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  • T H I R D E D I T I O N

    A Guide to Practical

    GEOTECHNICALENGINEERING

    in Southern Africa

    First Edition January 1976 written and compiled byIH Braatvedt Pr Eng, BSc (Eng), MICE, FSAICE

    Second Edition December 1986 revised and updated byJP Everett Pr Eng, BSc (Eng), FSAICE

    Third Edition July 1995 re-written and updated byG Byrne Pr Eng, BSc (Eng), MSAICE

    JP Everett Pr Eng, BSc (Eng), FSAICEK Schwartz Pr Eng, BSc (Eng), GDE, FSAICE

    assisted by

    EA Friedlaender Pr Eng, BSc (Eng), MSAICEN Mackintosh NH Dip (Civ Eng), MSAICE

    C Wetter BSc (Eng)

  • THE PURPOSE OF THIS BOOK

    When Frankipile South Africa first published "The Guide" in 1976 the main purpose was tocreate a practical reference on all aspects of soil investigation and piling as carried out by thecompany in Southern Africa at that time. Judging from the popularity of the first edition thisobjective was achieved and most design engineers in Southern Africa have a copy on theirbookshelves.

    The second edition was published in 1986 as an update of the first and it was equally popular.

    This, the third edition, is in fact a re-write of the book as Frankipile has expanded its activitiesinto soil improvement and lateral support as well as environmental engineering. The name ofthe Guide has thus changed to include all aspects of Geotechnical Engineering as carried out bythe Company in Southern Africa.

    The purpose of the book, however, remains the same; it is a reference with a wealth of practicalinformation on geotechnical topics which we are confident all those who receive a copy willfind extremely useful.

    The contents of this book are presented in good faith. As in all geotechnical design the methodsand data presented in the book must be interpreted and used with a degree of knowledge,experience and judgement. Frankipile South Africa (Pty) Ltd does not hold itself in any wayresponsible for any inaccuracies or errors in the book or for any interpretation thereof bypersons other than its own employees.

    The company acknowledges, with appreciation, the contribution by Messrs. OVE ARUP &PARTNERS to the section on pilecap design.

  • FOREWORD

    by PROFESSOR KEN KNIGHT

    Over the twenty years since Ian Braatvedt wrote the original Guide to Piling and Foundation

    Systems the book has become a standard text for all those in the industry in Southern Africa. It

    is also widely used by many outside the industry and don't be surprised i/you come across a

    copy in any country of the world.

    What has made the Guide such a valuable text is the wealth of practical information it contains

    on piling as well as a number of other geotechnical topics.

    Franki's product diversification has been dramatic since the publishing of the second edition in

    1986. Through its subsidiary GeoFranki the company has entered the lateral support market

    and has considerably increased its market share in soil improvement. There have been other

    product improvements which have been developed and the company is also involved in

    environmental engineering. These developments are all part of Franki's ongoing drive for

    improvement which is backed up by some of the most experienced geotechnical engineers in the

    country.

    With all the changes it is not surprising that John Everett and his editorial team decided that

    the third edition of the Guide had to involve a change in name which in turn signifies that the

    book now covers a much wider cross section of geotechnical engineering. As such this edition

    will no doubt prove an even more valuable reference.

    PROFESSOR K. KNIGHT PrEng

    Durban, July 1995.

  • CONTENTSPage

    1.0 FRANKIPILE SOUTH AFRICA (PTY) LIMITED 1

    2.0 GEOTECHNICAL INVESTIGATION 42.2 FIELD INVESTIGATION TECHNIQUES 92.3 GEOTECHNICAL ENGINEERING LABORATORY SERVICES 27

    3.0 SOIL AND ROCK CLASSIFICATION AND DESIGN PARAMETERS 303.1 NOTES ON SOIL PROFILING 303.2 NOTES ON ROCK MASS DESCRIPTION 373.3 INTERPRETATION OF GEOTECHNICAL INVESTIGATION AND

    LABORATORY / IN-SITU TESTING DATA 43

    4.0 FACTORS INFLUENCING THE SELECTION OF A PILE TYPE 61

    5.0 CLASSIFICATION OF PILING SYSTEMS 63

    6.0 SUMMARY DETAILS OF PILING SYSTEMS 64

    7.0 TECHNICAL DETAILS OF PILING SYSTEMS 667.1 FRANKI DRIVEN CAST-IN-SITU PILES 667.2 DRIVEN TUBE PILES 767.3 PRECAST PILES 827.4 STEEL H-PILE 897.5 TIMBER PILES 937.6 AUGER PILES 957.7 UNDERSLURRY PILES 1037.8 CONTINUOUS FLIGHT AUGER (CFA) PILE 1127.9 FORUM BORED PILE 1177.10 OSCILLATOR PILE 1227.11 CAISSON PILES 127

    8.0 UNDERPINNING 1318.1 OLD FOUNDATION REMOVED AND NEW FOUNDATION

    PROVIDED 1338.2 NEW FOOTING LOCATED UNDER THE EXISTING ONE 1348.3 JACK PILES UNDER THE EXISTING FOUNDATION 1368.4 PILES ALONGSIDE THE EXISTING FOUNDATION 1388.5 NEW PILED FOUNDATION AND COLUMN 1398.6 PILES THROUGH EXISTING FOUNDATION 139

    9.0 PILE LOAD AND INTEGRITY TESTING 1429.1 PILE LOAD TESTING 1429.2 INTEGRITY TESTING OF PILES 147

    10.0 FACTORS INFLUENCING THE SELECTION OF A SOIL IMPROVEMENTSYSTEM 151

    11.0 CLASSIFICATION OF SOIL IMPROVEMENT SYSTEMS 153

  • 12.0 SUMMARY DETAILS OF SOIL IMPROVEMENT SYSTEMS 154

    13.0 TECHNICAL DETAILS OF SOIL IMPROVEMENT SYSTEMS 15613.1 VIBRATORY COMPACTION 15613.2 DYNAMIC COMPACTION 16113.3 COMPACTION GROUTING 16613.4 VIBRATORY REPLACEMENT 16813.5 DYNAMIC REPLACEMENT 17113.6 DRIVEN STONE COLUMNS 17313.7 ACCELERATED CONSOLIDATION 17513.8 JET GROUTING 17813.9 LIME COLUMNS 180

    14.0 FACTORS INFLUENCING THE SELECTION OF A LATERAL SUPPORTSYSTEM 182

    15.0 CLASSIFICATION OF LATERAL SUPPORT SYSTEMS 184

    16.0 SUMMARY DETAILS OF LATERAL SUPPORT SYSTEMS 188

    17.0 TECHNICAL DETAILS OF LATERAL SUPPORT SYSTEMS 19017.1 STEEL SHEET PILES 19017.2 STEEL SOLDIERS 19717.3 CONCRETE SOLDIER PILES 20017.4 CONTIGUOUS AND SECANT PILE WALLS 20317.5 DIAPHRAGM WALLS 20617.6 PROP SUPPORTS 21017.7 POST STRESSED ANCHORS 21217.8 ANCHOR PILES 21817.9 GEONAILS 22017.10 RETICULATED MICROPILES 22517.10 SOIL DOWELLING 227

    18.0 PROBLEM SOILS AND THEIR FOUNDATION SOLUTIONS 22818.1 EXPANSIVE SOILS 22918.2 COLLAPSIBLE SOILS 23418.3 SOFT CLAYS 23618.4 DOLOMITES 238

    19.0 ENVIRONMENTAL ENGINEERING 24119.1 GROUNDWATER MONITORING 24119.2 MONITORING OF SURFACE WATER 24219.3 CONTAINMENT / REMEDIATION 242

    20.0 DESIGN AIDS: PILING 24520.1 PILE CAPACITY TO RESIST COMPRESSIVE LOAD 24520.2 PILE CAPACITY TO RESIST UPLIFT LOAD 26020.3 PILE CAPACITY TO RESIST LATERAL LOAD 26220.4 THE DESIGN OF PILES FOR HEAVING SUBSOIL CONDITIONS 26520.5 FACTORS OF SAFETY 26820.6 ANALYSIS AND DESIGN OF PILE GROUPS 27020.7 SETTLEMENT OF A SINGLE PILE AND PILE GROUPS 273

  • 20.8 STRUCTURAL DESIGN OF PILE SHAFTS 28020.9 STRUCTURAL DESIGN OF PILE CAPS 284

    21.0 DESIGN AIDS: SOIL IMPROVEMENT 30121.1 SOIL COMPACTION 30121.2 SOIL REPLACEMENT 30621.3 ACCELERATED CONSOLIDATION 310

    22.0 DESIGN AIDS: LATERAL SUPPORT 31222.1 DESIGN PARAMETERS 31222.2 EARTH PRESSURES 31422.3 WATER PRESSURES AND SURCHARGE LOADS 31622.4 EXTERNALLY STABILISED SYSTEMS 31922.5 INTERNALLY STABILISED SYSTEMS 32622.6 FACTORS OF SAFETY 33022.7 MOVEMENTS ASSOCIATED WITH EXCAVATION 332

    23.0 REFERENCE INFORMATION 33423.1 NORMAL PLANT CLEARANCE REQUIREMENTS 33423.2 PILING RIG DIMENSIONS 33623.3 BENDING MOMENTS IN BEAMS 34023.4 MENSURATION OF PLANE SURFACES 34123.5 MENSURATION OF SOLIDS 34223.6 PROPERTIES OF SECTIONS 343

    24.0 QUALITY ASSURANCE 344

    REFERENCES 347

    INDEX 352

  • 11.0 FRANKIPILE SOUTH AFRICA (PTY) LIMITED

    The South African company in the worldwide Franki group was started by Mr. WallyRowland in 1946. The initial seeds had already been sown early in 1939 but the secondWorld War broke out in September and Wally joined up with the South African forces.

    At the end of the war The Franki Piling Company of South Africa, as it was initially named,was registered and the first contract was secured. This involved the installation of eight pilesfor a building in Paarden Eiland and a steam driven piling machine was used to install thepiles which were standard Franki driven cast-in-situ piles.

    By 1952 Franki had branch offices in Johannesburg, Cape Town and Durban. In 1955 WallyRowland returned to the UK to take up the position of Assistant Works Director with theBritish Franki company.

    Ian Braatvedt took over as Managing Director in 1961 and under his guidance the companygrew steadily. Large contracts such as the Alusaf Bayside Smelter in Richards Bay, theMondi Paper Mill in Durban and Iscor Steel Works in Newcastle were secured in the latesixties and early seventies and these really helped Franki to establish itself as the leadingpiling company in the country .

    In 1968 Franki started a soil investigation subsidiary which is known as Soiltech. Today ithas a full complement of soil investigation and field testing equipment as well as a fullyequipped soils laboratory .It has recently entered the environmental investigation field.

    The need to diversify into other geotechnical fields led to the formation of GeoFranki in1987. GeoFranki's main areas of activity are lateral support, ground improvement,micropiling, grouting and cut-off walls.

    The South African company today has over forty major production rigs and an employeecomplement in excess of 600. It has offices in Johannesburg, Cape Town, Durban andHarare. It operates in Africa and the Indian Ocean Islands.

    FRANKI INTERNATIONALFrankipile South Africa is a wholly owned subsidiary of SA Franki BV which is a Belgiancompany. SA Franki BV has a number of subsidiaries around the world and interests in manyother international companies and this group is commonly referred to as Franki International.

    There is continual commercial and technical communication within the group as well as acommon product development interest. Frankipile South Africa can thus draw on thisinternational experience as well as obtain additional plant resources and personnel from thegroup if and when such a demand arises.

  • 2The following is a summary of the products and services which Frankipile South Africa andits subsidiaries can presently offer its clients and which are described in greater detail in thisguide.

    FIELD INVESTIGATION PILING

    Auger trial holes Franki cast-in-situ pile Test pits Driven tube pile Bulk and undisturbed sampling Precast pile Dynamic cone penetration test Steel H-pile Cone penetration test Timber pile Rotary core drilling Auger pile Standard penetration test Underslurry pile Vane shear test Continuous Flight Auger (CFA) pile Pressuremeter test Forum Bored pile Lugeon test Oscillator pile Piezometer installation Caisson pile Shelby and piston tube sampling Core orientation UNDERPINNING Rotary percussion drilling Plate load test SOIL IMPROVEMENT In-situ density test Geophysical techniques Vibratory compaction Ground water monitoring Dynamic compaction Well installation Compaction grouting Environmental investigation Vibratory replacement

    Dynamic replacementLABORATORY TESTING Driven stone columns

    Accelerated consolidation Triaxial compression Jet grouting Unconfined compression Lime columns Shear box Permeability LATERAL SUPPORT Odeometer Grading/Sieve analysis Steel sheet piles Hydrometer Steel soldiers Atterberg limits Concrete soldier piles Bulk density Contiguous/Secant pile walls Moisture density relationship Diaphragm walls California bearing ratio (CBR) Geonails PH Reticulated micropiles Conductivity Soil dowelling

    Tie back anchors

  • 3Frankipile South Africa has always adopted a policy of combining innovative design withmany years of practical experience to provide the most economical solution to a geotechnicalproblem. The company thus maintains a strong design capability as well as its professionallyrun contracting activities. Whilst not directly marketing this design capability, Franki makesevery use of it in negotiations with clients and in tenders where alternate designs arepermitted. The fact that Franki can offer the wide selection of products and services indicatedabove also results in the economic optimisation of design and so it is not surprising that thecompany secures a large percentage of its work through negotiation and through innovativedesign.

    With this considerable expertise Franki can offer a complete package deal includinginvestigating the site, the complete design of the foundation system and any lateral supportrequirements, pricing and drawing up the contract, execution of the work and final handover.It also has strategic partners it can draw on to form joint ventures where it considers thecombined skills and resources of the partners will provide the client with a morecomprehensive service and at a more competitive price.

    This is very much the case, for example, on large marine construction projects where Frankihas the piling and other geotechnical skills which are often a major feature of marine work. Ajoint venture partner with general marine civil experience thus forms a strong combinationwith which to tackle the design and construction of any marine contract. This type ofarrangement, however, is not limited to marine construction but can be arranged for any civilor building project with a significant geotechnical content.

  • 42.0 GEOTECHNICAL INVESTIGATION

    Soiltech, the division of Frankipile responsible for Geotechnical Investigations wasestablished in 1968 and offers a complete Geotechnical Service to consulting engineers andclient bodies as well as to the Company. The importance of obtaining adequate and reliableknowledge of sub-surface conditions at a sufficiently early stage cannot be over emphasisedwhen considering:

    The choice and design of an economical and technically sound foundation. Possible delays and additional expense due to inadequate soils information. Expensive foundation failures or overdesign. Potential contractor's claims based on inaccurate and/or inadequate soils information.Soiltech is able to offer a complete geotechnical investigation service comprising:

    Planning of the investigation. Execution of the field work and laboratory testing. Interpretation and reporting.The range of field work and laboratory testing that Soiltech can offer is outlined below inTable 2.0.l.

    Table 2.0.1- Range of Soiltech Services

    FIELD INVESTIGATION ANDIN-SITU TESTING

    LABORATORY TESTING

    Auger trial holes. Triaxial compression tests Test pits. Unconfined compression tests Bulk and undisturbed soil sampling. Shear box Dynamic cone penetration tests. Permeability Cone penetration tests. Oedometer test Rotary core drilling Grading/sieve analysis Standard Penetration Tests. Hydrometer Vane shear tests Atterberg limits Pressuremeter tests. Moisture density relationship Lugeon tests California bearing ratio (CBR) Piezometer installations Specific gravity Shelby and piston tube sampling Bulk density Core orientation pH Rotary percussion drilling Conductivity Vertical and horizontal plate load tests In-situ density tests Geophysical techniques Monitoring well installations Ground water monitoring and sampling

  • 5A further important aspect of Soiltech's activities lies in the environmental engineering field.This service provides for the collection of data with respect to potentially contaminated soils,surface and ground waters. For further details refer to SECTION 19.0 ENVIRONMENTALENGINEERING.

    2.1 GUIDE FOR PLANNING A GEOTECHNICAL INVESTIGATION

    The objectives of a geotechnical investigation may embrace any combination of thefollowing. (British Standard Code of Practice B35930: 1981):

    To assess the general suitability of the site for the proposed engineering works. To enable an adequate and economical design to be prepared- To foresee and provide against difficulties that may arise during construction owing to

    ground and other local conditions. To determine the causes of defects or failure in existing works and the remedial measures

    required. To advise on the availability and suitability of local materials for construction purposes.Taking the above objectives into consideration, the planning of a geotechnical investigationwill be influenced by the following main factors:

    The nature of the proposed engineering development. "If you do not know what you arelooking for in a site investigation you are not likely to find much of value" (Glossop,1968).

    The Geology and Geomorphology of the site. Access to and the remoteness of the site. The site topography, vegetation and drainage. The nature of adjacent developments. Knowledge of previous geotechnical investigations or foundation installations carried out

    in the area. In particular the opinions of persons such as local engineers, farmers andcontractors.

    Evidence of problem soil conditions (expansive or collapsible soils, dolomites, dispersivesoils, soft clays).

    The cost of an adequate investigation is very low in comparison to the total cost of theproject. The consequences of not providing sufficient, accurate and reliable geotechnicalinformation, however, can have a significant effect on a project and can lead to delays andextras during construction with associated costly claims. Experienced engineers have come torealise that a thorough geotechnical investigation is invariably paid for by the client, whetherit is carried out or not.

    If appropriate, the planning of a geotechnical investigation should be carried out in a phasedapproach. Phase one is an initial investigation to determine the site geology and to

  • 6define the problem. This is followed by phase two which is a far more extensive investigationin which the site geology is studied in greater detail and all the design parameters aredetermined. The phased approach will generally commence with a desk study and sitereconnaissance, followed by the fieldwork and laboratory testing.

    Conditions vary from site to site. Consequently, a variety of techniques has been developedto enable both the geotechnical engineer and specialist contractor to select the appropriateinvestigation procedures.

    An accurate description of the soil profile forms the basis of the geotechnical investigation.In some cases this maybe all that is required. In the majority of investigations, however, itwill be necessary to supplement an accurate description of the soil profile with appropriatein-situ testing and sampling, and possibly associated laboratory testing.

    Under appropriate conditions, particularly where the water table is at depth which isapplicable to large areas within the hinterland of Africa, the drilling of large diameter trialholes and/or the forming of test pits for visual inspection by a geotechnical engineer orengineering geologist, can be carried out. The advantages of this procedure are as follows:

    It allows for the soil profile to be examined in-situ in its natural state- Good quality undisturbed block samples can be cut from the auger hole or test pit

    sidewalls. Disturbed samples can also be taken from specific horizons identified duringprofiling.

    In-situ testing such as hand shear vane tests and horizontal plate bearing tests can beexecuted within the trial holes or test pits.

    The procedures adopted are fast and economical and provide for accurate andcomprehensive evaluation of site geotechnical conditions.

    Safety procedures when profiling and sampling in trial holes and test pits are extremelyimportant. All investigation work with trial holes and test pits must be carried out inaccordance with the SAICE Code of Practice for the safety of persons working in smalldiameter shafts and test pits for civil engineering purposes (1990).

    For certain projects it may be necessary to supplement the auger trial holes/test pits withadditional investigation procedures. A variety of techniques are available. These couldinclude dynamic cone penetration tests, rotary core drilling with associated sampling and in-situ testing techniques (standard penetration tests, vane shear tests, lugeon tests etc.).

    In the coastal regions and on sites with a high water table the use of trial holes and test pits isoften not feasible due to collapse of the sidewalls. In these areas the two standard methodsused in a geotechnical investigation are boreholes with standard penetration tests and conepenetration tests. These are supplemented where necessary with, amongst others, rotary coredrilling, vane shear tests, dynamic cone penetrometer tests and the recovery of undisturbedsamples using the Shelby tube method or piston sampling.

    Tables 2.1.1 and 2.1.2 are provided as a guide to assist in the planning of a geotechnicalinvestigation. These tables give typical details with regard to the field and laboratory tests

  • 7that could be carried out in stable soil profiles above the water table (Table 2.1.1) and insaturated variable soils (Table 2.1.2).

    Table 2.1.1 -Guide to planning a soils investigation in stable soil profiles above thewater table (usually residual soils or cohesive transported soils)

    Parameter Field Test Laboratory Test

    Description of the soil profile Auger trial holesTest pitsBoreholes with SPT

    Consistency of the soilprofile

    Dynamic cone penetrometer(DPSH)In-situ profiling of trialholes/test pits

    Undrained shear strength Recover undisturbed samplesfrom auger trial hole, test pitor borehole Vane shear test inborehole

    Undrained triaxialUnconfined compression test

    Effective angle of friction Effective cohesion-

    Recover undisturbed samplesfrom auger trial hole, test pitor borehole

    Drained triaxial Drainedshear box test Undrainedtriaxial with measurement ofpore water pressure

    Modulus of compressibility Cross-hole jacking test orPlate load test orPressuremeter test

    Oedometer test

    Index property tests Recover disturbed samplesfrom auger trial hole, test pitor borehole

    Grading analysis Atterberglimits Moisture content

    Permeability Recover undisturbed samplesfrom auger trial hole test -pitor borehole

    Falling or constant headpermeability

    Collapse Recover undisturbed samplesfrom auger trial hole, test -pitor borehole

    Double oedometer Collapsepotential test

    Heave Recover undisturbed and/ordisturbed samples from augertrial hole, test pit or borehole

    Double oedometer Swellunder load test Indexproperty test(disturbedsample)

    Level of Water Table Drill a trial hole or aborehole, leave for a periodof time for the water level tostabilise in the hole and thenmeasure the level

  • 8Table 2.1.2- Guide to planning a soils investigation in saturated, variable soilsusually encountered in coastal areas or adjacent to water courses

    Parameter Field Test Laboratory Test

    Description of the soil profile Boreholes with SPTConsistency of the soilprofile

    Dynamic cone penetrometer(DPSH) Cone penetrometertest(CPT) Boreholes withSPT

    Undrained shear strength Recover undisturbed samplesfrom borehole Vane sheartest in borehole Correlatewith in-situ penetrometertests

    Undrained triaxialUnconfined compression test

    Effective angle of friction

    Effective cohesion-

    Recover undisturbed samplesfrom boreholeCorrelate with in-situpenetrometer tests (sandysoils only)

    Drained triaxial Drainedshear box testUndrained triaxial withmeasurement of pore waterpressure

    Modulus of compressibility Pressuremeter test Correlatewith in-situ penetrometertests

    Oedometer test

    Index property tests Recover disturbed samplesfrom borehole

    Grading analysis Atterberglimits Moisture content

    Permeability Recover undisturbed samplesfrom borehole

    Falling or constant headpermeability

    Collapse Recover undisturbed samplesfrom borehole

    Double oedometer Collapsepotential test

    Heave Recover undisturbed and/ordisturbed samples fromborehole

    Double oedometer Swellunder load test Indexproperty test (disturbedsample)

    Level of Water Table Drill a borehole and leave fora period of time and measure

  • 92.2 FIELD INVESTIGATION TECHNIQUES

    The field investigation techniques that Soiltech offers and which are summarised in Table2.0.1 are discussed in more detail below.

    2.2.1 AUGER TRIAL HOLES

    The auger trial hole involves the drilling of a large diameter auger hole using a powerfulauger machine. A qualified person is then lowered in stages down the hole by means of asmall winch and is able to profile the hole by visually inspecting the sidewalls and the base.Furthermore, it is possible to cut large undisturbed samples from the sidewalls or base of thehole for later testing in the laboratory, as well as carry out cross-hole jacking tests and plateload tests as described in SECTION 2.2.7 in the trial hole excavation. Bulk sampling for thepurposes of evaluating the mineral content of materials on old dumps or within soil andweathered profiles, can also readily be accomplished using this technique.

    Auger trial holes provide a very quick and economical method for obtaining reliablegeotechnical information for a variety of engineering solutions and it is favoured by mostengineers and geologists. For the successful application of this technique, however, it isessential that the sIde walls of the trial holes remain stable during drilling and profiling. It isthus not suited to areas with a high water table where collapse of the sidewalls is most likel'l.

    It is possible to drill a large number of trial holes in a relatively short space of time whichmakes this an economical form of investigation. A minimum hole diameter of 750 mm isrequired for in-situ profiling purposes but trial holes of up to 2000 mm in diameter arepossible. Depths of up to 36 metres can be drilled in suitable materials. The technique isideally suited to sites with deeply weathered profiles. The auger trial hole can also penetrateinto soft rock and even harder fractured rock.

    Under suitable site conditions approximately eight 750 mm diameter auger holes to a depthof 10 metres can be drilled within a normal working day. It is also possible to profile thisnumber of holes within the same working day. The auger rig with its crew and ancillaryequipment is normally hired on a daily basis. Soiltech can arrange for the profiling of theholes by experienced qualified personnel from an independent geotechnical engineering firmshould this be required.

    To facilitate the profiling of the trial holes, a tripod frame fitted with a winch is positionedover the trial hole, the winch being connected via a steel wire rope to a specially designedbosun's chair. All operations are carried out in accordance with the S.A.I.C.E. Code ofPractice for the safety of persons working in small diameter shafts and test pits for civilengineering purposes (1990). Plastic sample bags, cling wrap, labels, tape measures andsampling tools form part of the standard equipment available on site. Under special sitecircumstances breathing apparatus and methanometers are made available on site.

  • 10

    AUGER RIGS FOR DRILLING TRIAL HOLES

    Soiltech has a variety of truck mounted auger rigs available for drilling trial holes. Details ofthese rigs are given in Table 2.2.1.1. Plate 2.2.1.1. shows the Williams LDH50 rig used fordrilling auger trial holes. The overall dimensions of the auger rigs are given in SECTION23.2 PILING RIG DIMENSIONS

    Table 2.2.1.1- Range of Auger Rigs Available

    Type of Auger Rig Max. DrillingTorque(Kgm)

    GrossVehicle Mass(Kg)

    Max Depth(m)

    Max. HoleDiameter(mm)

    Hotline 16MI20 3000 24400 16 1000Soilmech RTAH 11000 30000 32 1500Williams Digger LDH50 6818 28580 15 1000Williams Digger LDH80 6818 30000 24 2000WilliamsDiggerLLDHI20 13636 39310 36 2000

    2.2.2 TEST PITS

    The use of test pits as an investigation technique offers the same advantages in terms ofprofiling and sampling as described for auger trial holes. Test pits are easily formed with amechanical excavator or by hand, and therefore have the advantage of being relativelyinexpensive. The main disadvantages are that they are limited to depths of two to threemetres and cannot be used in areas of shallow water table. Test pits are therefore mostappropriate in areas with a relatively deep water table where competent soils or rock areanticipated at a relatively shallow depth. They are often used to investigate areas where thereis poor access for other types of equipment.

    In view of cost advantages, test pits are often used as a preliminary or first phase of theinvestigation. Where a competent soil or rock stratum occurs close to the ground surface, theprofiling and sampling of test pits may provide sufficient information for design purposesand no other form of testing is required. If, on the other hand, the excavation of test pitsdiscloses a much deeper soil profile, then it is essential to follow up the first phase withadditional investigation work. This is normally carried out using techniques which can reachto greater depths, such as auger trial holes and boreholes.

    It is extremely important to follow the correct safety procedures when profiling and samplingin test pits, and the SAICE Code of Practice for the safety of persons working in smalldiameter shafts and test pits for civil engineering purposes (1990) should be strictly adheredto at all times. Experience has shown that test pits are far more prone to collapse than augertrial holes, due to the fact that a rectangular pit is less stable than a circular trial hole. Evenhighly experienced engineers and geologists find it difficult to assess the stability of a test pitand serious accidents have been reported.

  • 11

    Plate 2.2.1.1. A Hotline rig for drilling auger trial holes

  • 12

    2.2.3 DYNAMIC CONE PENETRATION TESTING

    Dynamic Probe Light (DPL)

    This local standard of the Dynamic Probe Light test (ISSMFE Technical Committee onPenetration Testing, 1988) is used in many applications in South Africa. A 20 mm diameter,60 cone is driven into the soil by an 8 kg weight dropped through 575 mm. The results areexpressed as millimetres per blow. The original test (Van Vuuren, 1969) was designed for therapid determination of the California Bearing Ratio (CBR) to depths of about one metre forinvestigation into road pavement performance and design. Besides the original application inthe field of pavement evaluation and design, the test has also been used as a rough guide incompaction control and for estimating soil conditions for the design of shallow footings.

    The main advantage of this type of equipment is that it is light, portable, inexpensive tooperate and provides a continuous rough record of soil consistency over the depth tested. Thedisadvantages are that no sample is recovered, the nature of the equipment limits its depthcapability to three metres below surface and the equipment is not able to penetrate hardlenses or other obstructions (large gravel, boulders etc.). The ease and low cost with whichresults can be obtained, is therefore somewhat offset by the limitations of the test and theindirect approximation to soil conditions that it provides. A guide to the interpretation of theresults of this test can be found in SECTION 3.0 SOIL AND ROCK CLASSIFICATIONAND DESIGN PARAMETERS.

    Dynamic Probe Super Heavy (DPSH)In Southern Africa, considerable use is made of a local standard of the Dynamic Probe SuperHeavy test (ISSMFE Technical Committee on Penetration Testing, 1988). A 60 disposablecone, 50 mm in diameter, is fitted onto the bottom of an "E" size rod and driven into theground by a 63.5 kg hammer falling through 762 mm. The number of blows required to drivethe cone through each successive 300 mm of penetration is recorded. This provides anempirical indication of consistency. Once refusal depth is reached (more than 100 blows per300 mm), the driving rods are withdrawn by 600 mm. The disposable cone remains at thebase of the hole. The rods are then re-driven with the number of blows per 300 mm beingrecorded. These re-drive blow counts provide an indication of the skin friction acting on thedrive rods. Data collected from the DPSH test (including the re-drive figures) are presentedon a report sheet.

    A feature of the test is that it is very economical and can be rapidly and easily performed. Amajor disadvantage of the test is that no soil sample is obtained. In many instances thisdisadvantage can be overcome by adopting a variation to the test procedure by fitting aRaymond split-spoon sampler to the "E" rods, instead of the solid cone. This techniqueprovides a continuous disturbed representative sample of the soil profile. Any blow countsrecorded during this operation cannot, however, be correlated with those of the actual DPSHtest.

  • 13

    The DPSH rig is designed so that tests can be undertaken in areas that are not readilyaccessible, such as inside existing buildings and in narrow passage ways between buildings.Plate 2.2.3.1 shows a typical DPSH test rig.

    The DPSH is used under the following conditions:

    As economical supplementary data between boreholes on larger sites. On sites with erratic profiles (alluvial, colluvial or lacustrine deposits), it will locate

    softer areas. Probing for rock or hard strata- In conjunction with a soil profile it will provide rough consistency readings which can be

    plotted graphically. As the test closely approximates a driven pile, it is extensively employed for determining

    an estimate of skin friction and installation depths of driven cast-in-situ piles. In non-cohesive materials it is very reliable, but must be used with caution in cohesive soils. Thetest will also indicate pile driving conditions.

    Limitations of the test are:

    Driving refusal is frequently experienced on hard layers (such as very dense ferricretes orcalcretes, boulder horizons) which may be underlain by soft soil horizons.

    Differences in remoulding caused by the small diameter cone on the one hand and theconsiderably larger piling tube on the other,can lead to erroneous prediction of pileinstallation depth.

    Similar differences may occur when excessive pore pressures are set up during thedriving of a pile whereas this does not occur with the DPSH test.

    A graphical presentation of this data is presented in Figure 2.2.3.1. The interpretation of thetest results is generally associated with local experience. As a preliminary evaluation theblow counts can be taken as being roughly equivalent to the SPT N value (See SECTION2.2.5). In the interpretation, however, it is essential to take into account the influence of therod friction.

    2.2.4 CONE PENETRATION TESTING (CPT)

    This method was initially developed in the Netherlands in the 1930's where it was first usedas a means of determining the ultimate bearing capacity of driven piles founded in sand. Overthe years the test has been called the Dutch sounding test, the Dutch probe and the static conepenetration test. In terms of acceptable international standards (ISSMFE TechnicalCommittee on Penetration Testing, 1988) it is now referred to as the cone penetration test(CPT).

    In the CPT test a 60 cone with a cross sectional area of 1000 mm2, usually equipped with afriction sleeve which is of the same diameter of the cone and has an surface area of 1.5 x 104mm2, is pushed into the ground at a rate of 20 mm/sec. Separate measurements of cone

  • 14

    penetration resistance (point resistance), total penetration resistance and the side frictionresistance of the friction sleeve are made continuously throughout the test.

    The main advantages of the CPT are that the testing procedure is relatively simple andrepeatable, and the test results are more amenable to a rational analysis rather than relyingentirely on empirical correlation. The CPT also gives a virtually continuous record of soilresistance values throughout the depth of penetration.

    Figure 2.2.3.1 -Typical results from a DPSH test

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    The main limitations of the CPT test are as follows:

    Penetration depth limitations due to machine capacity. The technique is rarely effective in gravels and boulder horizons and is also not suited to

    weathered rock profiles. No samples are recovered.The data obtained from the cone penetration test may be employed to:

    Assist in the evaluation of the type and stratigraphy of the soils present. Interpolate ground conditions between control boreholes. Evaluate engineering parameters of soils (relative density, shear strength, compressibility

    characteristics, liquefaction potential). Assess driveability, bearing capacity and settlement of piled foundations.Mechanical cone penetrometers (Begeman, 1965) have a telescopic action which requires anouter probe sleeve and an inner rod. These mechanical cone penetrometers offer theadvantage of low equipment cost and simplicity of operation. They do, however, have thedisadvantages of a slow incremental procedure, limited accuracy in very soft soils and labourintensive data handling and presentation.

    With the electrical cone penetrometer the friction sleeve and cone point advance together as asingle system. The point resistance and local side shear are recorded continuously with theuse of built-in load-cells. An electrical cable located inside the rods connects the load cells torecording equipment at ground surface. Electrical cones carry a high initial equipment costand require skilled operators as well as adequate back-up for calibration and maintenance.They do, however, offer advantages over the mechanical penetrometer such as a more rapidprocedure, higher accuracy and repeatability , automatic data logging, reduction and plotting.

    One of the important applications of the CPT test is to evaluate variations of soil type withinthe soil profile. With mechanical and electrical cones extensive use is made of what is knownas the friction ratio as a means of soil classification (Jones, 1974, Schmertmann, 1975). Thefriction ratio is the ratio between sleeve friction and the point resistance and is expressed as apercentage.

    The most significant recent development in electric cone penetration testing is thedevelopment of the piezo-cone penetrometer test (CPTU) which incorporates a pore pressuresensor in the cone. This allows for the measurement of the pore water pressure present in thesoil during penetration. Pore pressure measurements during cone penetration testing providesmore details on the stratification and has added a new dimension to the interpretation ofcertain geotechnical parameters especially in loose or soft fine grained soil deposits. This hasresulted in CPTU testing becoming a prime tool for stratification logging of soil deposits(Jones and Rust, 1982, Campanella and Robertson, 1988).

  • 16

    Further advantages of the CPTU test over the conventional CPT are as follows (Campanellaand Robertson, 1988):

    The ability to distinguish between drained, partially drained and undrained penetration.The ability to evaluate flow and consolidation characteristics.

    The ability to assess equilibrium groundwater conditions.A guide to the interpretation of the results of CPT and CPTU tests can be found in SECTION3.0 SOIL AND ROCK CLASSIFICATION AND DESIGN PARAMETERS.

    2.2.5 ROTARY DRILLING, IN-SITU TESTING AND SAMPLING

    The rotary drilling technique is used to drill a borehole which is normally cased through theupper soil profile. Various methods for testing and sampling the soil during the drilling of theborehole are available and described later in this section. The most common of these is thestandard penetration test or SPT. Once the borehole reaches strata of rock consistency, rotarycore drilling is used to recover samples.

    ROTARY DRILLINGThe borehole is typically drilled through the upper soil layers using a casing fitted with adiamond/tungsten tipped casing shoe. A drilling fluid is used to remove the cuttings and flushthem to the surface where they can be sampled. This technique for advancing the borehole iscalled wash boring and the samples are known as wash samples. The borehole is advanced instages with samples taken at the various depths required. Plates 2.2.5.1 and 2.2.5.2 show twotypes of rotary drilling rigs.

    When materials of rock consistency are encountered and wash boring is no longer effective,rotary core drilling is used to advance the borehole and recover core samples. The cores aredrilled using a core barrel which is fitted with a diamond tipped or impregnated drill crown.The core barrel with drill crown is rotated by the drilling rig which also has the means tohydraulically crowd the drill stem. A drilling fluid is pumped through the core barrel to coolthe drill bit and flush the cuttings to the surface.

    The conventional core barrel can recover a 1.5 metre length of core at a time. Once the corebarrel is full, the drill stem with core barrel is withdrawn from the hole and the core sample isrecovered and stored in a core box. Core boxes are marked with the depths drilled so that avisual inspection of the core box shows what percentage of core was recovered relative to thedepth drilled. Cores are sometimes waxed to retain their natural moisture content. UCS andpoint load tests are often carried out on rock cores so as to determine the strength of the rock.This is an important factor when carrying out a geotechnical investigation for a contract onwhich piles will be required to penetrate the rock, as the piling contractors need to know thehardness of the rock to be able to assess penetration rates at the time of tender.

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    A variety of core barrels and appropriate crowns is available, allowing the driller to select themost suitable type for the particular materials being cored. Core barrel designs, such asdouble or triple tube, help to maximise the core recovery especially in the very soft andweathered rock strata. Heinz ( 1989) gives a detailed description of rotary core drillingtechniques and equipment. Soiltech complies with the Standard Specifications for SubsurfaceInvestigations (CSRA, 1993) in carrying out rotary drilling operations.

    IN-SITU TESTING

    Standard Penetration Test (SPT)This process was standardised in the 1920's and 1930's into what we know now as the

    Standard Penetration Test. In the execution of this test a standard 51 mm diameter split spoonsampler known as a Raymond Spoon is driven into the soil at the bottom of a borehole. Afree-fall hammer of 63.5 kg operating off a trip mechanism and falling through a height of762 mm provides the driving force. The number of blows required to drive the sampler each150 mm increment of a total of 450 mm penetration is recorded. The blow count for the first150 mm increment is discarded and the sum of the blow counts for the second and third 150mm increments is known as the SPT "N" value.

    The standard penetration test has become accepted world wide as a useful test in geotechnicalinvestigation and foundation design. SPT results in boreholes give an empirical qualitativeguide to the in-situ engineering properties of cohesive and cohesionless soils and provide asample of the soil for classification purposes.

    The results of the SPT can be affected by incorrect drilling and sampling procedures some ofwhich are given below (refer also to the Canadian Foundation Engineering Manual, 1985):

    Inadequate cleaning of the bottom of the borehole. Driving the spoon above the bottom of the casing. Failure to maintain sufficient hydrostatic head in the borehole. Not using the standard hammer drop or correct mass. Free fall of the hammer is not obtained. The tip of the spoon is damaged. Not recording blow counts and penetration accurately.It is thus extremely important that the drilling crew carrying out the tests is experienced inthis type of work. Even then it is advisable to carry out some CPT tests close to the boreholepositions to check the correlation between the two. This will give an indication as to whetherthe SPT values are reliable. The relationship between the SPT N value and engineeringproperties is empirical and some guidelines regarding the evaluation and interpretation ofSPT N values are given in SECTION 3.0 SOIL AND ROCK CLASSIFICATION ANDDESIGN PARAMETERS.

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    Plate 2.2.3.1 -DPSH Test Rig Plate 2.2.5.1- Skid MountedRotary Core Drilling Rig

    PLATE 2.2.5.2 -MOBILE B80 ROTARY CORE DRILLING RIG

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    Vane Shear Tests

    The vane shear test is routinely used to obtain undisturbed peak and remoulded undrainedshear strength. The test consists of placing a four bladed vane in the undisturbed soil androtating it from the surface to determine the torsional force required to cause a cylindricalsurface to be sheared by the vane. This force is then converted to a unit shearing resistance ofthe cylindrical surface as shown in Figure 2.2.5.1.

    A typical example of the equipment employed to apply torque to the steel rods from surfaceis also shown in Figure 2.2.5.1. The steel rods are housed in a sleeve in order to preventflexing and to protect the rods. The vane which is connected to the base of the steel rods ishoused within a "torpedo" attached to the base of the sleeve. The vane consists of a fourbladed cruciform. For standard tests the height of the vane should be twice the diameter. Theselection of the vane size is directly related to the consistency of the soil being tested, withlarger vane sizes being used in the softer soils.

    The test procedure is to advance the vane from the bottom of the torpedo in a single thrust tothe depth at which the test is to be conducted. Once the vane is in position, torque is appliedin a rotational sense at a slow rate using the gear driven surface equipment. Torsional force ismeasured and converted to unit shearing resistance in accordance with the followingassumptions:

    Penetration of the vane causes negligible disturbance, both in terms of changes ineffective stress and shear distortion.

    No drainage occurs before or during shear: The soil is isotropic and homogeneous. The soil fails on a cylindrical shear surface- The diameter of the shear surface is equal to the width of blades. At peak and remoulded strength, there is a uniform shear stress distribution across the

    shear surface. There is no progressive failure, so that at maximum torque shear stress at all points on the

    shear surface is equal to the undrained shear strength.

    The results of a vane shear test may be influenced by many factors:

    Type of soil, especially when permeable fabric exists. Strength and anisotropy. Disturbance due to insertion of the vane. Rate of rotation or strain rate. Time lapse between insertion of the vane and the beginning of the test. Progressive/instantaneous failure of the soil around the vane.It should be appreciated that the assumptions described above are not likely to apply at thesame time. The test is therefore limited to a restricted range of material types.

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    Figure 2.2.5.1 -Vane Shear Apparatus

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    Pressuremeter Tests

    The pressuremeter test was originally developed by Menard (1956) and comprises ahorizontal in-situ loading test carried in a borehole by means of a cylindrical expandableprobe. A major difference between categories of pressuremeter tests lies in the method ofinstallation of the device in the ground. In accordance with Mair and Wood (1987), thefollowing two broad categories of tests can be distinguished in terms of installation method:

    Menard type pressuremeter (MPM) test in which the device is installed in a borehole. Self-boring pressuremeter (SBP) test in which the device bores its own way into the

    ground usually from the bottom of a borehole.

    The following parameters can be deduced from the results of the pressuremeter test.

    Deformation modulus (i.e. compressibility). Undrained shear strength for clays or weak rocks. Effective angle of friction for sands- In-situ total horizontal stress.The degree of success in obtaining any of these parameters is essentially dependent upon thetype of test and the interpretation of the data. Consideration must also be given to possibledifferences in the properties of soil horizons measured in a horizontal direction by thepressuremeter, and those required for many design problems which are more concerned withvertical properties.

    For more details with regard to pressuremeter testing and its interpretation reference shouldbe made to Baquelin et al (1978), Windle and Wroth (1977) and Mair and Wood (1987).

    Lugeon TestingLugeon testing (also known as water pressure or packer testing) is carried out to measure thepermeability of the soil or rock at specific depths in a borehole. The equipment consists oftwo packers comprising steel tubes surrounded by inflatable rubber sleeves separated by aperforated length of steel tube. The spacing of the packers can be adjusted to the specificlength of soil or rock to be tested. The minimum length of packer sleeve is 700 mm to ensurea watertight seal. The packer arrangement is connected via high pressure tubing to a suitablepump on the surface. Data collected from the system is obtained by flow metres and pressuregauges. The above arrangement is known as a double-packer system. The system can beadapted, however, for so-called single packer tests, where testing is carried out between thepacker and the bottom of the hole.

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    The test consists of pumping water into the isolated zone of the borehole at three differentpressures, in the following typical sequence:

    1 st 10 min. at low pressure a2 nd 10 min. at medium pressure b3 rd 10 min. at high pressure c4 th 10 min. at medium pressure b -repeated5 th 10 min. at low pressure a- repeated

    The actual duration of each pressure stage is accurately timed. The pressures selected aredependant on the depth at which each test is carried out. The required pressures aremaintained to an accuracy of 5% during each pressure stage.

    Piezometer Installations

    Piezometers are installed in boreholes in order to provide information regarding the at restlevels of the ground water table. In addition, ground water pressure can be measured viamore specialised piezometers i.e. hydraulic, electrical and pneumatic.

    In general piezometers are installed into pre-cleaned holes by lowering a selected porous tipto approximately 500 mm above the bottom. The tip is surrounded by a filter of graded,washed silica sand and sealed off with a bentonite plug. The remainder of the borehole issealed by introducing cement/bentonite grout.

    SAMPLING

    Shelby and Piston Tube Sampling

    This sampling technique is employed to obtain undisturbed material from soft and very soft

    cohesive soils. The Shelby tube used to recover the samples, consists of a thin walledstainless steel tube with an internal diameter of approximately 75 mm. The leading edge ofthe tube is beveled and crimped such that the entry diameter is fractional smaller than thebody diameter. The tube is usually a half metre in length with the top end designed to fit intoan adapter. The adapter has a one-way valve built into it to allow water to escape so as toprevent compression of the sample.

    The Shelby tube sampler is attached to the drill string in place of a core barrel and is loweredto the base of the borehole and pressed into the soft material using the drill rig hydraulics.The sample and tube are then raised and the sample extruded on site. The sample should besealed and packed so as to maintain the in-situ moisture content and to resist damage duringnormal handling and transport.

    Under certain conditions, where the material to be sampled cannot be successfully obtainedvia the conventional Shelby tube technique, piston sampling may be employed. In theseinstances either a floating or rod-mounted piston is located in such a manner that the piston

  • 23

    rests on the top of the sample as it is pushed into the tube. The piston creates a vacuum whichallows for retention of the sample within the tube.

    Core Orientation

    Such surveys are carried out where information is required regarding the spatial orientationof planar features, palaeontological studies, etc. The techniques employed include thefollowing:

    Impression Core Orientation: this technique employs a hollow tube fixed to the base ofthe drill string filled with a suitable Plasticine material. The tube is lowered to the base ofthe pre-washed borehole and the orientator is pushed to seat onto the proud core break.The tube is withdrawn and the impression in the Plasticine matched with the bottom ofthe previous core run. Correct orientation is maintained during the raising and loweringof the drill string.

    .Integral Core Orientation: this technique involves the drilling of a pilot hole (E size orsimilar) to 1.5 metres below the base of the main borehole using centering bushes tocentre the pilot hole in the main borehole. An orientated bar or pipe is placed into thepilot hole and cemented into position. The orientated bar is overdrilled once the cementhas set. The technique can be employed in vertical or inclined holes, and is specificallyused where highly fractured formations have been intersected or the impression techniquecannot be employed.

    2.2.6 ROTARY PERCUSSION DRILLING

    There are two types of rotary drilling equipment. The one is known as a top drive rig and thisconsists of a drive head which remains above the surface and is connected via drill rods to adrill bit. The drive head rotates the drill string as well as imparts an impact force into therods. The drill bit impacting on the rock chips the rock and the chips are air flushed to thesurface.

    The other type of drilling equipment is very similar to the above but the impact force isgenerated by a down-the-hole hammer. This is a percussion hammer which is driven by airand which imparts a rapid series of impacts to the drill bit which is part of the hammer. Therotation drive to the drill stem is provided by a top drive head. The down-the-hole hammer isfavoured for geotechnical investigation purposes because of greater versatility and sensitivityparticularly when recording penetration times.

    The standard procedure in terms of geotechnical investigation is for percussion chips, whichare flushed to the surface by compressed air, to be collected at one metre intervals. Duringdrilling operations the operator is required to keep a record of penetration time per metre, airloss, levels of water strikes, intersection of cavities and anything else that may be of specificinterest to the logger of the borehole.

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    A borehole log is compiled from the inspection of the chip samples, an evaluation ofpenetration times and the other relevant information supplied by the driller. The nature of thetechnique is such that the compilation of the borehole log can be influenced by a number offactors that can lead to inaccurate interpretation of the soil/rock conditions. Some of the moreimportant of these factors are as follows:

    The highly disturbed nature of the chip samples recovered and the possibility ofcontamination of these samples.

    Total loss of sample in loose or soft layers. Incorrect interpretation of the penetration rate in relation to the hardness of the material

    being penetrated.

    From the discussion presented above it is apparent that, in terms of geotechnicalinvestigation, rotary percussion drilling can only be used to obtain a rough indication of thesoil/rock profile and is subject to a large number of inaccuracies which include to a largeextent the experience of the driller and the logger.

    The advantages of the rotary percussion technique are that it is relatively inexpensive whencompared with rotary coring, being about one tenth of the cost of rotary coring. Drillingproduction is also fast when compared to rotary coring with production rates of 80 to l00metres per day possible. It is also one of the few techniques that can be used to economicallypenetrate boulder horizons or layers of chert which are often encountered in dolomiticterrain.

    In South Africa the technique has been used successfully used as part of the overallgeotechnical investigation procedures used in dolomitic terrain (Wagener, 1984). Thetechnique is also used for the following applications:

    As probe holes to determine rock head depths. As probe holes to determine the depth and extent of old mine workings. To form boreholes for the conducting of in-situ tests (pressuremeter, lugeon tests). To form boreholes for the installation of geotechnical instrumentation (piezometers,

    extensometers, inclinometers, etc.).

    2.2.7 PLATE LOAD TESTS

    Plate load tests are usually carried out to determine the compressibility and occasionally thebearing capacity of soils and rocks. The test is a convenient and direct method of obtainingthese parameters and is often used in soils or rocks which cannot be sampled or where thestructure (joints etc.) may control the engineering behaviour of the soil/rock mass.

    In its simplest form, the plate load test comprises a rigid plate placed on the surface to betested. The load is provided by an hydraulic jack, using kentledge or an anchored beam asreaction. Figure 2.2.7.1. shows a typical test system. The plates used must be rigid andtypically vary in diameter from 200mm to l000mm.

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    The following procedures are adopted for the test:

    The test site is carefully levelled and the plate bedded into the layer being tested usingPlaster of Paris and/or bedding sand-

    Load is applied to the plate using a hydraulic jack in a series of predetermined steps. Thisapplication of load and the maximum load applied must be designed to conform with thetype and purpose of the testing being carried out.

    Plate settlement is usually measured by means of dial gauges. In order to measure any tiltof the plate it is advisable to have four measuring points. The dial gauges are usuallyfixed to a beam supported by posts bearing on the soil some distance from the loaded areato avoid the readings being influenced by the settlement of the plate.

    A variation to the standard test procedures can be implemented to allow the soil below theplate to be saturated at a specific load. The objective of this procedure is to allow thedetermination of any collapse properties associated with the material being tested.

    The widespread use of auger trial holes and test pits in Southern Africa has led to thedevelopment of light and portable horizontal plate load equipment suitable for use in trialholes and test pits. By carrying out the tests in a horizontal direction, the necessary reaction isprovided by the opposing faces of the trial hole or test pit. The bearing plates on either sideare of equal size and the test procedure is essentially the same as that used for vertical plateload tests. The distance between the plates is measured and the movement of each plate istaken as half the total on the assumption that the two plates have moved equally.

    Figure 2.2.7.1 -Example of Vertical Plate Load Arrangement

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    2.2.8 IN-SITU DENSITY TESTS

    In-situ density tests are mainly used for compaction control in roads and earthworksconstruction. In certain instances the determination of in-situ density may, however, formpart of an overall geotechnical investigation fieldwork programme. Both the sandreplacement method and nuclear methods are used for the determination of in-situ density.

    In the sand replacement method, the in-place dry density is determined by forming a hole in alayer and dividing the mass of the material removed from the hole by the volume of the hole,the latter being determined by filling the hole with a fine sand of known density .Thedisadvantage of this test is that the material removed from the hole needs to be dried to aconstant mass, usually overnight in a suitable oven. This means that a period of at least 12 to18 hours is required before results become available. The advantage of the test is that it givesan accurate value of in-situ dry density and in-situ moisture content.

    Nuclear systems for the determination of wet density and moisture content have becomepopular in recent years. One of the main advantages of this test procedure is that results areimmediately available. The disadvantage is that there are some potential inaccuraciesassociated with the results produced from this test. The inaccuracies are generally associatedwith the measurement of moisture content and can easily be overcome by taking a sample ateach test position for the laboratory determination of moisture content. To a large extent thisnegates the advantages of having results available immediately. On most roads andearthworks contracts the results of nuclear gauge tests are generally only accepted as acontrol procedure after suitable calibration with sand replacement tests has been carried out.

    Soiltech is able to offer both sand replacement and nuclear gauge density tests. These testsare carried out in accordance with the procedures recommended in TMH 1 ( 1986).

    2.2.9 GEOPHYSICAL TECHNIQUES

    Geophysical exploration is a form of field investigation in which a set of physicalmeasurements relating to the underlying soil or rock strata is made at ground surface or inboreholes. The measurements indicate variations in space or time of certain physicalproperties of the soil/rock materials. Geophysics is therefore a blend of physics and geologysince the physical measurements are interpreted in terms of subsurface geological conditions.The properties of soils/rock which are of significance in geophysical exploration are density,magnetic susceptibility, electrical conductivity , elasticity and thermal conductivity. Sincethese physical properties vary widely in soils/rocks at least one of these properties usuallyshows marked changes from place to place which can be measured by sufficiently sensitiveinstrumentation.

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    The main advantages of geophysical techniques are as follows:

    It is possible to carry out investigations of large areas rapidly and economically. The techniques can be used to locate critical areas for further field investigation.The disadvantage of the technique is that the results are dependent on the interpretation ofphysical measurements. These measurements are not in themselves geological orgeotechnical parameters relative to the site subsurface conditions. It is therefore essential thatgeophysics is carried out and interpreted in conjunction with a carefully planned drillingprogramme. The main application of geophysics in geotechnical investigations is theinterpolation of subsurface geological strata between carefully controlled drilling positions.

    The more common geophysical techniques used in geotechnical investigations are magnetics,gravity and resistivity. For more detailed information reference should be made to Darracott(1976), Bullock (1978), Griffiths and King (1965), Kleywegt and Enslin (1973) and Westand Dumbleton (1975).

    2.3 GEOTECHNICAL ENGINEERING LABORATORY SERVICES

    Standardised and consistent soil mechanics and materials testing, often forms the basis fordesign and site quality control in geotechnical and materials engineering. Soiltech has a fullyequipped soil mechanics and materials laboratory facility which provides a testing services toclients, consulting engineers and the Frankipile Group. A guide to testing procedures andrequirements for the commonly specified soil mechanics and materials tests is presented inTable 2.3.1. All relevant road type materials testing is carried out in accordance with TMH 1(1986). Soil mechanics testing is carried out in accordance with accepted published orInternational standards.

    In certain instances non-standard testing may be required. Through in-house expertiseSoiltech can assist clients to define the testing programme and ensure that the testing iscarried out to specified requirements.

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    Table 2.3.1 -Guide to Laboratory Procedures and Requirements

    Laboratory Test Parameter Determined Durationof Test inDays

    Sample Requirements

    Triaxial compression testUnconsolidated Undrained(UU)

    Undrained shear strengthof cohesive soils (Cu)

    3

    Consolidated Undrainedwith pore water pressure.measurements (CU)

    Effective shear strengthparameters c' or I>'

    5 to 7

    Consolidated drained test(CD)

    Effective shear strengthparameters c' or I>'

    7 to 10

    Undisturbed: Good qualitysealed block sample 300mrn x 200 mrn x150 mmthick. Shelby tube or pistonsampleDisturbed or remoulded:2 kg of representativesample

    Shear Box TestDrained Shear Box Effective shear strength

    parameters c' or I>'Residual shear strengthparameter I>'

    4

    5 to 7

    Undisturbed Good qualitysealed block: sample 300mm x 200 mm x150 mmthick. Shelby tube or pistonsampleDisturbed or remoulded:2 kg of representativesample

    Consolidation TestsConsolidation test soakedat11 kPa loaded to 1600 kPaand rebounded

    Compressibilitycharacteristics

    7

    Double oedometer test forcollapse

    Compressibility andcollapse characteristicsover full loading spectrum

    7

    Collapse potential test.Sample loaded to 200 kPa,saturated and rebounded

    Compressibility andcollapse characteristicsCollapse potential index

    3

    Double oedometer test forheave

    Swell characteristics overfull loading spectrum

    7

    Swell under load test Swell characteristics atspecified load

    3

    Undisturbed Good qualitysealed block sample 300 mmx 200 mm x: 150 mm thick.Shelby tube or piston sampleDisturbed or remoulded:2 kg of representativesample

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    Table 2.3.1 (Cont.) -Guide to Laboratory Procedures and Requirements

    Laboratory Test ParameterDetermined

    Duration ofTest in Days

    Sample Requirements

    PERMEABILITYTESTSFalling head orconstant head

    Coefficient ofpermeability

    3 for sandysoils7 to 10 forclayey soils

    Undisturbed:Good quality sealed blocksample 300 mm x 200 mmx150 mm thick. Shelby tubeor piston sample.

    Disturbed or remoulded:2 kg of representativesample

    BULK DENSITY Bulk densityDry densityMoisture content

    3 Good quality sealed blocksample 300 mm x 200 mmx150 mm thick

    Index propertiesGrading/sieveanalysis

    Particle sizedistribution to0.075mm

    3 2 kg sample of undisturbedor disturbed soil

    Hydrometer Particle sizedistribution from0.075mm to 0.002 mm

    Atterberg limits Liquid limit, plasticlimit, plasticity index

    Moisture content Moisture contentMoisture densityrelationshipMod AASHTOProctor

    Max. dry density andoptimum moisturecontent underspecified compactiveeffort

    2 40 kg of representativesample

    CALIFORNIABEARING RATIO(CBR)

    Mod AASHTOmoisture densitycurve. Plot of CBR vsdry density based onCBR at 3 compactiveefforts (ModAASHTO, Proctor,NRB)

    6 70 kg of representativesample

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    3.0 SOIL AND ROCK CLASSIFICATION ANDDESIGN PARAMETERS

    3.1 NOTES ON SOIL PROFILING

    As indicated in SECTION 2.0 GEOTECHNICAL INVESTIGATION, an accuratedescription of the soil profile forms the basis of the geotechnical investigation for anyengineering development. It is important that each layer is described in a consistent way toensure accurate interpretation of the soil profile by those involved in the geotechnical designand construction process.

    The description of the soil in profile, based on the work of Jennings, Brink and Williams(1973), is related to the following:

    Designation Heading ExampleM Moisture MoistC Colour Reddish BrownC Consistency StiffS Structure IntactS Soil Tvpe ClayO Origin Residual shale

    Moisture

    The moisture content is assessed as: DRY, SLIGHTLY MOIST, MOIST, VERY MOIST andWET. The assessment at the moisture content is dependant on the soil type. With a moisturecontent of say 20%, sand will probably be described as wet, whilst clay will probably bedescribed as slightly moist.

    Colour

    Colour is important for description and for correlation. Colour is described from the soil inprofile and also from a small sample of soil made into a creamy paste with water. A profile isMOTTLED when small exposures of different colours occur. A profile is BLOTCHED whenlarger exposures (say 75 mm and larger) of different colour occur. Colour charts obtainablefrom the South African Institution of Civil Engineers illustrate the main colours as well asvariations in hue and lightness of each colour. These charts illustrate the following colours.

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    Blue: Dusky Red: Dusky, DarkPale Pale, Light.

    Green: Dusky. Grey: DarkPale Light

    Olive: Dark Orange: Dark reddishLight Light reddish

    Brown: Dark Dark yellowishLight Light yellowishDark reddish Yellow: DarkLight reddish Light

    Consistency

    Consistency is a measure of the strength or density of the soil. Observations are based on theeffort required to dig into the soil or to mould it with the fingers. The consistency of cohesivesoils is based on the undrained shear strength and described as VERY SOFT, SOFT, FIRM,STIFF AND VERY STIFF. Consistency vs. Undrained shear strength guidelines are set outin SECTION 3.3. Non-cohesive soil consistency is based on the angle of shearing resistanceof the soil and described as VERY LOOSE, LOOSE, MEDIUM DENSE, DENSE ANDVERY DENSE. Consistency vs angle of shearing resistance guidelines are given inSECTION 3.3.

    Structure

    The presence and type of discontinuities in the soil mass define the structure. Structuralcharacteristics are generally related to cohesive soils in the following terms:

    INTACT Absence of fissures and joints, though tension cracks may occur in firmsamples when broken with a pick.

    FISSURED Presence of closed joints.SLICKENSIDED Highly polished fissures, usually indicative of expansive soils.

    SHATTERED Indicates fissures which have opened up and allowed entry of air, oftenassociated with expansive soils.

    MICRO-SHATTERED

    Shattering on a small scale with shattered fragments the size of sandgrains. If well developed, the soil appears granular when cut, but thegrains break down into clay and/or silt when wetted and rubbed.Indicates the presence of a highly expansive soil.

    LAMINATEDFOLIATED

    STRATIFIED

    Indicates that the soils show the laminated, foliated or stratifiedstructure of the parent rock or geological process from which they werederived.

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    Soil Type

    The soil type is described on the basis of the grain size of the individual particles. The basicgrain size classes are given below. Most natural soils occur as a combination of these classese.g. Silty clay or gravelly sand.

    BOULDERS Fragments of rock > 200 mmGRAVEL COBBLES 60mm -200mm

    COARSE 20mm -60mmMEDIUM 6mm -20mmFINE 2.0mm -6mm

    The range of size of boulders and gravel, the shape, theproportion by volume of the matrix and the description ofthe matrix are important.

    SAND COARSE 0.6mm -2.0mmMEDIUM 0.2mm -0.6mmFINE 0.06mm -O.2mm

    Sand particles are visible to the naked eye.SILTS 0.002mm -0.060mm

    Silts are barely gritty between fingers and thumb when wet,but are gritty on tongue against teeth. Silts are not easilyrolled into threads when moist. Silts exhibit dilatancy whenmoulded with water into a pat, (i.e. it increases its volumewhen shearing occurs which is illustrated by the film ofwater on the surface being absorbed if the pat is distorted.)Silts dry moderately quickly and can be dusted off thefingers. Dry lumps possess cohesion but powder easily inthe fingers.

    CLAY Particles less than 0.002 mmClay particles are flaky (not powdery) when broken andwill soften with the addition of water. They have a soapy orgreasy feel when wetted and rubbed on the palm of thehand. Clay sticks to fingers and dries slowly. There is nodilatancy or grittiness on tongue against teeth.

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    OriginIn any soil profile there are four basic categories of origin:

    Rock Residual soil Pedogenic material Transported soilIn the South African context, the demarcation between residual soils and overlyingtransported soils is often defined by the "pebble marker". This horizon is generallycharacterised by a gravel layer overlying the residual soil.

    RockMaterials described as rock comprise igneous, metamorphic or sedimentary (not pedogenic)horizons with unconfined compressive strengths of the intact or unjointed material in excessof 1000 KPa.

    Residual SoilA residual soil is formed from in-situ decomposition of rock. Decomposition can be causedby chemical weathering or mechanical disintegration which is a function of potentialevaporation (temperature, humidity, wind) and average annual precipitation.

    Pedogenic MaterialPedogenic material is residual or transported soil that has become strongly cemented orpartially replaced by one of the cementing agencies.

    Description Cementing Agency

    Ferricrete Iron oxide

    Calcrete Calcium carbonate

    Silcrete Silica

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    Transported SoilThis is soil which has been transported by a natural agency (water, wind, gravity) duringrelatively recent geological times (Pleistocene or Tertiary) and which has not undergonelithification into a sedimentary rock or cementation into a pedogenic material.

    Type Agency Source Resulting SoilTalus (scree andcoarse colluvium)

    Gravity Rock outcrops Unsorted angulargravel and boulders

    Hillwash (finecolluvium)

    Run-off Acid crystallineBasic crystallineArinaceous sedimentArgillaceoussediment

    Clayey sandClaySandClay or silt

    Alluvium (gullywash)

    Rivers, streams andgullies

    Various rocks andsoils

    BouldersGravelsSandsSiltsClays

    Lacustrine Deposits Streams terminatingin lake, pan or pool

    Various rocks andsoils

    SandSiltClay

    Estuarine Deposits Tidal rivers andwaters

    Mixed SandSiltClay

    Littoral Deposits Waves Mixed Beach sandAeolian Deposits Wind Mixed Sand and clayey

    sand

    Subsurface Water Condition

    The water table is that level or those levels in the soil where the water in the pores of the soiloccurs at atmospheric pressure, i.e. the level to which the water finds its own way in aborehole. The perched water table is a table which is only present in the soil temporarily. Itwill disappear and sometimes re-appear depending upon seasons or drainage conditions ofthe site. The permanent water table is the water table which persists throughout the seasonsof the year with only minor seasonal fluctuations of level.

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    A typical soil profile and a tabulation of the various soil symbols are given in Figures 3.1.1and 3.1.2 respectively.

    Figure 3.1.1- Example of typical soil profile

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    Figure 3.1.2- Typical Soil Symbols

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    3.2 NOTES ON ROCK MASS DESCRIPTION

    The accurate description of rock engineering conditions, like the requirements outlined forthe soil profile, necessitates a detailed and practical method of describing samples of rockcore retrieved from a rotary cored borehole, With these requirements in mind, the publicationA Guide to Core Logging for Rock Engineering by the Core Logging Committee of theSouth African Section of The Association of Engineering Geologist (1976) has become theaccepted norm for the description and interpretation of geological and rock engineeringconditions in South Africa.

    This method of logging rock cores was based on similar principles to those for soil profilingoutlined by Jennings et al (1973), but due to the complexity of rock mass behaviour subjectas it is to weathering and discontinuities, the soil profiling system was modified and adaptedto provide an adequate rock mass description. The core log contains descriptions of the rockmass parameters as well as discontinuity surfaces and the materials infilling these surfaces, ifany.

    3.2.1 DESCRIPTION OF PRIMARY ROCK MASS PARAMETERS

    Six basic rock mass parameters are used in the same way as soil descriptive parameters.These are tabulated and compared to the soil descriptors below.

    Soil Description Rock Mass DescriptionMoisture N/ AColour ColourConsistency WeatheringStructure Fabric and discontinuity surface spacingN/A HardnessSoil Type Rock TypeOrigin Stratigraphic horizon

    Colour

    Colour is the basic and most easily identifiable characteristic and colour variation is aprimary indication of weathering. The colour of a rock mass is generally related to itsmineralogy. Quartz and feldspar will give rise to light coloured rock while pyroxine andolivine give rise to dark coloured rock. Cores should be washed before logging and thecolour recorded on wet, recently broken surfaces. The standard Munsell colour chartobtainable from S.A.I.C.E should be used to describe the hue and the lightness of the colour.

    Where variable colour exists, the dominant colour of the rock mass should be given, followedby the secondary colour which usually exhibits a pattern such as: BANDED, STREAKED,BLOTCHED, MOTTLED, SPECKLED AND STAINED. Where inclusions, such asamygdales occur they should be described together with their colour .

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    Weathering

    Weathering of a rock mass is a process of alteration by mechanical, chemical or biologicalaction which significantly affects the behaviour of the rock material and the rock mass as awhole. The decomposition and the disintegration of a rock mass is given the term"weathering" and the degree of weathering is given in Table 3.2.1.

    Table 3.2.1 -Weathering of a rock mass

    DiagnosticFeature

    DescriptiveTerm

    DiscolorationExtent

    FractureCondition

    SurfaceCharacteristics

    OriginalTexture

    GrainBoundaryCondition

    Unweathered None Closed orDiscoloured

    Unchanged Preserved Tight

    SlightlyWeathered

    < 20% of fracturespacing on bothsides of fracture

    DiscolouredMay containthin filling

    Partialdiscoloration

    Preserved Tight

    MediumWeathered

    > 20% of fracturespacing on bothsides of fracture

    DiscolouredMay containthick filling

    Partial to completediscoloration notfriable exceptpoorly cementedrocks

    Preserved PartialOpening

    HighlyWeathered

    Throughout - Friable andpossibly pitted

    Mainlypreserved

    Partialseparation

    CompletelyWeathered

    Throughout Resembles a soil PartlyPreserved

    Completeseparation

    For detailed definition of the five degrees of weathering reference should be made to theoriginal publication.

    Fabric

    Fabric describes the structural and textural features of the rock material. Texture of the rockmass is governed by the size and arrangement of the individual grains. Table 3.2.2 givesrecommendations on grain size terminology.

    Table 3.2.2 -Fabric of a rock massDescription Size in mm Recognition Equivalent Soil Type

    Very fine grained 2.0 Grains measurable Gravel

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    Micro structural features such as foliation and banding give rise to anisotropic behaviour ofthe rock material for small scale features and the rock mass gives rise to this behaviour forlarger scale features. A spacing of 10mm is given as the boundary between micro structureand discontinuity surface. Table 3.2.3 outlines the terms given to both Micro structure anddiscontinuity surface.

    Discontinuity Surface Spacing

    This describes mechanical discontinuity, weakness planes or bedding planes. Two majorcategories of discontinuity surface are given by features characteristic of the origin such asbedding and features as a result of movement within the rock mass such as joints. In the corelog only the discontinuity surface spacing is given in the primary rock mass description. Anyadditional features are outlined separately. It is important to note that discontinuities causedby the drilling operation and the handling of the cores are not included in the description ofthe discontinuities. Table 3.2.3(a) and (b) gives descriptions of the discontinuity surfaces.

    Table 3.2.3(a) -Macro FeaturesDescriptions for Structural Features:Bedding, Foliation or Flow Banding

    Spacing in mm Description for Joints, Faults, orother Fractures

    Very thickly (bedded foliated or banded) < 1 000 Very widely (fractured or jointedThickly 300- 1 000 WidelyMedium 100- 300 Medium .Thinly 30- 100 CloselyVery thinly 10- 30 Very closely

    Table 3.2.3(b) -Micro FeaturesDescription for Micro-structural features:Lamination, Foliations or Cleavage

    Spacing in mm

    Intensely laminated (foliated or cleaved) 3- 10Very intensely < 3

    Rock Hardness

    Rock hardness is a measure of the strength of the rock material and plays a dominant role inthe behaviour of structures in rock engineering and in particular structural foundations suchas piles. The unconfined compressive strength is directly related to the hardness and isgraphically illustrated in Figure 3.3.10 and tabulated in Table 3.3.8.

    Rock Type and Stratigraphic HorizonThree basic rock types define the origin of a rock mass: Igneous, Metamorphic andSedimentary .The basic mineralogy and texture observed in the core together with knowledgeof the regional geology will enable the logger to name the rock type. The stratigraphichorizon which often identifies the behaviour and characteristics of the rock should precedethe rock type.

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    3.2.2 DESCRIPTIONS OF DISCONTINUITY SURFACES

    The behaviour of rock masses is often governed by the nature and spacing of thediscontinuity surfaces rather than the intact rock material properties. Recommendations withregard to the type and spacing of the discontinuity surface are given with the primary rockmass parameters. Descriptions of the nature of the discontinuity should incorporate thefollowing:

    Separation of fracture walls. Filling -the presence or absence of fill material within the discontinuity. Roughness -or nature of the asperities on the fractures. Orientation of the discontinuity.Table 32.4 gives values for a separation, filling and roughness of the discontinuity surface

    Table 3.2.4- Nature of discontinuity surfacesDescription of Separation of Fracture Walls

    Description Separation of walls in mmClosed 0

    Very Narrow 0- 0.1Narrow 0.1 1Wide 1 -5.0

    Very Wide 5- 25+

    Terminology for Presence or Absence of Fracture Filling Materials

    Description DefinitionClean No fracture filling materialStained Coloration of rock only. No recognisable filling materialFilled Fracture filled with recognisable filling material

    Roughness Classification

    Classification DescriptionSmooth Appears smooth and is essentially smooth to the touch. May

    be slickensided.Slightly Rough Asperities on the fracture: surfaces 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

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    The rock core descriptions together with drilling method, percentage core recovery , RQD(Rock Quality Designation) and Fracture frequency as well as type of test and test resultshould be indicated on the borehole log. For the symbolic representation of various rocktypes reference should be made to Figure 3.2.1.

    The core log together with the drilling record are combined for the compilation of a boreholelog. A typical log is given in Fire 3.2.2.

    Figure 3.2.1 -Typical rock symbols

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    Figure 3.2.2 -Typical borehole log

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    3.3 INTERPRETATION OF GEOTECHNICAL INVESTIGATION ANDLABORATORY / IN-SITU TESTING DATA

    Of key interest to the engineer interpreting the information contained in a geotechnicalinvestigation report, soil profile or set of laboratory or insitu test results is the allocation ofrepresentative geotechnical design parameters to the soil or rock profile.

    3.3.1 SOIL CLASSIFICATION

    The classification of the horizons encountered into soil type or rock is essential to correctlyevaluate and predict the properties and behaviour of a horizon. The classification of thematerial into sand, clay or rock must first be carried out before strength or compressibilitycharacteristics are assigned to it.

    There are several methods of classifying a soil. All of these methods have a broadclassification based on grain size. The Unified or the M.I.T. classification systems are mostcommonly used with the M.I.T. classification given in Table 3.3.1 and the Unified System isgiven in Table 3.3.2. The behaviour of the soil mass and the properties and parametersassigned to it will depend largely on whether it is classified as a sand, clay or rock.

    With penetration testing such as the CPT test (outlined in SECTION 2.2.5), where nosamples are recovered for grading and laboratory testing, methods of classifying soils basedon the test results have been developed. The method proposed by Schmertmann (1967)outlined in Figure 3.3.1 below and based on the CPT test results is commonly used. Thefriction ratio forms the basic guide as to weather the soil is cohesive or non-cohesive.

    A method of classifying soils based on the results of the CPTU test (outlined in SECTION2.2.5) has been presented locally by Jones and Rust (1982). This method of classification isoutlined in detail in Figure 3.3.2.

    When engineering works are constructed using soil, the response of the different soil types tocompaction and stabilisation is of great importance and compaction characteristics can bepredicted using the classification systems outlined above. For roads and earthworks theP.R.A system (Public Roads Administration after Allen 1945) of classification is often usedand reference should be made to it for these applications. This system classifies soils in termsof grain size, liquid limit and plasticity index and assigns a Group Index number to the soilwhich varies between 1 and 20. Soils with a Group Index less than 10 are predominantlycoarse grained and have good subgrade properties. Soils with a Group Index greater than 10have poor subgrade properties. Feats and highly organic soils are unsatisfactory as subgradematerial.

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    Table 3.3.1 -Particle size classes commonly used in engineering (the MassachusettsInstitute of Technology classification)

    Grainsize(mm)

    Classification Individualparticles

    visible using

    Mineralogicalcomposition

    Identificationtest

    Lessthan0.002

    Clay Electronmicroscope

    Sceondary minerals(clay minerals and Fe-oxides )

    Feels stickySoils handsShiny when wet

    0.002 -0.06

    Silt Microscope Primary andsecondary minerals

    Chalky feel onteeth When dryrubs off handsDilatant

    0.06 -0.20 Fine sand Hand lens Primaryminerals(mainlyquartz)

    Gritty feel onteeth

    2.0- 6.0 Fine gravel Naked eye Rocks(sometimes veinquartz)

    Observed withnaked eye

    6 -20 Medium gravel Naked eye Rocks Observed with.naked eye

    20 -60 Coarse gravel Naked eye Rocks Observed withnaked eye

    60 -200 Cobbles Naked eye Rocks Observed withnaked eye

    Morethan200

    Boulders Naked eye Rocks Observed withnaked eye

    The classification of the swelling potential for expansive soils based on clay content andplasticity index has been given by Williams and Donaldson (1973) and Seed (1978) in Figure3.3.3. Table 3.3.3 gives approximate swell values of clays for the range of potentialexpansiveness after v.d. Merwe (1975).

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    Table 3.3.2 Unified Soil Classification System

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    Figure 3.3.1 -Soil classification based on CPT test after Schmertmann (1967)

    Figure 3.3.2 -Soil classification based on CPTU test after Jones & Rust (1982)

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    (a) (b)Figure 3.3.3- Activity of expansive soils given by (a) Williams et al1973 and (b) Seed

    (1978)

    Table 3.3.3 -Potential Expansiveness of clays after v .d. Merwe (1975)

    Potential Expansiveness Heave: mm per m

    Very high > 80High 40

    Medium 20Low 0

    3.3.2 SOIL STRENGTH CLASSIFICATION

    Strength parameters can be assigned to soils or rocks based on:

    Descriptions of the strength in the soil profile. Index property tests. Empirical relationships with penetration test results. On direct measurement in-situ or in the laboratory .

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    For the purposes of shear strength evaluation soils have been divided into two broadcategories :

    Cohesionless soil