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South African Pavement Engineering Manual Chapter 7: Geotechnical Investigations and Design Considerations © 2013 South African National Roads Agency Ltd. All rights reserved. First edition published 2013 Printed in the Republic of South Africa SET: ISBN 978-1-920611-00-2 CHAPTER: ISBN 978-1-920611-07-1 www.nra.co.za [email protected]

SOUTH AFRICAN

PAVEMENT ENGINEERING MANUAL

Chapter 7

Geotechnical Investigations and Design Considerations

AN INITIATIVE OF THE SOUTH AFRICAN NATIONAL ROADS AGENCY LTD

Date of Issue: January 2013

Revision 1.0

1. Introduction

2. Pavement Composition and Behaviour

3. Materials Testing

4. Standards

5. Laboratory Management

6. Road Prism and Pavement Investigations

7. Geotechnical Investigations and Design Considerations

8. Material Sources

9. Materials Utilisation and Design

10. Pavement Design

11. Documentation and Tendering

12. Construction Equipment and Method Guidelines

13. Acceptance Control

14. Post-Construction

BACKGROUND

TESTING AND LABORATORY

INVESTIGATION

DESIGN

DOCUMENTATION AND TENDERING

IMPLEMENTATION

QUALITY MANAGEMENT

POST CONSTRUCTION

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South African Pavement Engineering Manual

Chapter 7: Geotechnical Investigations and Design Considerations

Preliminary Sections

Page ii

SCOPE

The South African Pavement Engineering Manual (SAPEM) is a reference manual for all aspects of pavement engineering. SAPEM is a best practice guide. There are many appropriate manuals and guidelines available for pavement engineering, which SAPEM does not replace. Rather, SAPEM provides details on these references, and where necessary, provides guidelines on their appropriate use. Where a topic is adequately covered in another guideline, the reference is provided. SAPEM strives to provide explanations of the basic concepts and terminology used in pavement engineering, and provides background information to the concepts and theories commonly used. SAPEM is appropriate for use at National, Provincial and Municipal level, as well as in the Metros. SAPEM is a valuable education and training tool, and is recommended reading for all entry level engineers, technologists and technicians involved in the pavement engineering industry. SAPEM is also useful for practising engineers who would like to access the latest appropriate reference guideline. SAPEM consists of 14 chapters. A brief description of each chapter is given below to provide the context for this chapter, Chapter 7. Chapter 1: Introduction discusses the application of this SAPEM manual, and the institutional responsibilities, statutory requirements, and, planning and time scheduling for pavement engineering projects. A glossary of terms and abbreviations used in all the SAPEM chapters is included in Appendix A. Chapter 2: Pavement Composition and Behaviour includes discussion on the history and basic principles of roads. Typical pavement structures, material characteristics and pavement types are given. The development of pavement distress and the functional performance of pavements are explained. As an introduction, and background for reference with other chapters, the basic principles of mechanics of materials and material science are outlined. Chapter 3: Materials Testing presents the tests used for all material types used in pavement structures. The tests are briefly described, and reference is made to the test number and where to obtain the full test method. Where possible and applicable, interesting observations or experiences with the tests are mentioned. Chapters 3 and 4 are complementary. Chapter 4: Standards follows the same format as Chapter 3, but discusses the standards used for the various tests. This includes applicable limits (minimum and maximum values) for test results. Material classification systems are given, as are guidelines on mix and materials composition. Chapter 5: Laboratory Management covers laboratory quality management, testing personnel, test methods, and the testing environment and equipment. Quality assurance issues, and health, safety and the environment are also discussed. Chapter 6: Road Prism and Pavement Investigation discusses all aspects of the road prism and pavement investigations, including legal and environmental requirements, materials testing, and the reporting of the investigations. Chapters 6 and 7 are complementary. Chapter 7: Geotechnical Investigations and Design Considerations covers the geotechnical investigations applicable to pavement structures. This includes potential problem subgrades, fills, cuts, structures and tunnels. Guidelines for the reporting of the investigations are provided. The personnel required for specialist geotechnical investigations are also recommended. Chapter 8: Material Sources provides information for sourcing materials from project quarries and borrow pits, commercial materials sources and alternative sources. Chapter 9: Materials Utilisation and Design discusses materials in the roadbed, earthworks (including cuts and fills) and all the pavement layers, including soils and gravels, crushed stones, cementitious materials, primes, stone precoating fluids and tack coats, bituminous binders, bitumen stabilised materials, asphalt, spray seals and micro surfacings, concrete, proprietary and certified products and block paving. The mix designs of all materials are discussed. Chapter 10: Pavement Design presents the philosophy of pavement design, methods of estimating design traffic and the pavement investigation process. Methods of structural capacity estimation for flexible, rigid and concrete block pavements are discussed.




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Chapter 11: Documentation and Tendering covers the different forms of contracts typical for road pavement projects; the design, contract and tender documentation; and, the tender process. Chapter 12: Construction Equipment and Method Guidelines presents the nature and requirements of construction equipment and different methods of construction. The construction of trial sections is also discussed. Chapters 12 and 13 are complementary, with Chapter 12 covering the proactive components of road construction, i.e., the method of construction. Chapter 13 covers the reactive components, i.e., checking the construction is done correctly. Chapter 13: Quality Management includes acceptance control processes, and quality plans. All the pavement layers and the road prism are discussed. The documentation involved in quality management is also discussed, and where applicable, provided. Chapter 14: Post-Construction incorporates the monitoring of pavements during the service life, the causes and mechanisms of distress, and the concepts of maintenance, rehabilitation and reconstruction.

FEEDBACK

SAPEM is a “living document”. The first edition was made available in electronic format in January 2013. It is envisaged that SAPEM will be updated after one year. Feedback from all interested parties in industry is appreciated, as this will keep SAPEM appropriate. To provide feedback on SAPEM, please email [email protected].




Page iv

ACKNOWLEDGEMENTS

This compilation of this manual was funded by the South African National Road Agency Limited (SANRAL). The project was coordinated on behalf of SANRAL by Kobus van der Walt and Steph Bredenhann. Professor Kim Jenkins, the SANRAL Chair in Pavement Engineering at Stellenbosch University, was the project manager. The Cement and Concrete Institute (C&CI) provided administrative support. The following people contributed to the compilation of Chapter 7: • Task Group Leader: Etienne Terblanche, SANRAL • Eugene Knottenbelt, Specialist Consultant • Alan Parrock, ARQ Consultants This SAPEM manual was edited by Dr Fenella Johns, Rubicon Solutions. Photos for this chapter were provided by: • Eugene Knottenbelt, Specialist Consultant • Etienne Terblanche, SANRAL • Professor Kim Jenkins, Stellenbosch University • Dr Fenella Johns, Rubicon Solutions • Dr Phil Paige-Green, CSIR Built Environment




Page v

TABLE OF CONTENTS

1. Introduction and Planning ............................................................................................................... 1 1.1 Objectives of a Progressive Geotechnical Investigation ................................................................ 3 1.2 Competencies, Responsibilities and General Considerations for Exploration Work .......................... 3

1.2.1 Consulting Engineering Company ..................................................................................... 3 1.2.2 Professional Staff and Supervisory Personnel .................................................................... 4 1.2.3 Registered Professional Staff, Staff-in-Training and Accredited Laboratory Field Staff .......... 4 1.2.4 Drilling and In Situ Testing Contractors ............................................................................ 4 1.2.5 Testing Laboratories ....................................................................................................... 5

2. Geotechnical Investigations ............................................................................................................ 6 2.1 Planning and Phasing of Geotechnical Investigations ................................................................... 6 2.2 Stability Assessment Investigations ............................................................................................ 9

2.2.1 General Policy ................................................................................................................. 9 2.2.2 Sub-Surface Investigations Related to Stability Assessment ............................................. 10 2.2.3 Reporting, Scheduling and Timing .................................................................................. 11

2.3 Procurement of Geotechnical Services ...................................................................................... 11 2.3.1 Consulting Geotechnical Engineering Services ................................................................. 11 2.3.2 Geotechnical and Drilling Contractors ............................................................................. 11

3. Potential Problem Subgrades ........................................................................................................ 12 3.1 Subsurface Instability .............................................................................................................. 12

3.1.1 Undermined Ground ...................................................................................................... 12 3.1.2 Dolomitic Subgrades ..................................................................................................... 12 3.1.3 Made or Filled-Up Ground .............................................................................................. 12 3.1.4 Problem Soils ................................................................................................................ 13

3.2 Subsurface Drainage Considerations ......................................................................................... 15 3.2.1 In Situ Subgrade ........................................................................................................... 15 3.2.2 Cuts ............................................................................................................................. 16 3.2.3 Underneath Embankments and Fills ............................................................................... 17

3.3 Design of Special Subgrade Treatment Types Underneath Buildings or Culvert Sites .................... 17 4. Fills ................................................................................................................................................ 19

4.1 New Fills ................................................................................................................................. 21 4.1.1 Fill Stability ................................................................................................................... 21 4.1.2 Settlement of Fills ......................................................................................................... 21 4.1.3 Special Considerations ................................................................................................... 22

4.2 Existing Fills ............................................................................................................................ 23 4.2.1 Toe Erosion .................................................................................................................. 23 4.2.2 Settlement ................................................................................................................... 24 4.2.3 Degradation ................................................................................................................. 25 4.2.4 Translational Slips ......................................................................................................... 25 4.2.5 Creep and Slide (Creeping Valley Slides) ........................................................................ 26 4.2.6 Internal Erosion and Piping ............................................................................................ 27 4.2.7 Stability Failure (Rotational Slips) ................................................................................... 27

4.3 Investigation Process ............................................................................................................... 28 5. Cuts ................................................................................................................................................ 29

5.1 Cut Slopes in Soils ................................................................................................................... 30 5.2 Cut Slopes in Rock ................................................................................................................... 31

5.2.1 Rock Falls and Slides ..................................................................................................... 32 5.2.2 Toppling Failures .......................................................................................................... 33 5.2.3 Block Slides .................................................................................................................. 34 5.2.4 Degradation ................................................................................................................. 37 5.2.5 Investigation Process .................................................................................................... 39

5.3 Failure of Existing Cuts ............................................................................................................ 39 5.3.1 Cut Slopes in Soils ........................................................................................................ 39 5.3.2 Cut Slopes in Rock ........................................................................................................ 42

6. Structures ...................................................................................................................................... 45 6.1 Intrusive Investigations for Bridge Upgrades ............................................................................. 45 6.2 Modus Operandi and Reporting ................................................................................................ 46




Page vi

7. Tunnels .......................................................................................................................................... 47 7.1 Stage 1: Desk Study and Site Reconnaissance (Pre-Feasibility) .................................................. 48

7.1.1 Desk Study ................................................................................................................... 48 7.1.2 Site Reconnaissance (Walkover Site Inspection).............................................................. 50 7.1.3 Site Reconnaissance Report ........................................................................................... 51

7.2 Stage 2: Preliminary Site Investigation (Feasibility) ................................................................... 52 7.2.1 Preliminary Tunnel Report ............................................................................................. 52

7.3 Stage 3: Detailed Site Investigations and Design ...................................................................... 52 7.3.1 Planning ....................................................................................................................... 52 7.3.2 Detailed Investigation Contract ...................................................................................... 53 7.3.3 Investigation Methods ................................................................................................... 53 7.3.4 Guidelines for Assessing Testing Requirements ............................................................... 54 7.3.5 Investigation of Old Mine Workings, Buildings and Structures .......................................... 55 7.3.6 Design ......................................................................................................................... 55 7.3.7 Detailed Tunnel Investigation Report ............................................................................. 56

7.4 Stage 4: Construction Stage Investigations .............................................................................. 57 7.5 Stage 5: Post Construction Monitoring ..................................................................................... 58

8. Composition of Test Data and Reporting ....................................................................................... 59 8.1 Preliminary Geotechnical and Materials Report .......................................................................... 59 8.2 Detailed Geotechnical and Materials Design Report .................................................................... 59 8.3 Project Document .................................................................................................................... 60

References and Bibliography ................................................................................................................... 61 Appendix A: Soil Profiling of Test Pits and Auger Holes Appendix B: Rock Profiling of Cores, Testpits or Quarry Faces Appendix C: Aspects Covered in the Detailed Geotechnical and Materials Exploration and Design

Report for Greenfield/Upgrade Projects Appendix D: Bridge and Culvert Foundation Investigation Appendix E: Examples of Special Roadbed Treatment Types




Page vii

LIST OF TABLES

Table 1. Registration and Affiliations Requirements ....................................................................................... 4 Table 2. Summary of General Activities During the Various Geotechnical Investigation Phases ......................... 7 Table 3. Progressive Investigation Stages for Tunnelling Projects .................................................................. 48

LIST OF FIGURES

Figure 1. Typical Flowchart for Road Prism, Structures and Tunnels Specialist Geotechnical Investigations ......... 2 Figure 2. Distribution of Expansive Soils and Collapsing Sands (Williams et al, 1985) ....................................... 13 Figure 3. Basic Concept of Additional Settlement due to collapse (after Schwartz, 1985) .................................. 14 Figure 4. Interceptor Drain (from TRH15, 1994) ............................................................................................ 16 Figure 5. Drainage Blanket (from TRH15, 1994) ............................................................................................ 16 Figure 6. Wick Drains Under Fill .................................................................................................................... 17 Figure 7. Typical Road Fill ............................................................................................................................ 19 Figure 8. Topographic Embankment Types: Side Slope Fills (from TRH10, 1994) ............................................ 19 Figure 9. Topographic Embankment Types: Gulley Fills (from TRH10, 1994) .................................................. 20 Figure 10. Topographic Embankment Types: Flat Fills (from TRH10, 1994) ...................................................... 20 Figure 11. Bump at Bridge Approach .............................................................................................................. 22 Figure 12. Toe Protection by Construction of Gabion Wall ................................................................................ 23 Figure 13. Preventing Settlement on High Fill .................................................................................................. 24 Figure 14. Inclinometer Probe ........................................................................................................................ 25 Figure 15. Prevention of Degradation and Collapse Settlement in High Fill ........................................................ 26 Figure 16. Slide or Slip (from TRH15, 1994) .................................................................................................... 26 Figure 17. Internal Erosion and Piping ............................................................................................................ 27 Figure 18. Stability Failure ............................................................................................................................. 28 Figure 19. Example of a Road Cut in Rock ...................................................................................................... 29 Figure 20. Cut Slope in Soils .......................................................................................................................... 30 Figure 21. Interceptor Drains ......................................................................................................................... 32 Figure 22. Catch Fences and Canopies on Chapmans’ Peak Drive in Cape Town ................................................ 32 Figure 23. Applying Rock Fall Netting and Shotcrete to Cut Slope ..................................................................... 33 Figure 24. Toppling and Block Failures ............................................................................................................ 33 Figure 25. Steep Block Slide ........................................................................................................................... 34 Figure 26. Slide on Unfavourable Bedding Plane .............................................................................................. 35 Figure 27. Dowelling as a Stabilisation Method ................................................................................................ 35 Figure 28. Gabion Cavity Wall to Retain Unfavourable Dip Strata ...................................................................... 36 Figure 29. Degradation of Sediments .............................................................................................................. 37 Figure 30. Enon Conglomerate near Knysna .................................................................................................... 38 Figure 31. Corestones Falling from Slope ........................................................................................................ 38 Figure 32. Erosion of Cut Face due to Inadequate Interceptor Drain above Slope .............................................. 39 Figure 33. Netting System and Re-Vegetating ................................................................................................. 40 Figure 34. Rotational Slip ............................................................................................................................... 41 Figure 35. Mud and Vegetation Slide on Kaaiman’s Pass .................................................................................. 42 Figure 36. Toppling Failure (from TRH18, 1993) .............................................................................................. 44 Figure 37. Pedestrian Bridge Over the N1 ....................................................................................................... 45 Figure 38. Scour around Bridge Piers .............................................................................................................. 46 Figure 39. Hugenot Tunnel ............................................................................................................................ 47 Figure 40. Google Earth Satellite Image of Joints and Faults in Gneissic Terrain in Kamieskroon Area of

Namaqualand ................................................................................................................................ 50 Figure 41. Changes in Vegetation as a Result of Filled Pit ................................................................................ 51 Figure 42. Tunnel Boring Machine at Entrance to Tunnel at Gautrain’s Rosebank Station ................................... 55

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gatory test by geologists, gists in ly ded



Section 1: Introduction and Planning

Page 5

• Complete the work on time and in accordance with the tender or quotation specifications. • Carry out the investigation according to these guidelines and other recognised standards and procedures. • Provide adequate and reliable data for interpretation purposes. 1.2.5 Testing Laboratories

It is a requirement that the fieldwork, as well as laboratory materials sampling and testing, be carried out by a SANAS accredited testing company approved by the road authority. See Chapter 5, Section 1.1 for more on laboratory accreditation.



Section 2: Geotechnical Investigations

Page 6

2. GEOTECHNICAL INVESTIGATIONS

2.1 Planning and Phasing of Geotechnical Investigations

Exploration work should be as sufficient as the engineering conditions warrant, and as the total scope of works requires. It cannot be emphasized too strongly that thorough planning is a foremost requirement and utmost care and diligence is required during the early planning stages, as well as the detailed investigation stages. The primary aim is to prepare an adequate design and to safeguard against problems during construction and the design life of the facility. The cost of adequate exploration is relatively low when compared with the total value of the project, and varies depending upon the job and the nature of the ground. An often-quoted cumulative figure is in the order of 1½% of the construction cost estimate. Legal issues, environmental issues and safety precautions are critically important during all stages of a geotechnical investigation. The following documents should therefore be studied and be readily available at all times to the entire investigation team. Consulting companies should ensure that all members of the investigation team, including consultants, contractors and laboratory staff involved with the fieldwork, are knowledgeable with the contents of these documents. • SAICE Code of Practice, “The Safety of Persons Working in Small Diameter Shafts and Test Pits for

geotechnical Engineering Purposes”, 2007. • The legal and environmental requirements and considerations elaborated upon in Chapter 1 (Section 3) and

Chapter 6 (Section 2). • SAICE Code of Practice, “Lateral Support in Surface Excavations”, 1989. • Occupational Health and Safety Act No. 85 of 1993 as amended, including the Regulations (2003). • TRH2: Geotechnical and Soil Engineering Mapping for Roads and the Storage of Materials Data (1992). Considering the aims and objectives of investigations, the planning of the investigation should take many, or all, of the following factors into consideration: • Definition of the total scope and the engineering objective. • Nature of the proposed road project. • Geology and geomorphology of the route or site(s). • Access and remoteness of sites. • Site topography, vegetation and drainage. • The nature of adjacent developments beyond road reserves. • Knowledge and data gathering of previous geotechnical investigations, for example, existing bridge

foundations. Opinions and observations from local engineers, land owners and contractors. • The identification of the various soil and rock types occurring in the area of the proposed road structure

project, and representative soil profiles. • Evidence of problem soil conditions, e.g., expansive or collapsible soils, possible shallow undermining,

dolomites, dispersive soils and soft clays. • Localised moisture conditions and ground water levels. • Upfront planning for drilling or augering of trial holes, test pits excavation and obtaining undisturbed or

disturbed samples for laboratory tests and in situ testing. These are required for the design of fills, cut slopes, bridge and culvert foundations.

For successful eventual completion of any geotechnical investigation for structures and tunnels, a logical and systematic approach should be followed, just as for road prism investigations or material sources investigations dealt with in Chapters 6 (Section 4) and 8 (Section 2). Generally, for new or greenfields works, the investigations should follow a progressive or phased approach, such as the one summarised in Table 2.

So

Ta

PuGeGe• • •

•

•

•

• • GeGe• •

• • •

NotFor 1. 2.

outh African Pa

ble 2. Summ

urpose of Investigeneral Phases: Ineotechnical Inves

Collection of availabDetermination of geIdentification of potstability problems Preliminary indicatioconditions Preliminary indicatiosources Identification of altealignments Interfacing with envRecommendations f

eneral Phases: Deotechnical Inves

Final choice of alterDetermination of gegeological conditionInterfacing with EIAPreliminary design oCost estimate of pro

te: practical reasons, thisEIA = Environmental EMP = Environmenta

avement Engin

ary of General A

gation nitial Assessmentstigation Phases:ble information eneral geology tential geological or

ons of foundation

on of construction mat

ernative sites and

vironmentalists for further investigatio

Detailed Assessmestigation Phases:rnative route locationseneral engineering ns A1 of structures and roadoject

s table is not confinedImpact Assessment l Management Plan

neering Manua

Activities During

Techniquest Report, Route L Reconnaissance

terial

ons

• Data reco• Regional t

agricultur• Walk-ove

ent Report, Prelim Preliminary Geo

d

• Soil and r• Geophysic• Test pittin• Core or a• Penetratio• Sampling • Classificat

to road structures an

ScopeIn Table 2, thprogramming these phases

al

Section 2

g the Various G

s ocation Report

e/ Desk Top Studyovery topographical, land usral and geological mapr investigation

minary Design Reotechnical and Marock mapping cal investigations ng uger drilling on tests and lab testing

tion

nd tunnels only.

of Investigationse geotechnical inveconsiderations varymay happen concu

Ch

: Geotechnical Inve

Page 7

eotechnical Inv

Repor

y Report (Pre-Fea

sage, pping

• Lay• Reg

or s• Sch• Rec• Des• Rec

port aterials Report (F

• All t• Clas• Rec• Disc• Rec• Rec

s estigations are very y from project to prrrently, or not all ph

hapter 7: Geote

estigations

vestigation Phas

rt Content

asibility) yout plan gional engineering geosources hematic profiles cord of existing informscription of known geocommendations for alt

easibility/viabilitthe applicable informassification and descripcord of investigation dcussion and interpretacommendations for chcommendations for de

comprehensive, comoject and physical chases are necessary

echnical Investig

ses

ological map (see Chap

mation ological conditions or pternative route location

ty) ation from the previouption of foundation andata, including problem

ation of general test pioice of location and ty

etailed design stage inv

mprising up to five pconditions also vary y for all projects.

gations and Desi

pter 8, Section 2) with

problems ns and further investig

s phase d construction materia

m areas it and borehole data, aype of bridges or strucvestigations

phases. In practicefrom site to site. T

gn Consideratio

h potential material typ

gations

als

and materials sourcesctures

e, however, Therefore, several o

ns

pes

of

South African Pavement Engineering Manual Chapter 7: Geotechnical Investigations and Design Considerations


Page 8

Purpose of Investigation Techniques Report Content

General Phases: Detailed Design and Documentation Report Geotechnical Investigation Phase: Detailed Geotechnical and Materials Design Report

• Obtain quantitative and qualitative information on foundation conditions and construction materials

• Interface with EMP2

• Core drilling, borehole tests and auger drilling

• Undisturbed samples • Laboratory and in situ testing

• Detailed engineering geological mapping and profiling • Quantitative and qualitative descriptions and results of detailed geo-investigations for bridge

or other structure foundations, cuts and fills and construction material sources including borrow pits and quarries; construction methods and alternatives. Pros and cons of each to be considered

• Proactive inclusion and tabulation of all necessary geotechnical engineering design parameters, settlement estimation parameters as evaluated and recommended by geotechnical engineer (who carried out the investigations) for bridge design engineers for each bridge, lateral support design engineers for each high fill or each deep cut or other type permanent lateral support structure required

• Recommendations for foundation treatments, e.g., undercutting, stabilising, grouting and lateral support

• Recommendations for further geotechnical investigation and/or monitoring during construction phase

General Phases: Construction Report Geotechnical Investigation Phase: Construction Report

• Comparison of actual vs. predicted conditions and attending to ad hoc problems

• Observation of behaviour of permanently anchored bridge foundations, lateral support systems and permanently anchored or bolted cuttings and fills, during the Contractual Liability Period

• Detailed site records • Photos • Monitoring foundation or slope

treatments and behaviour via instrumentation and surveillance

• Laboratory and in situ testing

• Detailed mapping • Photos • Records, measurements and results • Conclusions • Further long term actions or recommendations

General Phases: Special Maintenance Report Geotechnical Investigation Phase: Special Maintenance and/or Integrity Reports (typically every 8-10 years)

• Same as above, but at regular intervals during the expected eventual design life of the particular facility

• Monitoring of permanently installed devices and/or instruments (mechanically and/or electronically, e.g., deflections, stresses, pressures and water flow), and ongoing verification of integrity. To be assessed by specialist geotechnical engineer.

• Records, measurements and results • Evaluation and discussions • Conclusions • Recommendations for either immediate actions to be taken or longer term actions

Table 2 is stimulating sensible anshould alwaused, diges There can last phasedeformationstructures systems, peor permaneall fall into are normalrequiremenconstructiotunnel projproblems cthe employ 2.2 Sta

2.2.1 Gen

Geotechnicearly in theas these copractical, ejustify pote• Portions

− Dolo− Thic− Exis

• Possibleterrain.

• Fills or In the caseare also nothe borehofeasibility aare documefor dolomexperienced(Parts 1 & 2 Slope stabaffecting stbe investiginstability aembankmeof TRH18 detailed stcommencesthe chosen For structuthan 10 mefield investion the bageology, cplanned, ev

Chapt

included as athe upfront

nd comprehensays bear in msted and unde

be up to four e occurs durin and/or sand assets (ermanently anently anchoredthis very impolly planned ant. Sometimen and during jects or anch

can arise durinyers or infrastr

ability Asses

neral Policy

al desk study e route locatioould lead to reeconomical anential realignms of the route omitic or shallock active clayssting undergroe instability

r cuttings tha

e of stability aormally carriedole stage, etc.and viability oented in Coun

mite areas d in dolomite2), 2009.

bility of critictructures and/gated. Refeassessment gnts against sl(1993) and S

tage of this s after the finroute and its

res to be founetres), it is exigation commeasis of four climate and hvaluation and

South A

ter 7: Geot

a general guiplanning techsive Geotechn

mind that the perstood by othe

geotechnical ing constructtructural inte(over the lonnchored bridged road cut facortant fourth pnd contractedes, there is athe design lif

hored bridge fng the design ructure owners

ssment Inv

y

reports relateon stage, befoealignment of nd avoid signiment are:

passing oveow undermine or collapsing

ound services oof structure

at require spec

ssessment invd out in progr Some, or af the chosen ncil for Geosciare adequat

e work, as sp

cal cuttings a/or portal wallser to the inguidelines andliding given inSection 2 of investigatory

nal establishmhorizontal and

nded on high extremely impoences, the emsimple param

height. Stagdecision base

African Pav

technical In

Section 2: G

de to geotechniques; and nical and Mateprofessionally er design eng

investigation tion. Monitoegrity of ex

ng term) suche or viaduct sces and road phase. Speciad out to fulfila fifth phase,fe of the facilfoundations, life. Should

s should be in

vestigations

ed to the possore embarking the route. Foficant and ex

er: ed land sands

or features thaes or tunnels/p

cial lateral sup

vestigations foressive stagesll, of these stroute before ience (2002 ately competepecified in SA

and fill embas or tunnels, mnitial susceptd the stabilityn Sections 3.6

TRH10 (1994y work normaent or confirmd vertical align

embankmentsortant that be

mbankment is meters: topged, or proged investigatio

vement En

nvestigation

Geotechnical I

Page 9

chnical enginesecondly, to

erials Investigaevaluated geineers.

phases, of whoring the behexisting geoteh as lateral structure founembankment

al maintenancl this very im, which occulity. For examstability or cosuch problem

nformed.

s

sible deep inst on the Detai

or new construxpensive prob

at cannot be eportals or dee

pport measure

or structures as: firstly, the tages are requthe design ha

and 2007) andent and

ANS 1936

ankments must also tibility to y of high 6 and 3.7 4). The ally only mation of nments.

s (greater efore any classified

pography, gressively on stages

T

t•

•T

T

ngineering

s and Desig

nvestigations

eers and enginserve as a q

ation and Deseotechnical de

hich the haviour, echnical support dations, t slopes, ce works mportant rs after mple, in orrosion

ms arise,

tability of a poled Geotechniuction, alternalems, must b

economically rep cuttings or

es due to cons

and/or tunnelsdesk study, suired during tas progressed d Wagener (1

InTmnuE

DolomitThe methodolassessment odocumented athis manual. • “Engineeri

for AppropLand”, 200

• “ApproachThese are joinGeoScience anGeotechnical

These guidelinguidelines issu(2009).

Manual

gn Consider

neering geolouality checklisign Report. Tsign paramete

ortion of the rocal and Matertive route opt

be considered.

relocated embankment

traints such a

s on dolomitic econdly, the gthe route loca

too far. The985). It is es

Compilingnvestigationhe compiler of

must bear in meeds to be usenderstood by ngineers.

ic Sites ogies relating n dolomitic lanand are therefRefer to the ing Geological priate Develop02. h to Sites on Dntly published nd the SAIEG,Division of the

nes stand to bued by SABS,

rations

ogists to: firstst to ensure The compiler oers presented

oute should brials Design Rtions, which m. Instabilities

ts located on

as geometrics.

c land, such ingeophysical st

ation stage, toese investigatissential that i

g the Geotecn Design Repof any of the remind that the r

ed, digested aother Design

g to hazard annd are adequafore not repea

l Site Charactepment on Dolo

Dolomitic Landby the Counc

, and endorsede SAICE.

be surpassed bnamely SANS

tly, assist in an eventual

of the report need to be

be submitted eport stage,

may be more s that could

problematic

nvestigations tage, thirdly o assess the ive methods nvestigators

chnical port eports eport and

d risk ately ated in

erization omitic

d”, 2007. cil for d by the

by 1936

are then emroute alignmshould be laboratory t(2.2.2) and 2.2.2 Sub

Sub-surfaceevaluation the magnitreflected by For settlemsoft clayey even at a care on-grad In general, • Provide • Identify• Provide • Yield sa• Provide • Provide Cuts and frelating to and TRH18methods inscanning (MModern remgreenfields Sufficient iminimise poin height, stability con For road cuslopes are adequate sto slope fexceeds 10prove the orientation rock formaprofiles of tof water m The spacingcritical invebe devoted150 metrespurposes. spacing nemetres whe The depth present, asof the dept

Chapt

mbarked, detament for the pexpanded to testing, core l

d in Section 4.

b-Surface I

e studies reprof stability, setude of the ay cost or safet

ment consideraand silty mate

considerable dde sections an

sub-surface sa description

y and locate wgeotechnical

amples for testin situ moisall of the data

fills susceptiblcritical emban

8. The methonclude aerial MSS) methodsmote sensing projects. An

nvestigation oost constructiomust be des

nsiderations.

uts considerednormally util

slopes must befailure assess0 metres, spec

stability of and discontin

ations, and gethe soil and roust be made.

g and depth oestigation aread to them. Ats typical for loShorter interv

eeds to be coen defining the

of boreholess well as the wth to which s

South A

ter 7: Geot

ails of which cproposed roadjustify a mo

logging, and w

nvestigatio

resent an impoettlement or happlied load, uty aspects.

ations, the deerials and matdepth below tnd those with v

studies must: of the chara

weak or compparameters oting the geote

sture, water ta necessary fo

e to instabilitnkments and odologies empphoto interprs (TRH18). Ttechniques aexample is Li

of subsoil conon settlementsigned for slo

d as a sourceised to optime maintained. ments, wherecial geotechnicsuch deep cnuity surveyseotechnical deock encounter

of bore holes as normally ret least two borong fills, withvals are used fnsiderably rede extent of dis

s must be rewidth and heigsignificant stre

African Pav

technical In

Section 2: G

can be found d has been finore detailed stwater table me

ons Related

ortant phase eave. The deuniformity of

pth may be gterials with a cthe fill. The svery low fills.

cter and geopressible (orbtained from echnical engable and seepor preparation

ty are not oncritical cuttingployed vary, dretation, colouThese techniquare sometimesDAR, which is

nditions below. Regardless ope, horizonta

e of constructmise the cut/f

Regardless oe the depth cal investigatiocut slopes.

if in unweatesign. Detailred must be s

and auger hoepresent only reholes must probing in bfor short fills. duced and mascovered comp

elated to the ht of the propesses are pro

vement En

nvestigation

Geotechnical I

Page 10

in TRH10. If nalised, the intability investeasurements.

d to Stabilit

of the stabilityepth to which

geology and

greater than gcollapsible grastretches of ro

ometry of ther heaving) stin situ testin

gineering propage data. n of the engin

nly the deep gs are defineddepending onur infrared phues can be cos warranted fs a three dime

w all fills muof the initial sal slide and

tion materials,fill balance, aof initial susce

of a proposons are necesThese includ

thered or weaed descriptionsupplied, and

oles depends oa small percebe made ben

between for co In problem aay approach pressible depo

e geological cposed fill. On oduced by fill

ngineering

s and Desig

nvestigations

warranted, aitial road prism

tigation involv This is discu

ty Assessme

y investigationthe investigatsoils in the

generally requain structure aoad pavement

e underlying latrata. ng in borehooperties of th

neering solut

or high ones.d in Section 2n the stage, ahotography foombined with for early slopnsional radar

ust be carriedsusceptibility tbulging

, batter lthough

eptibility sed cut ssary to de joint athered ns, and special cognis

on the specificentage of the eath each maorrelation areas, the 15 to 20 osits.

conditions the basis loadings,

Retomslobu

Manual

gn Consider

nd provided thm investigatioving drilling, iussed in more

ent

n for roads, aion must be carea, and sev

uired for slide are especially st most vulnera

ayer or layers.

les and usinghe materials.

tion.

. The variou2.2.1 and are and on each or moisture stconstruction e stability stusystem that e

out to enabo failure, all fi

sance of the p

c geological cototal investiga

ajor fill, with in

Fills > egardless of tho failure, all filletres in heighope, and horizulging stability

BatteA batter slopeof a fill or retaslope of the c

rations

the horizontal on (Chapter 6,in situ testingdetail in the

and are necesscarried out is averity of the

stability probsusceptible toable to heavin

g probes.

us stages of ialso discusseparticular situtudies and mmaterial locat

udies, especiaenhances 3-D t

ble design proills in excess o

presence and

onditions. Beation, special ntervals of 10

10 metres he initial suscels in excess of

ht must be deszontal slide any consideration

er Slopes e is the backwaining wall, orcut.

and vertical , Section 4), g, sampling, next section

sary for any a function of problem as

blems. Wet, o settlement, ng problems

nvestigation ed in TRH10 uation. The

multi-spectral tion as well. ally on large topography.

ocedures to of 10 metres

implications

ecause these care should

00 metres to

eptibility f 10 signed for nd ns.

ward slope r the




Page 11

boreholes beneath fills should extend to a depth at least equal to a half width, or to twice the average height of the fill, unless incompressible layers are encountered at shallower depth. Boreholes for fill stability investigations may be terminated at shallower depths when bedrock is encountered. 2.2.3 Reporting, Scheduling and Timing

In addition to the guidelines given in Section 8 and Table 2 for the various reporting stages of project development, in general, for greenfields or new and/or upgrade road works projects, the following reports are necessary: • Desk Study Geotechnical Report is essential prior to, or at, route location stage. • Preliminary Geotechnical and Materials Report is required prior to the compilation of the Basic Planning

Report. • Detailed Geotechnical and Materials Design Report is required approximately a month prior to the

detailed design and documentation stage. 2.3 Procurement of Geotechnical Services

Services that are typically used for geotechnical investigations include geotechnical engineering consulting services and geotechnical or drilling contractor services. 2.3.1 Consulting Geotechnical Engineering Services

Certain road authorities’ in-house geotechnical and structural engineers first do their own planning, aimed at accurately determining the total scope of geotechnical investigatory work. This includes the evaluation of results and to prepare the necessary Geotechnical Design Report. Following this, the road authority’s tender procurement documents for the procurement of the geotechnical consulting engineer’s services are prepared, to find a suitable professional to carry out the required geotechnical investigations and prepare the design reports. Other road authorities appoint a suitable knowledgeable and reputable registered and trusted geotechnical engineering company, or a company with whom they normally work with to plan and carry out the necessary investigatory work and to compile the Geotechnical Design Reports. 2.3.2 Geotechnical and Drilling Contractors

The geotechnical engineer, who is to carry out the investigative work, must compile the proposed total scope of the work, together with its anticipated value and schedule. This must jointly be discussed with the responsible employer or road authority’s project manager and geotechnical engineer in a timely manner. Thereafter, tenders can be invited from geotechnical and drilling contractors, before contractors are appointed. This requirement applies to all geotechnical investigative work referred to in this Chapter, as well as Chapters 6 and 8. Tenders for geotechnical site exploration work are requested using documents conforming to the standard requirements of the particular road authority. For example, SANRAL’s latest pro-forma project document for sub-surface investigations, or for centre line and borrow pit investigations, together with its directives for the compilation of tender and contract documents could be used. These are issued by SANRAL on appointment. These could also be preceded by the Soil Engineering Map and Terrain Evaluation Report, especially for a greenfields project.

3. PO

3.1 Sub

The definiticonstructedlayers are cthe subgrad Problem suconstructio• Underm• Dolom• Made g• Proble

− Heawet

− Colla− Disp

• Saline These all performancproblem su 3.1.1 Und

A road, andcould take temporary details, of important finformationmines. Inconsideratioengineer toA specialisrecommend The genera 3.1.2 Dol

All road psubject to 2.2.1. Themostly durphase, to investigatioalso discuss 3.1.3 Mad

Roads and often crosslandfills, ol‘filled-up gcompressibadditional materials ogenerate e

Chapt

TENTIAL P

bsurface In

ion of ‘roadbed. The term ‘sconstructed ade is of param

ubgrades, reqn or pavemenmined areas itic subgradesground or fillem soils ving soils, exclays

apsible or compersive soils soils

have an effece or load cabgrades are d

dermined G

d the associatplace beneattunnels to be not only the for a new gren must be pron some caseson should be o collect thesest mining engdations for the

al procedures g

lomitic Sub

projects travea dolomite st

ese investigatiring the route

assess the on methods arsed in Chapte

de or Filled

road structurs zones underd constructio

ground’. Suble and potethreats. For

of various typexcessive met

South A

ter 7: Geot

PROBLEM

nstability

ed’ is the in sitsubgrade’ desnd includes fi

mount importa

uiring specialnt layer constru

s ed up ground

xpansive or s

mpressible soil

ect on the derrying ability,

discussed in th

Ground

ted structuresth a road or mined beneahistorical and

eenfields projeoactively obtas, these authogiven to appo

e data from thgineer is nore design or fur

given for stab

bgrades

rsing dolomittability investigons are carriee location ph

viability of re documentedr 6, Section 4.

d-Up Ground

res planned inlain by old ban sites and s

uch fills are entially collapr example, thpes, be envirothane, or, ha

African Pav

technical In

Section 3: Po

SUBGRAD

tu material onscribes the comll layers and/once.

ist geotechnicuction comme

hrinking subg

s or fills

esign of the the stability

he following se

s and tunnels,existing struct

ath an existing current mini

ect planned inained from thorities may aointing a comhe various sourmally appoinrther investiga

ility assessme

tic formationsgation as direed out in proghase or detail

the chosend in Wagener .4.2.

d

n urban or seackfills or mansports fields,

by nature sing, but cohey may cononmentally unave perched

vement En

nvestigation

otential Proble

Page 12

DES

n which the filmpleted earthor in situ mat

cal input or inences, include

grades and so

road and roaand the dur

ections, and a

, could cross actures and tung road reserveng activities, n an area whehe offices of talso refer to

mpetent personurces, and to cnted to carry ations.

ent investigatio

s shall first bected in Sectiogressive stageled assessme route. Th(1985) and a

emi-urban aren-made fills anin other wordnot only ve

ould also pontain unsuitabnfriendly, couseasonal wat

ngineering

s and Desig

em Subgrades

l, or in the abworks within tterials. It is,

nvestigation athe following

oft

ad structures,ability of the re also discuss

an already unnnels. Mininge. It is extrembut also futuere coal or otthe mining cothe particularn as a sub-cocarry out a pr

out the fin

ons in Section

be on es, ent he

are

as nd ds

ery se

ble uld ter

• Probthe The27,

• Probthe PidgSou

• Probthe InstEnvNov

The codata ansubgrato the g

Manual

gn Consider

s

bsence of any the road prismtherefore, obv

and construct:

, as well as constructed

sed in Chapte

dermined zong companies smely importantre mining actther mining acommissioner ar mining comnsultant to theliminary evalal evaluation,

2.2 should als

Recommend

oblem Soils in Se Art. Dolomitee Civil EngineeNo. 7 July, 19

oblem Soils in Se Art. Expansivegeon and Dayuth Africa. Vol.oblem Soils in Se Art, Proceedintitute for Enginvironmental Gevember 2008.

Test Data anmpilation and nd reporting odes should beguidelines give

rations

fill, pavemenm on which thvious that the

tion treatment

the construcfill or layer w

er 6 (Section 4

ne, or future usometimes alst to verify the

tivities. This ctivities take and/or chief

mpanies involvhe appointed gluation of its s, and to ma

so be taken in

ded Reading

South Africa –es by Dr F. Waer in South Afr985. South Africa –

ve Soils by Wily. The Civil En. 27, No. 7 JulSouth Africa –ngs, South Afrneering and eologists, 3–4

nd Reporting interpretation

on potential pre carried out aven in Section

t layers, are he pavement e stability of

t, before fill

ctability, the works. The .4).

undermining so apply for e extent and is especially place. This inspector of ved. Serious geotechnical significance. ake suitable

nto account.

– State of agener. rica. Vol.

– State of liams,

ngineer in ly, 1985.

– State of rican

g n of test roblem according 8.



Section 3: Potential Problem Subgrades

Page 13

tables. Special consideration should therefore be given to the planning of geotechnical investigations in such areas. The scope and results of these investigations should indicate whether the materials could be left in place after sufficient compaction, treated to serve as a roadbed, or removed entirely. Should the material be spoiled, the type and depth of material to be removed must be identified, the stability of the material whilst being excavated assessed, and the necessary construction plant identified. Should the filled up ground only require in situ compaction, the geotechnical engineer should indicate the proposed depth of in situ compaction and propose the densification process together with the type of plant most suitable for the compaction and to ensure stability of the materials. 3.1.4 Problem Soils

3.1.4.1 Heaving and Soft, Wet Clays

It is of paramount importance to establish the spatial distribution of partly saturated potentially heaving, shrinking and soft wet clays along a road, and where structures sensitive to movements are planned. Expansive clays are probably among the most widespread of the problem soils in South Africa. Maps are available indicating likely areas of these soils, an example of which is shown in Figure 2. Methods of assessing the possible heave and countermeasures of potentially expansive roadbeds have been developed (Weston, 1980).

Figure 2. Distribution of Expansive Soils and Collapsing Sands (Williams et al, 1985)

When assessing a route or site, recognizing the magnitude of the problem requires knowledge of the whole soil profile, not just the upper layers, which may be in inert transported or pedogenic horizons. The source of the problem may, thus, lie well below the depth of normal shallow (up to 2 metres) test pits. Problem clays as deep as five metres or more could affect pavements and structures. Investigation procedures, after an intensive planning stage, normally include: • Reconnaissance site visit (field mapping) making use of available geological and soil maps and geological

publications and, if available, aerial photo interpretation. • Fieldwork program using various types of trial pit, auger hole or core drilling rigs. The type of fieldwork

depends on the vertical extent of potentially expansive residual geological material and/or alluvial deposits. From the fieldwork, the soil profiles must be systematically described. Sealed disturbed and undisturbed samples must be obtained. Chapter 6, Section 4 contains additional details.

• Testing of samples in the laboratory. • Interpretation of the results from the field and laboratory tests, leading to the design of countermeasures. The eventual aim is to have confidence in estimates of:

• Amount• Consol• Draina Treating thlayers. CoVarious resusing a ran

3.1.4.2 So

Soils with asoils with aoccurring dto potentiastatic loadinleaching, mWetting upchange in v

Figure

Whilst thercollapse setneed to be on roads, uis necessarbe sufficienparticular railways wh

Chapt

t and variabilitlidation settlege and beari

he surface bedomplete removsearchers havenge of counter

oils and Fills

a collapsible ga collapsible fadecomposed sol collapse settng, as illustra

may withstandp can result involume in the

3. Basic C

re are a numbttlement occusatisfied unde

under certain cry for collapsent to cause shimportance fhere the subgr

South A

ter 7: Geot

ty of heave oement ing capacity

d underlain bval is ideal bue published thrmeasures whe

with a Colla

grain structureabric both in toils may havetlement, and wted in Figure

d relatively larn a large decresoil is associa

Concept of

ber of preconrs under staticer heavy dynacircumstancese to occur. Tear failure of

for roads, herade is continu

Sett

lem

ent

0

Infiltration duwater pond

Infiltration dbroken serv

African Pav

technical In

Section 3: Po

f the stiff, par

parameters o

by clays may ut, for variousheir experiencen the heaving

apsible Grain

e can adversethe field and ta collapsible

when wetted u3. A natural ge imposed sease in volumted with a cha

Additional

ditions that mc loads, not aamic loads. Rs, an increase he applicationbridging collo

eavy duty pauously subject

ue to ding

due to vices

SoilInc

d

t

vement En

nvestigation

otential Proble

Page 14

rtially saturate

of the normally

include partias reasons, mace with heaving layers canno

n Structure

ely affect the fthe laboratorygrain structurup can experisoil that has

stresses with sme and large mange in soil st

Settlement

must be satisfll of these pre

Research has sin the moistu

n of dynamic oidal material. avements, airted to dynami

pa

l initially partiacrease in moisdue to water in

time

t1

ngineering

s and Desig

em Subgrades

ed, potentially

y wet, soft clay

al or completeay not be the ng clays in Soot be removed

foundation of y have been dre. Loose, or ence collapse a collapsible small settlememagnitude setructure.

t due to col

fied before econditions shown that ure content loads may This is of

rfields and c loads. A

Time

Normal sesoil partia

Additional– no changpressure bin moistu

ally saturatedsture content nfilration at t1

Manual

gn Consider

s

expansive cla

ys underlying

e removal of tmost econom

outh African rod entirely (Wes

structures. Pdeveloped (Scpoorly compasettlement wsoil structure,ents at a low ttlement unde

llapse (afte

ettlement with ally saturated

l settlement ge in applied but increase ure content

RecoProblem SoilState of the by K. Swartzby H. Elges. South Africa1985.

rations

ays

a high emban

the potentiallmical or feasiboad constructston, 1980).

Procedures fochwartz, 1985)cted, fills are

without applyin, from decompin situ moistu

er an applied

er Schwartz

ommended Rils in South AfrArt. Collapsib

z and Dispersiv The Civil Eng. Vol. 27, No.

nkment

y expansive ble solution. tion projects

r identifying ). Naturally also subject

ng additional position and ure content. stress. The

z, 1985)

Reading frica – ble Soils ive Soils gineer in 7 July,

secondary associated Engineering• In situ

impact c• In situ • Remov• Chemic The degreeassessed foconstructio

3.1.4.3 Di

Dispersion grained fradispersive characterist• Ordina• Dispers

suscept Dispersion attractive (progressiveare carried

3.1.4.4 Sa

Many soils stabilizers, precipitatiosurfacing s(1998) idenSection 2.1the salts uslayers. (Net 3.2 Sub

An effectivconsisting ousing mapsinvestigatio Subsurface divided into• In situ s• Cuts • Underne 3.2.1 In S

The most cground watof buildingsMethods to• Longitu

illustrate

Chapt

aspect is the cost implicatio

g solutions to u densificatiocompaction densificatio

ve and reusecal stabilisat

e of densificator each road pn as dynamic

ispersive Soi

can occur in aaction of the clays. Naturtics:

ary clays, whisive clays, tible to erosion

occurs when (van der Waalely detached faway, thus ad

aline Soils

in arid areas such as lime an of these saseals. Convenntifies potenti0 and Chapte

sing lime treattterberg, 1979

bsurface Dr

ve subsurface of a desk studs and remote

ons. Due allow

drainage in o three generasubgrade

eath embankm

Situ Subgra

common applicter in the roas, either by in

o control groundinal and/ored in Figure 4

South A

ter 7: Geot

large reduction from the in

the collapse pon by various

on by surface e the material tion with com

tion and the project. Measwheel loads a

ils

any soil with hsoil has the

ral clays can

ich are relativewhich defloccn and piping.

the repulsivel’s) forces so from the surfadversely affec

have naturalland cement, walts in upper tional conducally problem

er 4, Section 2tment, or spec9)

rainage Con

drainage sysdy and a field e sensing, forwance should

road and roaal categories:

ments and fills

ade

cation of subsad subgrade antercepting in-ndwater includr diagonally 4.

African Pav

technical In

Section 3: Po

on in volume ncreased layer

problem of thes types of rolle

pounding (dynin compacted

mpaction

depth to whicsures that simpare an effectiv

high exchangee greatest infbe grouped i

ely erosion resculate in the

forces (electthat when thece and go intoting the subgr

ly high saline when construclayers in the

ctivity testing materials and.7. This involcial preventativ

nsideration

tem cannot binvestigation. r example, aebe made for s

ad structure c

s

surface drainand below the-flows or encode:

spaced inte

vement En

nvestigation

otential Proble

Page 15

that collapsibr works quanti

e roadbed or sers (COLTO S

namic consolidlayers at pred

ch densificatioply avoid wate

ve shear failure

eable sodium fluence in eninto two main

sistant presence of

rical surface fe clay mass iso suspension.rade. (Elges,

contents. Thcting layer woe pavement,

as specified d the necessalves removal ove measures t

ns

be designed w Methods and

erial photo inseasonal fluctu

construction c

age is to contre surface bed ouraging out-

erceptor dr

ngineering

s and Desig

em Subgrades

ble subgradesties required.

subgrade incluSection 3300 C

dation) determined mo

on is requireder penetratinge triggering m

percentage (Engineering apn categories

f relatively pu

forces) betwes in contact w If the water1985)

hese salts canorks. Certain hresulting in dfor gravels iry corrective

of the problemthat minimise

without a weld aids during tterpretation, uations in the

an be

rol the levels flows.

rains,

Morobt•

•

•

Manual

gn Consider

s

s experience w

ude the followiClause 3305(b

oisture conten

d are factors tg the collapsibechanism.

ESP) values, evplications, thiwith fundame

ure water an

en individual with water, ind

is flowing, th

n negatively inhighly soluble deterioration on the COLTOaction can be

m material, redthe movemen

l-planned comthe initial recofollowed by tmoisture regi

Drainagere detailed ained from: SANRAL (200Manual, ChaTRH15 (1994)Drainage FoTRH18 (1993)InvestigatioConstructionof Road Cutt

rations

with compacti

ing methods: b)) including

nts

that must beble layers are r

even in sand. is discussion entally difficu

nd are, there

clay particles dividual clay phe dispersed c

nfluence convsalts can also

of compactedO Standard Spe taken. Seeduction of the nt of the salts

mprehensive ionnaissance stthe normal pme.

e Informatioinformation

06): Drainageapter 9 4): Subsurfacor Roads ): The

on, Design, n and Mainte

ttings

on, and the

high energy

individually risky in road

As the fine-focuses on

lt erodibility

fore, highly

exceed the particles are clay particles

entional soil o lead to the layers and pecifications

e Chapter 3, solubility of through the

nvestigation tage include hysical field

n may be

e

ce

enance




Page 16

• Ground water lowering, in extreme cases. • Geotextile enclosed sloping drainage blankets for interception of general seepage under the top of subgrade

and at cut-fill transitions, as illustrated in Figure 5.

Figure 4. Interceptor Drain (from TRH15, 1994)

Figure 5. Drainage Blanket (from TRH15, 1994)

3.2.2 Cuts

The investigation and control of groundwater is thoroughly dealt with in Section 5, where investigations into the stability of cuttings are discussed. It is important to drain the road pavement within a cut or the surface bed of buildings to be placed within a cut. Pore water pressures caused by the available head in the adjacent cut or from the adjacent uphill road may lead to pavement distress. Provision for subsurface drainage must therefore be made in the road foundation in cuttings. The provision of permanent subsoil drains below the surface or next to the pavement layers in cuttings normally also goes hand in hand with the provision of lined side drain surface drainage systems next to the paved road, in conjunction with sealed shoulders.




Page 17

3.2.3 Underneath Embankments and Fills

The general problems of embankment stability and settlement are considered in Section 4. Cases may arise where road structures or buildings associated with a road project need to be founded on constructed fill embankments. Following the initial normal shallow centreline soil survey during the preliminary or detailed design stage, the detailed geotechnical investigations for embankments and fills must be adequately planned to allow the necessary design calculations for typical solutions. To avoid settlement and/or instability of fills built on soft wet formations, drainage of the roadbed is normally the first operation, followed by the removal of unsuitable materials thereafter, if possible. Depending on the subsurface circumstances found on individual sites, special drainage measures have to be designed. These include: • For high embankments, complicated vertical wick drains (Figure 6) or sand piles installed below ground level

in conjunction with geotextile wrapped sand or gravel horizontal drainage blankets (Figure 5). The settlement versus time should be monitored during construction.

• Introducing transverse and longitudinal temporary drainage trenches in a clayey subgrade with a pioneer layer, or rock fill compacted in situ, prior to the embankment construction.

• Where fills are to be constructed against sloping natural terrain, drainage blankets (Figure 5) used with longitudinal collector drains installed parallel to the slope or on benches, with rock toes at the bottom, should be considered.

Figure 6. Wick Drains Under Fill

3.3 Design of Special Subgrade Treatment Types Underneath Buildings or Culvert Sites

Typical examples of special roadbed treatment types are discussed and presented in Chapter 6, Section 4.4 and further examples are included in Chapter 9, Section 9.2. All portions of problematic subgrades identified underneath culvert and building sites should be categorised into uniform sections. Each uniform section should receive either the standard roadbed treatment, or a special roadbed treatment as specified by the geotechnical and pavement design engineers. These special roadbed treatment types shall therefore not be the standard types as referred to in COLTO Clause 3305 (a) to (d), but shall be a combination of specially designed operations and methods. For example: • Dynamic compaction methods (deep or shallow) over thick compressible fills, followed by conventional

earthworks and a three-pass roller compaction. • A long period of pre-wetting heaving clays at subgrade level that are left in place below the road fill. • On a heaving clay subgrade, a combination of several precautionary measures may be required. For example,

removing the dessicated partly saturated clay layers and replacing with compacted inert materials.




Page 18

• For a high embankment on swampy ground, before constructing the fill a combination of several precautionary measures might be required that involve several construction operations, such as a geogrid mattress or geotextiles in combination with natural sand blankets.

The Detailed Geotechnical and Materials Design Report (Sections 8.2 and 8.3) should clearly elaborate on the details of such special measures, as specified in Chapter 6, Section 7 and in Appendices A to E of this Chapter.

4. FIL

Fills, or emfills includematerials fo

Road authotheir respefills. Theseand defininavailable toincluding thTRH10 (19investigatio Road fills alocated, thconventionagenerally trecorded on

Fig

Chapt

LLS

bankments, ae reducing theor fills are gen

orities generactive requirem

e are particulang the area too the engineerhe TRH range994) are peons or designin

are generally dhat is, a sideal (symmetricreated as a sn separate de

ure 8. To

South A

ter 7: Geot

are when soils e grade along

nerally obtaine

lly have standments and porly important o investigate. r that address e. In the specrtinent, and ng fills.

described by te fill (Figure cally shaped single entity asign sheets or

opographic

African Pav

technical In

S

are placed ovg a road or red from cuts (S

Figure 7

dard plans anlicies for the when determi In addition,the design ancific case of rshould be

the topograph8), a gulley

or “flat”) filland the invesr files.

Embankme

vement En

nvestigation

Section 4: Fill

Page 19

ver a section oraising the roSection 5). A

7. Typical

nd specificatiodesign and coining the footpthere are ma

nd constructioroad fills, TRHconsulted wh

hical units whey fill (Figure(Figure 10).

stigatory and

ent Types:

ngineering

s and Desig

ls

of land to elevoadbed out ofA typical road

Road Fill

ons describingonstruction ofprint of the fillany guidelinesn of road fills,

H9 (1992) andhen planning

erein they are 9) or as a Each fill is

test data are

Side Slope

Manual

gn Consider

vate the grounf problem arefill is shown in

g f l s , d g

e a s e

Fills (from

InDesigninMore detbe obtain• TRH9

of Roa• TRH1

DesigEmba

rations

nd level. Theeas. In hilly n Figure 7.

TRH10, 19

nvestigating ng Fills tailed informaned from: 9 (1992): Con

oad Embankme10 (1994): Thgn of Road ankments

reasons for terrain, the

994)

and

ation may

struction ents he

F

Provided thand that sunder the gmetres, or obvious sigengineer. Twill generainvestigatioconcordant• Desk st• Field re• Invest• Analyti Where reqgeotechnicaexercise or of such spengineer’s

Chapt

Figure 9. T

Figure 10. hat there are uitable constrguidance of swhere fills ar

gns of instabiliThis ensures tally interact wons (see Figut with the maintudy during weconnaissanigative phaseic and a desig

uired, superval engineer mas part of th

pecial measurbrief.

South A

ter 7: Geot

Topographi

Topograph

no problematruction materiuitably experire to be constty in the areathat adequatewith the geotre 1 flowchan investigationwhich all availa

nce where note gn phase

vision of suchmay have to be main constres may also

African Pav

technical In

S

ic Embankm

hic Embank

tic roadbed coials are readilenced enginetructed traversa, it is prudente investigatorytechnical engrt). The actns: able informatie is taken of f

measures asbe provided foruction phase.be included

vement En

nvestigation

Section 4: Fill

Page 20

ment Types

kment Type

onditions (as dly available, c

eers. Howevesing very deet to employ thy, design and gineer or leadtivities are ge

on is collectedfeatures releva

s prescribed or either as a. Post-construin the specia

ngineering

s and Desig

ls

s: Gulley Fi

es: Flat Fill

described in Sconventional fr, where the

ep gulleys, on he services of construction p

der of the inenerally cond

d and assessedant to the fills

by the speciapre-construct

uction monitoralist geotechn

Manual

gn Consider

lls (from TR

s (from TRH

Section 3 and fills can be invertical heightsteep side sloan experience

procedures arevestigatory teucted in a st

d and cuts bein

alist tion ring nical

Thesecarefulong tthe filslope stabili

rations

RH10, 1994

H10, 1994)

Chapter 6, Snvestigated ant of such fills opes, or wher

ced specialist ge followed. Theam for the taged approa

ng investigated

Fills > 10 e fills need to ully designed tterm settlemell, and to ensuand foundatioity.

4)

)

Section 4.4), nd designed exceeds 10

re there are geotechnical his specialist road prism ch, running

d

metres be to limit nt within

ure good on

4.1 New

4.1.1 Fill

Generally, rquality andmaterials bmetres in v• Ensure • Ensure • A proba Fill stabilitydeterminatidesign, inclby the geot Similarly, tcompressibcan be carr• Vane s

bottom and the

• SPT TeSPT “compre

• Menard(camcomstrength

• Penetr− Han

handrecoof la

− DynDCPCha

− Dyn• Probes

shear ssubsurfa

Laboratory undisturbed(quick, undof options eShear box the bottom 4.1.2 Set

As a fill is ca result of tconsolidatiodisplacemeis dependee.g., loadintermed secinfinite in d

Chapt

w Fills

Stability

roadbed charad density are become more vertical height limited longa minimum faability of fai

y assessmenion of the strluding long tetechnical engi

the strength bility and permried out. In sishear tests: of the hole a

e peak value isest (see ChaptN” value assibility of soil Pressuremmeter) also h of soils and rometers: d held/pocketd to the caliorded on the sarge diameter amic cone pe

P N values, Cpter 5, Sectionamic probe su

s: The CPT anstrength of finface strata suc

shear strengd samples obtdrained tests aexist such as dtests involve . Triaxial test

ttlement of

constructed, ththe escape of on occurring fent that occursnt on the permng during concondary settlemduration!

South A

ter 7: Geot

acteristics havcontrolled. Hand more signbe designed t term settlem

actor of safetlure acceptab

t requires prrength paramrm erosion prneer.

and moisturemeability, need

tu evaluation The tests are

and then pushs used to calcuter 5, Section and undrainels are readily a

meters and provide measoft rock.

t penetrometeibration markscale. This is cauger holes. netrometer (D

CBR values, an 5.4.5 and Chuper heavy (Dnd CUPT testsne grained soch as differing

ths may be dtained from teand slow, satudiffering confiinducing sheats are discusse

Fills

he vertical strair or water f

for a unit incrs with the resmeability of thnstruction, is tment. Second

African Pav

technical In

S

ve a greater inHowever, as tnificant. Mostto: ment within tty (FOS) of 1

ble to the emp

rior determinmeters, setting

otection and s

e condition od to be establisof shear stren

e performed ahing the seleculate the shea4.4.4). Correl

ed shear stavailable. the self-drilli

ans of deter

er: The instruk and the macommonly don

DCP): Correlatand bearing hapter 10, SecPSH) testing f

s (see Chapterils through thcoefficients o

determined onest holes (see urated drainednement pressuar failure in a ed in Chapter

resses on the from the voidsrease in pressultant reductio

he soil. Consoltermed primadary settlemen

vement En

nvestigation

Section 4: Fill

Page 21

nfluence on thethe height of t road authori

the high fill its1.5 for slope aployer or client

nation of theg density requstorm water m

of the subgrashed so that angth can be mat any depth cted vane intoar strength of tations betweetrength and

ing pressurermining the

ment is pusheaximum readine on the side

tions exist betstrength (q)

ction 7.3) for settlementr 6, Section 4he entire soil of permeability

n both disturb Chapter 6, S

d tests) or undures, differingcylindrical soi3, Section 4.6

underlying sos and the movsure in a soil on in volume lidation or sett

ary settlementnt in deep org

ngineering

s and Desig

ls

e behaviour of the fill increties therefore

self and foundatiot.

e quality of uirements, se

measures. Thi

ade materialsaccurate settle

made by way oby first drillin

o the stratum the soil. en the

the

meter shear

ed by ing is ewalls

tween (see

t estimation pu4.3.4) provide

profile. Thisy, which may b

bed samples (Section 6.3). Tdrained and drg loading ratesil specimen by6.3.

oils increase. ving of the soli

is defined as is called constlement that tt. Settlementanic alluvium

•

•

Manual

gn Consider

f fills than theases, the strerequire that a

n stability

available conttlement verifs involves var

s beneath thement predictif field tests su

ng to the requto be tested.

urposes a means for

s is very usefube of great sig

laboratory coTest methods rained triaxial s, or measuriny sliding the t

Deformation ods closer to eathe soil’s com

solidation settltakes place ovt that takes pof very low pe

Settleme

Primary settshort period oloading in conSecondary sover a long timalluvium of vethe secondaryalmost infinite

rations

e fill itself as thength and deall high fills ex

nstruction mafication and brious methods

he proposed ons and stabiuch as: uired depth, cA torque is t

measuring thful to pick up gnificance.

ompacted specs include shea testing, wher

ng pore pressutop of the she

or consolidatioach other. Thempressibility. lement, the ra

ver a short perplace over a lermeability ca

ent

tlement occuof time, i.e., dnstruction. settlement ocme. In deep oery low permey settlement ce in duration!

he materials nsity of the xceeding 10

aterials, the batter slope s of analyses

fill, and its lity analyses

cleaning the then applied

e undrained changes in

cimens) and rbox testing re a number ure changes. ear box over

on occurs as e amount of The vertical ate of which riod of time, long time is an be almost

urs over a uring

ccurs organic

eability, can be

Fill settlemeand water drainage steffects are bridges, as

Modelling ageotechnicais necessarinstallation measure wCPT and pressureme Laboratory disturbed (dimensionaconservativincluded in To ensure sthe specialconventionasettlement. 4.1.3 Spe

Special con• Substa

meet thand enconstru

• Toe promay nemay ext

Chapt

ent can have runoff. It a

tructures, pipecompoundedillustrated in

and predictingal engineers. ry. Field meas

of piezometwater pressures

CUPT testseter (camcome

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successful fillsl field testingal road prism. Early identif

ecial Consid

nsiderations foandard or nohe standards fncapsulation vction alternatiotection: W

eed to be incotend a conside

South A

ter 7: Geot

a significant imalso affects thes and even . Note for exFigure 11.

Fig

g fill settlemenKnowledge of

surement of pters or pumps. Settlement

s, Menard Peter). See the

on of the cand undisturbon test, the oof the effectivmples tested.

s, it is necessag, sampling a

m investigationfication of the

derations

or geotechnicaon-conventiofor fill materialviable, the gives utilising s

Where the toe orporated into erable height

African Pav

technical In

S

mpact on the he long term cables and pixample, “bum

gure 11. B

nt is generallyf the in situ pepermeability isping tests int can also be Pressuremetere previous sec

consolidation bed soils canoedometer. Hve drainage pa

ary to appoint and laboratorns (Chapter 6problem allow

l engineers whonal construcls and costs ofeotechnical euch materials.of a fill is closthe design ofabove the toe

vement En

nvestigation

Section 4: Fill

Page 22

performance integrity of t

ipelines. Wherps” at bridge

ump at Brid

y carried out ermeability of s carried out

n boreholes. predicted from

rs and the ction.

characteristicbe made us

However, thesaths in the m

the specialistry testing can6, Section 4).ws this to be c

hen dealing wction materf spoiling rend

engineer may. se or adjacentf the fill to pr

e.

ngineering

s and Desig

ls

of both the rothe fill and asre such settleapproaches,

dge Approa

by specialist the subsoils through the Piezometers

m SPT tests, self-drilling

cs of both ing the one se are often materials are

t geotechnical n be planned. It is oftencommenced in

with fills are: ials: Where der phased or y be tasked

t to a water crevent toe ero

Manual

gn Consider

oad pavementssociated stru

ement is differwhich results

ach

engineer at ad and conduc

useful to pra timely man

large volumesslow construcwith consider

ourse, specialosion in the lo

OeThe oedomdimensionaused to decharacterishowever, hthe samplein situ the laterally co

rations

t in terms of ructures, i.e., rential, these in impact loa

an opportune tcted in unisore-load fills tonner.

s of cut matection or speciaring various

l toe protectioong term. Suc

edometer Tesmeter test is a al consolidatio

etermine consostics. The testhas its limitatioe is confined wmaterial is no

onfined.

iding quality bridges and detrimental

ading on the

time so that on with the o accelerate

erials do not al placement design and

on measures h protection

sts one-

on test olidation t ons as whereas ot



Section 4: Fills

Page 23

• Side Fills: Where long side fills occur and clear lines of drainage are not evident, it may be prudent to design sub-drainage systems so that the fill does not act as a water retention structure.

• Gulley Fills: Abrupt drop-offs in bedrock on the sides of gulleys, or where the depth of transported materials makes the interception of water flow on the bedrock interface difficult.

• Retention structures: Where the optimal slopes cannot be achieved due to steep crossfalls of existing slopes, or any other constraints and retention structures such as crib wall, gabion structures or retaining block walls are required, these should be designed for long term performance. If the fills are major in size (> 10 m) they should be designed and constructed under the guidance of a geotechnical engineer.

4.2 Existing Fills

Problems with existing fills manifest in various ways, including: • Toe erosion • Settlement or differential settlement • Degradation of materials • Translational slips (shallow displacements) • Creep and slide (creeping valley slides) • Internal erosion and piping • Stability failure (rotational slips) 4.2.1 Toe Erosion

Toe erosion probably leads to the highest incidence of all fill problems and failures. This is especially a problem where a fill lies adjacent to a water course subject to periodic or flash flooding. The removal of material from the toe area results in loss of support and is followed by progressive side slope collapse. Typically, longitudinal cracking occurs on the upper reaches of the slope, progressively moving into the road shoulder and traffic lanes, depending on the steepness of the slope and the extent of the erosion. Remedying such damage poses major problems and may include reconstruction of the outer edge of the fill with some special precautionary measures to prevent future occurrences and to stabilise over-steep slopes. Such precautionary measures can be anchored gabions, reinforced earth walls or soil nails. An example of gabion wall construction to limit toe erosion is shown in Figure 12.

Figure 12. Toe Protection by Construction of Gabion Wall

4.2.2 Set

Settlement grain struct

Some oldersubsoils! foundationslasting remservices pre• Causes• Curren• Potentia• Rate of Various meare availabstarting poi• Monito

Figure 1• Invest• Remed

enhance

Chapt

ttlement

occurs graduture of the ma

r fills have seIn many inst

s to bridge stmedial measureevented, it is ns of settlemennt stage reachal for further f settlement

ethods for moble to the geoint for such in

oring: settlem14 igatory: rota

dial methodsements, flatte

Rstism

South A

ter 7: Geot

ually as the material realigns

Figure

ettled to such tances, such sructures, mayes are to be imnecessary to e

nt ed settlement

onitoring, inveotechnical engvestigations.

ment gauges,

ry drilling, pros: jet groutinger slope

Remedial mesettlement othe N2 outsidncluded the

slope and stamoisture reg

African Pav

technical In

S

moisture and as. This results

13. Preven

an extent thsettlement of y sever electricmplemented, aestablish:

estigating and gineer, as list

, surveys, inc

obing, down th, curtain grout

easures to arf this high fide Grahamstflattening o

abilising the gimes.

vement En

nvestigation

Section 4: Fill

Page 24

air migrates os in a denser m

nting Settle

hat the drainaabutment fillsc and fibre opand damage t

determining ted below. R

clinometer su

he hole testingting, compact

rrest ill, on town,

of the

ngineering

s and Desig

ls

out the matermaterial, with

ement on H

age pipes ands for exampleptic cables, anto structures a

remedial actiReliable as-bu

urveys using

g tion grouting,

Manual

gn Consider

ial, the materthe surface gr

High Fill

structures hae, also places nd sever wateand

ons uilt data is, ho

an inclinome

installation of

Reliabbest sinvest

rations

rial consolidatradually lower

ave disappearadditional loa

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owever, alwa

eter probe il

f additional pile

As-Builts ble as-builts arstarting point ftigations!

tes, and the ring.

red into the ads on piled pipelines. If

ays the best

lustrated in

es, drainage

re the for most



Section 4: Fills

Page 25

Figure 14. Inclinometer Probe

Collapse settlement occurs in fills that are not compacted adequately, generally as a result of insufficient moisture and/or insufficient compaction effort, similarly to natural collapsible soils. On wetting up, densification occurs (with or without external load, its own mass is usually sufficient to cause collapse) and failure of the fill usually follows. Adequate control of the compaction is essential to avoid such problems. A picture of such a fill has been included in Figure 15. 4.2.3 Degradation

The degradation of materials in fill slopes with the passage of time can be problematic. Rapidly weathering tillites, dolerites, basalts and mudrocks have resulted in incidences of severe longitudinal cracking and even deformation of significant proportions along the eastern and north eastern areas of South Africa. Solutions may include stabilising moisture regimes, encapsulation and sometimes even removal and replacement of some of these materials. The solution chosen must be supported by sound analysis, including determining risk by the geotechnical engineer. A good example of a combined case of degradation and collapse settlement is the 30 meter high fill near Grahamstown along the N2. The problem has been arrested by stabilising moisture regimes and adding compacted fill benches to lower portions of each side slope. This is illustrated in Figure 15, and is the same high fill as in Figure 13. 4.2.4 Translational Slips

Translational slips, sloughs or shallow displacements are generally rainfall induced following sustained periods of precipitation. They are generally shallow, parallel to the fill slope and occur along the wetted front, usually at the interface between the topsoil and vegetation and the compacted fill layers. An example of a slide or slip is given in Figure 16. These slips need to be repaired early, as with time tension cracks develop upslope and eventually into the road pavement, due to loss of support. Solutions include water management and, in the worst case scenario, reconstruction of the outer edge.

4.2.5 Cre

Creep and gulley typecolluvium omovement such small • Physica

− Anch− Butt

• Water − Cut − Sub− Butt

Chapt

Figure 15.

eep and Slid

slide probleme fills in ruggeor even old along the soimovements thal restraint, hored pile retatress walls managemenoff drains -horizontal dratress drains

South A

ter 7: Geot

. Preventio

Figure

de (Creepin

ms are also knoed topographlandslide debil/bedrock intehat they are nsuch as aining walls

nt, for exampl

ains

African Pav

technical In

S

on of Degra

e 16. Slide

ng Valley Sl

own as creepiy. The fills mbris, which aerface, slow dnot normally vi

e

vement En

nvestigation

Section 4: Fill

Page 26

adation and

or Slip (fro

ides)

ing valley slidmay be foundeare sometimesdownslope creisually discern

ngineering

s and Desig

ls

d Collapse S

om TRH15,

es. These slided on transpos marginally eep takes placnible. Solution

Manual

gn Consider

Settlement i

1994)

des are a comorted materiastable. Whe

ce. In South ns include:

SlakSlaking is a mudrocks (elose their strstresses arereduction in when expos

rations

in High Fill

mmon mode oals such as alen assisted bAfrica, these

king phenomenon

especially) swetrength when te relieved fromn confinement,sed to air and

of distress in luvial wash, by moisture slides have

whereby ell and their

m a , and water.

These solutsome cases 4.2.6 Int

Internal eroto slake. Anleading to cDecember rectification

At Towthe gro

4.2.7 Sta

Stability faisaturation aroad is shosands. The• Remova• Leaking• Failure • Migrat• Abnorm The failuresolutions indrains.

Chapt

tions require is in South Afri

ternal Erosi

osion and pipiny uncontrollecollapse of th1977. The

n of such prob

wnshill on theound causing

ability Failu

ilure or rotatioand thus high own in Figure e causes of theal of vegetatig pipes of drainage sion of water

mal sustained p

surfaces maynclude restrain

South A

ter 7: Geot

in depth analyca, bridging th

on and Pipi

ing failures oced water flow e fill. An exapiping and s

blems.

e N3 outsideg a pipe chim

wall was co

Fig

re (Rotatio

onal slips in apore water p18. These aese failures mion

systems r within the fillprecipitation

y be circular nt, such as re

African Pav

technical In

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yses and modhe entire area

ing

ccur when thethrough the fi

ample of this islope failure i

e Pietermaritmney hole, reonstructed to

ure 17. Int

onal Slips)

an existing fillressures at a re more preva

may include:

l or its foundan

in homogenoetaining struct

vement En

nvestigation

Section 4: Fill

Page 27

delling to detea has been nec

e material useill can result inis Town’s Hill is shown in

tzburg, stormesulting in cro contain the

ternal Eros

are generallypoint in the fialent in fills c

ation on falling

ous materials tures, or wate

ngineering

s and Desig

ls

rmine the mocessary.

d to constructn removal of malong the N3Figure 17. S

mwater at threep at the toe toe bulge c

sion and Pip

y the result ofll or in its foun

constructed fro

g grades

or non-circulaer manageme

PrThe infailuresolutiofieldwofull spein “RoaSection

Manual

gn Consider

ost appropriate

t the fill is dismaterial and t near PietermSpecialist adv

he crest of thoe of the slo

creep failure.

ping

f some unforendation. An exom fine graine

ar in non-homent such as cu

roblem Fills vestigation ints and identifyi

ons and alternaork. This mayectrum of, invad Prism Inven 4.

rations

e engineering

spersive, erodthe developme

maritzburg, whvice is necess

he slope seepope. A gabio.

eseen event cxample from ted cohesionle

mogenous soilut off and su

to the causes ing appropriatatives requirey include somevestigations deestigations” Ch

solution. In

ible or likely ent of voids, hich failed in sary for the

ped into on cavity

causing local the side of a ess soils and

s. Remedial ub-horizontal

of fill te s e, or the escribed hapter 6,

4.3 Inv

InvestigatinThis may inbe conduct Generally, aphased appinvestigatio• Desk st• Site rec• Detaile

− Test− Drill− Prob− Pore− Mon

• Analys• Docum• Post co In most caThese are thus be con Periodic intechnologis

Chapt

vestigation

ng the causesnclude some, ted by an expe

after being approach as for non, tailored antudy whereinconnaissanc

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ases, the remsometimes ounfined to the g

spection of est should ideal

South A

ter 7: Geot

Process

s of failures inor the full spe

erienced geote

ppointed to invnormal road pd limited to th

n all available ice where the etion, including

ure monitoringvements ent and designd possibly sitemonitoring.

edial works foutside the scogeotechnical a

existing fills bly be part of a

African Pav

technical In

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Figure 1

n fills and deteectrum of, invechnical engin

vestigate a paprism investigahe specific neeinformation is extent of the pg (as required

g

n of a remedie supervision.

or a fill failurope of normal aspects of the

by an experieany road autho

vement En

nvestigation

Section 4: Fill

Page 28

18. Stabilit

ermining engivestigations deneer.

articular failureations (Chapteeds. Such an collected and

problem and p)

ial solution.

re include theactivities of tworks.

enced geotecority’s manage

ngineering

s and Desig

ls

y Failure

ineering optioescribed in th

e or failures, ter 6, Section 4approach com

d studied. possible cause

e repair of thethe geotechni

chnical engineement system

Manual

gn Consider

ns and alternis chapter. Th

the geotechnic4). This ensuremprises:

es are identifie

e road surfaccal engineer,

eer or m.

InsPerexpspeshoanyman

rations

natives requirehese investigat

cal engineer ces a rational, w

ed.

ce and drainagand the supe

Periodicspection of Friodic inspectioperienced geotecialist or techould ideally be y road authoritnagement sys

es fieldwork. tions should

carries out a well planned

ge systems. ervision may

Fills ons by an technical nologist part of

ty’s stems.

5. CUT

Road cuts exposes theinclude a tounweatherecomplicate local metam

As for roadrequiremento determinavailable tobe consulte The engineFor this readesigned bfactor of sacuts as lowof the cut.examination Each cut shthe case of For the geoengineeringestablisheddetermine necessary tout specificharacterisianalyses, a It is evidengeotechnicathe routinehandling an

Chapt

TS

are necessarye subsurface sopsoil horizon,ed rock. Momatters furth

morphism of th

d fills, the vants and policiene the footpro the engineered.

eering problemason, most roaby an experienafety (FOS) grw as 3 metres . In some cn of the curre

hould be regaf shallow cuts

otechnical engg properties od. In Chapter

these propeto obtain the ic tasks suching the variound determinin

nt that the mal engineer’s e road prism nd transportat

South A

ter 7: Geot

y where the esoil and rock s, a transporte

ost deep cuts her, there mayhe materials a

Figur

arious road as for the desigint of the cutr addressing t

ms that can bad authoritiesnced geotechneater than 1.5require specia

cases, wideninnt condition a

rded as a singin uniform ma

gineer to analyof each mate6, Section 4.

rties and coservices of anh as the idus rock types fng the potentia

ost economicafield investiginvestigations

tion perspectiv

African Pav

technical In

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elevation is tostratum. An ed soil overlyinare composi

y be different and even fract

re 19. Exam

uthorities havgn, constructiotting and defihe design and

be expected ws require that nical engineer5. This is, howalist attention ng of some mand its past pe

gle entity and aterials, must

yse a cut sloperial need to 3, the differennditions are n experiencedentification ofor strength aal for planar a

al and rationagations, in situs. This is ave.

vement En

nvestigation

Section 5: Cut

Page 29

oo high and nexample of a rng residual soiite, comprisinrock types p

turing and fau

mple of a R

ve standard pon and maintene the area t

d construction

with cuts are mcuts deeper tr. This is to wever, not a bdue to advers

much deeper erformance.

all informatiobe gathered a

pe, an accuratbe known. nt methods odescribed.

d engineering of faults andand durability, and wedge fail

al approach isu testing andalso convenien

ngineering

s and Desig

ts

eeds to be loroad cut is shoils and highly g more than resent in succlting.

Road Cut in

plans and speenance of roadto be investigof road cuts,

many and genthan 10 metreensure the lo

blanket requirese conditions, cuts can be

on regarding tand reported s

te profile of suIn addition, tf investigationIt may alsogeologist to c

d fracture zocarrying out

lures for rock.

s to carry out sampling, dunt from a sam

Manual

gn Consider

wered. The cown in Figure weathered soone of these

cessive strata,

Rock

ecifications layd cuts. These gated. There a

including TRH

nerally increases in vertical dong term stabement as thersometimes oncarried out w

hat cut, albeitseparately.

ubsurface matthe groundwans to o be carry ones, joint

t the uring mple

DesiMoremay TRH1InveConsMainCutt

rations

construction o19. A typical

oft rock gradinse soil or roc, e.g., igneous

ying out theiare particularare also manyH18 (1993), w

se with the ddepth be invesbility and a slore will be instanly evident onwithout much

t very little inf

terials is requiater regime n

Investigatigning Cuts e detailed infobe obtained f18 (1993): Thestigation, Dstruction andntenance of tings.

of road cuts profile may

ng into hard, k types. To s intrusions,

r respective ly important y guidelines

which should

epth of cut. stigated and ope stability ances where n excavation more than

formation in

ired and the needs to be

ting and

rmation from he Design,

d Road

Where nececarry out tsampled mparticle distdeterminatipermeabilitand X-ray drequire gerelevant roa For conven 5.1 Cut

An example• Steep s• Unconso• Adverse• Change• Unexpe• Erosion

Cut slope fa• Creep,

creep is• Rotatio

materia• Transla

strengthor a mu

Failure can process in area of thefield reconn

Chapt

essary, the gethe works th

materials genetribution analyions. Some ty testing, reqdiffraction anaological expead authority’s

ience, and cla

t Slopes in S

e of a cut slopslopes olidated loosee groundwates in groundwected surcharn by surface r

ailures manifewhen slopes

s illustrated in onal slips, wals. ational slipsh, discontinuitud-rush develo

also occur whessence remo

e cut. The expnaissance and

Thdereqwi

South A

ter 7: Geot

eotechnical enhat require hirally compriseysis, the deter

tests, such quire the servialysis of rock ertise. The ge

procurement

arity of discuss

Soils

pe in soils is sh

e material ter conditions water conditiorges runoff exacerb

est in the formare close to tFigure 17.

where the fail

s, where movties or along wops (Figure 16

hen the area oves lateral sperienced geo take these in

his cut slope egradation ofquiring an atde debris tra

African Pav

technical In

S

ngineer must s/her expertis

es routine tesrmination of thas consolidomces of specialsamples for m

eotechnical eguidelines.

sion, cuts are

hown in Figure

ons

bated by abnor

Figure 20

m of: he angle of re

ure surface m

vement takes wetted fronts.6).

within which tupport. Stresotechnical engto account in

in soil showf whitish softtenuation wap.

vement En

nvestigation

Section 5: Cut

Page 30

witness the inse. The labo

sting of materhe soil constanmeter, shearblised laboratomineral identi

engineer need

hereinafter cla

e 20. Instabili

rmal sustained

0. Cut Slop

epose and wh

may be circul

place along In extreme c

the cut is to bss relief followgineer will be the investigat

ws ft tuff wall and a

ngineering

s and Desig

ts

nvestigations ratory testingrials, such as nts, CBR and Ubox, triaxial ries. Thin secfication generds to follow

assified as cut

ity of soil slop

d heavy precip

pe in Soils

ere movemen

ar or non-circ

the interfacecases, the ma

be excavated iws with moveable to ident

tions, analysis

Manual

gn Consider

and g of soil

UCS and tion rally the

t slopes in soil

es is generally

pitation

nt is relatively

cular in the c

e of layers ofaterials may be

is marginally sments stretchify such signsand design.

Thesecarefulong tsuffici

rations

ls and cut slop

y attributable

slow. An exa

case of non-h

f different or ecome so wet

stable and thehing upslope, s and indicato

Cuts > 10 e cuts need toully designed tterm stability aient factor of

pes in rock.

to:

ample of toe

homogenous

inadequate t that a flow

e excavation beyond the

ors from the

metres o be to ensure and a safety.

Knowledge types, densstability anaMethod is gfor planar o In view of This allows For examplof the slope The resultsprobability road reservother meassoils in the Many of thThere shouwhen necesproblem co• Localise• Signs of• Stress • Crack f• Bulging 5.2 Cut

To adequatslopes is re• Rock fa• Topplin• Block s• Degrad The causes• Loss of • Excava• Unfavou

− Frac− Faul− Igne

• Nature − Stru− Stat− Join− Bedd

• Water p• Unfavou• Undercu• Stress r• Erosion • Absence

Example

Chapt

of overburdesity, and sheaalyses are gengenerally usedor non-circular

the variability the evaluatiole, the effect e can be evalu

s of these anof failure targve limitations sures to improslope.

he problems auld, thus, alwassary, approp

ompounds. Thed seepage, sf previous mrelief movemformation g of the slope

t Slopes in

tely investigatequired. Failualls and slidesng failures slides from pldation throug

s of the failurevegetation

ation method urable geologcture zones lting eous intrusionof the rock m

ucture te of weatherinting ding pressures deveurable dip of sutting of dippirelief in deep c

e, or inadeqes of an inade

South A

ter 7: Geot

en or soil thicr strength) ennerally performd for analysingr slip surfaces

y of the materon of the sensiof variations iuated.

nalyses enablget, or to a fac

or other phyove the stabilit

associated witays be provisriate steps ca

he kinds of prosee Figure 17

movement ments

e

Rock

te, analyse anures in rock slos

lanar and wedgh weathering

es are many, in

gical conditio

s materials

ng

eloping along strata ng strata cuts

uate capacityequate and an

African Pav

technical In

S

ckness, grounnables the modmed using sofg circular surfa

(Bishop, 1955

ial properties,itivity of morein the shear s

e the geotecctor of safety ysical constraity of the soil s

th slopes in sion for obtainn be taken tooblems that cofrom Townsh

nd design cutsopes can take

dge failures

ncluding:

ons

discontinuities

y, of an imp adequate inte

vement En

nvestigation

Section 5: Cut

Page 31

ndwater conditdelling of the ftware packagace failures wh5; Janbu, 1954

, probabilistic e than one desstrength, cohe

chnical engine(FOS) > 1.5.

ints, the engislope, such as

soils only becning the advico rectify the siould become aill, Kwazulu-N

s in rock, an umany forms i

s

permeable anerceptor drain

ngineering

s and Desig

ts

tions and theproposed slopes, of which mhile Janbu’s Ge4)

methods of asign parameteesion and mois

eer to design Where this ineer must dedrainage of th

come apparence of an expetuation beforeapparent are:atal

understandingincluding:

d effective un are shown in

Manual

gn Consider

e in situ matepe by the geotmany are avaieneralised Me

nalysis are user and its contsture condition

the minimums impractical, esign adequathe phreatic su

nt once constrienced geotee the

g of the mecha

upper storm n Figure 21.

This of soporesfilled

rations

erials propertietechnical engiilable. Bishopethod is favour

sed by most ptribution to slons on the ove

m slope to ppossibly beca

te retention murface situate

truction has cechnical engin

anisms of fail

water interce

Phreatic Suris the subsurf

oil or rock in ws and interstic

d with fluid.

es (material neer. Slope

p’s Simplified red by some

practitioners. ope stability. erall stability

produce the ause of cost, measures or ed within the

commenced. eer so that,

ures in rock

eptor drain.

rface face zone

which all ces are



Section 5: Cuts

Page 32

An inadequate interceptor drain which is also unlined.

A properly design, lined interceptor drain above the crest of the slope.

Figure 21. Interceptor Drains

5.2.1 Rock Falls and Slides

5.2.1.1 Natural Slopes

Rock falls and slides in natural slopes above road cuts or fills remain a difficult challenge for the geotechnical engineer, especially in steep topography and when large in extent. Such rock falls and slides generally occur as a result of progressive weathering or loss of support due to erosion or vegetation loss, usually exacerbated or caused by sustained precipitation. Injudicious use of explosives during construction may also trigger such movements. Successful solutions have been obtained with: • Catch fences strengthened by cables and poles to intercept and retain falling or rolling rocks, see Figure 22. • Reinforced canopies to protect traffic and convey slide debris over the road, also illustrated in Figure 22.

Catch Fences Construction of Reinforced Canopy

Figure 22. Catch Fences and Canopies on Chapmans’ Peak Drive in Cape Town

5.2.1.2 Constructed Cut Slopes

In constructed cut slopes, rock falls or slides may occur in fracture and fault zones. The geotechnical engineer will recognise the potential for such occurrences during the field reconnaissance stage and may require geological assistance and aerial photographs to determine the extent. Ravelling of fractured rock may be kept at bay by rock fall netting nailed to the surface or in shotcrete, and mesh solutions with adequate provision for drainage, as illustrated in Figure 23.



Section 5: Cuts

Page 33

Applying Rock Fall Netting and Shotcrete to Cut Slope

Rock Cut Widening: Anchored, Meshed and Gunite Applied for Stability

Figure 23. Applying Rock Fall Netting and Shotcrete to Cut Slope

5.2.2 Toppling Failures

Toppling failures are more frequent in natural slopes and are generally in steeply dipping or highly jointed bedded strata such as sandstones, shales and metamorphics, which have laminated or foliated structures, such as schists. Toppling may also occur at the crest of a constructed cut slope as a result of loss of laterally and vertically support, sometimes exacerbated by pore water pressure development in the joints. This may be a result of the erosion or degradation (weathering) of adjacent or underlying strata that can be exacerbated by adverse jointing. Determining the potential for toppling failures in the design stage is difficult, especially if there are no outcrops. It is often only apparent during and after construction. An experienced engineering geologist may be able to deduce the potential of such problems from the discontinuity patterns on rock outcrops and on exposed rocks in test pits. An example of a toppling failure, is shown in Figure 24.

Figure 24. Toppling and Block Failures



Section 5: Cuts

Page 34

5.2.3 Block Slides

Block slides may be the result of: • Undercutting and intersecting of dipping strata • Intersecting discontinuities in the rock mass

5.2.3.1 Dipping Strata (Planar Failures)

The undercutting and intersecting of dipping strata are probably the greatest single cause of cut failures, examples of which are shown in Figure 25 and Figure 26. The experienced engineering geologist or geotechnical engineer should recognise the potential from the desk study, using regional geology and site reconnaissance stages including land form and topography, and the study of rock outcrops and existing cuts. If the potential is not identified in these stages, it should be detected during the preliminary investigation stage. It may even be necessary to realign the road to the other side of a valley to avoid such problems.

Figure 25. Steep Block Slide

The inclinatexisting outcore orientaskills of bogeologist. Ilogging is o Where the avoided, vaand long te• Reinforc• Gabion • Concret• Dowelin• Coverin

Chapt

tion of dippingtcrops, studiesation during roth a competIt is for suchonly done by e

intersection oarious optionserm. These inced concrete wwalls

te buttresses ng, bolting or ag with shotcre

South A

ter 7: Geot

Figure 2

g strata can bs on rock exprotary drilling.tent drilling ch reasons thaexperienced en

of dipping strs are availableclude retaininwalls

anchoring lamete to prevent

Figure 2

African Pav

technical In

S

26. Slide on

be assessed froosed in test p This is a speontractor andat most road ngineering geo

ata in a cut fe to provide ag structures s

minated or clost spalling and

27. Dowell

vement En

nvestigation

Section 5: Cut

Page 35

n Unfavour

om joint orienpits and bulldoecialised exercd an experien

authorities sologists.

face is evidena safe slope isuch as:

sely bedded stdelay weather

ling as a St

ngineering

s and Desig

ts

rable Beddin

ntation studiesozer slots, andcise requiring nced engineerspecify that c

nt and cannot n both the sh

trata, as illustrring (see Figu

tabilisation

Manual

gn Consider

ng Plane

s of by the ring ore

be hort

rated in Figurere 23)

Method

Most rthat codone bengine

rations

e 27

Core Loggiroad authoritieore logging is by experienceeering geologi

ing es specify only

ed ists.

The retentidrainage ho The failureparameters• Rock jo• Contin• Dry and• Angle o• Depth o• Cohesi The assessfilling mateinvestigatiorange of va

5.2.3.2 In

Where twoon these dblock (wedgpotential. whether thexposed roexcavation Prior recognecessary e The expert recovered c Other parawedge failuAgain, a prepresent tcut to each

Chapt

Figur

ion of free droles to preven

e mode in dis are required int shear streuity of rock jo

d wet densityof friction of of tension craion along rock

sment of the erial and the ons. The geoalues to the va

ntersecting D

o daylighting discontinuities ge) failure is iJoint surveys

his is likely in ock in test pits

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Section 5: Cut

Page 36

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Section 5: Cut

Page 37

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Section 5: Cuts

Page 38

Figure 30. Enon Conglomerate near Knysna

To mitigate these failures, steps are taken to curtail water flowing down or penetrating into the cut slope from the top. Additional measures to reduce the likelihood of such collapse posing a hazard to road users include lined interceptor drains at the crest of slopes, physical barriers, drop-zones or even shotcreting. A well-designed interceptor drain at the crest of a cut slope is illustrated in Figure 21.

5.2.4.3 Basic Crystalline Materials

Many of the basalts and dolerites in South Africa are prone to rapid weathering (Orr, 1979). On exposure to the atmosphere these materials deteriorate rapidly, visible as the deposition of fine material at the foot of the slope. The weathering also causes a loss of the matrix around large corestones (or spheroids), which eventually fall from the slope as illustrated in Figure 31. Application of mesh and shotcrete is usually the best solution, but the problems need to be identified before, or during construction, and excavation.

Figure 31. Corestones Falling from Slope

Corestones falling from slope due to inadequate debris trap width unable to attenuate material.



Section 5: Cuts

Page 39

5.2.5 Investigation Process

As with the investigation of large (high) embankments, the experienced geotechnical engineer’s investigation needs should be programmed and coordinated to take place under the routine road prism investigations, wherever possible. This also provides the means and opportunity for the execution of these works and facilitates interaction between the geotechnical engineer and/or leader of the routine investigations and the experienced geotechnical engineer. They also provide for the ancillary needs, such as traffic accommodation, sample storage and transport. The kinds of investigations the geotechnical engineer is likely to require are: • Investigate groundwater conditions • In situ testing to determine permeability of the subsoils • In situ testing to determine strength parameters • Disturbed and undisturbed sampling for routine and specialised testing 5.3 Failure of Existing Cuts

In this section, typical problems in existing cuts are discussed, first for cuts in soils and then for cuts in rocks. 5.3.1 Cut Slopes in Soils

Problems in cut slopes in soils include: • Erosion • Creep • Materials degradation • Ravelling • Stability failure (rotational slips) • Translational slips

5.3.1.1 Erosion

Erosion in existing cut slopes occurs from: • Excessive runoff from above the slope crest due to either the absence, or inadequate capacity, of lined

interceptor or cut off drains, as illustrated in Figure 32 • Interceptor drains filled with debris and not cleaned • Leaking services • Heavy, sustained rainfall

Figure 32. Erosion of Cut Face due to Inadequate Interceptor Drain above Slope



Section 5: Cuts

Page 40

The extent of damage is exacerbated by the presence of dispersive or erodible materials (see Chapter 6, Section 4.4.6). Severe erosion, as may occur after abnormal rainfall, may render portions of a slope unstable or susceptible to translational slides, and in such cases may require special measures to reinstate the slopes. Many repairs by maintenance staff are unsuccessful, and the situation sometimes degrades to such a state that major remedial measures are required. Solutions may include: • Provision of adequately lined interceptor or cut off drains • Repairing leaking services • Re-top soiling and re-vegetating the slope • Applying soil retention systems such as biojutes and netting systems

5.3.1.2 Creep

Creep describes the situation where soil slopes are somewhat steeper than their angle of repose and the soil particles slide over each other to reach a state of equilibrium. Creep is usually limited to the outer edges of a slope and is slow. But, it is accelerated by deep wetting. Creep is very common in fine grained materials of low cohesion, such as sands. Following heavy rainfall, the situation could transform into a translational failure.

5.3.1.3 Degradation of Materials

Materials degradation takes place through weathering (decomposition), stress relief and by exposure to the elements, as described in Section 5.2.4. Where severe, the geotechnical engineer needs to address the problem.

5.3.1.4 Ravelling

Ravelling in soils occurs as a result of the removal of the finer particle support for larger particles by rain or wind, which then roll down the slope. Where severe, the geotechnical engineer needs to address the problem. Solutions vary from re-top soiling and re-vegetating the slope to applying soil retention systems, such as biojutes and netting systems (Figure 33), held in place by wooden pegs or soil nails, dowels or galvanised steel pins.

Figure 33. Netting System and Re-Vegetating

5.3.1.5 Stability Failure (Rotational Slips)

Stability failures or rotational slips vary in severity from minor, causing partial road closures, to catastrophic, rendering a road unusable for many months. An example of a rotational slip is shown in Figure 34. These failures may happen overnight, with little warning to alert road users. Road officials or maintenance staff may, however, recognise signs of imminent failure and raise the alarm. These signs include: • Cracking in the road or shoulder



Section 5: Cuts

Page 41

• Cracking in the slope above the cut or in the cut off/interceptor drain • Humps forming in the cut slope • Material displacements, into the side drain or roadway • Sag development in the roadway or shoulder • Water seeping or piping out of the cut slope • Trees falling over or away from the vertical • Increased animal activity, movement away from the affected area

Figure 34. Rotational Slip

The first reaction to any such occurrence or signs of imminent failure should be to safeguard the users of the road by immediately erecting the necessary road signs and closing the road to traffic. The routine road maintenance manager or relevant road authority should be contacted immediately, and will arrange immediate inspection by their engineering staff. SANRAL requires a monitoring action to be performed when such an event takes place and have special slope monitoring forms for this purpose. Following this, a geotechnical engineer may be appointed for an assessment of the failure and an investigation into the causes and likely remedial solutions. The geotechnical engineer will, from his field inspection and the available information, be able to form a quick assessment of the type of failure, its extent and probable cause, and recommend what action should be taken to remedy the situation. An investigation may be needed to verify assumptions, to determine the extent of the movements, to determine what conditions to allow for in modelling the failure and to determine the ground water, soil density and soil strength parameters to use in any analyses. Such investigations take the form of those outlined for the investigations for new cuts (Section 4.2.7). Because the cost of a road closure to the economy can be vast, most road authorities will have a contingent amount in the annual budget for the investigation and repair of such failures. Some road authorities even have an accelerated system in place for obtaining approval to proceed with the procurement of services in emergency circumstances.

5.3.1.6 Translational Slips

These are slips where movement takes place along the interface of layers of different or inadequate strength, or along wetted fronts. Invariably these movements take place after abnormal and/or sustained rainfall. These are sometimes referred to as rain induced instability, and the failures are generally shallow and parallel to the original slopes. Various researchers have investigated this phenomenon, and correlations have been made with rainfall intensity, duration and the time lapse before movement occurs. In some cases, movements took place after 3 days while in other cases after only 8 days of continuous rainfall. The material grading, thickness, density, permeability, upslope catchment area and vegetation all influence the moisture penetration, rate of movement and time before equilibrium is breached. Where the materials become saturated, a slide or a mud-rush may develop. An example from Kaaiman’s Pass between George and Wilderness is shown in Figure 35.

Rotational slip of an existing cut. Inadequately stabilised by toe gabions only.

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Section 5: Cut

Page 42

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Section 5: Cuts

Page 43

• Rock bolting and/or dowelling to secure blocks • Protecting soft, weathering susceptible strata by shotcreting

5.3.2.3 Rock Slides

Rock slides are generally the result of planar or wedge type failures.

(i) Wedge Failures

Wedge failures in existing slopes occur where two day lighting discontinuities intersect behind the cut face, and a wedge of rock resting on the discontinuities slides down along the intersection. Such failures can be triggered by extreme precipitation or seismic events, or ongoing weathering and opening of joints from thermal changes and stress relief. The reaction to an occurrence depends on the extent and consequences of the failure. That is, how large the wedge is, whether it affected the road, the verge or side drain, and whether the safety of the travelling public was endangered. Such reaction may therefore vary from clearing the debris to road or lane closures, and is usually followed by joint orientation surveys and analysis by a geotechnical engineer. Remedial measures could include concrete buttresses, rock bolting and even the installation of cable anchors. An example of a wedge failure is given in Figure 24.

(ii) Planar Failures

Planar failures occur along planar surfaces including bedding planes, joints and planes of movement in metamorphic rocks, particularly with cleavage, laminated or schistose (flaky layer) structures. The most common planar type failure in existing rock cuts occurs when dipping strata are undercut or when such strata are intersected in a rock cut. Movement occurs when the plane along which failure occurs is steeper than the angle of friction. Rising pore water pressures, which provide uplifting forces thereby lowering the friction along the failure surface, are generally the trigger of such movements. Remedial measures may include the securing of in place rock slabs that remain on the slope, for example, concrete buttresses, doweling or bolting laminated or closely bedded strata, and covering with shotcrete to prevent spalling and delay weathering. The retention of free drainage is crucial to the stability of such slopes. Most of the remedial measures include installing drainage systems to prevent pore water pressures developing and to lower the water table. In carrying out plane failure analysis the following parameters are required by the geotechnical engineer: • Rock joint shear strength (cohesion and friction angle) • Density (total unit weight) of the sliding mass • Angle of friction of the sliding surface • Depth of tension crack • Continuity of rock joints

5.3.2.4 Toppling Failure

Toppling failures in existing constructed rock cuts generally occur at the crest of cuts. A toppling failure is illustrated in Figure 36. They usually occur in bedded or jointed strata such as sandstones, shales and metamorphics which have laminated or foliated structures, such as schist. They can also occur in other formations such as dolerites, or any materials where the centre of gravity of individual blocks falls outside of the base of the block. Toppling occurs as a result of loss of support, laterally and vertically sometimes exacerbated by pore water pressure development in the joints. This may be a result of the erosion or degradation of adjacent or underlying strata, sometimes exacerbated by adverse jointing. Remedial measures include rock bolting and/or dowelling to secure blocks, and protect soft, weathering susceptible strata by shotcreting.



Section 5: Cuts

Page 44

Figure 36. Toppling Failure (from TRH18, 1993)

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Section 6: Structures

Page 46

Figure 38. Scour around Bridge Piers

6.2 Modus Operandi and Reporting

The modus operandi for planning, scoping, responsibility, acquisition of tenders, methodology and execution of geotechnical investigations for structures are fully documented in Chapter 7 of SANRAL’s Code of Procedure for the Planning and Design of Highway and Road Structures in South Africa (2011) and also in Annexures 18.2 and 18.3 thereof. All of this has been included at the end of this Chapter as Appendix D. The compilation and interpretation of test data and reporting is carried out in accordance with Section 8.

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Section 7: Tunnels

Page 50

Garmap suite of street, topographic and waterways maps, or online-based information systems such as Google Maps and Google Earth.

(vii) Satellite Imagery

The availability of online satellite images of all portions of the earth makes this tool particularly useful, especially during the initial stages of a project for identification of major geological or topographical features. Whilst basic images are available to all, high resolution images may have to be purchased. Digital images may be exported in electronic format for use in reports or as background information on plans or maps. An example of an image from Google Earth is shown in Figure 40.

Figure 40. Google Earth Satellite Image of Joints and Faults in Gneissic Terrain in Kamieskroon Area of Namaqualand

(viii) Ortho Photographs

These are available at a scale at 1:10 000. Unlike aerial photographs, ortho photographs have been corrected for distortion over the full area of the photograph. Contours from these and similar maps are useful to create a first-order digital terrain model (DTM) of the site.

7.1.2 Site Reconnaissance (Walkover Site Inspection)

In carrying out a reconnaissance of the corridor along possible tunnel alignments, it is essential to map rock outcrops, the position and dip of boundaries and faults, and other geological features. Particular attention should be paid to land use and topographical features. Attention should also be given to general accessibility. Long established local land owners must be engaged in discussion with long established local land owners.

(i) Land use

The following features in an urban, rural or agricultural environment should be identified: • Urban Environment

− Position and description of buildings and structures − Evidence of subsurface structures − Pipes and tunnels that may be affected by tunnelling, whether by drilling and blasting or boring − Industries that have the potential to spill, such as, filling stations and chemical works on or near the line of

the tunnel



Section 7: Tunnels

Page 51

• Rural environment − Evidence of any subsurface structures, such as pipelines − Mining and quarrying as may be indicated by spoil heaps, stockpiles and excavated pits − Inspection of nearby road and railroad cuttings, borrow pits and quarries may provide confirmation of regional

geology • Agricultural

− Changes in vegetation or crops, which could be as a result of filled pits, as illustrated in Figure 41. − Changes in stratigraphy − Subsurface moisture conditions

Figure 41. Changes in Vegetation as a Result of Filled Pit

(ii) Topographical Features

• Surface and land forms may provide indications of: − Instability − Shallow holes − Changes in slope − Landslides − Subsidence − Depressions

• Springs, subsurface water channels Particular attention should be paid to the possible portal areas. The survey should ideally be preceded by Aerial Photo Interpretation (API) to identify points of geological interest or importance. Photographic records of all significant observed features are essential. If the site is not readily accessible due to remoteness, security concerns or socio-political sensitivity, the site reconnaissance (walkover) survey would then probably form part of the Stage 2: Preliminary Investigation Stage (Feasibility Stage). 7.1.3 Site Reconnaissance Report

The compilation of this report should be in accordance with the employer’s requirements and/or the guidelines given in Section 8.

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Section 7: Tunnels

Page 53

• Unstable or caving ground • Rock faults, fracture zones, fissuring, jointing and bedding surfaces • Weathering levels • Igneous intrusions • Cavities in soluble formations such as limestone or dolomites Further to obtaining information required for the location and design of the tunnel, shafts and portals, information is also required for construction purposes, including: • Selecting the method of excavation and construction • Predicting stability and timing of support installation • Predicting type of support • Predicting and controlling water conditions • Predicting overbreak, assessing the need for special expedients • Ensuring the safety of the works and workers Areas of uniformity, suited to particular methods of tunnelling, should be established. The selection and investigation of portal positions, generally in hillside or valley locations, must be carefully carried out as these can be in difficult ground conditions. Unloading during excavation may result in instability, fracture or ground movements where unstable surface deposits are located. In planning these investigations, the requirements of the Occupational Health and Safety Act (OHS, 1993), the National Environmental Management Act, (NEMA, 1998) as well as other pertinent legislation covering the environment and other legal issues as described in Chapters 1 (Section 3) and Chapter 6 (Section 2) must be considered. Large projects may also warrant the appointment of a full time site safety officer. The consultant must be aware of the specific safety requirements of the particular client. 7.3.2 Detailed Investigation Contract

The same procedures for the procurement of specialised services and tenders detailed in Section 2.3 should be followed. In preparing the required documentation, the specific project specifications need to be comprehensive and make due allowance for necessary changes as the investigation and information appraisal proceeds. The contractor should be required to appoint a geotechnical engineer or an engineering geologist competent in all aspects of the investigatory work, to work in close liaison with the engineer’s representatives. 7.3.3 Investigation Methods

The following investigation methods are used for tunnel investigations:

(i) Rotary Core Drilling, Core Recovery and In Situ Testing

Boreholes should be sited at each portal, shaft and key positions to interpret geological features, such as faults. These may be identified during the preliminary investigation stage from aerial photo interpretation, geophysical testing and field reconnaissance. Further boreholes are sited to interpolate between points and to fill any gaps. As a three dimensional understanding of the site is required, some of the holes are off-axis. Boreholes should extend to at least two tunnel diameters below the proposed invert level. Where boring appears feasible, further boreholes should be located clear of the tunnelling line to avoid interference with tunnel construction. Where cut and cover operations are envisaged, holes should be within the excavated strip. Inclined holes are necessary to provide the required information, especially in dipping strata. Good core recovery (> 90%) is required, necessitating the use of split double tube or triple tube core barrels. In soft ground, provision should be made for continuous undisturbed sampling. The presence or absence of groundwater is a critical factor in tunnelling, particularly when tunnels are driven beneath rivers or lakes. Moderate inflows can slow progress and be expensive to control. High inflows can destroy face stability, result in mud rushes and chimneying. Water table measurements and seasonal variations should be made utilising piezometers (see Chapter 5, Section 4.5.3). Note should be made of all water strikes and of artesian conditions. Groundwater flow characteristics can be determined by pumping tests. In examining the feasibility of dewatering or lowering groundwater tables, the effect of these on ground settlement, neighbouring structures and on groundwater supplies should be considered.



Section 7: Tunnels

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Accurate borehole locations on site and as marked on plans is essential. Borehole survey techniques should be used at intervals to check inclination and azimuth. Where piezometers are not installed, all boreholes and penetrations should be backfilled by tremie grouting. Comprehensive drilling and in situ testing records are necessary. In situ testing in soft ground conditions may include pressuremeter, dilatometer, vane shear, SPT’s, CPT, CUPT and other probings. In situ testing in rock includes packer tests.

(ii) Trial Pits

Trial pits are generally used in soft ground at portal, shaft and shaft positions as well as for shallow tunnelling. They allow direct profiling and undisturbed sampling as well as in situ testing, such as penetrometer and jacking tests. Careful consideration must be given to the positioning of trial pits as they can cause difficulties during construction. All holes need to be backfilled with suitable compacted materials. The safety measures provided in SAICE’s “Code of Practise: The Safety of Persons Working in Small Diameter Shafts and Test Pits for Civil Engineering Purposes” (2003) must be adhered to at all times.

(iii) Large Diameter Boreholes

Headings or shafts allow deeper in situ inspection, testing and sampling at crucial positions. These provide vital information such as stand up time in potentially unstable formations. They may also allow for rock bolt testing and in situ stress measurements in rock as described in Section 7.4 “Construction Stage Investigations” of SAICE’s 2003 Code of Practice.

(iv) Field Trials

Field trials remove some of the uncertainties regarding interpretation of test data. Examples are: • Short trial tunnels, driven to assess actual tunnelling conditions and the suitability of support measures such as

rock bolting, shotcrete and mesh, steel arches and grouting. • Pilot tunnels along the line or parallel to the proposed main tunnel. These enable full scale assessment of

tunnelling conditions and in situ testing to enable the design of tailor made support, as well as providing access to allow for multiple headings, whilst providing an escape route in the event of an emergency.

These methods are, however, both costly and time consuming. Their application is largely a function of the size and complexity of the tunnel project. 7.3.4 Guidelines for Assessing Testing Requirements

7.3.4.1 Tunnelling in Soils

Laboratory testing of soils includes classification tests as well as strength, consolidation and permeability tests. In granular soils, stability and support are largely a function of ground water flow. Early indications can be gained from water rest levels and permeability tests, but more reliable measurements require the installation of piezometers. Particle size distribution and porosity are inputs to assess the suitability of various stabilising methods, such as dewatering, ground freezing, slurry, bentonite shields or grouting. In cohesive soils, stability and support are largely a function of the in situ shear strength. Measurements of shear strength can be carried out by in situ vane tests, and in stiff firm clays, by laboratory triaxial tests on undisturbed samples.

7.3.4.2 Tunnelling in Rock

The stability of the rock is a function of the rock mass and rock material properties. Rock mass properties can only be determined by core logging, down the hole photography, borehole to borehole geophysical methods and field trials. Laboratory testing to assess material properties include: • Unconfined or triaxial compression tests, particularly where rock is weak relative to overburden pressures.

These are also useful for support considerations. • Tensile and indirect tensile tests, which are also useful for support considerations. • In situ measurement of ground stresses using photo-elastic cells or pressuremeters, dilatometers and Goodman

Jacking in soft rock. These are also useful for support considerations. • Creep, swell or slake tests, particularly in argillaceous rocks. • Mineralogical analysis for swell potential.

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Section 7: Tunnels

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7.3.6.1 Design Philosophy

In the design of tunnels, the limiting equilibrium or working stress philosophy is traditionally followed. This relies on a global lumped factor of safety against failure, and occasionally for serviceability. More recently, geotechnical design has followed structural design in adopting partial factors of safety and a limit states design approach. The choice as to which approach is followed may be specified by the client, left to the choice of the designer, or regulated. Eurocode 7 is regulated in the UK since 2010 (Eurocode, 2004).

The selected design philosophy generally allows for an “observational method approach”. This involves developing a base design using the most likely values for the geotechnical parameters, based on the information available, and not necessarily using a conservative selection based on variation in the data. The designer has to identify the shortcomings in the data and in the predicted geotechnical behaviour. These lead to the derivation of a plan of monitoring during construction to identify critical limits to trigger the implementation of predetermined contingency actions, for which provision is been made. Some clients are, however, sceptical of such an approach.

7.3.6.2 Design Parameters

In the selection of appropriate design parameters, the specialist geotechnical consultant has to consider the type of tunnel, applied loading, dynamics, settlement criteria and the nature of the geology, i.e., stratigraphy and stress history. These parameters should also account for: the in situ state of the geo-materials, for example normally consolidated or over consolidated; and soil-structure interactions, such as, drained or undrained behaviour; and, strain levels. There are two classes of geotechnical design parameters, fundamental and specific: • Fundamental parameters: These are dependant only on the properties of the material constituents and are

independent of the in situ state and structure of the material. They are typically determined from basic testing on disturbed or reconstituted samples. Sophisticated analysis and design calculations are required to take account of stress history, applied stress paths and the effects of structure and fabric. The critical state or steady state effective angle of friction represents an example of a fundamental strength parameter.

• Specific parameters: These, in addition to the material constituents, are influenced by the in situ state and the structure or fabric of the material. These parameters are typically determined from specialised testing that model the structural loading on high quality undisturbed samples that preserve the in situ state of the material. The resulting parameters represent all the behavioural aspects associated with the in situ material under the intended loading. These parameters can, therefore, be used in relatively simple design calculations. An example of such a parameter is the tangent Young’s modulus of a material, determined from a triaxial test on an undisturbed sample, loaded with an appropriate stress increment.

Identifying points of changes in ground or water conditions requiring changes in design are of major importance. Such areas may be very small in extent, but they are of no lesser significance to the safety of the users, the integrity of the construction, or the functionality. Characteristic values of design parameters are derived using statistical methods and defined confidence levels. Due cognisance must be taken of the sample size. The more limited the amount of information, the less reliable the statistical interpretation. Where large volumes of data are generated, it is appropriate to represent the data using statistics such as sample size, average value, standard deviation, and percentiles, and to identify outliers. These statistical values are particularly useful in carrying out sensitivity analyses during the design process. Statistical data can best be presented graphically and can, at least, provides some indication of the nature of the distribution of the data. Considerable experience is, however, required when using statistical concepts in geotechnical engineering. Simple averaging of values does not properly account for the variability of the parameter, or for parameter dependencies. It is common practice to model natural phenomena using the normal probability distribution. This assumption simplifies the manipulation of statistical data and the prediction of confidence levels where the average and median values coincide. Geotechnical data, however, do not always conform to a normal distribution, and even if it does, the distribution is likely to be “flat”, that is with a large amount of variability. It is essential that the consultant liaises with the rest of the design team during this phase of investigation to ensure that appropriate design parameters are determined, and that these parameters are understood and correctly used by the designers. 7.3.7 Detailed Tunnel Investigation Report

The guidelines given in Section 8 should be used to compile the report, and should also include:



Section 7: Tunnels

Page 57

• All the information gained from earlier investigations as well as borehole reports, log sheets, test results and geological plans, and sections showing their positions together with all strata and groundwater levels encountered in the boreholes. Symbolic codes and colours should be used to distinguish between different soil and rock types, see Figures 10 and 11 in Chapter 5, Section 4.3.4. The soil and rock types must be fully described, and areas of inferred geological structure shown with an indication of the degree of confidence of the interpolations.

• Additional information such as plans showing: − Services, structures, and condition reports − Position and condition of underground mineshafts and workings, and measures needed to stabilise them − Presence and characteristics of groundwater, mine gases and other hazardous substances

• Consulting engineer’s interpretation of the investigation results and expected ground conditions. Due consideration must being given to possible problems in tunnelling, controlling groundwater and providing temporary and permanent support.

• Proposed design and supporting plans and drawings. The observed, measured and inferred conditions and properties on which the design is based must be given, highlighting any special, relevant geotechnical features. The classification of the ground into zones of similar ground and water conditions, and construction and support methods is similarly important.

• Recommendations for investigations during the construction stage. SAICE’s Site Investigation Code of Practice (2009) should also be consulted for more information. 7.4 Stage 4: Construction Stage Investigations

It is essential that predictions made on the ground structure and materials are confirmed as construction proceeds. This includes continuous updating of geological sections, recording water inflows, joint spacing and orientation, regular sampling and testing of rock or soil samples, and other relevant data such as overbreak occurrences. Probing ahead, by drilling short distances ahead of the tunnel face, gives advance warning of undiscovered fault and fracture zones, material changes and hazards, such as, water bearing fissures. This also provides a means of treating materials ahead of the drive. The construction of test adits allows the execution of in situ stress measurements to determine lining requirements. These measurements include uniaxial tests using flat jacks, biaxial tests using doorstopper cells and Leeman/CSIR cells for triaxial stress measurements. Continual defection or convergence measurements, rock bolts and grouting tests, as well as shotcrete trials, are regularly conducted to determine their efficacy for both primary support and the final lining. Ongoing monitoring of structures, buildings, as well as the ground surface in the corridor of the tunnel, is a further necessity. Post construction reports and records must include: • All test and geological data • Construction experience in the ground conditions encountered • Equipment and methods employed • Hazards and difficulties encountered, and measures adopted to address these. The importance of this phase cannot be over-emphasised as the whole of the tunnel structure is exposed during construction. Many recommendations made in the geotechnical reports may have to be altered or even reversed based on the evidence, which becomes available during construction. If conditions on the exposed site turn out to be more favourable than indicated by the site investigation, the design may possibly be altered, with significant cost savings. The ongoing assessment of actual conditions and analyses with those predicted is, and must, remain an integral part of the whole design approach, as is post construction monitoring described in the next section. The Construction Report compiled by the supervising engineers on completion of the construction project should include a specific section or volume covering the construction of the tunnel, problems encountered, solutions executed, as-built records, plans, geological sections, logs, and, test and monitoring data.

7.5 Sta

Post constrterm or pomay take tha wide spefeatures dic Measuremeelectronic mconvergencencounterereached. Iand measumay be ma A variety oidentified adevice that A rational aengineer foparameters The assesssaving modto codes, soverstated.

Chapt

age 5: Post

ruction monitost constructiohe form of rouectrum of meactate the level

ents may takemeasuring devce measuremeed. Deflectionn many cases

ures must be pade.

of sensors are as requiring a t transmits dat

approach is toor the first fes, with periodic

sment of the ddifications on fstandards and.

South A

ter 7: Geot

t Constructi

oring is carrieon design assuutine recordingasurements anl, degree and

e the form ovices embeddents and are

ns may continus, the final defput in place in

available inclhigh level of

ta in real time

o have the resew years of sc overviews at

data collected future projectsd guidelines.

African Pav

technical In

Se

ion Monitor

ed out to monumptions. It g of instrumennd inspectionsfrequency of s

of s simple sued within or otaken at reg

ue over a numflection measun the design

luding strain gmonitoring, thto a centre o

sults of the onservice. Thert longer interv

during ongois, or may suggWhatever the

vement En

nvestigation

ection 7: Tunn

Page 58

ring

nitor the behaalso provides nts by operatis as describedsuch monitorin

urvey of targeonto a structugular interval

mber of years,urements onlyand construct

gauges, extenhe output fromr a person, or

ngoing monitoreafter, the mvals.

ng monitoringgest changes e reason, the

ngineering

s and Desig

nels

aviour of the can ongoing vonal staff or sd below. Theng.

ets attached ural member.s at areas w but should st

y occur after mtion stage suc

nsometers andm such electror even to a rem

oring assessedmonitoring dat

g provides useto the design value of post

Manual

gn Consider

completed tunverification of surveys by come particular tu

to critical ele These typica

where less favtabilise as a nmany years of ch that these

d pressure traonic devices cmote warning

d by the desigta could be a

eful data, whicprocess that f

t-completion m

MeasuThe vaconstrucannot informasaving projectwith whstanda

rations

nnel and to vthe tunnel’s i

mpetent persounnel and its

ements, or, sally include devourable condnew state of ef service. Henlong-term me

ansducers. In can be linked device.

gner and the gassessed agai

ch may bring form the basismeasurements

Post-Construrements alue of post-uction monitort be overstatedation can leadmeasures for

ts and can prohich to updaterds and guide

validate long integrity. It ons covering site specific

sophisticated eflection and ditions were quilibrium is

nce, budgets easurements

those areas to a cellular

geotechnical inst suitable

about cost-s of updates s cannot be

ruction

ring d. The d to cost-

future ovide data e codes, elines.

8. CO

This sectioinvestigatioChapters 6 The stipulafor reportinmay perhapAlso, the leauthority. The formatauthority hdetermine t 8.1 Pre

Prior to suMaterials Rand, should The followi• Genera

stabilityCOLTO identifie

• Broad within tsubbasesourcessources

• Availabiand grabe reco

• Possibledolomitmateria

• Proposatypes bproposedepend

• Likely sdiscusse

• Likely ttraffic apropose

• Preliminstructur

8.2 Det

Aspects to Report, anprojects, arcase of tunguidelines g

Chapt

OMPOSITIO

on stipulates ons planning, and 8.

ations given inng for other aups also have

evel of detail to

t in which tohas their stiputhe required fo

eliminary Ge

bmission of tReport is submd, therefore, b

ng aspects shal geology any and road loc

(1998). If ed. nature of ththe road resere or base cous not too far s. ility of materavel. Where tmmended, if ne material ce formations,

als or soft satuals for safe bbased on the ed batter slopeing on geomesubsurface ged. traffic load sare reported. ed. A cost bennary list of res is provided

tailed Geote

be covered innd the recomre given in Chnnels, an additgiven in Sectio

South A

ter 7: Geot

Sectio

ON OF TES

the requiremdesign, tende

n Sections 8.1uthorities or cdifferent or ao be included

o report both ulations that mformats.

eotechnica

the Basic Planmitted and appbe approved in

ould be commnd geomorphcation. Also, tportions of t

he materials rve, and theirrse material lfrom the roa

rial sources othese resourcenecessary. characteristic possible sha

urated soil conatter slopesresults of ex

es, based on setrical alignmeground wate

spectrum, an A provisionanefit analysis obridges, lar

d in kilometre

echnical an

n the Detailedmmended inde

apter 6 and intional detailedon 7.3.7.

African Pav

technical In

on 8: Compos

ST DATA AN

ments for the er and constr

to 8.3 belowclients. The vadditional requin the reports

laboratory anmust be follow

l and Mater

nning Report proved. This rn advance of s

mented on in thology of thethe generally ehe route are

resources avpossible influ

ikely to be avd reserve? O

of hard aggrees are in short

cs that may llow underminditions.

s, expectationsxisting data astability conditnt and volume

er conditions

d the possibilal pavement of the proposerge culvertssequence.

nd Materials

d Geotechnicaexing for gren Appendix C od report shall

vement En

nvestigation

sition of Test

Page 59

ND REPOR

composition ruction purpos

w reflect the rearious clients

uirements as ts and tender d

nd field test wed. For eac

rials Report

for greenfieldreport containsubmission of

the Preliminarye area, and thexpected excaunderlain by

vailable withinuence on the vailable from tOr, will mater

egate for concrt supply, expr

affect the gning, expansiv

s on shrinkageand preliminations during thes required dus and the po

lity of growth design and

ed pavement dand other i

s Design Re

al and Materiaeenfields and of this Chaptebe prepared a

ngineering

s and Desig

Data and Rep

RTING

of test datases. This sect

equirements oor road autho

to what needsdocuments mu

results is notch project, co

t

ds or new prons informationthe Basic Plan

y Geotechnicaeir effects on avatability clasy dolomite or

n the area direbasic planningthe road prismrial need to b

crete and uppropriation may

eometric gradve soils, deep

e or bulking fary drilling ahe basic plannue to geometrossible influen

due to futurealternatives (designs is supimportant

eport

als Design upgrade

er. In the along the

Manual

gn Consider

orting

a and reportition is relevan

of SANRAL, buorities using ors to be covereust be determ

t covered in tontact the app

ojects, a Preliinfluencing th

nning Report.

l and Materialthe geotechn

sses must be r undermined

ectly next to tg. For examp

m, or from exibe imported fr

er pavement y be desirable

ding. For exply weathered

factors, and pand augeringning, may eveic design requce on the ro

e economic de(without detaipplied.

Reportinand Field TeThe format intesting is not chapter. Eachtheir stipulatiofollowed. Forthe applicabledetermine the

rations

ing for the gnt to this cha

ut provide goor prescribing ted in the vario

mined by the cl

this chapter. plicable road

iminary Geotehe Basic Plann

ls Report: nical and matediscussed, as ground, the

the route, andple, is selecteisting or poterom commerc

layers, and sue at this stage

xample, the soils, lack of

possible bridgeg investigat

entually have tuirements. oad pavement

evelopments, iled analysis t

ng on Laboraesting n which to repocovered in thh road authorons that mustr each project,e road authorite required form

geotechnical apter and to

od guidance this manual, ous reports. lient or road

Each road authority to

echnical and ning Report,

erials design, specified in

se must be

d specifically d subgrade, ntial borrow cially owned

uitable sand e and should

presence of f weathered

e foundation tions. The to be flatter,

t design are

or attracted thereof) are

atory

ort is ity has be , contact ty to mats.

SANRAL reqroad authoand copiedprior to the The prograagreed andservices fosufficiently changes fro 8.3 Pro

The projectInvestigatioinclude the8.2, Chapteoften referr For cross cin the sequ• General

route in• Physio

drainag• Road p

types trreserve

• Speciadescribe

• Cuts anand excconstru

• Soil sudesigneprism atender o

• “Key pmateriaborrow

• Constrcuttingscharacteproposeincludinstabilisa

• All impolisted oconsidefoundatGeotechare inclu

• The pav• Traffic

Chapt

quires two coprity’s project m

d to the regioe finalisation th

amme for the d recorded i

or the projectin advance o

om delaying to

oject Docum

t document don and Utilisate separately ber 6, Section red to as the “

checking purpoence given: lized geologyn terms of engography chape, land use, vprism or cenraversed by th. l drainage, ed and detailend fills are tacavation potection material

urvey sheets ied roadbed treare discussed. or contract do

plan” indicatinals for the pavepit, quarry or

ruction mates, borrow pitseristics and med method of ng the variousation, also inclortant new str tabulated in

erations, advation or pile fohnical and Mauded as Appevement invedata and ana

South A

ter 7: Geot

Sectio

pies, in draft fmanager or geonal manager hereof.

submission an the relevat. Submissio

of the compilato the program

ment

etails providetion”. For greound Detailed7. Where ap

“Tender Docum

oses, the esse

y chapter desgineering geolopter describinvegetation andntre line invhe route, and

or other preced. For exampabulated and ential of mates or crushed aindicating the eatment types

These sheeocuments. ng the positionement layers, cuttings, are

erials are inclus, quarries andmaterials utiliworking the

s types of cemluded. ructures and

n kilometre seantages and oundation evaterials Designndices.

estigation analyses.

African Pav

technical In

on 8: Compos

form, are firsteotechnical enfor purposes

nd approval ont agreementon of the reption of tender

mmed tender d

d here are speenfields workd and Final Gepplicable, Doloments”.

ential informat

scribing the roogy. g average m

d water resourvestigation.

which cutting

cautionary meple, constructidiscussed, anerials encountand screened required road

s proposed. Cts prepared a

n of the propin relation to included, guiduded in a chad sand sourcesation of eacsource, must

ment, quality o

d bridges, orquence, includdisadvantagesluated are als Report. All t

nd pavement

vement En

nvestigation

sition of Test

Page 60

t submitted tongineer with as of discussion

of these report for consultport should nr documents,date.

pecifically fromks, and upgradeotechnical anomite Stability

tion listed belo

oad construct

minimum and rces.

An engineerigs are propose

easures requion on dolomitd their stabilittered in cutsaggregate, pr

dbed preparatCharacteristics at AO-size mu

posed borrow the road cent

delines for whpter summarises as specifiedch proposed t be describedof water, and

r bridges to bding recommes, as well asso included. test results, s

t design aspe

ngineering

s and Desig

Data and Rep

o the responsiba covering lettn and approv

rts should be ing engineerinevertheless to limit possib

m SANRAL’s “Vde projects, thnd Materials Dy Reports are

ow is included

ion aspects o

maximum te

ing descriptioed for use as

ired to ensurtic land. ty measures ris provided.

rovide details ation types, eithof the materi

ust be reduced

pit or quarrietre line. Test ich are in the sing the utilisad in Chapter borrow pit, qd. Commentsd sand for use

e widened as endations for s typical settThese are ge

oil profiles, bo

ects as specifie

Manual

gn Consider

orting

ble er,

val,

as ng be ble

Volume 6 – Gehese particularDesign Report

also included

d in this docum

of the area tra

emperatures,

n of all road borrow pits or

e the stability

ecommended Where cutt

and include onher the standaal occurring wd to A2 or A1

es, or cuts to results for all Chapter 6 appation of mater8 and in Chapquarry or cutts regarding the in premixed

part of an uptheir foundinglement analysenerally takenorehole logs, a

ed in Chapters

RequiThe rethis secrequireThey aguidanother a

rations

eotechnical anr project docut(s) referred td. These doc

ment, but not

aversed by th

rainfall, topo

construction r quarries insi

y of the road

. Also, the prtings used asn the key planard types or awithin and bel1 size for inclu

be utilised ascentre line an

pendices. rials from the pter 7, Appentting, togethehe availability concrete, asp

pgrading progg. Details, in

yses for eachn from the Fiand in situ tes

s 6 and 10.

SANRAL’s Rrements

eporting stipulaction reflect thements of SANalso provide gonce for reportinauthorities or

nd Materials uments must o in Section cuments are

t necessarily

he proposed

graphy and

soil or rock ide the road

d prism are

roposed use sources of

n. any specially ow the road usion in the

s sources of nd proposed

road prism, ndix A. The r with their of cement,

phalt or soil

gramme, are cluding cost alternative nal Detailed sting results

Reporting

ations in he NRAL. ood ng for clients.



References and Bibliography

Page 61

REFERENCES AND BIBLIOGRAPHY

BISHOP. A.W. 1955. The Use of the Slip Circle in the Stability Analysis of Slopes. Geotechnique, 7(1): 7-17.

BRINK, A.B.A. 1979, 1981, 1983, 1985. Engineering Geology of Southern Africa. Volumes 1 to 4.

BRITISH STANDARDS. 1981. BS 5930: Code of Practice for Site Investigations. British Standards Institution. London.

COLTO. 1998. Standard Specifications for Road and Bridge Works for State Road Authorities. Committee for Land and Transport Officials. Pretoria.

COUNCIL FOR GEOSCIENCE. 2002. Engineering Geological Site Characterisation for Appropriate Development on Dolomitic Land. DRAFT. Council for Geoscience and South African Institute for Engineering Geologists.

COUNCIL FOR GEOSCIENCE. 2007. Approach to Sites on Dolomitic Land. Available from www.geoscience.org.za.

DME. 2004. Environmental Management Programme. Regulations 48 to 51 of Govt. Gazette # 26275 of 23 April 2004. Department of Minerals and Energy.

DME. 2002. Environmental Management Programme. Regulation 52 submitted in support of application for a prospecting right or mining permit in terms of The Minerals and Petroleum Resources Development Act (Act 28 of 2002). Department of Minerals and Energy.

ELGES, H. Problem Soils in South Africa – State of the Art. Dispersive Soils. The Civil Engineer In South Africa, Vol. 27 No. 7 July 1985.

EUROCODE 7. 2004. Geotechnical Design. Part 1 General Rules, Part 2 Design Assisted by Laboratory Testing and Part 3 Design Assisted by Field Testing. European Committee for Standardization. CEN.

JANBU. N. 1954. Stability Analysis of Slopes with Dimensionless Parameters. Harvard Soil Mech. Serv. 46:81 pp.

NEMA. 1998. National Environmental Management Act. Act 107 of 1998.

NETTERBERG. F. 1979. Salt Damage to Roads - An Interim guide to its Diagnosis, Prevention and Repair. Journal for the Institute of Municipal Engineers of South Africa (IMIESA), 4(9), 13-17.

OHS. 1993. Occupational Health & Safety Act No. 85 of 1993, As Amended.

ORR, C.M. 1979. Rapid Weathering Dolerites. The Civil Engineer in South Africa. July 1979. pp 161-167.

PINTO, P.E., Lupoi, A., Franchin, P. and Monti, G. 2003. Seismic Design of Bridges Accounting for Spatial Variation of Ground Motion. ACI International Conference on Seismic Design of Bridges. San Diego. 2003.

SAICE. 1989. Code of Practice: Lateral Support in Surface Excavations. South African Institution of Civil Engineering, Geotechnical Division.

SAICE. 2002. Guidelines for Soil and Rock Logging in South Africa. South African Institution of Civil Engineering, Geotechnical Division.

SAICE. 2003. Code of Practice: The Safety of Persons Working in Small Diameter Shafts and Test Pits for Civil Engineering Purposes. South African Institution of Civil Engineering, Geotechnical Division.

SAICE. 2009. Site Investigation Code of Practice. 1st Edition. South African Institution of Civil Engineering, Geotechnical Division.

SACS. 1980. Stratigraphy of South Africa. Geological Survey of South Africa, Handbook 8. South African Committee on Stratigraphy.

SANRAL. 2011. Updated Code of Procedure for the Planning and Design of Highway and Road Structures in South Africa. South African National Roads Agency Limited.



References and Bibliography

Page 62

SANRAL. 2006. Drainage Manual. 5th - Edition fully Revised. South African National Roads Agency Limited. ISBN 1-86844-328-0.

SANS 1936. 2009. Development of Dolomite Land Part 1: General Principals and Requirements (ICS 07.060; 93.020) and Part 2: Geotechnical Investigations and Determinations (ICS 07.060:93.020). SABS webstore www.sabs.co.za.

SANS 10610 Series. 2008. Basis of Structural Design and Actions for Buildings and Industrial Structures. South African National Standards. Pretoria. DRAFT. SABS webstore www.sabs.co.za.

SCHWARTZ. K. 1985. Problem Soils in South Africa – State of the Art. Collapsible Soils. The Civil Engineer In South Africa, Vol. 27 No. 7 July 1985.

TRH2. 1996. Geotechnical and Soil Engineering Mapping for Roads and the Storage of Materials Data. Technical Recommendations for Highways. ISBN 0 7988 1776 8. CSRA. Pretoria (available for download www.nra.co.za)

TRH9. 1992. Construction of Road Embankments. Technical Recommendations for Highways. ISBN 0 7988 2272 4. CSRA. Pretoria (available for download www.nra.co.za)

TRH10. 1994. The Design of Road Embankments. Technical Recommendations for Highways. ISBN 1 86844 093 1. CSRA. Pretoria (available for download www.nra.co.za)

TRH15. 1994. Subsurface Drainage for Roads. DRAFT. Technical Recommendations for Highways. ISBN 1 86844 155 5. CSRA. Pretoria (available for download www.nra.co.za)

TRH18. 1993. The Investigation, Design, Construction and Maintenance of Road Cuttings. Technical Recommendations for Highways. ISBN 1 86844 094 X. CSRA. Pretoria (available for download www.nra.co.za)

WAGENER, F. 1985. Problem Soils in South Africa – State of the Art. Dolomites. The Civil Engineer in South Africa, Vol 27 No. 7 July 1985.

WEST, G., Carter, P.G., Dumbleton, M.J. and Dumbleton, L.M. 1980. Site Investigation for Tunnels. Lake.

WESTON, D.J. 1980. Expansive Roadbed Treatment for Southern Africa. Proceedings for 4th International Conference on Expansive Soils. Denver.

SOIL

No engineeimportance • Moistu• Streng• Volume• Permea The purposconsistent, present in o It is therefcharacteristfollows arpreferred Descripti

This guidelengineeringJanuary 19soil/rock invof proposedthe AO-Soipurposes. As what foimportancembodiedon site with As directedcan be dividand uncemstrongly ce They can bdeposits, or The descripWilliams, inIn cases wto ‘hardnesdescription

Moi(i)

For examplmay depen

Colo(ii)

Using Burlanatural statpit profile tTable A.1.

L (AND WE

ering structuree that the follo

ure/water, wgth, which affeetric changeability, which

se of classifyconcise, and

order to enabl

fore importanttics mentionere not to beby SANRAL

ion of Soils

line briefly deg purposes in973) and subsevestigations. d symbols to l Survey Draw

ollows is onlyce that all ind in Section 1h them for qua

in the Introdded into the tw

mented deposimented depos

be further subr combination

ption of soils n the followinghere weatheress’ and ‘ degrorder then be

isture Condit

le, dry, slightld on the grad

our

and’s colour dite in the test to the next.

SA

EATHERED

e is better thowing aspects

which affects itects its stabilite, which affecth concerns rat

ying the soils d systematic ile useful conc

t that any soid above, bote seen as tfor use in th

and Rocks

escribes the Jn Southern Afequently updaSome additionbe used as awing in the D

y a brief sumnvestigatory1 of “Guideliality assurance

uction chaptewo principal gits, while the sits.

bdivided into fs of these.

in test pit prog order: mois

red /decomposree of weatheecomes MCHW

tions

y moist, moisding and/or the

iscs or Munselpit profile, butMottling or bl

APEM CHA

D ROCK) PR

an the materof its characte

s entire behavty and ultimatets possible disttes of drainage

and rocks enternationallylusions to be d

l classificationh in terms ofthe only claheir projects.

in Test Pits

Jennings, Brinfrica” (as origated in 2002, nal guidelines bbreviations oDetailed Repo

mmary, as amy site staff hnes for Soil e purposes.

r of the abovegroups; ‘soils’ a

term ’rocks’

four further ca

ofiles should uture conditionsed rock is enering’ as defiWSSO, where

st, very moist,e clay content

ll colour chart t should be delotching etc. s

A - 1

APTER 7: A

ROFILING

rials on whicher are adequa

viour e bearing captortion of the e within the so

encountered dy accepted medrawn therefr

n adopted, shf material chassification s.

s and Auge

nk and Williaginally publishas directed beare given in T

on simplified sorts, or on sim

mended for Shave a copyand Rock Lo

ementioned upand ‘rocks’, threfers to the

ategories, i.e.

utilize the folln, colour, consncountered, pined in Sectioe H refers to h

, or wet, with t of the materi

as the standaetermined in ashould also be

APPENDIX

G OF TEST

, or of whichtely described

acity structure oil, affecting c

during site exethod of descom.

ould make usaracteristics asystems ava

er Holes

ms paper “Rhed in the Civelow, which isTables A.1 to soil profiles anmplified soil p

SANRAL’s owy of the aboogging in Sou

pdated publicahe term ‘soil’ e hard, rigid o

rock, residua

lowing descripsistency, struc

profilers may uon 3 of the 20hardness and W

moist being ial.

ard. For unifoa wet state we noted. Abb

X A

PITS AND

it is built. Id:

changes in bot

xploration is cribing the va

se of a systemnd classificati

ailable, but

evised guide vil Engineer ins now advocatA.4 and A.6 ond cross-sectioprofiles prepar

wn purposeovementioneuth Africa (2

ation, geologicembracing the or weathered

al soil, transpo

ptors accordincture, soil typeunder ‘consiste002 documenW to the degre

around the O

rmity, the colohen comparinbreviations for

AUGER HO

It is therefore

th strength an

to provide aarious types o

m that would on methodolorather those

to soil profiln S.A. Vol. 1ted for use in

of this Appendons normally red for pavem

es, it is of ted updated 2nd Impress

cal formationscomparativelyto some deg

orted soil, and

ng to Jenningse and origin (ency’ wish to

nt referred to ree of weather

MC of the ma

our should beg materials frr the colours a

OLES

e of primary

nd volume

n accepted, of materials

address the ogy. What e that are

ing for civil 5, No. 1 in all SANRAL ix in respect depicted on

ment design

he utmost version as ion 2002)”

s or deposits y soft, loose gree, and/or

d pedogenic

s, Brink and (MCCSSO). rather refer above. The

ring.

aterial. This

e noted in its om one test are given in

Table A.1

Colour Black Blue Brown Green Grey Khaki

Con(iii)

The consisteffort requiA.3 give the Table A.2

ConsisteVery Loos

Loose Medium D

Dense

Very Dens

Table A.3

ConsisteVery soft

Soft

Firm

Stiff

Very stiff

Sometimes rock, nor fit Table A.4 g Table A.4

ConsisteVery weak

Weakly ce

Cemented

Strongly c

Very stron

1. Standardand Cros

Abbr

nsistency

tency is a meaired to dig intoe recommend

2. Consiste

ncy se

Density

se

3. Consiste

ncy

there is diffit into the gran

gives a guide t

4. Naturally

ncy kly cemented

emented

d

cemented

ngly cemented

d Abbreviatss-Sections

reviation CBl. MB. OBr. RGn. WG. YKh.

asure of the do the soil, or ted definitions

ency of Gran

NomenclV loose

Loose Med dense

Dense

V dense

ency of Coh

NomenclV soft

Soft

Firm

Stiff

V stiff

culty in classinular scale, e.g

to terms that c

y or Artifici

NomenclV W cem

W Cem

Cem

Str cem

d V Str Cem

tions for Mas or Simplifi

Colour Mauve Orange Red White Yellow

density, hardnto mould it wiof consistency

nular Soils

ature DesVeryCrumSma

e ConspickVeryof geHightools

esive Soils

ature DescPick easilEasil– 40Indeup tpenePenepick pick Indeby b

ifying the cong. pedogenic

can be used.

ially Cemen

ature DescSomand CanncrumDisinMatedisloFirmindeblade

Handfirm

A - 2

ain Colour ied Soil Pro

AbbreviaM. O. R. W. Y.

ness or toughnith the fingers

cy.

scription y easily excavambles very easall resistance tosiderable resis

y high resistaneological pick h resistance tos for excavatio

cription head can ea

ly moulded byly penetrated

0 mm; mouldeented by thumto 10 mm; vetrated with aetrated by thupoint into sofor excavation

ented by thumblow of pick po

nsistency of ac materials, or

nted Soils

cription me material ca

thumb. Disintnot be crumbmbled by strontegrates undeerial crumbles odged with som

m blows of sntations of 1me. d-held specimblow. Similar

Descriptionofiles

ation

ness of the sos. e.g., very l

ated with spadsily when scrao penetration stance to pen

nce to penetrafor excavation

o repeated bloon

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observation betc. Table A.

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n produced

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cimen show with a knife

with single

Stru(iv)

This indicatcohesive sostructure as Table A.5

Structure

Intact Fissured

Slickensid

Shattered

Micro-shatStratified LaminatedFoliated Pinholed

Honeycom

Matrix-supClast-supp

Soil(v)

The soil typthe grain siMIT (Massa Table A.6

Grain siz(mm)

< 0.002

0.002 to0.06

0.06 to 0.0.2 to 0.60.6 to 2.02.0 to 6

6 to 20

20 to 60

60 to 200

> 200 * Dilatancoccurs. If water will abecome du NB: It is imimportant iviability of a

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5. Structur

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nce, or absennular structure

able A.5.

re of Cohesi

Description

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Size Classe

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gravel

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menclature

Cl

St

F. S M. S. C. S.

F. Grav

M. Grav

C. Grav

Pb

Bl material consi

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n into the dilat

percentage booulder Excavat

A - 3

in the soil ancorded. Cohes

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nly used in E

Mineralog

Secondary minerals &

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mm) which m

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Engineering

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minerals (clayFe-oxides)

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ly packed soil ne hand and sn the palm, o

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Orig(vi)

It is extremtransportedprove moreexample resurroundingvery importtransported Table A.7

TransporSoil Type

Talus (coacolluvium)

Hill wash colluvium)

Alluvial orgulley wasLacustrinedeposit

Estuarine deposit

Aeolian deposit Littoral de

Sandy soimixed orig

Wat(vii)

Some referwithin the table whencomplete a(1973) give

Anc(viii)

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gin

mely importand or a fill. It e difficult for tesidual shalegs, i.e., the totant to be abld soil’s origin a

7. Origins o

rted e

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arse )

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(fine )

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r sh

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e Streain pansubtein cavTidal tides salineWind

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ls of gin

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ter Table

rence should adepth investig the accompa

and proper guen in the Biblio

cillary Notes

ant features sh.e high/mediuf carbonate, ir

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e, or even moaborated upon

at the bottomany type of au

f machine usevation, or was

nt to determiis generally

he transported. In determopography andle to identify wassists in the i

of Transpor

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ty

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ms or gulleys

m depositing n, lake or erranean pool vernous rock rivers and depositing int

e water

es

twash, wind, tes

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to Accompa

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, (of replaced

re commonly n in the notes

m of the hole ger used, or n

ed for excavatiit an existing

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rted Soils in

Source R

Any rock outcroppiabove talAcid crystBasic crysArenaceosedimentaArgillaceosedimentaDependscatchmenUsually msource

to Mixed

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Various

de to the waterofiler should to each profil how this diste end of this M

ny Each Soil

rded, including, more accura

ns, salt crystal

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the gravel ma, as it indicate

should be recnot and on wh

ion should alsopen face, et

A - 4

n of the soil, describe theove e.g. windbature of the as well as the

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n Southern

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er table in thedistinguish be

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l Profile

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or at least t residual soilsblown sand, tr

transported e climate, e.g.originate from

g geological be

Africa

Soil Type

Unsorted anggravel and bo

Clayey sandClay Sand Clay or silt

Gravel (roundsands, silts &Sand Silt Clay

Sand Silt Clay Sand

Beach sand

Sandy/gravel

e soil profile, eetween a perc

ed in terms of be made, are

following: wan of the layer

be noted as th

uld in any casebetween trans

he comment ane has actually

g. Williams LD

to describe ws beneath theransported clamaterial, one

., for wind-blom man-made ehaviour as illu

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ly Codicoflo

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ater table, rates of fill (if any

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DH 80 Auger, T

whether it is e pebble markay, or originatie needs to own sands. Itfills. A knowlustrated in Ta

Associated ngineering

Geological Prolope instability

rain structure eave rain structure eave or high ompressibility

ll possible pro

ompressibility eave or high ompressibility

uicksand igh sensitivity

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that it is not eal) or a permaideline dated e paper by Je

e of inflow inty), or roots, an

nt out possible

scribed on theesidual soils.

as to whetherdid.

TLB-Case 580

residual, or ker, but can ng from, for inspect the t is similarly ledge of the ble A.7.

oblems y

blems

n

n

ric; acteristics; subject to

encountered anent water 2002. More nnings et al

to test pit or nt workings,

e collapsible

e profile, but

this was at

G (4X4), or

A - 5

Figure A.1. Standard Symbols for Soil Profiles (after Franki, 1995)

A - 6

Figure A.2. Standard Symbols for Profiling Rocks (after Franki, 1995)

B - 1

SAPEM CHAPTER 3: APPENDIX B

ROCK PROFILING OF CORES, TESTPITS OR QUARRY FACES

The geological classification and identification of rocks is a very complex science requiring a high level of skill and experience. Any errors or oversights in this process invariably lead to claims by the contractor during the construction phase and it is thus a requirement that all logging be carried out by a professional and experienced engineering geologist or geotechnical engineer. Notwithstanding the above, a full geological appraisal may be unnecessarily detailed if the scope is only restricted to centreline soil on uniform geology on flat topography and some borrow pit investigations. For bridge structures, cuttings, lateral support systems, quarry and deep soil/rock road prism surveys, the detailed methods described in Section 3 of “Guidelines for Soil and Rock Logging in South Africa (2nd Impression)” should be followed. This method prescribes the description of rock in the following order (MCWFDHR): • Moisture • Colour • Weathering • Fabric • Discontinuities • Hardness • Rock Name In addition, especially where the water table position from measurements is known, or when holes are drilled on topographical locations where wet conditions are to be expected during certain times of the year, the moisture condition (M), (e.g. “wet” below W.T.) for each layer should also be recorded before the colour (C) on the core log. The depth of the water table (if any) should be indicated. In addition, the existence of any potentially deleterious secondary minerals such as clay, shale, mica, sulphides or soluble salts in potential quarries, must be identified and commented upon. If the presence of such minerals is suspected, it is considered prudent to carry out further microscopic/X-ray assessment of thin slides in order to more accurately identify and quantify potential problems. As what follows is either a repetition of tables in the above-mentioned SAICE, AEG and SAIEG approved document, or are additional guideline descriptors as amended for SANRAL’s own purposes, it is recommended that all investigatory site staff have copies of both documents with them on site for quality assurance purposes. Table B.1. Colour

Term Description Speckled Very small patches of colour: < 2 mm Mottled Irregular patches of colour: 2 – 6 mm Blotched Large irregular patches of colour: 6 – 20 mm Banded Approximately parallel bands of varying colour* Streaked Randomly orientated streaks of colour* Stained Local colour variations associated with discontinuity surfaces

* Describe colour thickness using bedding thickness criteria (e.g. thickly banded, thinly streaked, etc).

B - 2

Table B.2. Weathering

Degree of Weathering

Extent of Discolouration

Fracture Condition

Surface Characteristics

Original Fabric

Grain Boundary Condition

Unweathered None Closed or stained.

Unchanged Preserved Tight

Slightly weathered

< 20% of fracture spacing on both sides of fracture

Discoloured, may contain thin filling.

Partial discolouration. Often unweathered rock colour.

Preserved Tight

Moderately weathered

> 20% fracture spacing on both sides of fracture

Discoloured, may contain thick filling.

Partial to complete discolouration. Not friable except poorly cemented rocks.

Preserved Partial opening

Highly weathered

Throughout - Friable, possibly pitted. Mainly preserved

Partial separation. Not easily indented with knife. Does not slake.

Completely weathered (Residual soil)

Throughout - Resembles a soil. Partially preserved

Complete separation. Easily indented with knife. Slakes.

Table B.3. Fabric or Grain Size Classification

Classification Size (mm) Recognition Very fine grained < 0.2 Individual grains cannot be seen with a hand lens Fine grained 0.2 – 0.6 Just visible as individual grains under hand lens Medium grained 0.6 – 2 Grains clearly visible under hand lens, just visible to the naked eye Coarse grained 2 – 6 Grains clearly visible to the naked eye Very coarse grained > 6 Grains measurable

Table B.4. Discontinuity Spacing

Separation (mm) Micro-Structure Spacing (foliation, cleavage, bedding,

etc.)

Discontinuity Surface Spacing (fractures, joints,

etc.) < 6 Very intensely Very highly

6 - 20 Intensely Very highly 20 - 60 Very thinly Highly

60 – 200 Thinly Highly 200 – 600 Medium Moderately 600 – 2000 Thickly Slightly

> 2000 Very thickly Very slightly Table B.5. Discontinuity Surface Description

Joint filling Joint fill type Definition (wall separation specified in mm) Clean No fracture filling Stained Colouration of rock only. No recognisable filling material. Filled Fracture filled with finite thickness Discontinuity orientation Discontinuity inclinations (i.e. of joints, bedding, faults) Roughness of discontinuity planes Classification Description Smooth Appears smooth and is essentially smooth to the touch. May be slickensided*. Slightly rough Asperities on the fracture surface are visible and can be distinctly felt. Medium rough Asperities are clearly visible and fracture surface feels abrasive. Rough Large angular asperities can be seen. Some ridge and high side angle steps evident. Very rough Near vertical steps and ridges occur on the fracture surface.

* Where slickensides occur, the direction of the slickensides should be recorded.

B - 3

Table B.6. Rock Hardness

Hardness COLTO Classification

Description Range of Minimum UCS (MPa)

Very soft rock R1 Material crumbles under firm blows of pick point. Can be peeled with a knife. SPT refusal. Too hard to cut triaxial sample by hand.

1 – 3

Soft rock R2 Firm blows with pick point: 2 – 4 mm indentation. Can just be scraped with a knife.

3 – 10

Medium hard rock R3 Firm blows of pick head will break hand held specimen. Cannot be scraped or peeled with a knife.

10 – 25

Hard rock R4 Breaks with difficulty, rings when struck. Point load or laboratory test results necessary to distinguish between categories.

25 – 70 Very hard rock R5 70 – 200 Extremely hard rock - > 200

The Rock Name is the last facet to be described in the MCWFDHR sequence to be recorded/described on the core log, two typical example formats are appended at the end of this Appendix. The end product “Borehole Log” is not complete until the additional relevant data (obtained from the driller’s field sheets) has also been recorded and which is normally entered on to the left-hand side of the borehole log sheet. The core log (right-hand side) of the borehole log purely comprises a description of the recovered core, whereas the entire borehole log includes the relevant data applicable to the actual drilling of the hole, (some of it quantified/analysed) viz. machine type, drill runs, core barrel sizes, casings, RQD determination, core recovery, sampling and in situ testing data, water loss and water rest levels etc., all which are equally critically important inputs to be entered onto the borehole log by the profiler, to ensure an overall accurate end-product.

C - 1

SAPEM CHAPTER 7: APPENDIX C

ASPECTS COVERED IN THE DETAILED GEOTECHNICAL AND MATERIALS EXPLORATION AND DESIGN REPORT FOR GREENFIELD/UPGRADE PROJECTS

C.1 Introductory Executive Summary

• Appointment: The terms of Reference describing the Consulting Engineer’s Commission and Scope and Programming of Geotechnical Investigative Works.

• General Description of Project. • Summary of Problem Areas, Design Recommendations and Special Construction Requirements. C.2 Physiography

Location and general nature of terrain. Also cover or cross refer to Environmental Management Plan if already dealt with separately. Some of these sections may be dealt with together, e.g., Topography and Drainage • Topography • Drainage • Climate • Vegetation • Land use • Infrastructure C.3 Geology

• General geology of area (Refer to Geological Plans, Soil Survey Maps, Sections, etc.) • Detailed geology and geomorphology along route • Influence of geology and geomorphology on design and construction • Effect of geology and geomorphology on availability of construction materials • Geologically unstable areas (e.g. sinkholes, natural slopes shallowly undermined land, etc.) C.4 Road Prism Investigation

This section should contain a detailed description of the route with regard to cuts, fills, and the identification of problem areas. (Refer to Chapter 6, Section 4). Include numbering of cuts and fills and problem areas with associated important stake values. It should also describe the identified problem areas in which instance, unless similar conditions are encountered, each area must be described separately, e.g., fills over swampy areas or sections of the route underlain by dolomite or shallowly undermined land. C.4.1 Soil Survey and Subsurface Investigations

(i) Description of Investigations

NB : If portion of route is underlain by dolomite, cross-refer to the separate Dolomite Stability Investigation Report carried out during the Route Location/Preliminary Geotechnical and Materials Investigation Report stage. Include this preceding report into the Detailed Geotechnical and Materials Design Report if possible. Mention when the various detailed investigations took place and by whom they were undertaken. State the number of test pits dug or the number of auger holes drilled, the number of boreholes drilled and cored, the number of disturbed and undisturbed samples taken and for what purpose. Elaborate on the geophysical exploration methods used. Refer to plans, sections, etc., showing positions of all test pits, boreholes, etc. Also mention where the test results, logs, plans, etc., are bound in the Report. Use the prescribed forms/formats specified in this Manual.

(ii) Results of Soil Survey

This section should include geotechnical evaluation and discussion on: • Moisture conditions and water tables. Tabulate marshy/vlei areas along route. • Construction materials (suitability thereof) available from boxed–out excavations within road prism. When it

comes to cuttings, discuss suitability and tests results for various materials encountered.

C - 2

• Location and extent of unsuitable founding material below fills, warranting C.4.2 (ii). • Identification, depth(s) and quantities of suitable topsoil along the route. • Identification and quantities of unsuitable (spoil) materials along the route and in cuttings. NB: Clayey topsoil/

overburden sources can be utilised meaningfully for topsoiling/reinstatement of the environment and landscaping purposes respectively.

• Excavatability in cuttings (more fully elaborated upon in C.4.3 below) • Proposed special treatment types for roadbed/in situ subgrade, as referred to in Chapter 6, Section 4 , and as

indicated on the AO-Soil Survey Plans vs. km distances • Proposed standard road bed treatment types as discussed in Chapter 6, Section 4, and as also indicated on the

AO–Soil Survey Plans vs. chainages. Refer to test results, tables, plans, chainages, etc. where relevant. Use the prescribed forms. C.4.2 Stability Assessments and Proposals

(i) Dolomitic Land or Shallowly Undermined Land

Appropriate reference should be made here to any preceding Dolomite Stability Investigation Report(s) prepared (during the early stages of the investigation) and such reports could be appended to this Detailed Geotechnical & Materials Investigation and Design Report.

(ii) Embankments

• Discuss the stability of the embankments considering founding conditions, potential lateral sliding, anticipated settlement (type, extent, period), or heave. NB: Consider behaviour of existing embankments/road fills as appropriate.

• If special measures are required to improve the stability of certain embankments, discuss for each the embankment geometry the proposed measures, e.g., the removal of unsuitable materials, special sub-surface drainage measures, monitoring of seepage, the construction of pioneer layers, the provision of reinforcement, rock toes and rock fills, the need for impact rolling, progressive construction and/or surcharging, required on-going monitoring, possible lateral support systems required, etc. Elaborate on proposed systems to be considered, e.g., Reinforced Earth (NB patented trade name – rather use other term such as “Soil reinforcement” otherwise other suppliers complain), piled anchored walls, etc. Refer to test data, borehole information, include calculations, provide plans and geological cross sections, typical details, sketches and preliminary breakdown of additional costs as necessary.

• Recommend drainage measures and required culvert class, etc. List precautionary measures relating to storm water handling.

• Recommend slope batters. • Recommend erosion control measures and options. • Provide stability analysis outputs where appropriate. • Discuss the various proposed in place subgrade treatment types envisaged for the various embankments and also

indicate this on the Soil Survey Plans vs. km-distances. (See C.4.1 (ii) above). Explain/indicate typical details for each type on the Soil Survey plans.

(iii) Cuttings

• Tabulate and discuss the geometry of all new (also upgrade projects) cuttings and pro-actively specify the surface and subsurface drainage requirements in terms of Chapters 4 & 5 of TRH 18: 1993. NB: In the case of upgrade projects, also consider experience gained from history of the existing cuttings, via available Slope Management System.

• By considering individual cases and site specific geology, recommend rock fall control (TRH 18:1993 Chapter 5.6.1) for cuttings susceptible to this phenomenon. (NB: In the case of upgrade projects, also consider available incident data obtained from existing Slope Management System.)

• Recommend permanent erosion control measures. • Discuss the general stability of the cuttings considering geological features, in situ materials, moisture conditions,

water table and the recommended permanent drainage measures. Recommend safe and maintainable batter slopes.

• Discuss proposals to enhance the stability of certain cuttings, e.g., special drainage measures, flatter or benched slopes, special methods of excavation (see C.4.3. below also), permanent rock bolting or active anchors, other retaining systems such as local gabions or concrete retaining block walls, bolted meshing, with or without guniting, required on-going monitoring, etc. Refer to test data, joint orientation surveys, borehole information,

C - 3

provide plans and geological cross sections, typical details and sketches, as well as preliminary breakdown of additional costs as necessary. NB: Do not forget experience gained from the history of existing cuttings.

• Provide stability analysis outputs where appropriate. • Discuss the proposed in place subgrade treatment envisaged for each cutting, and indicate this on the Soil Survey

Plans versus the km-distance. C.4.2 Classification of Excavation • Tabulate per cutting, divide into depth zones as may be applicable, insert specified excavation classification (e.g.

in accordance with COLTO). Provide proposed definition and preliminary assessment of bulking factors, etc. (Refer to test pit/auger hole and /or core borehole positions and logs, provide plans, geological cross-sections, seismic data, or other geophysical exploration methods if applicable, etc. as necessary).

• Then, tabulate the proposed classifications per cutting for tender documentation purposes. (Tabulate volumes, i.e., in situ cut volumes as well as percentage of each class of excavation, these volumes adjusted to compacted fill, or layer work volumes, for tender quantification purposes, or for possible use of the Mass Earthworks (cut to fill) proportion thereof, in the Mass Haul Diagram referred to below.)

C.5 CONSTRUCTION MATERIALS

(i) General Introduction

Elaborate on the various types of materials required for the specific project in hand.

(ii) Usable Material from Road Prism (Refer to C.4.1 (ii) where necessary)

Discuss efforts attempting to attain balance of earthworks, referring to Mass Haul Diagram as applicable and where necessary. Discuss origin and quantities of spoil, proposed spoil areas, etc. Summarise quantity and implications of usage including stockpiling or spoiling of surplus effect on balance of earthworks, costs, effect on construction program, etc., absolute proposed usage of the various in situ materials based on the results discussed in C.4.1(ii).

(iii) Borrowpits (Refer to Chapter 8)

Discuss the positions, practical haul distance, quantity, quality and suitability of the materials. Elaborate on the general shortcomings/good attributes of the various materials and how these can best be put to use, e.g., by modification/stabilization. Use the prescribed forms referred to in sections C.8 to C.10 in this Appendix. Discuss the environmental issues associated with the borrow pit and any special measures that may have to be implemented during their exploitation. Refer to test data, borrow pit plans, etc. where necessary. Indicate where the test data are bound in the report. Any implications and/or limitations with respect to future closure of the borrow pit according to the standard Environmental Management Plan (EMP) should also be included. For commercial sources, list name of source, location, product range, material test results, quantities available and contact details.

(iv) Rock Quarries (Refer to Chapter 8)

Discuss the position, quality, quantity, suitability, method of working, and other aspects for each proposed quarry. Use the prescribe forms referred to in sections C.8 to C.10. Mention environmental issues associated with the quarry and any special measures that may have to be implemented during their exploitation. Refer to test data, plans, sketches, etc. and also mention where the data is bound in the report. Copies or references to copies of the approved EMP should be included in the report together with discussion on any associated cost implications. For existing as well as potential commercial sources, each quarry must be listed together with product range, the relevant location and owner contact details. Refer to test data and any other relevant information that may be bound elsewhere in the report.

(v) Sand Sources (Refer to Chapter 8)

As for C.5 (iii) and (iv) above.

(vi) Water Sources

Discuss aspects such as: • Location of sources

C - 4

• Owner details • Seasonal availability (perennial; non-perennial) • Quantity available • Water test results (salinity, potability, etc) • Suitability for specific applications Refer to results and evaluation of any testing undertaken. C.6 Pavement Design

(i) General Introduction

(ii) Traffic Surveys and Growth Projections (refer to data)

(iii) Alternative Pavement Designs and Calculations

(iv) Cost-Benefit Analyses

(v) Influence of Terrain, Drainage, Geology and Construction Materials on Pavement Design

(vi) Summary and Proposed Pavement Design for:

• Freeway • Ancillary roads

(vii) Summary of Schedule of Quantities Together with Cost Estimate

C.7 Structures

NB: The Geotechnical Investigation and Design Report shall be signed by both the compiler and the geotechnical engineer who planned/supervised the investigation, evaluated the results, prepared the geotechnical/foundation design parameters and recommended the most appropriate foundation type. The Geotechnical Investigation Design Report shall also be a Design Report, i.e. the report shall provide clear guidance by the geotechnical engineer to the structural/bridge engineers, enabling the selection of the most appropriate solution and foundation type for the structure/bridge envisaged and the allowable differential settlements. The responsible geotechnical engineer shall evaluate and elaborate in the report on alternative foundation systems and/or solutions, if ground conditions or depth to a competent founding horizon suggest such a possibility. Settlement and load capacity analyses should be summarised in the report. The design report shall thus not only contain all of the necessary soil (and/or groundwater) parameters required for the design of the proposed foundation, (or pile type) for each bridge/major culvert/minor culvert, but also for the respective approach embankments. It should be realised that in some cases the detailed designs of foundations/piles/abutments are to be carried out by another geotechnical engineer who was not originally involved in the geotechnical investigation. The report shall be compiled under the headings and in the sequence listed below: • Introduction • Description of the site(s) * • Geology, soil profile and water table * • Investigations carried out * • Geotechnical evaluation * • Evaluation of alternative foundation systems/types * • Recommendations * • References • Annexures NB: The items marked * shall be dealt with under the heading of each structure for which investigations have been conducted. [The Geotechnical Investigation Design Report including appropriate Appendices as directed by the Project Manager, needs to be bound into Volume 6 of the tender documents. The Volume 6 report, together with the inspection of the site, shall provide the contractor with sufficient information to reasonably anticipate any problems which may occur during the execution of the works. This will enable the contractor to tender a realistic price for the construction of the work and to select the most appropriate equipment and techniques].

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The aspects covered under the above-mentioned headings shall include, but not be limited to, the following, as relevant:

(i) Introduction

• Terms of reference and description of the project, with specific reference to the structures involved. • Description of the stage, as described in Chapter 6 and the purpose for which the investigation was conducted.

(ii) Description of the Site(s)

• Location of the site(s) • Accessibility of the site(s) • Trafficability of the site for construction equipment • Listing of sources from which data is available or was obtained • Description of regional geology, geomorphology, vegetation, drainage and other general features of importance

(iii) Geology, Soil Profile and Water Table

• Formation(s) underlying site • Typical soil profiles described • Water table information • Geological cross-section provided if applicable

(iv) Investigations Carried Out

• Name(s) of firm(s) responsible for the field work (consultant, contractor). • Name(s) of person(s) responsible for the interpretation of the geophysical work and for the profiling and/or core

logging. • Date(s) on which the work was conducted. • Description of the types of field work undertaken number of pits, auger holes or boreholes and probes, and

equipment used. • Laboratory testing programme on soils/rock (including groundwater quality testing w.r.t. possible effect on

concrete.

(v) Geotechnical Evaluation

• Discussion of “stability classes” (if on dolomite formation). • Evaluation of the soils encountered, identifying their stability or potential problems they may present e.g.,

tendency to heave, collapse, settle. • Evaluation of hard rock geology (if encountered) identifying the type, quality, strength, degree of weathering,

fracturing, excavatability classes. Mention reference used to arrive at excavation classes. • Provide geotechnical/foundation design (or pile design) parameters etc. • Potential for boulders and other obstructions to be encountered in deep seated foundations. • Discussion of problems experienced during investigation or to be expected during construction. • Discussion/evaluation of groundwater table(s) and expected variations. • Discussion of field and laboratory testing (including chemical tests) carried out i.e.,

− Evaluation of results obtained and comments on their reliability. − Evaluation of in situ testing results/geophysical investigations.

(vi) Evaluation of Alternative Foundation Systems/Types

• Maximum tolerable total settlement(s) and maximum tolerable differential settlement(s) applicable to the various bridge foundation components, as obtained from bridge design engineer.

• Discuss and evaluate alternative foundation types with pros and cons to be considered by bridge or structural engineers.

• Motivate preferred foundation (or pile) type.

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(vii) Recommendations

• Excavatability classes (i.r.o conventional foundations and caissons, or for piling). • Founding options to be considered (in the light of (vi) above). • Estimated safe bearing pressure and predicted foundation settlements (differential and total) for the respective

materials/depths on which founding could be considered. • Recommended founding depth and allowable bearing pressure at that depth. • Precautionary protective measures against corrosion of concrete/steel in foundations. • Recommended pile type (if piling seems essential/economically viable). • Recommended design parameters, e.g., friction values and rock socket parameters for the design of piles. • Specified FOS to be designed for piling; and applicable pile design code. • Recommended supplementary geotechnical investigations to be conducted or to be allowed/budgeted for during

construction phase (if any). • Construction problems anticipated.

(viii) References

• List reference used for the classification of materials in respect of soil condition and rock hardness and excavatability classes.

• Others as applicable to the investigation, evaluation, or to the recommendations. (ix) Annexures • Locality plan to appropriate scale • Results of geophysical investigations (if any) • Borehole, auger hole and test pit logs (with coordinates and elevations) • Photographs of borehole cores recovered • Laboratory test results/in situ testing results • Geological cross-section(s) drawings (if appropriate) • Drawings to scale, for each bridge/major culvert or other structure, showing the location(s) including levels of all

positions investigated, physical features of the site and setting out points in relation to proposed bridge foundation layout(s).

C.8 Laboratory Test Data

Reporting (w.r.t. the Road Prism Exploration, borrow pits, quarries and commercial sources) shall only be carried out using the standardised series of reporting sheets. In special instances, e.g., foundation indicators, consolidation, shear box, triaxial tests, etc., modified laboratory test sheets will be accepted, i.e., where no standard form exists. All pavement materials designs should be recorded on the standard D3, etc. forms used for the As Built Materials Books. Individual results recorded on forms emblazoned with a commercial laboratory’s name and logo will not be acceptable for inclusion in the Reports and Project Documents. Seismic data should be tabulated and also reported/shown on the Centreline Soil Survey Long Section/Plan drawings. C.9 Subsurface Investigation Data

Standard boreholes log sheets must be used for all boreholes and auger holes. An example thereof is bound in Chapter 7, Appendix B. Any laboratory test results on soil or groundwater samples retrieved from trial holes, which cannot be reported on these sheets, should be presented on appropriate sheets. C.10 Drawings

The following drawings should be included in the Detailed Geotechnical and Materials Investigation Report: • Key plan • Geological plans and sections • Soils map (if required) • Centreline soil survey long section/plans • Long sections, cross sections of deep cuttings * and high embankments * (See NOTE below)

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• Layout plan(s) of proposed quarries/borrow pits (including test pit positions and cross sections based on the soil profiles and borehole logs

• Other special plans and drawings, pertaining to each particular problem area as required • Interpreted seismic or other geophysical exploration data NOTE: If certain cuttings and/or embankments were subjected to supplementary detail geotechnical investigations (over and above, the normal road prism exploration) in order to arrive at Stability Assessments and Proposals (in terms of Section C.4.2. of this Appendix), additional plans and sections indicating the position of these supplementary investigation positions and explaining the various soil/rock horizons encountered/investigated including water-table(s), etc., should be presented including preliminary plans/sections depicting the stability proposals/sequence of construction features, etc. Also, if material from cuttings is to be used as sources for pavement layer materials, plans indicating the position and number of the cutting as well as the exact location and coordinates of test pits/auger holes, or core boreholes are required. The source remains a cutting and should not be renamed a borrow pit.

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SAPEM CHAPTER 7: APPENDIX D

BRIDGE AND CULVERT FOUNDATION INVESTIGATION

Note: THESE EXTRACTS ARE FROM ROAD AUTHORITY SANRAL’S CODE OF PROCEDURE FOR THE PLANNING AND DESIGN OF HIGHWAY AND ROAD STRUCTURES IN SOUTH AFRICA (FEB. 2002), WHICH IS CONSIDERED TO REPRESENT GOOD PRACTICE) NOTE: The following pages in this Appendix D are extracts from Chapter 7 and Annexures 18.2 & 18.3 of the above-mentioned SANRAL Code of Procedure dated February 2002. It will be noted that some of the content has been updated (in italics) as well as additional guidelines included here and there (in italics), in order to align it with Chapter C7 of the report writing guidelines as outlined in Chapters 6 and 7 of the SAPEM manual. D.7 Geotechnical Investigations

D.7.1 Introduction NB: This entire Appendix needs to be read in conjunction with Chapter 7, Section 2 and/or Chapter 6, as the specific project type or case in question may require. This abstract generally sets out the procedure for Geotechnical Investigations for Structures other than Tunnels. The purpose of geotechnical investigations in this case is to provide an accurate assessment of subsurface conditions for all types of highway and road structures, including toll-buildings, etc., forming part of a particular project. The geo-investigations are therefore aimed at arming the Geotechnical Engineer/Engineering-Geologist in arriving at the various soil/rock/groundwater parameters/properties necessary for settlement and/or stability prediction and other soil/structure interactions cum design. In other words, for them to consider in a technical sense and then to select and recommend suitable foundation types for adequate and economic foundation designs for each and every facility. Also the bridge versus approach embankment interaction, bridge abutment settlements and slopes need to be looked into, etc. It is essential that thorough upfront planning be done by the responsible Geotechnical Engineers/Engineering-Geologist, the investigative work then be carried in a competent manner, soil and rock profiles, groundwater conditions are described in detail using standard terminology, the necessary samples be recovered, the results are reported in full, the geotechnical evaluations and calculations are prepared by experts and the validity of the information is not disclaimed by such professionals. The eventual preparation of a comprehensive and reliable Geotechnical Investigation and Design Report to be included in the Tender Documents. It also needs to provide guidance to Contractors in assessing risks, with the preparation of tenders and with the execution of the work. In cases where existing works are to be modified and/or extended, the information obtained from the original investigations shall be used to plan additional investigations, if any. Where investigations are contemplated for New work, enquiries should be made to ascertain whether any previous investigations have been carried out in the area. Certain local authorities maintain data banks and much valuable information can be obtained from such sources. Depending on circumstances, investigations may extend from superficial visual inspections to sophisticated surface and subsurface testing. These will have to be agreed with the Client at the appropriate stage of work. D.7.2 Scope of Investigations The scope of investigations contemplated for the stages described in Chapter 6, Section 1.3, is given as a guide. These stages are mostly applicable to new “Greenfield” projects and therefore thee scope of investigations for any specific project will thus have to be modified in conjunction with the Client to suit the specific project, the circumstances and conditions.

D.7.2.1 Preliminary Investigation and/or Route Location Stage

The subsurface conditions shall be assessed by visual inspection of local ground conditions, examination of the available geological records and information contained in the section dealing with ‘Preliminary Geotechnical and Materials Report’ in this manual. At Sites for Bridges with deck areas exceeding 750 m2 , the extent of the investigation should be of a sufficient scope and nature so as to reveal whether problematic founding conditions are present or not.

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D.7.2.2 Preliminary Design (Basic Planning) Stage

Exploratory subsurface (drilling) investigations on the centre line of the road shall be carried out for those major bridges and culverts at which problematic founding conditions are expected.

D.7.2.3 Detail Design and Documentation Stage

It is essential that a general geotechnical investigation of foundations for structures, based on the findings of the preliminary (basic) design of the road, be completed before the conceptual design of any structure is contemplated. Based on these results, conceptual designs could be prepared. It is possible that during the preparation of the conceptual designs it will come to light that detailed information with regard to the foundation conditions is lacking. In this event, a further phase of the foundation investigation should be entered into during which parameters that have a direct bearing on the proposed designs may be determined. Thus, depending on the information that is available on the foundations and the extent of the planned works, a three-stage foundation investigation might be required. These stages would consist of a preliminary stage, a general investigation stage and a detail investigation stage. D.7.3 Quotations and Tenders The Geotechnical Engineer shall discuss the proposed investigations with the Client before commissioning any work on behalf of the Client. After agreement has been reached on the work to be undertaken and whether geophysical investigations are required, the engineer shall obtain at least three quotations for such geophysical investigations (refer to Section D.7.5.3), and he shall submit a report including his recommendation to the client for a ruling. After the geophysical investigations have been completed the engineer shall prepare draft tender documents for the detailed investigation which will include some or all of the following: exploratory holes, in situ testing, laboratory testing, survey to set out and pick up positions and levels of exploratory holes, profiling holes, logging cores and photographing of cores. The draft documents shall be submitted to the Client for approval before tenders are obtained for the work. In the case of SANRAL projects, documentation shall be based on the SANRAL Pro Forma document for Geotechnical Investigations, with the FIDIC General conditions for construction for building and engineering works designed by the Employer (1999). The new Standard Specification for Subsurface Investigations (2010) and any other specific Project Specifications shall apply. Open tenders shall be invited for the work unless the estimated value of the work is considered by the client to be too low to justify calling for open tenders. In such cases, contractors selected with the approval of the client, shall be invited to quote for the work. D.7.4 Responsibility for Investigations and Designs Geotechnical Investigations, the ensuing geotechnical evaluations and foundation design recommendations should be carried out and prepared by knowledgeable and experienced Geotechnical Engineers (Registered Professional Engineers). The logging/profiling of test holes/joint surveys of open rock faces, etc., should ideally be done by Engineering-Geologists (Registered Natural Scientists) or by Registered Geotechnical Engineers who are experienced in the type of investigative fieldwork envisaged. D.7.5 Extent and Sequence of Investigation This section describes the general procedure only and does not prescribe in detail how the investigations should be undertaken. The investigation normally takes place in a number of phases. (Refer to D.7.2 above). The phases include a desk study, site reconnaissance, preliminary field work, detailed investigation and verification of conditions during construction. In certain instances, the process may be iterative, with some phases being repeated prior to final site selection and commencement of detailed investigation. The Geotechnical Investigation shall be planned to obtain the necessary information at minimum cost. In planning an investigation it is important to consider the cost of the foundation and the sensitivity to foundation movement of the structural system being supported. The following is a guide to the information which may be obtained in the various phases:

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D.7.5.1 Desk Study

• Topographical maps and aerial photographs should be consulted to gain information on the general topography and prominent features.

• Geological and soil maps should be consulted to gain information on the basic geology and soils. • Local authorities and other organisations should be approached to establish whether they have knowledge of

investigations conducted in the area or have records available. The Greater Johannesburg Metropolitan Council, for example, maintains a comprehensive data bank.

• The government mining engineer should be approached for information on mining operations where such operations are known to have been undertaken.

• The study of overlapping aerial photographs through a stereoscope will usually be of value in identifying geological features such as faults, dykes, geological boundaries, rock and soil types, rock exposures, drainage patterns, etc. These features are often not apparent in the field.

D.7.5.2 Site Reconnaissance

A site reconnaissance should be undertaken to gain geotechnical information for visible features, establish the suitability of various geophysical testing methods and investigate accessibility for drilling equipment. Features such as boundary fences, gates, rail tracks, transmission lines, telephone lines, water pipes, electricity cables, exposed rock, exposed material in cuttings and quarries, depressions, sinkholes, springs, boreholes, changes in natural vegetation and damage to structures should be recorded.

D.7.5.3 Geophysical Investigations

Wherever practicable, for example on sites underlain by dolomite, where it is an essential part of the investigation, a geophysical investigation shall first be undertaken and may comprise a seismic or resistivity, or gravimetric, or electromagnetic evaluation of the subsurface conditions of sufficient extent and depth to assist in the selection of the most appropriate and economic detailed investigation, as well as in the positioning of the bases. It should be noted that a proper geophysical investigation can substantially reduce the number of boreholes required at any site. Recommended geophysical methods are summarized in Annexure 18.2.

D.7.5.4 Detailed Investigations – Exploratory Holes

D.7.5.4 (a) Purpose

The purpose of exploratory holes is to permit visual examination, testing of the in situ material and for the recovery of samples to appropriate depth.

D.7.5.4 (b) Choice of Equipment

In most instances, advantages are gained from using similar equipment, both in terms of type and capacity, for the detailed investigation as will be used for the construction of the foundations. For example, where augered piles are expected to be installed and circumstances permit, it is preferable to include the use of a large diameter auger rig similar to that which will be used for the installation of piles. This will provide a direct indication of the problems likely to be experienced during construction. Conversely, the use of a backactor for the excavation of test pits holds distinct advantages on a site where it is certain that shallow spread footings are envisaged. Rotary core drilling is often the most suitable method of investigation below water level (or below high groundwater tables), for recovery of undisturbed samples and for coring into hard materials. This would include various in situ testing methods carried out in boreholes, auger holes or trial pits. For investigating the conditions in dolomitic areas, “down the hole hammer” percussion boreholes are normally drilled, as they have been found to be the most effective. Only operators experienced in dolomite should be used for this work. The chips collected must be logged by an experienced chip logger and any voids encountered during drilling must be diligently recorded.

D.7.5.4 (c) Sequence of Work

Generally hand or machine (backactor) excavated test pits would be used first, followed by large diameter auger holes (if access is possible), and finally small diameter cored holes if necessary. Planning should be flexible enough so that the work can be varied as necessary in the light of fresh information. To obtain the greatest benefit from the investigation, it is essential that there is adequate direction and supervision of the work by competent personnel who have appropriate knowledge and experience and the authority to decide on variations to the investigation when required.

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D.7.5.4 (d) Safety and Personnel and the General Public

The safety requirements specified in the new SAICE Code of Practise on the Safety of Men working in Small Diameter Shafts and Test Pits for Geotechnical Engineering Purposes (2008) and in the new Standard Specifications for Subsurface Investigations (2010), shall be complied with, as well as those in the Occupational Health and Safety Act (Act 85 of 1993) including the new Regulations.

D.7.5.4 (e) Spacing and Depth

The foundation investigation shall cover the full length and width of the structure including the approach embankments. Additional holes may be required beyond the extent of the structure to establish the locations of geological discontinuities In general, for bridges the number of exploratory holes required depends on the lengths of the individual bases, information gained from investigations and the variability of the subsurface conditions. The following is a rough guide for the initial selection of the number of exploratory holes at each base:

Length of bases Recommended Number of Exploratory Holes at Each Base

Up to 5 m 1 Between 5 and 15 m 2 Between 15 and 30 m 3 Longer than 30 m 4

Where one hole per base is required, the holes shall be located at alternating ends of the individual bases. A minimum of two holes is required at each river bridge base, unless reliable information indicates uniform conditions. For culverts and retaining walls, where exploratory holes are required, the initial pattern of holes should be staggered along the length of the structure. The holes shall be placed approximately 15 m apart. For approach embankments, where exploratory holes are required, the initial layout of the holes should be a grid pattern with the holes about 30 m apart measured along the road centre line and at 20 m apart measured at right angles to the road centre line.

D.7.5.4 (f) Preparation of Records, Logging and Profiling

This work shall be in accordance with the prescriptions given in the SAPEM Appendices and in the appropriate chapters in the new Standard Specifications for Subsurface Investigations (2010), including specified additional Project Specifications (for the specific project in hand) in this regard.

D.7.5.4 (g) Material of Archaeological Interest

If material is exposed which may be of archaeological or palaeontological interest, work at that location shall be stopped immediately. The area shall be fenced off and the engineer shall refer the matter to the National Monuments Council for assessment in order that further procedures may be planned. D.7.6 Geotechnical Investigation Design Report NB: This section must be read in conjunction with Section 2.2.3 in Chapter 7. NOTE: The Geotechnical Investigation and Design Report shall be signed by both the Compiler/Writer of the report and by the Geotechnical Engineer who planned/supervised the investigation, evaluated the results, prepared the geotechnical/foundation design parameters and recommended the most appropriate foundation type. NB: The Geotechnical Investigation Design Report shall always also serve the purpose of a Design Report w.r.t. the geotechnical components (such as bridge foundations or toll-building foundations) of a road project, i.e., the report shall contain geotechnical parameters for design and shall also provide clear guidance to the Structural/Bridge Design Engineers (guidance as prepared by the Geotechnical Engineer who carried out the geotechnical investigation) enabling the selection of the most appropriate solution and foundation type for each building or structure/bridge and its particular allowable differential settlements. [Or, the required details contained in the Report for example pertaining to high embankments/deep cuttings/lateral support measures, is normally aimed at the attention of the Road Engineer.]

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The responsible Geotechnical Engineer shall also evaluate and elaborate in the Report on alternative foundation systems and/or solutions, if ground conditions or depth to a competent founding horizon suggest such a possibility. Settlement and load capacity analyses/calculations should be summarised in the report. Lateral support/slope stability analyses/calculations, as well as alternative solutions, shall be summarised as well. This Geotechnical Investigation Design Report shall thus not only contain all of the necessary soil/rock (and/or groundwater) parameters required for the design of the proposed high embankments and/or deep cuttings, but shall also give clear guidance with respect to the proposed foundation (or pile type) for each bridge/major culvert /minor culvert, including the respective approach embankments. The reason for this requirement, over and above the fact that it is any case required from a Quality Assurance point of view, is that in some cases, depending on the type of tender documentation, or depending on the structuring or phasing of the project by individual Road Authorities, the detailed designs of foundations/piles/abutments or of lateral support systems are in many cases eventually the responsibility of another Geotechnical Engineer who was never involved in the original Geotechnical Investigation. To include and to provide all the necessary interpreted geotechnical design parameters are therefore an essential and vital element in any geotechnical investigation design report. The Report shall be compiled under the headings and in the sequence listed below: • Introduction • Description of the site(s) * • Geology, soil profile and water table* • Investigations carried out * • Test results/data • Geotechnical evaluation * • Evaluation of alternative foundation systems/types * • Recommendations * • References • Annexures Note: * The items marked * shall be dealt with under the heading of each structure for which investigations had been conducted.

[The Geotechnical Investigation Design Report including appropriate Appendices thereof as directed by the Project Manager, need to be bound into the Volume 6 section of the tender documents (see Section 14.2.5). The Volume 6 report, together with the inspection of the site, shall provide the contractor with sufficient information to reasonably anticipate any problems that may occur during execution of the works. This will enable the contractor to tender a realistic price for the construction of the work and to select the most appropriate equipment and techniques]. The aspects covered under the above-mentioned headings shall include, but not be limited to, the following, as relevant:

D.7.6.1 Introduction

• Terms of reference and description of the project, with specific reference to the structures involved. • Description of the stage, as described in Chapter 6, Section 1.3, and the purpose for which the investigation was

conducted.

D.7.6.2 Description of the Site(s)

• Location of the site(s) • Accessibility of the site(s) • Trafficability of the site for construction equipment • Listing of sources from which data is available or was obtained • Description of regional geology, geomorphology, topography, vegetation, drainage and other general features of

importance

D.7.6.3 Geology, Soil Profile and Water Table

• Formation(s) underlying site • Typical soil profiles described

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• Water table information • Geological cross-section provided if applicable

D.7.6.4 Investigations Carried Out

• Name(s) of firm(s) responsible for the field work (consultant, contractor) • Name(s) of person(s) responsible for the interpretation of the geophysical work and for the profiling and/or core

logging. • Date(s) on which the work was conducted • Description of the types of field work undertaken number of pits, auger holes or boreholes and probes, and

equipment used • Laboratory testing programme on soils/rock, (including groundwater quality testing w.r.t. possible effect on

concrete)

D.7.6.5 Test Results

• Summary of test results • Discussion of results (factual)

D.7.6.6 Geotechnical Evaluation

• Discussion of “stability classes” (if on dolomite formation). • Evaluation/interpretation of the soils encountered, identifying their stability or potential problems they may

present, e.g., tendency to heave, collapse, settle. • Evaluation/interpretation of hard rock geology (if encountered) identifying the type, quality, strength, degree of

weathering, fracturing, excavatability classes. [Mention reference used to arrive at excavatability classes.] • Provide geotechnical/foundation design (or pile design) parameters, etc. • Potential for boulders and other obstructions to be encountered in deep seated foundations. • Discussion/interpretation of problems experienced during investigation or to be expected during construction. • Discussion/interpretation of groundwater table(s) and expected variations. • Discussion/interpretation of field and laboratory testing (including chemical tests) carried out, i.e.,

- Evaluation of results obtained and comments on their reliability. - Evaluation of in situ testing results/geophysical investigations.

D.7.6.7 Evaluation of Alternative Foundation Systems/Types

• Discuss and evaluate alternative foundation types, with pros and cons to be considered by bridge or structural engineers.

• Motivate preferred foundation (or pile) type

D.7.6.8 Recommendations

• Excavatability classes (i.r.o conventional foundations and caissons, or for piling). • Maximum tolerable total settlement(s) and maximum tolerable differential settlement(s) applicable to the various

bridge foundation components, as obtained from bridge design engineer. • Type of foundation best suited. • Founding options to be considered. Estimated safe bearing pressure and settlement for the respective

materials/depths on which founding could be considered. • Recommended founding depth and allowable bearing pressure at that depth. • Precautionary protective measures against corrosion of concrete/ steel. • Recommended pile type (if piling seems essential). • Recommended design parameters e.g. friction values and rock socket parameters for the design of piles. • Specified FOS to be designed for piling; applicable pile design code. • Recommended supplementary geotechnical investigations to be conducted, or to allow for during construction

phase (if any). • Construction problems anticipated.

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D.7.6.9 References

• List reference for the classification of materials in respect of soil condition and rock hardness and excavatability classes.

• Others as applicable to the investigation, evaluation, or to the recommendations.

D.7.6.10 Annexures

• Locality plan to appropriate scale • Results of geophysical investigations (if any) • Borehole, auger hole and test pit logs (with coordinates and elevations) • Photographs of borehole cores recovered • Laboratory test results/In situ testing results • Geological cross-section (s) drawings (if appropriate) • Drawings to scale, for each bridge/ major culvert or other structure, showing the location(s) including levels of all

positions investigated, physical features of the site and setting out points in relation to proposed bridge foundation layout(s).

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ANNEXURE 18.2: GEOTECHNICAL INVESTIGATIONS

Table 18.2.1: Geophysical Methods in Ground Investigation [Table 3, BS 5930 (1981)]

Problem Example Method And Remarks Geological Stratigraphical Sediments over bedrock

(i) Sands & gravels over bedrock, water table low in sands & gravels (ii) Sands & gravels overlying clay, water table high in sand & gravels (iii) Clay over bedrock Sediments over bedrock generally

Land Seismic refraction Resistivity Resistivity or seismic refraction Marine Continuous seismic reflection profiling

Erosional (for caverns; see shafts below)

Buried Channel Buried karstic surface

Seismic Refraction Resistivity for feature wider than depth of cover Resistivity contouring

Structural Buried fault, dykes Resistivity Contouring Seismic reflection or refraction Magnetic gravimetric (large faults)

Resources Water Location of aquifer Location of saline/potable interface

Resistivity and seismic refraction

Sand and gravel Sand, gravel over clay Gravel banks

Land: Resistivity Marine: Continuous seismic profiling, side scan sonar, echo sounding

Rock Intrusive in sedimentary rocks Magnetic (weathering may give low resistivity)

Clay Clay pockets Resistivity Engineering parameters

Modulus of elasticity, density and porosity

Dynamic deformation modulus Check on effects of ground treatment

Seismic velocity at surface, or with single or multiple boreholes (cross hole transmission) Boreholes geophysics

Rock rippability Choice of excavation methods Seismic (velocities at surface) Corrosivity of soils

Pipeline surveys Surface resistivity, redox potential

Buried artifacts

Cables Pipes

Trenches on land Submarine trenches Submarine pipelines

Magnetometer Electromagnetic field detectors Echo sounding, side scan sonar Side scan sonar, magnetic, continuous seismic profiling (especially if thought to be partially buried) with high frequency pinger

Shafts, adits and caverns

Shaft, sink holes, mine workings Resistivity Magnetometer contouring, infra-red air photography on clear areas Cross hole transmission Detailed gravity for large systems

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ANNEXURE 18.3: TESTS

Table 18.3.1 Some Laboratory Tests on Soils

Test Material Sample Type

Remarks References

Gradings Analysis Sieving Sedimentation

Granular soils and gravels Cohesive and fine grained soils

D

D

Usually carried out in conjunction with Atterberg limit tests to give an indication of the soil behaviour and to classify the soil

SANS 3001 BS 1377 (1975)

Atterberg Limits Cohesive and fine grained soils D Plastic limit, liquid limit, plasticity index and linear shrinkage. Give indication of soil behaviour

SANS 3001

Moisture Content Soil or rocks D/U Frequently carried out as part of other tests. Required for determination of degree of saturation Essential for expansive clay investigations

SANS 3001 BS 1377 (1975)

Specific Gravity Soils or rocks D Used in conjunction with other tests such as density, moisture content and sedimentation

SANS 3001 BS 1377 (1975)

Bulk Density Soils D/U May be carried out on undisturbed samples in the lab Cohesionless soils must be tested in situ Used with above two tests to determine degree of saturation and void ratio

SANS 3001 BS 1377 (1975)

Triaxial Compression Undrained unconsolidated Consolidated undrained with p.w.p. measurements Consolidated drained

Saturated, normally consolidated clays Saturated normally consolidated clays Partially saturated clays (soaked) Clayey sands, sandy, clays, silts Partially saturated clays (soaked)

U

U

U

U

Undrained shear strength (Ф=0) Short term stability In fissured clays, sample size has a significant effect Effective strength parameters (c’, Ф’) Effective strength parameters (c’, Ф’) Long term stability

Bishop & Henkel (1962) Marsland (1971) Bishop & Henkel (1962) Akroyd (1957) Bishop & Henkel (1962) Akroyd (1957)

Direct Shear Box Immediate (b) Drained

Saturated clayey sands, silts and clays Clayey sands, sandy clays & silts Dry or saturated sands

U

U R

Undrained shear strength. Triaxial tests generally preferred Effective strength parameters (c’, Ф’) Angle of shearing resistance (c’=0)

Akroyd (1957) Akroyd (1957) Akroyd (1957) Bishop (1948)

Unconfined Compressive Strength

Saturated intact clays U Simple and rapid substitute for undrained triaxial test

Akroyd (1957)

One Dimensional Consolidation Triaxial Consolidation Rowe Cell Consolidation

Cohesive and fine grained soils Cohesive and fine grained soils Recompacted sands Cohesive and fine grained soils

U

U R

U/R

Gives measure of compressibility, pre-consolidation pressure and coefficient of consolidation. Triaxial consolidation gives measure of elastic modulus Rowe cell uses larger samples and confining pressure may be varied

Akroyd (1957) Akroyd (1957) Bishop & Henkel (1962) Rowe & Barden (1966)

D = Disturbed

I = In situ

R = Remoulded

U = Undisturbed

D – 10

Table 18.3.2. Some Laboratory Tests on Rock

Test Material Sample Type

Remarks References

Moisture Content, Bulk Density, Porosity

All rocks C/L Gives indication of strength, modulus of elasticity and degree of weathering

Int Soc Rock Mech (1979)

Swelling Test Mainly argillaceous rocks

C/L Indicates moisture sensitivity of rock and possible volume changes

Duncan et al (1968)

Point Load Test Isotropic rocks C/L Quick and cheap indicator of rock strength Useful aid to core logging

Uniaxial Compression Test

Most rocks which can be cored

C Strength of intact rock Upper limit for jointed rock mass strength Widely used for predicting bearing capacity and skin friction Gives elastic properties of “intact” rock core if strain is measured This will over-estimate modulus of jointed rock

Hoek (1977) Hawkes & Mellor (1970) Clark (1966)

Triaxial Compression Test

Very soft/soft rock “intact” weathered rock

C As above Only weak rocks may be tested with commonly available equipment

Hoek (1977)

Direct Shear Box Test

Usually applied to rock discontinuities or intact rock

L/I Gives shear strength along discontinuities or of intact soft rocks

Hoek (1977)

C = Core Sample I = In situ L = Lump Sample

D – 11

Table 18.3.3. Some In Situ Field Tests

Test Material Remarks References Standard Penetration Test (SPT)

Mainly sands and weak rocks Also used on other soils

Refer CSRA Standard Specifications for Subsurface Investigations Performed generally at 1.5 m intervals in boreholes Gives indication of consistency/relative density of soil Results correlated with many soil properties and empirical design methods

Webb (1976) SAICE & NITRR (1978) Sanglerat (1972) Ervin (1983)

Dynamic Cone Test or Dynamic Spoon Test

Most soils Performed by driving cone or spoon with no intermediate drilling or reaming of hole Not as widely accepted as SPT test but cheaper to perform Disturbed sample obtain from spoon test Results correlated with SPT results

Webb (1976) SAICE & NITRR (1978) Sanglerat (1972) Ervin (1983)

Static Cone Test (Dutch Probe)

Loose granular soils and soft to firm clays

Gives point resistance (cone) and total resistance (cone and friction sleeve) Results correlated with bearing capacity and compressibility

TMG6 (1984) Webb (1976) SAICE & NITRR (1978) Sanglerat (1972) Ervin (1983)

Piezocone Saturated, loose, granular soils and soft to firm clays

Tip resistance, sleeve resistance and dynamic pore pressure are measured while continuously driving the probe into the ground

Clemence (ED) (1986)

Pressuremeter Soils and weak rocks Pressuremeters may either be inserted into boreholes, be driven into the ground in a slotted casing or be self boring Results give indication of elastic modulus and soil strength

SAICE & NITRR (1978) Menard (1965) Windle & Wroth (1977) Ervin (1983)

Goodman Jack Soft to hard rocks Jack inserted into NX sized borehole Rock loaded by curved plates and deformations measured May be installed in horizontally drilled holes and rotated to determine degree of anisotropy Results give indication of elastic modulus of in situ rock mass

Goodman et al (1968)

Piezometer All soils and rocks Used to determine groundwater pressure at various depths in the ground In permeable ground, standpipe piezometers are used; but in impermeable conditions or where rapid response is required, hydraulic, pneumatic or electric piezometers are used

SAICE & NITRR (1978) BS 5930 (1981) Penman (1960)

Vane Shear Test

Saturated cohesive soils Normally restricted to saturated clays with an undrained shear strength of less than 100 kPa This method can give peak and residual undrained shear strengths

SAICE & NITRR (1978) BS 5930 (1981) Ervin (1983)

Plate Bearing Test

Moist soils and soft rocks Generally above water table

Test performed in trench or auger hole by jacking circular plates against the soil/rock May be carried out horizontally (across width of hole) or vertically (jacking against a kentledge) Size of plate depends on the zone of influence and hole size and stiffness of material generally 75 – 300 mm for horizontal tests and 200 – 1000 mm for vertical test

Ervin (1983) Wrench (1984)

E - 1

SAPEM CHAPTER 7: APPENDIX E

EXAMPLES OF SPECIAL ROADBED TREATMENT TYPES

For SANRAL projects: To be entered onto soil survey drawings in SANRAL’s Volume 6 & Detailed Design Drawings, and in Tender Documents.

Roadbed Type

Description Explanation

A1 COLTO Clause 3305(b) Three-pass roller compaction A2 COLTO Clause 3305(c) Preparing and compacting the in situ roadbed (ISRB)

to 90% MOD AASHTO density

B COLTO Clause 3305 (c) As above but the in situ roadbed can be processed in situ and compacted on 90% MOD AASHTO density

C1 COLTO Clause 3305 (d) In situ treatment of the roadbed by ripping the rock at roadbed level to be processed as BSL (bottom selected layer) according to COLTO Clause 3304 (b)

C2 COLTO Clause 3305 (d) As above but blasting the rock at roadbed level to be processed as BSL

D CUT OR FILL

This special treatment shall comprise of the following over and above benching in as required: (see Drawings) • Draining the roadbed in accordance with COLTO Clause 3305 (e) • Removing unsuitable material to a minimum depth of 400mm below BSL,

even if in cut, in accordance with COLTO Clause 3305 (a) • Provisional geotextile (type….. or similar) at minimum depth of 650mm

below BSL • 500mm (minimum) Compacted pioneer rock layer (provisional 250mm

penetration) • Compacted blinding fill separation layer of 150mm thickness on top of

pioneer layer • Fill layers, if in fill as specified • (Structural layers as specified)

For seasonal soggy conditions of limited depth (< 1 m)

E FILL

This special roadbed treatment shall comprise of the following over and above benching-in as required: (see Drawings) • Draining the roadbed in accordance with COLTO Clause 3305 (e) • Removing unsuitable material to specified depth (950mm) below fill

layers (or in exceptional cases below BSL) in accordance with COLTO Clause 3305 (a)

• Provisional heavy duty geotextile (type ….. or similar) at reduced excavation level

• 750 mm (minimum) Compacted pioneer rock layer (provisional 250 mm penetration)

• 300 mm Sifted gravel filter blanket layer of top of pioneer layer • 150 mm Compacted blinding fill separation layer on top of pioneer layer • 150mm Compacted blinding fill separation layer on top of filter blanket

layer • (Structural layers as specified)

For permanent soggy conditions overlain by ≥ 1m of unsuitable soils

This special treatment shall comprise of the following over and above benching in as required: (see Drawings) • Draining the roadbed in accordance with COLTO Clause 3305 (e) • Removing unsuitable material to specified depth (1950mm) below fill

layer (or in exceptional cases below BSL) in accordance with Clause 3305 (a)

• Provisional heavy duty geotextile (type …… or similar) at reduced excavation levels

• 17500 mm (minimum) Compacted pioneer rock layer (provisional 250 mm penetration)

• 300 mm Sifted gravel filter blanket layer of top of pioneer layer • 150 mm Compacted blinding fill separation layer on top of pioneer layer • 150 mm Compacted blinding fill separation layer on top of filter blanket

layer • Fill layers, as specified • (Structural layers as specified)

For permanent soggy conditions overlain by ≥ 2 m of unsuitable soils