l e n g t h = 1. 2 m

= 5 3%

L = 0 < 10 0 m m

M e c hani c al break c ause d by dr illing pro c es s

L = 20 0 m m

L = 0 N o re c over y

FIGURE 13 RQD MEASUREMENT PROCEDURE



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RQD should be employed only for core of ‘N’ size or larger (i.e. about 50 mm diameter or greater), as smaller core could bias the results. RQD was originally intended to be measured only over a full core run. There may be valid applications of RQD where it is measured over a specific length, or within specific rock mass units. If such deviations to the original calculation method are made they shall be explained with the reported RQD values. 6.2.10 Classification of the rock mass 6.2.10.1 Weathering grades Where a weathering profile is exposed in an outcrop or an excavation the degree of weathering of the rock mass should be classified using the terms and grades in Table 24. If an alternative rock mass weathering scheme is used it shall be documented. TABLE 24 ROCK MASS WEATHERING GRADES


Grade

Descriptive term

IA

Fresh; no visible sign of rock material weathering

IB

Fresh except for staining on major defect surfaces

II

Some to all of the rock mass is discoloured by slight weathering

III

Less than 35% of the mass is weathered to a soil

IV

More than 35% of the mass is weathered to a soil with rock present as a discontinuous framework or corestones

V

Virtually all of the rock mass is weathered to a soil but the original mass structure still largely intact

6.2.10.2 Duricrust grades Where a duricrust has developed in a weathering profile and is exposed in outcrop or excavation, the degree of development of the duricrust may be classified. The terms in Table 25 should be used. If alternative duricrust classification schemes are used they shall be documented.



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TABLE 25 DURICRUST MASS GRADES Graphic log

Structure term

Grade

Massive or hardspan

DI

More than 90% of the ground consists of duricrust rock material which forms a continuous framework.

DII

Between 50% and 90% of the ground consists of duricrust rock material which forms a continuous framework around soil materials (vuggy) or rock materials (patchy).

DIII

Less than 50% of the ground consists of gravel and cobble sized nodules (rounded or subrounded) or fragments (angular or subangular) of duricrust rock material and it is described as a soil.


Vuggy or patchy

Nodular or fragmental

Description

NOTE: Cavities or vugs within the rockmass should be described in terms of size, frequency and continuity.

6.2.10.3 Rock mass classification schemes Rock mass classification schemes may be used to develop a model of the characteristics of a rock mass. They require the systematic collection of information including the description and classification of rock, soil and water, which is transformed into numerical or ranked information that may be used to support engineering design. A large variety of classification schemes have been developed ranging from simple to complex. All of the schemes are limited in their application. For example, classification schemes that have been developed to predict tunnel support requirements are seldom relevant to slope stability issues and vice versa. Many rock mass classification systems assume that the rock mass is isotropic, which is rarely the case. If a particular rock mass classification scheme is to be adopted for design, the required inputs should be recognized prior to commencing work so that all relevant information is collected during the geotechnical site investigation.



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6.3

58

Surface water and groundwater observations

6.3.1 Surface water Observations shall be made of evidence of surface water flows, seepages, ponding, past flooding and any tidal influences in and around the project site. Where there is evidence of surface water flow, this shall be recorded. Information on past rainfall shall be collected. 6.3.2 Groundwater Movement of groundwater can be inferred from signs indicating discharge zones (such as seeps, vegetation and precipitation of salts) or inflow zones (such as sinkholes or flow into seepage areas) and such areas shall be mapped. Groundwater inflows and outflows encountered during subsurface investigations shall be recorded where feasible. Records of inflow and outflow during borehole drilling shall include the depth and an indication of the magnitude of the flow volume. Groundwater levels encountered during subsurface investigations shall be measured, where feasible, together with the time at which water level measurements are made and additional measurements should be carried out at the beginning and end of each shift.


The construction method of any piezometers and standpipes shall be recorded. A survey level of the collar of the monitoring well or surveying the level of points of emergence of seepage shall be measured. As groundwater levels can vary with time, multiple and ideally continuous groundwater level measurements should be made. 6.3.3 Groundwater quality Observations of turbidity, colour, temperature, or odour should be made. Groundwater should not be tasted due to the risk of contamination by toxic substances. Strong odour can also be an indication of contamination by volatile substances and protective measures shall be employed where there is any suspicion of a risk to field personnel. Groundwater sampling methods shall be adopted that ensure the representativeness of samples and preserve the integrity of samples. 6.4 Gases Hazardous gases such as methane, carbon dioxide and carbon monoxide, can pose risks for the geotechnical site investigation and project development and may be a health and safety hazard which needs consideration. The possible presence of hazardous gases may be inferred from site history. Where required, procedures for detecting and monitoring these gases shall be implemented. BS 8576:2013 provides guidance on the investigation for hazardous ground gases.



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AS 1726:2017

APPENDIX A

GEOTECHNICAL SITE INVESTIGATION TECHNIQUES (Informative) A wide variety of techniques and tests are available for geotechnical site investigations. Listed below are examples of techniques that are commonly considered. Reference should be made to the relevant Australian Standard or other test method for requirements such as sample condition and size. (a)

Geological studies, including: (i)

Regional geological mapping.

(ii)

Geological mapping of excavations and outcrops.

(iii) Geomorphological mapping.


(b)

(iv)

Borehole logging.

(v)

Detailed logging of test pits, excavations and exposures.

Geophysical investigations, including: (i)

Magnetic methods.

(ii)

Seismic methods using refraction, reflection and surface waves.

(iii) Ground penetration radar.

(c)

(d)

(iv)

Electrical resistivity measurement.

(v)

Electromagnetic methods.

(vi)

Geophysical borehole logging, involving seismic, electrical, gravimetric and radiometric logging and sonic testing, and cone penetration testing with the measurement of shear wave velocity and electrical resistivity or conductivity.

Drilling and sampling used to locate specific targets, to determine the vertical profile and lateral variability of the ground, including the groundwater conditions, to collect soil and rock samples, to perform in situ tests to determine mechanical properties of the ground, and for borehole imaging. Common methods include: (i)

Trial pits and trenches.

(ii)

Boring and drilling using rotary core drilling, auger boring and percussion drilling.

In situ probing to enable the assessment of engineering parameters of the ground, including: (i)

Plate bearing test.

(ii)

California bearing ratio.

(iii) Light weight deflectometer. (iv)

Density measurement.

(v)

Standard penetration test.

(vi)

Dynamic penetration tests, such as the dynamic cone penetrometer (refer to AS 1289.6.3.2) or the Perth sand penetrometer (refer to AS 1289.6.3.3).

(vii) Specialized cone penetration tests, such as the static cone, piezo cone, electrical conductivity cone, and seismic cone. www.standards.org.au


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(viii) Full flow penetrometers (ball, T-bar and plate). (ix)

Flat dilatometer tests.

(x)

Vane shear test.

(xi)

Pressuremeter test.

(xii) Borehole impression packer. (xiii) Core orientation device. (xiv) Video visual inspection (e.g. borehole periscope, TV, and photography). (e)

In situ methods for obtaining relatively undisturbed samples that enable the evaluation of engineering properties in the laboratory, including block sampling and tube sampling using push-tube and piston samplers.

(f)

In situ rock testing in excavations and galleries, including: (i)

Direct shear tests.

(ii)

Plate bearing test.

(iii) In situ stress measurement. (iv)


(g)

Point load strength test.

Slope and excavation stability monitoring, including the use of: (i)

Inclinometer.

(ii)

Extensometer.

(iii) Piezometers (e.g. vibrating wire piezometers). (iv)

Surface markers and settlements plates.

(v)

Earth pressure cells.

(vi)

Tilt sensors.

(h)

Blasting tests and vibration monitoring.

(i)

Topographic studies, including satellite and aerial imagery and remote sensing.

(j)

Groundwater studies and sampling, including: (i)

Packer tests.

(ii)

Rising head, constant head and falling head tests.

(iii) Pumping tests. (iv)

Groundwater level measurement.

(v)

Chemical and microbiological water quality.

(vi)

Soil vapour.

(vii) Water sampling with lysimeters.



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APPENDIX B

LABORATORY EXAMINATION AND TESTING (Informative) Laboratory testing provides a means of identifying and classifying soil and rock properties. In Table B1, the letter ‘X’ indicates some of the commonly considered laboratory tests. Reference should be made to the relevant Australian Standard or other test method for such requirements as sample condition and size. TABLE B1 LIST OF LABORATORY TESTS

Rock

Aggregates

Recycled masonry and concrete

Pavement materials

Consistency, structure and particle size

X

X

X

X

X

Colour, inclusions, and accessory materials

X

X

X

X

X

Geological description

X

X

X

X

X

Defects and weathering

X

X

X

Moisture content

X

X

X

X

X

Particle size distribution

X

X

X

X

Hydrometer analysis

X

X

X

Liquid limit, plastic limit and linear shrinkage

X

X

X

Emerson class number

X

Pinhole dispersion

X

Hole erosion test

X

In situ density

X

X

X

Particle density

X

X

X

Dry density/moisture relationship

X

Min/max density of cohesionless materials

X


Test/Examination

Visual examination

Classification

Material density

Aggregate bulk density and unit mass Deformation

Water

Soil

Material type

X

Consolidometer/oedometer

X

Shrink/swell index

X

Soil suction measurement

X

Modulus and Poisson’s ratio

X

X

X

X

X

X

X

X

X (continued)



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TABLE B1 (continued)

Pavement materials

X

X

Aggregate crushing value

X

X

Sodium sulfate soundness

X

X

Los Angeles abrasion

X

X

Aggregate polishing value

X

X

Alkali silica reactivity

X

X

Wet/dry strength variation

X

X

X

X

X

X

Soil

Rock

Strength/Durability

Unconfined compression

X

X

Triaxial compression (drained or undrained)

X

X

Direct shear

X

X

Triaxial extension

X

X

Point load strength index


California bearing ratio

Organic matter

Chemical tests

X

X

X

X

X

Brazilian indirect tensile strength

X

Slake durability

X

Abrasivity

X

Seismic velocity

X

Porosity/water absorption

X

Cerchar abrasion index

X

Goodrich drillability

X

Cuttability

X

Deval attrition

X X

Aggregates X

Test/Examination

Water


Material type

X

X

X

X

X

X

pH

X

X

Cation exchange capacity

X

X

Anion/cation balance

X

X

Total dissolve solids

X

X

X

Sulfate

X

X

X

X

X

X

Chloride

X

X

X

X

X

X

Organic matter

X

X

X

X

X

X

Acid sulfate

X

X

X

Total salinity and acidity

X

X

Electrical conductivity

X

X (continued)



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AS 1726:2017

TABLE B1 (continued)

Mineralogical tests

Hydraulic tests

X

X-ray diffraction

X

Falling head permeability

X

Constant head permeability

X

Triaxial permeability

X

X

X

X

Pavement materials


Water

Aggregates X

X


Thermal properties

Petrographic analysis

Rock

Test/Examination

Soil

Material type



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APPENDIX C

GROUNDWATER CONSIDERATIONS (Informative) Investigation of groundwater in the context of geotechnical site investigation is typically associated with identification of groundwater head distribution, groundwater flow direction, response to rainfall, response to other factors (such as pumping, tidal variation and changing river levels) and hydraulic properties of water bearing soil and rock. Groundwater chemistry can have a significant impact on in-ground infrastructure in contact with groundwater. The presence of iron, manganese and calcium precipitates of hydroxides and carbonates that can clog drainage systems and elevated acidity and elevated chloride or sulfate concentrations can cause durability problems.


Assessment of the presence of contamination as a result of previous site usage can also be important, although this is not addressed in this Standard. An important part of any geotechnical site investigation is the identification of the groundwater level and of any artesian pressures. The variation of groundwater level or pressure over a given period of time may also require evaluation. Reliable information on groundwater levels within the depth proposed for excavations and pile borings and within the zone of influence of foundation pressures is vital to many aspects of foundation design and construction. Changes to groundwater conditions associated with a project have the potential to affect groundwater levels and quality at a distance from the site. This zone of potential influence on groundwater can be much wider than for soil and rock excavation. In addition, groundwater effects may take considerable time to develop or may be relevant only during extreme conditions such as during flooding or high rainfall events. A conceptual groundwater model should be developed as part of the overall geotechnical model where groundwater is a relevant consideration to the investigation. This is a simplified representation of the groundwater system and its behaviour in a form useful to the project. The conceptual model could range from a brief description of the salient features to a detailed presentation incorporating hydrogeological sections illustrating interpreted flow paths, recharge sources and discharge areas. Consideration of potential groundwater impacts associated with a project should occur at each stage of development of the geotechnical site investigation beginning with the desk study. Planning of geotechnical site investigations should include but not be limited to consideration of the following groundwater related factors: (a)

Groundwater levels.

(b)

Groundwater flow directions.

(c)

Hydraulic properties of geological horizons.

(d)

Existing and potential beneficial use of local groundwater.

(e)

Location and type of neighbouring groundwater users.

(f)

Nearby groundwater dependent ecosystems.

(g)

Surface and groundwater bodies within the likely zone of influence.

(h)

Rainfall and groundwater response to rainfall.

(i)

Groundwater chemistry.



65

Contamination.

(k)

Recharge and discharge processes.

(l)

Site drainage.

(m)

Legislative requirements.


(j)

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APPENDIX D

PROBLEMATIC MATERIALS (Informative) A number of different materials may pose particular problems or issues when encountered during geotechnical site investigation or construction. The degree to which a soil or rock may be problematic is a function of— (a)

the nature of the soil (mineralogy, fabric, geotechnical and geochemical properties);

(b)

the geological processes that caused it to be formed; and

(c)

current processes (e.g. weathering, erosion, human activity).

Past and present climate play a major role in the development of soil profiles. Human activity is also an important factor in determining soil behaviour. Site investigation techniques should take these factors into account, and field and laboratory tests carried out to establish the existence and engineering properties of problematic soils.


Some of the more common examples are described briefly below: (i)

Acid generating rocks—naturally occurring rocks that contain an abundance of sulfides mainly in the form of pyrite (FeS2 ). These materials may oxidize to create acids, resulting in acid rock drainage when the acid is dissolved in surface or groundwater. Acid rock drainage occurs naturally within some environments as part of the rock weathering process but is exacerbated by large-scale earth disturbances characteristic of mining and other large construction activities.

(ii)

Acid sulfate soils—naturally occurring soils that contain iron sulfides mainly in the form of pyrite (FeS2 ). The oxidation of pyrite and other sulfides to sulfates can occur during earthworks construction and dewatering, where the soils may be disturbed and exposed to air. While the reactions can be complex the overall result is the conversion of pyrite to iron hydroxides and sulfuric acid, potentially leading to pH values as low as 2 or 3. The effects can pose a significant risk to human health and the environment, in particular groundwater resource contamination by acid, arsenic and heavy metals. Other effects may include ground-heave and the corrosion of buried concrete and steel structures.

(iii) Arid soils—formed when evaporation exceeds rainfall and there is a soil-moisture deficit. The soils may have unusual engineering properties due to extreme desiccation, the presence of precipitated salts, high void ratio, mechanical and chemical weathering, etc. Diurnal temperature changes may cause accelerated disintegration of materials and lithification to occur. (iv)

Collapsible soils—either naturally occurring or formed through human activities. An open metastable structure is a prerequisite and is developed via bonding mechanisms which may include capillary forces (suction) or cementing agents such as clay, sesquioxides, and salts. Collapse may occur when nett stresses due to loading and saturation exceed the yield strength of the bonding materials.



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(v)

Degradable rocks—geological materials or formations that in their in situ form may be assigned names or appearances that imply rock-like behaviour. However, once disturbed, some of these materials retain the character of rock, but others may degrade to soil-size particles and exhibit soil-like strength and stiffness. In geological terms, all of the soils and rocks in the earth’s crust are ‘degradable’ in a time frame that is relevant to the long-term performance of engineering projects. Sedimentary rocks constitute the bulk of degradable rocks worldwide, with shale being a prime example, but weathered igneous and metamorphic rocks may also fall into this category.

(vi)

Dispersive soils—soils which, by the nature of their mineralogy and their pore water chemistry, are susceptible to separation of individual clay particles through fine fissures or cracks under seepage flows. The dispersivity of a soil is directly related to its clay mineralogy. Soils with montmorillonite tend to be dispersive, while kaolinite and related minerals (e.g. halloysite) are non-dispersive, and illite is moderately dispersive. The pore water chemistry affects the diffuse double layer geometry and electrical charge. Low electrolyte (pore water) salt concentrations lead to a large diffuse double layer and higher dispersivity (e.g. percolation of a saline soil with fresh water can lead to dispersion). Cation exchange (e.g. Ca++ exchanged for Na+) leads to a smaller double layer and lower dispersivity.


Dispersive soils may be identified from laboratory testing including Emerson class number, pinhole test, and various chemical tests on the soil pore water (e.g. sodium adsorption ratio and exchangeable sodium percentage). (vii) Expansive soils—change in volume in response to changes in moisture content. Changes in moisture content may be induced by seasonal variation or human activity. Such activities can include changes to site drainage, establishment or removal of trees and vegetation, and leakage from tanks or pipes. Shrink-swell behaviour is a function of clay mineralogy and clay content, and the soil-moisture deficit pertaining to the site. (viii) Glacial soils—can vary from sheared basal layers to unsorted mixtures of boulders, gravel, sand, silt and clay. Deposition occurs via a process of pressure and shear beneath the glacier as it advances, and may also be deposited as the ice melts. These processes can lead to spatially very variable soil conditions that contain features that can impact on the mass behaviour thus making the selection of geotechnical design parameters difficult. (ix)

Liquefiable soils—soils capable of undergoing continued deformation at constant low residual stress, or no residual resistance, due to the build-up and maintenance of high pore-water pressures. This behaviour may be due to either static or cyclic stress applications.

(x)

Mudstone—the general name given to fine-grained very low strength sedimentary rocks such as claystone, siltstone and shale that consist of clay and/or silt sized particles that are cemented to form a rock material that often transitions to a hard soil. Depending on their composition and mode of formation, particularly with regard to the clay mineralogy, they may display a range of problematic engineering behaviours such as low strength, poor durability, volume change, and a propensity to slake or disaggregate in water. Such behaviours may be due to the combined effect of natural weathering processes and the impact of engineering works. Mudstones often contain iron oxides and hydroxides, and the iron sulfide mineral pyrite. The pyrite can be problematic due to the generation of acid on oxidation and additional oxides and hydroxides and gypsum (resulting in ground heave).



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(xi)

68

Non-engineered fills—materials that have been placed or deposited by human processes without appropriate treatment. They may consist of natural material (soil/rock) and artificial material such as building waste, domestic waste, mining and quarry waste, and industrial waste. These materials may settle variably, have poor bearing capacity and may undergo significant movements due to causes other than imposed loading. Other problems associated with some wastes include contamination, spontaneous combustion and emission of gas.

(xii) Organic peat soils—highly compressible and exhibit creep behaviour. Other properties include low bulk density and low undrained shear strength. Their engineering behaviour is dependent on their moisture content and organic content and these are the most important index tests. Surcharging is a commonly used technique to manage settlement of roads and structures, with the design criterion usually being to build out sufficient settlement during construction to cover both primary and secondary settlement expected over the design life.


(xiii) Sensitive soils (clays)—those which lose a portion of their strength and stiffness when remoulded. This is mainly due to reorientation of particles into less favourable positions during the remoulding process. A thixotropic soil is one that regains a portion of its strength with time, usually following some initial mechanical disturbance. (xiv) Soluble geomaterials—such as carbonate soil and rock (limestone and dolomite), gypsum, salt and varieties of these can be dissolved to form cavities leading to ground failure and surface subsidence. Sinkholes (or dolines) commonly occur in the soil cover overlying fissured and cavernous limestone, and can range in size from 1 m to 100 m in diameter and depth. Karst is a term that describes the suite of landforms associated with soluble rocks and karst conditions are probably the most variable encountered and difficult to investigate. (xv) Tropical soils—formed primarily by in situ weathering processes and occur in tropical regions where temperatures and rainfall are high, leading to chemical weathering of primary minerals, and increased penetration of weathering agencies. Weathering is initiated within the joints of the parent rock and gradually penetrates into the rock mass. A common feature of tropical soils is the presence of iron and aluminium oxides (often referred to as sesquioxides), which are released by weathering and are not dissolved hence remaining in situ. These oxides are important because they have an increasing effect on soil stiffness and strength and may provide a curb on soil reactivity. When testing for Atterberg Limits, the clays in certain tropical soils may permanently aggregate under oven and even air drying. This can result in particle size distributions misleadingly indicating sand sized classifications. However, in situ and where protected from desiccation, they would classify as silts or clays. Similarly, such aggregation may also adjust Atterberg Limits to give false classifications, e.g. SILT when the true in situ classification should be CLAY.



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APPENDIX E

SYMBOLS (Informative) E1 GEOLOGICAL BOUNDARIES AND STRUCTURES MAPPING SYMBOLS Suggested mapping symbols for geological boundaries and structures are provided in Figure E1. Additional or alternative symbols should be used as necessary.

O b ser ve d g e o l o g i c al b o u n d ar y, p o s it i o n k n ow n O b ser ve d g e o l o g i c al b o u n d ar y, p o s it i o n a p prox im ate ?

?

25


25

G e o l o g i c al b o u n d ar y, inter prete d or inferre d

?

B e d d in g

25

Fo li at i o n

25

Cleavag e

A nt i c li n e, F1

J o i nt

S y n c l i n e, F2

Plu n g e of fo l d, or d er an d t y p e in d i c ate d w it h a p pro pr i ate sy m b o l s

25

25

Plun g e of l i n e at i o n on plane

Fault or fault zo n e, s h eare d zo n e

U

U

U

Un c o nfor mit y

FIGURE E1 MAPPING SYMBOLS FOR GEOLOGICAL BOUNDARIES AND STRUCTURES

E2 GEOLOGICAL SOIL AND ROCK MAPPING SYMBOLS Suggested mapping symbols for soils and rocks are provided in Figure E2. Additional or alternative symbols should be used as necessary.




AS 1726:2017


RO CKS SOILS

SEDIMENTARY

M E TAM ORPHIC

IGNEOUS

B oul d er s an d c o b b l e s

L i m e s to n e

C o ar s e g r a i n e d

C o ar s e g r a i n e d

Gravel

C o n g l o m er ate

Medium grained

Medium grained

Sand

Bre c c ia

Fine grained

Fine grained

Silt

S a n d s to n e

Clay

S i l t s to n e

Weat h ere d profile

Peat

M u d s to n e

D ur i c r u s t

WE ATHERED PROFILES AN D DURICRUSTS


Silty sand

Tu f f

Gy p sum, Ro c ks alt etc.

FIGURE E2 GEOLOGICAL MAPPING SYMBOLS FOR SOILS AND ROCKS

FILL

Fill

70

Coal

NOT E: C omp osit e soi l t y p e s m ay b e sig n i f ie d by c ombi ne d sy mb ol s, e.g.

71

AS 1726:2017

E3 GEOMORPHOLOGICAL MAPPING SYMBOLS Suggested geomorphological mapping symbols are provided in Figure E3. Additional or alternative symbols should be used as necessary.

S h ar p C o n c ave Rounded Break of slo p e S h ar p C o nvex Rounded

10

Clif f


S c ar p

S l o p e an g l e of fac et

T T

Te n s i o n c r ac k

Inter m it te nt fl ow

C o nt in u o u s f l ow

O ut fl ow

Infl ow

S t a n d i n g water

Dam p - re e d s

S pr in g

L an d s li d e

Ro c k fall

M u d s li d e

FIGURE E3 GEOMORPHOLOGICAL MAPPING SYMBOLS



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APPENDIX F

COMMENTARY (Informative) F1 INDUSTRY SURVEY In 2011, the Australian Geomechanics Society (AGS) issued a survey to its members and stakeholders that considered the possibility of revising AS 1726—1993. The survey comprised a total of 25 questions, 17 pertaining to the technical content of a revised Standard. This edition of the Standard has been informed by the results of that survey. F2 CHANGES FROM PREVIOUS REVISION There are a number of changes and updates in this revision, and details of the most significant changes and additions between the editions of AS 1726 are summarized in Table F1 below. TABLE F1 MAJOR REVISIONS Accessed by MONASH UNIVERSITY LIBRARY on 23 May 2017 (Document currency not guaranteed when printed)

Content in AS 1726—1993

Changes in this edition

Comment

General

The main body of the document is The main document now provides normative. There are now six informative requirements for the execution of Appendices. effective geotechnical site investigations and provides a standardized system for the description and classification of soils and rocks.

Appendix A—Description and classification of soils and rocks for geotechnical purposes

Material descriptions, which were informative, are now normative.

The process for describing soils and rock is now largely normative and has been moved to the main body of text.

The boundary defining the change from coarse to fine grained soil was previously set at 50% of soil by weight greater than or finer than 0.075 mm particle size. This assessment is now made according to whether the total dry mass of coarse fractions exceeds 65% (a coarse soil) or the total dry mass of fine fractions exceeds 35% (a fine soil) (refer to Clause 6.1).

In the revised Standard a behavioural approach has been adopted when identifying, naming and classifying soil.

The means of describing carbonate rocks A need for a classification and has been revised and the means of description system for these material describing and classifying duricrusts types was identified. have now been included (refer to Clause 6.1). The description of rock materials, rock defects and rock masses has been significantly revised (refer to Clause 6.2).

A need for a normative classification and description system for rocks and rock masses was identified. (continued)



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AS 1726:2017

TABLE F1 (continued)


Content in AS 1726—1993

Changes in this edition

Comment

Appendix B Field test methods (Informative)

An informative Appendix A lists the most common geotechnical site investigation techniques, replacing the former Appendix B.

Appendix E Commentary

The former informative Appendix mainly The majority of items in the former provided guidance for the execution of Appendix E are now included in the geotechnical site investigations. main body of the Standard, with most now being mandatory.

A3.4 Condition of rock material Table A8

The Uniaxial Compressive Strength augmented by the Point Load Strength Index has been used to classify rock material strength (refer to Clause 6.2.4.1).

—

Table A9 Rock material weathering classification

The terms ‘highly weathered’ (HW) and ‘moderately weathered’ (MW) have been included (Table 17).

—

New addition

A description of geotechnical models and To comply with modern practice the the process to be followed in their development of geotechnical models development have now been introduced was included. (refer to Clause 5.2).

New addition

Guidance in relation to groundwater aspects of geotechnical site investigations is provided.

In the 1993 Standard there was little discussion of groundwater.

New addition

A new clause was added regarding the need to comply with work health and legislation (refer to Clause 5.3.1).

This was in recognition of the current working environment of geotechnical professionals.

New addition

Description of the geological origin of soil is now mandatory (refer to Clause 6.1).

This was included for consistency with the practice of developing a geological model.


Examples of common testing methods have been provided, but the list is not intended to be exhaustive.


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BIBLIOGRAPHY Informative referenced documents AS 1289 1289.5.6.1 1289.6.3.1 1289.6.3.2 1289.6.3.3 1289.6.5.1


3798

Methods of testing soils for engineering purposes (series) Mehtod 5.6.1: Soil compaction and density tests—Compaction control test— Density index method for a cohesionless material Method 6.3.1: Soil strength and consolidation tests—Determination of the penetration resistance of a soil—Standard penetration test (SPT) Method 6.3.2: Soil strength and consolidation tests—Determination of the penetration resistance of a soil—9 kg dynamic cone penetrometer test Method 6.3.3: Soil strength and consolidation tests—Determination of the penetration resistance of a soil—Perth sand penetrometer test Method 6.5.1: Soil strength and consolidation tests—Determination of the static cone penetration resistance of a soil—Field test using a mechanical and electrical cone or friction-cone penetrometer Guidelines on earthworks for commercial and residential developments

ISO 14689 14689-1 BS 8576

Geotechnical investigation and testing—Identification and classification of rock Part 1: Identification and description Guidance on investigations for ground gas. Permanent gases and Volatile Organic Compounds (VOCs)

Related documents Attention is drawn to the following related documents: 1

Casserly, Ann-Marie. ‘Guidelines for the Preparation of the Ground Report’. Association of Geotechnical and Geoenvironmental Specialists. 26 July 2003.

2

CRIA, ‘Site investigation manual’. Special Publication SP 25. CRIA, London. 1983.

3

Dearman, WR. Engineering Geological Mapping. Butterworth-Heineman. 1991.

4

Deere, DU and Deere, DW. ‘Rock Quality Designation (RQD) After Twenty Years’. Contract Report GL-89-1. Army Corps of Engineers. Washington DC, 1989.

5

Deere, DU, Hendron, AJ Jr. Patton, FD and Cording, EJ. ‘Design of Surface and Near Surface Construction in Rock’, Failure and Breakage of Rock, Fairhurst, C. (Ed.), Soc. of Min. Eng. AIME, New York. 1967. pp. 237–302.

6

Essex, Randall, J. ‘Geotechnical Baseline Reports for Construction: Suggested Guidelines’. American Society of Civil Engineers. 2007.

7

Matula, M. ‘Recommended symbols for engineering geological mapping report by the IAEG Commission on Engineering Geological Mapping’. Bulletin of the International Association of Engineering Geology. Volume 24, Issue 1. December 1981. pp. 227– 234.



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Matula, M. ‘Rock and soil description and classification for engineering geological mapping report by the IAEG Commission on Engineering Geological Mapping’.. Bulletin of the International Association of Engineering Geology. Volume 24, Issue 1. December 1981. pp. 235–274.

9

Munsell, AH. ‘A Colour Notation’. Geo. H. Ellis Co. Boston. 1905.

10

Parry, S et al. ‘Engineering Geological Models: An Introduction, IAEG Commission 25’. Bulletin of the Engineering Geology and the Environment. Online publication. 18 February 2014.

11

Ulusay, R (ed.). ‘The ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 2007–2014’. ISRM, Springer. 2015.

12

Ulusay, R and Hudson, JA. ‘The Complete ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 1974–2006’. ISRM Turkish National Group, Turkey. April 2007.


8




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