tanzania - road field testing manual - 2003

8/9/2019 Tanzania - Road Field Testing Manual - 2003

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THE UNITED REPUBLIC TANZANIAMINISTRYWORKS


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Field Testing Manual - 2003

TANROADS Central Materials Laboratory (CML)

THE U ITED R PUBLIC OF ANZANIA

M NISTRY OF WORKS

Field Testing

Manual - 2003


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April 2003

ISBN 9987-8891-4-X

Repro uct on o extracts rom t s Manua may e ma e su ect

to due acknowledgement of the source.

A t oug t s Manua s e eve to e correct at t e t me o

printing, Ministry of Works does not accept any contractual,

tortious or other form of liability for its contents or for any

consequences ar s ng rom ts use. Peop e us ng t e n ormat on

conta ne n t e Manua s ou app y an re y on t e r own s

and judgement to the particular issue that they are considering.

Printed by: Elanders Novum AS, Oslo Norway

ayout: an var sen, nterconsu t s o orway


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Preface

An important part of a quality assurance system in civil construction works is a complete description of test procedures. This

involves having a Laboratory Testing Manual and a Field Testing Manual comprising a precise and simple description of test

procedures and necessary forms for records and presentation of the test results. It is in this context that this Field TestingManual has been prepared. The Laboratory Testing Manual was prepared and launched in the year 2000 to form a complete

system of testing standards for road works. This system is complemented by the launching of the Pavement an Materials

Design Manual-1999 and the Standard Specications for Road Works-2000 from where test limits for material quality and

extent of testing programmes are specied.

These manuals form part of the development of Tanzanian National Standards and Guidelines under the Institutional Co-

operation in the Road Sector Programme Agreement between the Government of the United Republic of Tanzania and the

Kingdom of Norway.

The Field Testing Manual describes techniques to be applied during testing in the eld of geotechnique, material prospecting

and alignment surveys, construction control, pavement evaluation and axle load surveys. The testing and sampling proce-

dures are clearly specied and their elds of application and limitations are clearly described. Moreover, the test procedures

are simplied to a practical approach, without compromising the correct procedure to be followed for each test.

This Manual will provide an invaluable documentation of eld techniques to the benet of both engineers and technicians

working in the road construction industry in the country and also other areas related to foundations for structures.

Dar es Salaam,

.

a.g Chief Executive Ofcer

TANROADS


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Acknowledgements

The Field Testing manual 2003 has been prepared as a component under the Institutional Cooperation between TAN-

ROADS, CML and the Norwegian Public Roads administration (NPRA). The Government of Tanzania and the NorwegianAgency for International Development (NORAD) have jointly nanced the project, which forms a part of a programme to

establiosh technical standards and guidelines for highway engineering.

This Manual has been prepared by a Working Group consisting of the following members:

Mr. C. Overby NPRA Chairman

Mr. S. Rutajama CML Member

Mr. S. Nergaard Noteby, consultant Member

Mr. R. Johansen ViaNova, consultant Secretary

The Working Group wish to acknowledge engineers and technicians at CML for their valuable comments during the prepara-

tion of this Manual.

Photographs were provided by:

C. Overby NPRA

M. T. Keganne Roughton International

- Rolf Johansen Vianova

- M. Besta CML


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Summary of TerminologyDenitions of terms and abbreviations are presented in full inAppendix 7. Selected terms, denitions and abbreviations are

tabulated below for ease of reference in the use of this manual.

Base course

Bituminous binders

- Bitumen emulsion (anionic, cationic, inverted)

- Cutback bitumen (e.g. MC3000, MC800, MC30)

- Penetration grade bitumen (e.g. 60/70, 80/100)

Bituminous layers

- Asphalt concrete surfacing C

- Bitumen emulsion mix EMIX cold)

- Dense bitumen macadam BM hot)

- Foamed bitumen mix BMIX cold)

- Large aggregate mix for bases AMBS hot)

- Penetration macadam M cold)

Bituminous seals- Emulsion fogspray

- lurry seal

- urface treatments:

urface dressing

ape seal

tta seal

and seal

Cemented materials (lime or cement)

- C4 tabilised, UCS 4 MPa

- C2 tabilised, UCS >2 MPa

- C1 tabilised, UCS >1 MPa

- CM Modied, UCS 0.5 MPa

Climatic zones- Dry

- Moderate

- Wet

Design depth

Earthworks

- Fill

- Improved subgrade layers

- Roadbed

Environmental Impact Assessment

Fogspray (Sprayed on a surface dressing)

Granular materials

- CRR Crushed fresh rock- CRS Crushed stones and oversize

- G80 Natural gravel CBR > 0%

- G60 Natural gravel CBR > 0%

- G45 Natural gravel CBR >45%

- G25 Natural gravel CBR >25%

Gravel roads

- GC rading coefcient

- GW ravel wearing course

- P hrinkage product (LSx%pass.75mm)

Materials for earthworks

- DR ump rock: un-sorted rock

- G15 Natural gravel/soil CBR > 5%

- G7 Natural gravel/soil CBR > %

- G3 Natural gravel/soil CBR > %

Materials testing methodsBR - alifornia bearing ratio

- ra ng mo u us

- n t a consumpt on o me

- iquid limit

- near s r n age

- aximum dry density

- pt mum mo sture content

- ast c ty n ex

- lastic limit

- ggregate strengt nes va ue

UCS - nconned compression strength

Materials testing standards

ssue y t e mer can ssoc at on or tate g way

cials

ASTM Issued by the American Society for Testing and Materials

r t s tan ar

entra ater a s a oratory n stry o or s ,

Norwegian Public Roads Administration

ec n ca et o s or g ways out r can ser es o

standards)

Prime (Sprayed on granular layers)

Problem soils

- xpansive soils

- ispersive soils

- aline soils/water

Subbase

Subgrade

- mproved subgrade layers

- n-situ subgrade and ll

15 CBR > 15%

7 CBR > 7%

3 CBR > 3%

Surfacing

- inder course, bituminous hot mix

- ravel wearing course

- urface treatments

- earing course, bituminous hot mix

Tack coat (Sprayed on bituminous layers)

Trafc

- esign period- 80 - Equivalent standard axle (8160 kg)

- eavy vehicles: > t un-laden weight

Very heavy goods vehicles: 4 or more axles

Heavy goods vehicles: 3 axles

Medium goods vehicles: 2 axles

Buses: > 40 seats

- ight vehicles: < 3t un-laden weight

- VEF Vehicle equivalency factor (the number of E80 per

heavy vehicle)

Unfavourable subgrade conditions

- avities, termites, rodents

- igh water table and swamps

- ells- et spots


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Pavement Details


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Table of Contents1 INTRODUCTION...........................................................................................................................................................3

1.1 Background, purpose and scope .............................................................................................................................3

1.2 Structure of the Field Testing Manual 2003 ...........................................................................................................4

1.3 Layout.....................................................................................................................................................................4

2 GEOTECHNIQUE .........................................................................................................................................................7

2.1 Planning of investigations - methodology..............................................................................................................7

2.2 Ground investigations.............................................................................................................................................9

2.3 Soundings ............................................................................................................................................................12

2.4 Borings .................................................................................................................................................................13

2.5 Sampling ..............................................................................................................................................................15

2.6 Handling, transport and storage of samples .........................................................................................................19

2.7 Recording ............................................................................................................................................................19

2.8 Geotechnical test methods....................................................................................................................................20

3 PAVEMENT EVALUATION .......................................................................................................................................39

3.1 Pavement distress .................................................................................................................................................39

3.2 Methodology ........................................................................................................................................................42

3.3 Detailed condition surveys .................................................................................................................................. 45

3.4 Pavement strength structural surveys ............................................................................................................... 49

3.5 Test pit proling and sampling ............................................................................................................................52

3.6 Homogenous sections...........................................................................................................................................55

4 AXLE LOAD SURVEYS..............................................................................................................................................58

4.1 Introduction ..........................................................................................................................................................58

4.2 Resources for axle load surveys...........................................................................................................................58

4.3 Condition of survey sites......................................................................................................................................59

4.4 Weighing...............................................................................................................................................................62

4.5 Recording and reporting.......................................................................................................................................64

5 MATERIAL PROSPECTING AND ALIGNMENT SURVEYS...............................................................................71

5.1 Introduction ..........................................................................................................................................................71

5.2 Methodology ........................................................................................................................................................71

5.3 Alignment soil surveys.........................................................................................................................................77

5.4 Soils and gravel sources .......................................................................................................................................80

5.5 Rock Sources........................................................................................................................................................83

CONSTRUCTION CONTROL...................................................................................................................................89

6.1 Introduction ..........................................................................................................................................................89

6.2 Earthworks and unbound layers ...........................................................................................................................89

6.3 Cemented Layers ..................................................................................................................................................94

6.4 Bituminous Layers ...............................................................................................................................................95

6.5 Bituminous Seals ..................................................................................................................................................98

6.6 Concrete..............................................................................................................................................................101

6.7 Construction control test methods......................................................................................................................104


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Appendix 1: CML laboratory and eld test methods ..............................................................................................................121

Appendix 2: Soil proling descriptions after Brinks and Jennings......................................................................................... 123

Appendix 3: CUSUM method for delineation of homogenous sections................................................................................. 124

Appendix 4: The MERLIN method for measuring roughness................................................................................................125

Appendix 5: Layout of survey sites and trafc saty measures..............................................................................................128

Appendix 6: Design Trafc Loading - example......................................................................................................................129

Appendix 7: Denitions, terms, prexes and basic units ........................................................................................................131

Appendix 8: Abbreviations .....................................................................................................................................................135

Appendix 9: Worksheets .........................................................................................................................................................138

LIST OF TABLES

Table 2.1: Samples of soils or rock using various methods of sampling. Expected classications. .....................................18

Table 3.1: Typical types of distress associated with pavement performance........................................................................39

Table 3.2: Possible causes of trafc-associated distress........................................................................................................ 1

Table 3.3: Possible causes of non-trafc-associated distress. ............................................................................................... 1

Table 3.4: Minimum required test frequencies for pavement evaluation. ............................................................................ 4

Table 3.5: Data obtained in the detailed conditions survey. .................................................................................................. 5

Table 3.6: Condition rating, visual evaluation. ..................................................................................................................... 6

Table 3.7: Condition rating, rut depth measurements. .......................................................................................................... 7

Table 3.8: Condition rating, roughness measurements.......................................................................................................... 8

Table 3.9: Condition rating, maximum surface deection, Benkelman Beam......................................................................52

Table 4.1: Heavy vehicle categories...................................................................................................................................... 62

Table 4.2 Trafc load distribution between lanes. ...............................................................................................................66

Table 4.3 Trafc Load Classes - TLC .................................................................................................................................. 4

Table 5.1: Required size of sample. ...................................................................................................................................... 6

Table 5.2: Design depth measured from nished road level. ............................................................................................... 8

Table 5.3: Sampling frequency. ............................................................................................................................................. 9

Table 5.4: Borrow pit investigations, minimum test frequency.............................................................................................82

Table 6.1: Methods and purposes of the eld testing activities.............................................................................................90

Table 6.2: Sampling Frequencies, earthworks and layerwork. .............................................................................................90

Table 6.3: Density test methods. Inherent weakness of method and common operator errors. ............................................92

Table 6.4: Testing frequencies, eld density for earthworks and layerwork......................................................................... 93

Table 6.5: Test methods for moisture content. Features of each method ..............................................................................93

Table 6.6: Sampling frequencies for bituminous materials. ..................................................................................................95

Table 6.7: Testing frequencies for eld density testing of bituminous materials. .................................................................96

Table 6.8: Sampling frequencies for bituminous seals........................................................................................................100


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1



LIST OF FIGURES

Figure Pavement Details ...................................................................................................................................................vi

Figure 2.1: Example of areas inuencing the works at a far distance from the site. ..............................................................10

Figure 2.2: Principle of vane testing. ......................................................................................................................................26

Figure 2.3: U100 (U4) core sampler assembly. ......................................................................................................................30

Figure 3.1: Sequence of pavement evaluation leading to rehabilitation design...................................................................... 3

Figure 3.2: Rebound deection measurements using Benkelman Beam................................................................................ 51

Figure 3.3: Assessing data for determination of homogenous sections..................................................................................55

Figure 4.1: Sources of error at the weighing site surface gradient. .....................................................................................60

Figure 4.2: Sources of error at the weighing site surface evenness. ....................................................................................60

Figure 4.3: Sources of error at the weighing site surface evenness by the scale. ................................................................61

Figure 4.4: Sources of error at the weighing site surface evenness, consequences. ............................................................61

Figure 4.5: System for recording axle congurations............................................................................................................. 64

Figure 5.1: Use of information from eld surveys in pavement design. ................................................................................ 2

Figure 5.2: Principle of required quantity for material prospecting vs. theoretical quantity from the project drawings ....... 2

Figure 5.3: Minimum sample size of soils as a function of particle size................................................................................ 4

Figure 5.4: Method of sampling from trial pit.. ...................................................................................................................... 5

Figure 5.5: Reducing the sample size by quartering............................................................................................................... 5

Figure 5.6: An example of good labelling. ............................................................................................................................. 6

Figure 5.7: Examples, longitudinal prole. Information from trial pits. ................................................................................ 8

Figure 5.8: Theoretical material volumes - without loss - in natural, loose and compacted states. ......................................81

Figure 5.9: Typical loss of available material volumes during the process of winning natural gravel

for pavement layers. .............................................................................................................................................82Figure 5.10: Core box before placing wooden rods for marking core loss...............................................................................86


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TANROADS Central Materials Laboratory (CML)2 Chapter 1Introduction

ch1

1 INTRODUCTION

hapter 1: Table of Contents

1.1 ackground, purpose and scope .......................................................... 2

1.2 Structure of the Field Testing Manual - 2003 ..................................... 3

1.3 ayout .................................................................................................... 3

1 Introduction

2

6

3

5

Appendices


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Central Materials Laboratory (CML) TANROADS

3Chapter 1Introduction

ch1

1 NTRODUCTION

. ac groun , purpose an scope

The Field Testing Manual - 2003 forms part of the development of Tanzanian

Standards, Specications and Guidelines for roads, that Ministry of Works and

Tanroads are conducting under the programme for institutional cooperation with

the Norwegian Public Roads Administration. The following documents have

already been prepared and were launched under endorsement by the Ministry of

Works:

Pavement and Materials Design Manual - 1999

Laboratory Testing Manual - 2000

tandard Specications for Road Works - 2000

It is vitally important that the documents are rmly based on the same platform

regarding methods of testing, interpretation of results and application in the pro-

cess for planning, design, construction and maintenance of roads. An important

part of this process is the work being carried out in the eld, to form the basis

or road design, quality control and methods applied during construction and

maintenance.

The Field Testing Manual - 2003 serves the purpose of setting standards for

eld investigations and eld testing, and is a reference book providing advice

or engineers and technicians involved in such work. The Manual is prepared

with links to the above documents in respect of method and minimum require-ments for investigations and data collection. This includes investigations for

new projects as well as evaluation of existing roads with the purpose of utilising

the pavement structure in rehabilitation and upgrading of the road. Appropriate

standards of workmanship in road construction and maintenance, as described

in the above documents, is reected in the Field Testing Manual - 2003 in de-

scriptions of appropriate construction quality control.

The Manual is prepared with emphasis on being a practical handbook that

provides appropriate cost effective investigations of sufcient accuracy for the

purpose.


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TANROADS Central Materials Laboratory (CML)4 Chapter 1Introduction

ch1

. Structure of the Field Testinganua -

The Field Testing Manual 2003 is divided into its major chapters according to

thepurpose of collecting the information in the eld, i.e.:

1 Introduction:

urpose ntro uct on to t e anua wt ac graoun an purpose an

scope.

2 Geotechnique:

Purpose: Investigations related to stability of foundations for e.g. bridges

and other structures, stability of embankments and cuttings.

3 Pavement evaluation:

urpose: Assessment of the condition of existing pavements, to formbasis for optimal design of rehabilitation measures.

4 Axle load surveys:

urpose: Assessment of existing trafc loading to form the basis for

projection of future trafc loading for the purpose of pavement

design and design of rehabilitation measures.

5 Material prospecting and alignment surveys:

Purpose: Pavement design of new roads and supply of construction

materials for both new road construction and rehabilitation.

Construction control:

Purpose: Quality Control during construction.

. ayouParts of the Manual are printed with the same layout as the method sheets of the

Laboratory Testing Manual - 2000. This is considered a superior layout where

a number of standardised methods are being described, but is not ideal way of

presenting large amounts of informative text. A mixed layout has therefore been

chosen for the Field Testing Manual - 2003 in order to make a user friendly

format and to capture the best of both layouts. Wherever practical, the method

sheet layout has been applied due to its more concise format.


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5Chapter 2Geotechnique

ch2Field Testing Manual - 2003


2 Geotechnique

1

6

3

5

Appendices

Chapter 2: Table of Contents

2.1 lanning of investigations - methodology.......................................7

2.1.1 General ...................................................................................

2.1.2 Objectives............................................................... ...............

2.1.3 ype, extent and stages of site investigations ........................

2.1.4 Desk study.............................................................................. 8

2.1.5 Site reconnaissance ............................................................... 8

2.1.6 Detailed studies ..................................................................... 8

2.1.7 Construction and performance appraisal................................ 9

2.2 Ground investigations ......................................................................

2.2.1 Purpose of ground investigations........................................... 9

2.2.2 Project stages.......................................................................... 92.2.3 Requirements.......................................................................... 9

2.2.4 Procedures.............................................................................. 9

2.2.5 ypes of ground investigations ........................................... 10

2.2.6 Extent of ground investigations ........................................... 10

2.2.7 Choice of methods for ground investigation........................ 11

2.2.8 Personnel.............................................................................. 11

2.3 Soundings ........................................................................................ 12

2.3.1 General ................................................................................. 12

2.3.2 Static soundings ................................................................... 12

2.3.3 Sounding tests in boreholes ................................................. 12

2.3.4 Dynamic soundings ............................................................. 12

2 GEOTECHNIQUE


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6 Chapter 2Geotechnique



2.4 orings............................................................................................. 3

2.4.1 General ................................................................................. 13

2.4.2 Boring methods .................................................................... 13

2.5 Sampling.......................................................................................... 5

2.5.1 Sampling techniques ........................................................... 15

2.5.2 Sample disturbance classes .................................................. 15

2.5.3 Disturbed samples ............................................................... 16

2.5.4 Un-disturbed samples........................................................... 17

2.5.5 Choice of sample method depending on soil conditions...... 17

2.5.6 Field classication and sample size .................................... 18

2.6 andling, transport and storage of samples ................................ 9

2.7 ecording ........................................................................................ 9

2.7.1 Field recording ..................................................................... 19

2.7.2 Reporting ............................................................................. 19

2.8 Geotechnical test methods ............................................................. 0


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2 GEOTECHNIQUE

. Planning of investigations -

me o o ogy

2.1.1 General

It is now common to use the term site investigation in a wide sense, considering

not only the sampling or exploration of the ground, but the complete aspect of

investigations to assess the suitability of a site for executing civil works.

Geotechnical ground investigation covers a series of investigation types fromengineering geological mapping by various means to detailed boring and sam-

pling for laboratory testing or in situ testing of soil/rock engineering properties.

The extent and method of investigation should rst be decided based on the

technical requirements of the project, as established through the initial evalua-

tion stages. This initial phase may include a preliminary ground investigation.Ground investigation specialists should be consulted at this stage.

The investigation programme thus planned by the specialist may be changed to

utilize the available resources. However, the Client must be made aware of any

particular aspects of the project which may not be properly investigated due to

lack of resources, either nancial or technical, so that this may be properly ac-counted for in the design and subsequent construction of the works.

2.1.2 Objectives

The primary objective of most site investigations is to secure sufcient informa-tion to enable a safe and economical design to be made. Thereby the construc-tion can proceed without any difculties and in-service performance or safety is

not adversely affected.

An important objective of site investigations is to determine the effect of

changes to the surroundings that will incur as a consequence of implementing

the project. E.g. the construction of high embankments may affect large areas

beyond the project location.

2.1.3 ype, extent and stages of site investigations

Type and extentThe type and extent of site investigation depends on:

Proposed works.

Conditions of the site.

Project stage.

Available resources.

By proceding in stages the investigation can always seek to verify and expand

information collected previously.

Procedure

The general investigation procedure is proceeding in stages:

1. Desk study.

2. Site reconnaissance.

3. Detailed study for design, including ground investigations.

By proceding in stages the investigation canalways seek to verify and expand information

collected previously.


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During and after construction, the investigations may continue:

4. Follow up during construction.

5. Post-construction appraisal/performance evaluation.

2.1.4 Desk study

The objectives of the desk study are:

o collect all existing information regarding the proposed works and the

conditions of the site.

o learn as much as possible from previous experience and studies, and

about adjacent property that may be affected by the works. This includes

a study of the previous use of the site and of previous projects in the area,

heir design, construction and performance.

The desk study should also obtain information regarding existing services etc.

that must be considered for the project and when conducting the actual ground

investigations. The following information may be required:

and survey, i.e. maps, aerial photographs, ownership, present use, existingstructures.

ermitted use and restrictions, i.e. land acquisitions, general and local regu-

ations and rights of way.

pproaches and access.

Climate, i.e. temperature, rainfall, seasons etc.

Ground conditions, i.e. geology, soil and vegetation, maps and reports and

ydrogeology.

Sources of material for construction, e.g. existing borrow pits.

Services, i.e. drainage, water, electricity, telephone.

2.1.5 Site reconnaissance

The site or project area should be inspected thoroughly, preferably by foot. The

objective of such a reconnaissance is to gather as much information as possible,

by observation of the ground and geological features and the performance of

any existing constructions. A note of local practices and resources is important.

Vegetation, river courses, erosion gullies, existing borrows and cuttings can

reveal important information, such as signs of swell or collapse, settlement and

cracks, in existing structures. Vehicles and even light aircraft may be appropri-

ate in the case of large project areas.

2.1.6 Detailed studies

This investigation stage includes the ground- and materials investigations prop-

er, and other investigations that may be appropriate, like a topographical survey.In the case of a dam or a bridge for example, the question of possible ooding,

erosion or changes to the surroundings may require hydrological and other

environmental studies. The kind of detailed information required for design and

construction is as follows:

Detailed Land survey

erial photography.

Ground conditions.

ydrogeology and hydrography.

Climate.

Sources of materials for construction.

isposal of waste and surplus materials. djacent properties and services.

Site reconnaissance prior to ground investi-

gations is of paramount importance.


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2.1.7 Construction and performance appraisal

This stage is primarily to ensure that the design is adjusted as required if the

conditions revealed by the construction differ from the results and assumptions

of the pre-construction investigations.

2.2 round investigations

2.2.1 urpose of ground investigations

Site and ground investigations of several types may be required in a road con-

struction project:

Sites for new works.

Defects or failures of existing works.

Safety of existing works or structures.

Materials for constructional purposes.

2.2.2 roject stages

Engineering construction projects are usually carried out through different

stages, normally identied as:

Feasibility study and preliminary design.

Detailed design.

Construction stage.

The various planning stages are most distinct in major projects. The contractor

or builder may be engaged at an early stage and thus take part in the nal design

or more commonly come in after the nal design.

2.2.3 equ remen s

To meet the primary objectives of the site investigation, the ground investiga-

tion should generally satisfy the following basic requirements:

Clarify the geology of the site.

Establish the soil and rock prole.

Establish the ground water prole.

Establish the engineering properties of the ground.

Cover all ground which may be permanently or temporarily changed by the

project.

There may also be other requirements particular to each project, and the basic

requirements must be detailed.

2.2.4 rocedures

The general procedures for ground investigations are as follows, based on the

results of the desk study, site reconnaissance and an evaluation of the project

type and stage:

1. Dene the objective of the investigation.

2. Decide the extent of the investigation.

3. Decide the method of investigation.

4. Carry out eld and laboratory work, possibly by stages.

5. Reinstate all pits etc. by carefully backlled, and any pits that have to be

left open and unattended should be fenced off or properly secured with

other appropriate methods.

he results should be continuously evaluatedo see if the objectives are met, and plans andme o s s ou e correc e necessary.


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Laboratory testing forms a considerable part of the total cost of investigation

and the laboratory test programme shall therefore be devised by the engineer re-

sponsibility for the overall execution of the project including the nancial side.

The extent of investigation conducted at the various planning stages may vary

widely. Some feasibility studies may not require a detailed ground investigationat all, if all the necessary information is available from the desk study and site

reconnaissance.

2.2.5 Types of ground investigations

The type of ground investigations and the methods used will of course vary

widely from case to case. The different methods of ground investigation are as

follows:

rial pits, shafts and headings.

Soundings, borings. Tests in boreholes.

Other in situ or eld tests.

Sampling, laboratory tests. Geophysical methods.

emote sensing.

The method of investigation to be used is decided by the:

Character of the ground.

echnical requirements.

Character of the site.

vailability of equipment and personnel.

Cost.

2.2.6 Extent of ground investigations

GeneralThe extent of investigations required, will vary from case to case depending on

the project type and stage, the ground conditions and previous knowledge about

the conditions. It is important that an experienced engineer carries out a eld

assessment to locate areas affected by the works that are not obvious at rst

sight. An example of such a situation is illustrated inFigure 2.1. Some general

guidelines are given below.

Figure 2.1: Example of areas inuencing the works at a far distance from the site.

M

Drill rig in position on site.


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LocationThe exploration points pits or boreholes should be located such that the general

conditions of the site are established, at the same time ensuring that sufcient

detailed information is obtained. Consequently, the greater the ground variationsthe greater the number of exploration points required. For ordinary structures a

grid pattern of spacing 10 to 30 metres is often used. Minor structures coveringa small area should be investigated in a minimum of three points.

The exploration points, borings or pits should be positioned so as not to inter-

ere with the proposed construction by disturbing the ground at the foundationlevel or by opening up for water from deep aquifers.

Depth of investigationThe general rule is to investigate to the depth which may be affected by the

works

For foundations of structures, the stressed depth is normally one and a halftimes the loaded area, measured below the base of the foundation. In the case of

light structures the project may inuence the ground moisture regime, causing

swell or collapse to greater depths. It is therefore always desirable to determine

the total thickness of deposits of such soils.

For pile foundations simple rules cannot be given. The investigation depth hasto be decided and revised on the basis of results of the investigations in each

individual case. Sufcient capacity to carry the pile loads has to be proven, and

investigations for pile foundations may include test piling and load testing.

Embankments should be investigated to a depth sufcient to check possible

shear failures through the foundation strata, evaluate settlements and, in the caseof dams, check seepage conditions. Cuts and excavations should be investigated

to a depth sufcient to evaluate the deformation and stability conditions, givingdue regards to ground water and any soft strata.

2.2.7 Choice of methods for ground investigation

The following issues should be taken into consideration in the choice of method

or ground investigations:

Project requirements.

ground conditions.

project budget.

available time, equipment and personnel resources.

When evaluating alternative ground investigation methods the logistics of

operating in the local environment is important, such as access to water for drill-

ing. E.g. both core drilling and cable percussion methods require water, whereas

augers dont.

2.2.8 ersonnel

Ground investigations should be planned and directed by a senior engineer orgeologist also responsible for assessing and interpreting the results. The supervi-

sion of eld work may be delegated to qualied engineers or geologists assisted

by trained senior eld technicians or drilling supervisors. This personnel should

be conversant with eld description and classication of soils and rock and theinvestigation methods used.

Borehole/test pits logging and eld material descriptions are normally the respon-

sibility of the driller/technician and should be checked by the eld supervisor.

Investigation of ground water level bysimple methods.


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. Soundings

2.3.1 General

The sounding tests are purely empirical. They are simple to perform and have

been in use for many years. Consequently there is a wealth of experience,

data and correlations from all parts of the world, linking the test results to soil

parameters and performance of structures, to ensure a reasonably condent

interpretation of the results.

Soundings from the surface without sampling and without pre-boring, may be

carried out by several means; and consists in its simplest form of the driving

of a steel rod into the ground until hard stratum is located. However, standard

procedures have been developed to enable the systematic recording of relative

resistance of various soil layers and the accumulation of empirical relationships

between sounding resistance and soil engineering characteristics. Such meth-

ods are:

ynamic soundings.

Static soundings.

eight- and Rotary soundings.

Both static and rotary sounding systems with electronic or hydraulic recording

of the resistance to penetration have lately been developed.

2.3.2 Static soundings

Static soundings or cone penetration tests (CPT) of several types are in wide

spread use. The tests are known by a number of terms depending on manufac-

turer etc., for example Dutch cone testing. The basic principle of all such tests

is that a rod is pushed into the ground and the resistance on the point and/or theshaft is measured by various means. The equipment is either anchored to the

ground by screws and/or employ heavy dead weights/drill rigs to give the neces-

sary reaction forces for the penetration.

2.3.3 Sounding tests in boreholes

Borehole tests are of several kinds and varies from the determination of resis-

tance to penetration (SPT or CPT) to direct measurement of shear strength of

clays. Some soundings normally carried out without the use of independent

boreholes, may also be performed from the bottom of boreholes.

2.3.4 Dynamic soundingsThe main use of all direct dynamic soundings i.e. soundings not requiring bore-

holes, is to give a rapid and cheap test of relative conditions within a site or to

compare different sites.

The simple method of driving a steel rod into the soil until it meets resistance is

only useful for determining the depth to a hard stratum like rock or calcrete/hard

laterite, under a relatively shallow layer of softer soil. The most widely used

dynamic sounding test is the Standard Penetration Tests (SPT). The sample

obtained in SPT is used for soil identication.

Simple soundings may give a relative measure of the hardness of the ground

provided the penetration depth per hammer blow or within a certain time whenusing the percussion drill, is recorded. The resistance to penetration depends on

the soil type, and experienced drillers may be able to distinguish cohesive and


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rictional materials by the feel and sound of the drill steel. The dynamic sound-

ing method has limited penetration in rm ground and are not suitable for use in

coarse soils or soils containing rock fragments etc.

Standardisation of the sounding procedure and equipment; the drill steel rods

and point, the hammer weight, drop height and blow rate etc., has increased theuse of dynamic soundings to give a better indication of the type of soil present

and to determine the bearing capacity of the ground by empirical means in the

case of sands and gravels (frictional soils), particularly for the design of piles.

2.4 Borings

2.4.1 General

Borings are required for sampling the ground or to provide a hole in which to

conduct tests of the in-situ properties. The type of boring to be used depends on

the purpose and the ground conditions. The most important ground parameters

affecting the boring operations are:

The self supporting ability of the ground.

The content of larger particle size, cobbles etc.

In general cohesive soils are self supporting, so are some cemented sands and

silts, whereas granular materials below the ground water level are unstable.

The borehole sides may be supported by inserting linings of steel casing, or

by lling the borehole with a head of water or heavy liquids like a bentonite

suspension called mud or slurry. The worst ground conditions to drill through

are layers of boulders.

2.4.2 oring methods

Borings may be carried out by various methods:

Auger borings. By hand or mechanical.

Percussion boring. Cable rig.

Rotary drilling. Core drilling.

Wash borings.

Other methods.

Auger borings

Auger borings may either be conducted by hand or by mechanical means, and

there are various types in use.

Hand augers are used in self supporting ground without large gravels or cobbles,

down to a depth of 2 to 5 metres. Disturbed samples may be obtained and open

tube samplers may be used from the bottom of the hole. Small portable power

augers may drill to depths exceeding 10 metres and casings may be used if

necessary.

Disturbed samples may be obtained by lifting the auger out of the ground or by

spinning the material up in case of the continuous ight auger. Auger borings

are mainly used in cohesive (self supporting) soil. Casings may be inserted in

cohesionless soil.

Some augers have a hollow stem, permitting the use of a drive sampler through

the stem. This type of auger acts as a casing of internal diameter 75 to 150 mm

and may also be used for deep drilling below the water table.

Two types of Auger.


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A disadvantage with samples from mechanical augers is that the material

brought up becomes mixed, layering is thus difcult to detect and so is the

transition to rock particularly in the case of soft, weathered rocks so common in

Tanzania. The basement gneisses for example will often appear as a sand.

Percussion boringsPercussion borings loosens the ground with a drop chisel. The spoils are mixed

with water and lifted out of the hole by a shell or baler.

The shell may be used as a boring tool in loose granular materials below theground water level. Other tools used are a clay cutter.

The clay cutter and shell bring up disturbed material that are sufciently repre-sentative to identify the strata. Samples may also be taken from the bottom of

the hole. However, some of the percussion boring procedures, such as adding

water to a dry hole in clay or working with a water level other than the groundwater level, may not be acceptable from a soil exploration point of view.

There is usually some disturbance of the soil below the bottom of the borehole,

from which samples are taken, and it is very difcult to detect thin layers of soil

and minor geological features with this method. Percussion boring can be em-

ployed in most types of soil, including those containing cobbles and boulders.The rig for percussion boring is very versatile and can normally be tted with a

hydraulic power unit and attachments for mechanical augering, rotary core drill-

ing and cone penetration testing.

Rotary drillingRotary drilling is the traditional drilling method for investigations of rock, but

the method is also used in soils. It is particularly useful in the kind of layered

hard/soft strata typical for the regions of volcanic rocks, tuff and ashes.

There are two forms of rotary drilling, open hole drilling and core drilling. Open

hole drilling, which is generally used in soils and weak rock, uses a cutting bitto break down all the material within the diameter of the hole. Water or mud is

used to ush out the material. Open hole drilling can only be used as a means of

advancing the hole, the drilling rods can then be removed to allow tube samplesto be taken or in situ tests to be carried out. In core drilling, which is used in

rocks and hard clays, the bit cuts an annular hole in the material and an intact

core enters the barrel, to be removed as a sample. However, the natural water

content of the material is liable to be increased due to contact with the drillinguid. Typical core diameters are 41 mm, 54 mm and 76 mm, but can range up to

165 mm. The larger diameters are used in difcult rock.The advantage of rotary drilling in soils is that progress is much faster than with

other investigation methods and disturbance of the soil below the borehole is

slight. The method is not suitable if the soil contains a high percentage of gravel(or larger) particles as they tend to rotate beneath the bit and are not broken up.

Rock core samplersRotary core samples are obtained by the core drilling method, mainly used for

sampling of rock. Sampling is done by double or triple tube core barrels. As

for soil, greater diameter gives better samples. A core size of 76 mm is usually

satisfactory, but 100 to 150 mm and the triple barrel technique gives the bestresults in weak, watered or fractured rock.A core size of 76 mm is usually satisfactory,

but 100 to 150 mm and the triple barreltechnique gives the best results in weak,watered or fractured rock.


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as or ng Wash borings break up the ground by the percussive action of a chisel in com-

bination with the erosive force of water being jetted out through narrow holes in

the chisel. The water also washes the soil particles to the surface.

Wash boring is mostly used in sand and ner soils. Casing or drilling mud isused in collapsing ground. The method cannot be used to obtain soil samples as

the soil brought to the surface is not representative of the strata being worked.

However, this boring technique causes no or little disturbance to the soil im-

mediately below the bottom of the hole, enabling tube samples to be taken or in

situ tests like the SPT to be carried out. The method is also used to determine

the depth to rock below ne grained soils.

2.5 Sampling

2.5.1 Sampling techniques

There are four main techniques for sampling the ground:

Taking disturbed samples from the drill tools or from excavating equipment

in the course of boring or excavation.

Drive sampling, in which a tube or split tube sampler having a sharp cutting

edge at its lower end is forced into the ground either by a static thrust or by

dynamic impact.

Rotary sampling, in which a tube with a cutter at its lower end is rotated

into the ground, thereby producing a core sample.

Taking block samples specially cut by hand from a trial pit, shaft or heading.

2.5.2 Sample disturbance classes

There are ve disturbance classes for samples depending on the degree to which

they have been disturbed by the process of sampling, handling and transport

until nally laboratory testing:

Class 1 Classication, moisture content, density, strength, deformation

and consolidation characteristics.

Class 2 Classication, moisture content, density.

Class 3 Classication, moisture content.

Class 4 Classication.

Class 5 None sequence of strata only.

Within the ve classes there are two main categories for practically denoting the

samples:

Disturbed samples.

Undisturbed samples.

Class 1Class 1 samples for precise determination of strength and deformation charac-

teristics may be impossible to obtain in sensitive cohesive soils, and of non-co-

hesive soils from below the water table.

Residual soils represent a particular problem for Class 1 sampling as they tend

to swell during sampling, often resulting in permanent damage to the soil struc-

he principal types of tube samplers are: Open tube samplers Stationary piston samplers Continuous sampler Compressed air sampler Rotary core sampler


25/155




ture. This swell is due to lack of internal suction in partly saturated soils, and

even in the case of saturated soils, an open structure with large voids will not be

able to maintain suction without volumetric expansion and desaturation.

Class 2Class 2 is taking of disturbed samples with additional requirements to obtain

eld/bulk density of the soils. Determination of the eld density may be ex-

ecuted by:

lock sampling.

Core cutter method (shoe cutter).

Split spoon sampler.

Classes 3 to 5Classes 3 to 5 are the commonly called disturbed samples. Apart from the actual

sampling, the quality also depends on how the sample is sealed, transported,

stored, and treated in the laboratory. The most important consideration is to

observe that class 3 requres sealed packaging for measuring moisture content inthe laboratory.

2.5.3 Disturbed samples

ObjectivesDisturbed samples, which are used mainly for soil classication tests, visual

classication and compaction tests. Disturbed samples have the following fea-

tures:

he same particle size distribution (grading) as the in-situ soil. he soil structure has been signicantly damaged.

he water content may be different from that of the in-situ soil.

Sampling methodsDisturbed samples can be excavated from trial pits or obtained from the toolsused to advance boreholes (e.g. from augers and the clay cutter) and from the

sampler of the SPT tests. The soil recovered from the shell in percussion boring

is decient in nes and is therefore unsuitable for use as a disturbed sample.

Trial pits, shafts and headings supply the most detailed and reliable data on the

soil in-situ conditions, enabling visual examination of strata boundaries and soilfabric.

Trial pits

Trial pits may be dug by hand or a light mechanical excavator in all soil types

above the ground water level. Excavation below the ground water level inpermeable soils will require dewatering, and the safe excavation depth is very

limited.

Shafts and headingsShafts are deep pits, normally hand excavated and supported by timbering or

bored by piling rigs. Headings or edits are inspection galleries excavated later-ally into the side of a shaft or from the surface of a steep hill. Both roof and

sides are supported.

Shafts and headings are not excavated below the ground water level of perme-

able ground. Because of the expense, they are normally only used for very large

and costly structures; dams, tunnelling projects etc. Headings are frequentlyused for the investigation of rock or soil/rock in the case of dam abutments.

Safety precautions must be observed, eseciallys op ng or suppor ng o e s es o eep p s e-fore personnel are allowed to enter trial pits. Sam-pling and inspection should be done immediatelyupon excava on o unsuppor e p s.


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2.5.4 n- s ur e samp es

ObjectivesUndisturbed samples are required to determine the strength and volume stability

characteristics of the soil. Undisturbed samples must preserve both the in-situ

structure and water content of the soil.

Sampling methodsUndisturbed samples can be cut by hand from trial pits or obtained by special

samplers, refer sample techniques b), c) and d) above. However, the quality of

such samples can vary considerably, depending on the sampler, the sampling

technique used and the ground conditions.

Open tube samplers. U4 core samplingU4, i.e. general purpose 100 mm diameter sampler, is used in all cohesive soils

and weak rock. A sample catcher or core-catcher is used to aid the recovery of

silty or sandy soil which tend to fall out upon withdrawal of the sampler.

The U4 sampler may either be forced down in one continuous movement or

be hammered down. When forced down, samples of non-sensitive, ne cohe-

sive soils of stiff or lower consistency may give Class 1 samples (highest class

undisturbed). However, the normal quality is Class 2 or even lower if hammered

into hard ground.

Open tube samplers other than U4Other open tube samplers of varying diameters, but of the same general working

principle as the U4 type are also in use. Special thin walled samplers have been

developed to improve the sample quality, but piston samplers are preferable.

Piston samplersThe standard 54 mm sampler (Geonor type) is designed to be driven down to

undisturbed soil well below the bottom of the borehole, where the thin walled

cylinder is pressed down in one continuous movement. The sampler is used in

silt and clay and will give Class 1 samples in soft to medium ground.

42 mm penetration sampler for use with dynamic sounding equipment of the

percussion drill type, may give Class 3 samples for classication and natural

moisture content.

Other piston samplers of sample diameter up to 100 mm or greater may be used

in special cases, for example to obtain samples of research quality.

2.5.5 Choice of sample method depending on soil conditions

Table 2.1 indicates which methods for ground investigations are suitable for

different types of soil conditions, and the class of disturbance to the sample that

can be expected for each method

e g es qua y samp e s are o a n e y ocsampling.

U4 core sample.


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Soil type, rock Samplers, tests Classication, comments

on-cohesive soils

containing boulders,

cobbles or gravels

Pit is desirable.

Percussion rigs with shell and chisel,with casing to support the borehole sides Class 5 disturbed sample only

Penetration tests are of imited use inground with boulders and cobbles, but are

useful in gravel and sandan

CPT tests are preferable to SPT below GWL.

Test pits or augers are useful, with casing or

hollow stem below GWL.

ston sampers or tu es w t core catc er.

Silt

Thin walled piston sampler Class 2 sample

tu es w t out core catc er Class 3 sample

Vane test Un-drained shear strength of clayey silt

CPT tests are preferable to SPT. Below GWL

ard, weathered tropical,

or over-conso ate c ay

Augers or cable percussion methods can be used. -

n wa e p ston samp er ass to

U4 tubes Class 1 to 3

amp e p t, cut oc samp ng e su te

Core drilling equipmentIn very stiff materials (sample is affected by

drilling water).

Soft clay

Augers or cable percussion methods can be used. -

n wa e pston samp er Class 1

U4 tubes Class 2

Vane test or CPT n-s tu s ear strengt .

Clays with gravel, cobbles

or ou ersTest pit is preferable. -

oc

Normally core drilling equipment is used. -

Cable percussion methods, sampled using U4

tubes with reinforced cutting shoe.In weak and weathered rocks, tuffs etc

Table 2.1: Samples of soils or rock using various methods of sampling. Expected clas-sications.

2.5.6 Field classication and sample size

Classication of samples in the eld should follow the method after Brinks and

Jennings as described inAppendix 2.

Determination of the eld density as part of the classication may be executed

by:

lock sampling. Core cutter method (shoe cutter). Split spoon sampler.

The required size of sample for indicator and compaction tests in the laboratorytests are given in Chapter 5.2.3 - Samplingfor various types of soils. Minimum

sample sizes are specied in theLaboratory Testing Manual - 2000 for each

geotechnical laboratory test.


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. Handling, transport and storage ofsamp es

Laboratory testing of samples shall be carried out as soon as possible after sam-

pling. Any necessary storage and handling must be such that the quality of thesample is not reduced or the class of disturbance of the sample is not changed

by the time they reach the laboratory. Undisturbed samples shall be cushioned

against jolting and vibrations, especially during transportation when there is a

great risk of such damage to the samples.

Loss of moisture from samples shall be prevented by appropriate means such as

use of waxing, rubber capping, plastic cling foil or other means as appropriate.

Special care should be taken if the samples have to be stored for an extended

period of time before testing.

2.7 Recording

2.7.1 ield recording

Sample descriptionField sample description and classication is part of the sampling procedure and

shall be carried out as set out in Chapter 5 - Materials prospecting and align-

ment surveys.

The aims of eld descriptions, in-situ testing and laboratory testing of samples

of soil and rock are:

1. To identify and classify the samples with a view to making use of past expe-

rience with materials of similar geological age, origin and condition; and

2. to obtain soil and rock parameters relevant to the technical objectives of the

investigation.

RecordingProper eld procedures include accurate setting out with reference to an identi-

able permanent physical object which should also be shown on the plan draw-

ing of the investigation. Normally, the ground level of test pits, bore holes etc.

should be determined.

All samples must be labelled with a unique sample identication including:

1. Project name.2. Date.

3. Location and elevation of borehole.

4. Depth.

5. Method of sampling.

6. Description.

. Remarks etc.

2.7.2 eporting

eneral

All eld work should be reported on standardised forms, which will also serve

as check lists for the personnel, to ensure that all relevant data for interpreta-

tion of the results are collected. A copy of the report should always follow the

samples to the laboratory.

Purpose made box for storage and shipmentf core samples.


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Soils and materials distribution mapsIn most investigations, the preparation of special soils and materials maps is a

very powerful way to compile, analyse and present all site investigation data.

On maps one should combine on one map all known topographical and soils/

materials features, such as:

General geology. xisting borrow pits. nown areas of clay. ock outcrops etc.

The technique of compiling data on maps is particularly useful for feasibility-

or preliminary studies, but will also aid the efcient planning and execution of

detailed ground investigations. Such maps are also very useful in locating the

optimal road alignment or position of a dam or bridge site.

2.8 Geotechnical test methodsField Tests

F2.01 Soundings Cone penetration - CPT BS1377: Part 9: 1990

BS5930: 1999

. Soundings Standard penetration test - SPT and

continuous core penetration test - CCPT

BS1377: Part 9: 1990

BS5930: 1999

F2.03 Soundings Vane test BS1377: Part 9: 1990

BS5930: 1999

. or ng U100 (U4) sampling, undisturbed samples BS5930: 1999

F2.05 Ground water ore pressure, groun wa er eve BS5930: 1999

F2.06 Ground water Permeability tests for soils and rocks BS5930: 1999

F2.07 Ground water Ground water sampling BS5930: 1999

F2.08 In-situt strenght Plate loading test BS1377: Part 9: 1990


30/155




Objective

The uses of the CPT test have traditionally been to predict pile driving resistance,

skin friction and end bearing capacity of driven piles in non cohesive soils re-

gardless of the groundwater conditions. The test with continuous resistance

recording is also commonly used to investigate clays. As with other probingsystems, the test only gives an indication of the soil type, and traditional boring

and sampling is required for a positive soil determination, using the CPT for

rapid interpolation between boreholes.

Description of method

The basic test procedure is to record the resistance when pushing the cone a

xed distance into the ground ahead of the outer rods, and then to push the

outer rods down into contact with the point and further advancing the cone and

outer ro s toget er to t e next test ept . e res stance w en a vanc ng t e

outer rods may also be recorded. The latest equipment registers the point resist-

ance electrically by sensors inside the point, enabling the recording of a contin-

uous resistance prole, including the pore water pressures. This type of equip-

ment may detect very thin soil layers. The cone or penetrometer point is at the

end of a string of inner rods running inside hollow outer rods sleeve or shaft.

Use of the CPT test is limited by the safe load that can be carried by the cone,

and the force available for pushing the penetrometer into the ground. Pene-

tration will normally have to be terminated when dense sand or gravel, coarse

gravels, cobbles or rock is encountered. Going from soft ground directly into

roc or co es may rea t e po nt.

Note that although the results of the CPT test may be analysed by soil mecha-

nics theory, the correlations between cone resistance bearing capacity, settle-

ment and shear strength are partly based on experience with certain soil types

and should thus be used with caution for other types of soil.

Cone penetration tests may also be conducted in boreholes.

References

BS 1377 : Part 9 : 1990 gives details on test procedure for CPT.

BS 5930 describes the procedure for a test variety called the Static

Dynamic Probing, combining the advantages of the CPT with the greater

penetration in rm ground of the dynamic penetration test.

ithout friction sleeve

r c on s eeve

Field investigations

Centra Materia s La oratoryeo ec n queest Method no F 2.01

oundings:

Cone Penetration Test - CPT

CPT test assembly.


31/155




Objective and description of method

The standard penetration test (SPT) is a dynamic penetration test for determi-

nation of relative strength or relative density of soils and weathered rock, and

for taking samples for identication of soils in the ground. The test is carried out

using a thick-walled sample tube with an open ended point split spoon or split

barrel sampler. The outside diameter of the sampler is 50 mm. This is driven

into the ground at the bottom of the borehole by blows from a standard weight

falling through a standard distance. The blow count gives an indication of the

density of the ground. The small sample that is recovered will have suffered

some disturbance but can normally be used for identication purposes.

The basis of the test consists of dropping with a free fall a hammer of mass

63.5 kg on to a drive head from a height of 760 mm. The number of such blows

necessary to achieve a penetration of the split-barrel sampler of 300 mm,

following a 150 mm seating drive, is regarded as the penetration resistance (N).

The SPT test may be carried out with a solid cone point suitable for hard

ground. This test is denoted Continuous Cone Penetration Test (CCPT).

CCPTThe Continuous Cone Penetration Test (CCPT) is performed in gravel and

coarse soils and is conducted in the usual way as for SPT except that the

sampler is replaced by a solid steel cone of the same outside diameter, with a

60 apex cone. The continuation of this description refers to the SPT test.

Advantages and limitations

The SPT is probably the most widely used in-situ test in the world. The test

assumes a carefully cleaned out borehole, established by a method which will

not disturb the ground below the bottom of the hole.

Advantages Great merit of the test.

Simple and inexpensive test.

he soil strength parameters which can be inferred are approximate, butmay give a useful guide in ground conditions where it may not be possible

o obtain borehole samples of adequate quality, e.g. gravels, sands, silts,

clay containing sand or gravel and weak rock.

Limitations Samples are disturbed, thus the soil strength parameters which can be in

erred are approximate.

hen the test is carried out in granular soils below groundwater level, thesoil may become loosened.

No disturbance may be impossible to achieve ingranular soils below the ground water level, whichmay be loosened by ow towards the borehole. Insuc con ons, n-s u es s per orme n epen-dently of a borehole should be considered, e.g.the CPT test.

BS 1377 : Part 9 : 1990 denotes the CCPT testSPT(C).

e es s some mes carr e ou n ore o esconsiderably larger in diameter than those used for

groun nves ga on wor , e.g. n e cons ruc onof bored piles. The result of the SPT is dependentupon the diameter of the borehole. Tests shouldno e regar e as w en per orme nboreholes with diameter larger than 150 mm.Boreholes with reduced diameter shall continuefor min. 1m before SPT commences.

In conditions where the quality of the undisturbedsamp e s suspec , e.g. very s y or very san yclays, or hard clays, it is often advantageous toalternate the sampling with standard penetrationes s o c ec e s r eng .

Centra Materia s La oratory


eo ec n queest Method no F 2.02

Soundings:

Standard penetration test - SPT andContinuous Cone Penetration Test - CCPT

SPT sampler.


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Apparatus

Boring equipment.The boring equipment shall be capable of providing a clean hole before insertion

of the sampler and shall ensure that the penetration test can be performed in

relatively undisturbed soil. When wash boring, a side-discharge bit shall be used

and not a bottom-discharge bit. The process of jetting through an open tube samp-

ler and then testing when the desired depth is reached shall not be permitted.

When boring in soil that will not allow a hole to remain stable, casing and/or

mud shall be used. The area that is exposed in the base of the borehole prior to

testing may inuence the result and consequently the borehole diameter shall

always be reported.

Split barrel sampler assemblyThe sampler assembly shall have the shape and dimensions shown in the

gure to the left. The drive shoe and split barrel, both having a uniform bore of

the same diameter, shall be made of steel with a smooth surface externally and

internally. The drive shoe shall be made of hardened steel. It shall be replacedwhen it becomes damaged or distorted to avoid the test result being affected.

The coupling shall contain a 25 mm nominal diameter ball check valve seated in

an orice of not less than 22 mm nominal diameter which shall be located below

the venting. The ball and its seat shall be constructed and maintained to provide

a watertight seal when the sampler is withdrawn. Alternative designs of check

valves are permitted provided they give equal or better performance.

Drive rodsThe rods used for driving the sampler assembly shall be tightly coupled by

screw joints and shall comply with BS 4019.

Minimum stiffness, general:.............................. type AW drill rods

Minimum stiffness, holes deeper than 20 m:.... type BW drill rods

Maximum rod weight: ....................................... 10.0 kg/m

Only straight rods shall be used and, the relative deections shall not be greater

than 1 in 1000 when measured over the whole length of each rod.

Drive assemblyThe drive assembly of an overall mass not exceeding 115 kg shall comprise the

following.

A hammer made of steel and weighing 63.5 + 0.5 kg.

A pick-up and release mechanism which shall ensure that the hammer has afree fall of 760 + 20 mm, and shall not inuence the acceleration and decel-

eration of the hammer or the rods. The velocity of the hammer shall be neg-ligible when the hammer is released at its upper limit.

A guide arrangement which shall permit the hammer to drop with minimalresistance and to ensure the hammer strikes the anvil squarely.

A drive-head (anvil) made of steel, with a mass between 15 kg and 20 kg,which shall be tightly screwed to the top of the drive rods.

Procedure

Preparing the boreholeClean out the borehole carefully to the test elevation using equipment that will

ensure the soil to be tested is not disturbed. When boring below the ground-

water ta e ma nta n at a t mes t e water or mu eve n t e ore o e at a

sufcient distance above the groundwater level to minimize disturbance of the

er o c c ec s or ro s ra g ness s a emade on site, including the threaded connectionsbetween consecutive rods.

"

"

"

"

"

PT slip barrel sampler assembly.


33/155




soil at the base of the borehole. Maintain the water or mud level in the borehole

throughout the test to ensure hydraulic balance at the test elevation.

Executing the testLower the sampler assembly to the bottom of the borehole on the drive rodswith the drive assembly on top. Record the initial penetration under this total

dead-weight. Where this penetration exceeds 450 mm omit the seating drive

and test drive and record the N value as zero. After the initial penetration, carry

out the test in two stages:

. Seating drive s ng stan ar ows t e seat ng r ve s a e a penetrat on

of 150 mm or 25 blows whichever is rst reached.

2. Test drive: The number of blows required for a further penetration of 300

mm and this is termed the penetration resistance (N). If the 300 mm pene-

ration cannot be achieved in 50 blows terminate the test drive. For test driv-

ing in soft rock the test drive should be terminated after 100 blows if a pene-

ration of 300 mm has not been achieved.

InterpretationInterpretation is part of foundation design, that should contain an site investi-

gation report including interpretation of the data. There is a lack of enforced and

consistent international standardization for the drilling technique and SPT tests

equipment. SPT results and soil parameters derived from data outside Tanzania

may therefore not correlate with results from SPTs derived in accordance with

practices in the country.

References BS 5930 : 1999 BS 1377 : Part 9 : 1990 eview of relevant literature:

CLAYTON, C.R.I. The standard penetration test (SPT): Methods and use.

IRIA Report no. 143. London: CIRIA 1995.

Withdraw the drilling tools slowly from the groundand up the borehole (when lled with water) to pre-ven suc on an consequen oosen ng o e soto be tested. When casing is used, do not drive itbelow the level at which the test is to commence.

The rate of application of hammer blows shall notbe excessive such that there is the possibility ofnot achieving the standard drop or preventingequ r um con ons preva ng e ween succes-sive blows.


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Centra Materia s La oratoryeo ec n queTest Method no F 2.03

Soundings:

Vane test

ObjectivesVane tests are used for determining the in-situ shear strength of fully saturated

cohesive soils (clays). The test can be extended to measure the re-moulded

strength of the soil.

Description of method

A steel vane at the end of a high tensile steel rod is pushed into the clay belowthe bottom of the borehole and torque is subsequently applied to induce shear

failure of the clay cylinder contained by the blades of the vane. With this type it

is not always possible to penetrate to the desired stratum without the assistance

of pre-boring. The torque required to rotate the vane can be related to the shear

strength of the soil.

In soft to medium strength clays this test may be carried out independently of

a borehole by jacking the vane into the ground in a protective casing. At the

required depth, the vane is advanced ahead of the casing, the test conducted,

and the vane and casing forced to the next test depth.

The vane test is normally restricted to fully saturated clays of un-drained shear

strength up to about 100 kN/m2, and is particularly useful in soft, sensitive

clays where sample disturbance may inuence laboratory results. It has little

app ca ty to part y saturate an cemente so s.

Advantages and limitations

AdvantagesA main advantage is that the test itself causes little disturbance of the ground

and is carried out below the bottom of the borehole in virtually undisturbed

ground.

m a ons

If the test is carried out in soil that is not uniform and contains only thin layersof laminations of sand or dense silt, the torque may be misleadingly high.

Results are unreliable in materials with signicant coarse silt or sand content.

The results are questionable in stronger clays or if the soil tends to dilate on

shearing or is ssured. The presence of rootlets in organic soils, and also of

coarse particles, may lead to erroneous results.

mall hand operated vane test instrumentsre available for use in the sides or bottomf an excavation.

he un-drained shear strength determined byan n-s u vane es s norma y no equa o eaverage value measured at failure in the eld,e.g. in the failure of an embankment on soft clay.

he discrepancy between eld and vane shearstrengths is found to vary with the plasticity of theclay and other factors.

Vane.


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Apparatuse vane test apparatus s a e e t er t e ore o e or penetrat on type, as

illustrated. Small hand held equipment is only suitable as indicator tests.

Principle of vane testing.


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VaneThe vane of cruciform shape, should be of preferably of high grade stainless

steel with

tanzania - road field testing manual - 2003

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