Tanzania field testing manual (2003)

THE UNITED REPUBLIC TANZANIA
MINISTRY WORKS
FieldTestingManual-2003-MinistryofWorksTANROADS,Tanzania
April 2003
ISBN 9987-8891-4-X ��

i
Field Testing Manual - 2003
TANROADS Central Materials Laboratory (CML)
THE UNITED REPUBLIC OF TANZANIA
MINISTRY OF WORKS
Field Testing
Manual - 2003

ii
April 2003
ISBN 9987-8891-4-X
Reproduction of extracts from this Manual may be made subject
to due acknowledgement of the source.
Although this Manual is believed to be correct at the time of
printing, Ministry of Works does not accept any contractual,
tortious or other form of liability for its contents or for any
consequences arising from its use. People using the information
contained in the Manual should apply and rely on their own skill
and judgement to the particular issue that they are considering.
Printed by: Elanders Novum AS, Oslo Norway
Layout: Jan Edvardsen, Interconsult ASA Oslo Norway

iii
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 Testing
Manual 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 Specifications for Road Works-2000 from where test limits for material quality and
extent of testing programmes are specified.
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 field of geotechnique, material prospecting
and alignment surveys, construction control, pavement evaluation and axle load surveys. The testing and sampling proce-
dures are clearly specified and their fields of application and limitations are clearly described. Moreover, the test procedures
are simplified to a practical approach, without compromising the correct procedure to be followed for each test.
This Manual will provide an invaluable documentation of field techniques to the benefit 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,
April 2003April 2003
F. MarmoF. Marmo
a.g Chief Executive Officer
TANROADS

iv
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 Norwegian
Agency for International Development (NORAD) have jointly financed 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

v
Summary of Terminology
Definitions of terms and abbreviations are presented in full in Appendix 7. Selected terms, definitions 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 AC
- Bitumen emulsion mix BEMIX (cold)
- Dense bitumen macadam DBM (hot)
- Foamed bitumen mix FBMIX (cold)
- Large aggregate mix for bases LAMBS (hot)
- Penetration macadam PM (cold)
Bituminous seals
- Emulsion fogspray
- Slurry seal
- Surface treatments:
Surface dressing
Cape seal
Otta seal
Sand seal
Cemented materials (lime or cement)
- C4 Stabilised, UCS >4 MPa
- CM Modified, 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 >80%
Gravel roads
- GC Grading coefficient
- GW Gravel wearing course
- SP Shrinkage product (LSx%pass.75mm)
Materials for earthworks
- DR Dump rock: un-sorted rock
- G15 Natural gravel/soil CBR >15%
Materials testing methods
CBR - California bearing ratio
GM - Grading modulus
ICL - Initial consumption of lime
LL - Liquid limit
LS - Linear shrinkage
MDD - Maximum dry density
OMC - Optimum moisture content
PI - Plasticity index
PL - Plastic limit
TFV - Aggregate strength (10% fines value)
UCS - Unconfined compression strength
Materials testing standards
AASHTO - Issued by the American Association for State Highway Of
ficials
ASTM - Issued by the American Society for Testing and Materials
BS - British Standard
CMLCMLCML - Central Materials Laboratory (Ministry of Works),
NPRANPRANPRA - Norwegian Public Roads Administration
TMH - Technical Methods for Highways (South African series of
standards)
Prime (Sprayed on granular layers)
Problem soils
- Expansive soils
- Dispersive soils
- Saline soils/water
Subbase
Subgrade
- Improved subgrade layers
- In-situ subgrade and fill
S15 CBR > 15%
S7 CBR > 7%
S3 CBR > 3%
Surfacing
- Binder course, bituminous hot mix
- Gravel wearing course
- Surface treatments
- Wearing course, bituminous hot mix
Tack coat (Sprayed on bituminous layers)
Traffic
- Design period
- E80 - Equivalent standard axle (8160 kg)
- Heavy vehicles: > 3t un-laden weight
Very heavy goods vehicles: 4 or more axles
Heavy goods vehicles: 3 axles
Medium goods vehicles: 2 axles
Buses: > 40 seats
- Light vehicles: < 3t un-laden weight
- VEF Vehicle equivalency factor (the number of E80 per
heavy vehicle)
Unfavourable subgrade conditions
- Cavities, termites, rodents
- High water table and swamps
- Wells
- Wet spots

vi
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Pavement Details

vii
Table of Contents
1 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 profiling 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
6 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

viii
Appendix 1: CML laboratory and field test methods..............................................................................................................121
Appendix 2: Soil profiling 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 traffic safity measures..............................................................................................128
Appendix 6: Design Traffic Loading - example......................................................................................................................129
Appendix 7: Definitions, terms, prefixes 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 classifications......................................18
Table 3.1: Typical types of distress associated with pavement performance........................................................................39
Table 3.2: Possible causes of traffic-associated distress........................................................................................................41
Table 3.3: Possible causes of non-traffic-associated distress. ...............................................................................................41
Table 3.4: Minimum required test frequencies for pavement evaluation. ............................................................................44
Table 3.5: Data obtained in the detailed conditions survey...................................................................................................45
Table 3.6: Condition rating, visual evaluation. .....................................................................................................................46
Table 3.7: Condition rating, rut depth measurements. ..........................................................................................................47
Table 3.8: Condition rating, roughness measurements..........................................................................................................48
Table 3.9: Condition rating, maximum surface deflection, Benkelman Beam......................................................................52
Table 4.1: Heavy vehicle categories......................................................................................................................................62
Table 4.2 Traffic load distribution between lanes. ...............................................................................................................66
Table 4.3 Traffic Load Classes - TLC ..................................................................................................................................74
Table 5.1: Required size of sample. ......................................................................................................................................76
Table 5.2: Design depth measured from finished road level. ...............................................................................................78
Table 5.3: Sampling frequency..............................................................................................................................................79
Table 5.4: Borrow pit investigations, minimum test frequency.............................................................................................82
Table 6.1: Methods and purposes of the field 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, field 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 field density testing of bituminous materials..................................................................96
Table 6.8: Sampling frequencies for bituminous seals........................................................................................................100

1
LIST OF FIGURES
Figure Pavement Details...................................................................................................................................................vi
Figure 2.1: Example of areas influencing 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......................................................................43
Figure 3.2: Rebound deflection 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 configurations.............................................................................................................64
Figure 5.1: Use of information from field surveys in pavement design. ................................................................................72
Figure 5.2: Principle of required quantity for material prospecting vs. theoretical quantity from the project drawings .......72
Figure 5.3: Minimum sample size of soils as a function of particle size................................................................................74
Figure 5.4: Method of sampling from trial pit.. ......................................................................................................................75
Figure 5.5: Reducing the sample size by quartering...............................................................................................................75
Figure 5.6: An example of good labelling. .............................................................................................................................76
Figure 5.7: Examples, longitudinal profile. Information from trial pits. ................................................................................78
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. .............................................................................................................................................82
Figure 5.10: Core box before placing wooden rods for marking core loss...............................................................................86

TANROADS Central Materials Laboratory (CML)2 Chapter 1
Introduction
ch1
1 INTRODUCTION
Chapter 1: Table of Contents
1.1 Background, purpose and scope.......................................................... 2
1.2 Structure of the Field Testing Manual - 2003..................................... 3
1.3 Layout .................................................................................................... 3
1 Introduction
2
6
3
4
Construction control
Pavement evaluation
Axle load surveys
5 Material prospecting and
alignment surveys
Appendices
Geotechnique

Central Materials Laboratory (CML) TANROADS 3Chapter 1
Introduction
ch1
1 INTRODUCTION
1.1 Background, purpose and scope
The Field Testing Manual - 2003 forms part of the development of Tanzanian
Standards, Specifications 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
► Standard Specifications for Road Works - 2000
It is vitally important that the documents are firmly 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 field, to form the basis
for road design, quality control and methods applied during construction and
maintenance.
The Field Testing Manual - 2003 serves the purpose of setting standards for
field investigations and field testing, and is a reference book providing advice
for 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 reflected 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 sufficient accuracy for the
purpose.

TANROADS Central Materials Laboratory (CML)4 Chapter 1
Introduction
ch1
1.2 Structure of the Field Testing
Manual - 2003
The Field Testing Manual – 2003 is divided into its major chapters according to
the purpose of collecting the information in the field, i.e.:
1 Introduction:
Purpose: Introduction to the Manual with backgraound and purpose and
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:
Purpose: Assessment of the condition of existing pavements, to form
basis for optimal design of rehabilitation measures.
4 Axle load surveys:
Purpose: Assessment of existing traffic loading to form the basis for
projection of future traffic 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.
6 Construction control:
Purpose: Quality Control during construction.
1.3 Layout
Parts 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.

5Chapter 2
Geotechnique
ch2Field Testing Manual - 2003
Central Materials Laboratory (CML) TANROADS
2 Geotechnique
1 Introduction
6
3
4
Construction control
Pavement evaluation
Axle load surveys
5 Material prospecting and
alignment surveys
Appendices
Chapter 2: Table of Contents
2.1 Planning of investigations - methodology....................................... 7
2.1.1 General ................................................................................... 7
2.1.2 Objectives............................................................................... 7
2.1.3 Type, extent and stages of site investigations ........................ 7
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 ...................................................................... 9
2.2.1 Purpose of ground investigations........................................... 9
2.2.2 Project stages.......................................................................... 9
2.2.3 Requirements.......................................................................... 9
2.2.4 Procedures.............................................................................. 9
2.2.5 Types 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

6 Chapter 2
Geotechnique
ch2 Field Testing Manual - 2003
2.4 Borings............................................................................................. 13
2.4.1 General ................................................................................. 13
2.4.2 Boring methods.................................................................... 13
2.5 Sampling.......................................................................................... 15
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 classification and sample size ..................................... 18
2.6 Handling, transport and storage of samples ................................ 19
2.7 Recording ........................................................................................ 19
2.7.1 Field recording ..................................................................... 19
2.7.2 Reporting.............................................................................. 19
2.8 Geotechnical test methods ............................................................. 20

7Chapter 2
Geotechnique
2 GEOTECHNIQUE
2.1 Planning of investigations -
methodology
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 from
engineering 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 first 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 financial 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 sufficient informa-
tion to enable a safe and economical design to be made. Thereby the construc-
tion can proceed without any difficulties 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 Type, extent and stages of site investigations
Type and extent
The 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 can
always seek to verify and expand information
collected previously.

8 Chapter 2
Geotechnique
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:
● Τo collect all existing information regarding the proposed works and the
conditions of the site.
● Τo 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,
their 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:
● Land survey, i.e. maps, aerial photographs, ownership, present use, existing
structures.
● Permitted use and restrictions, i.e. land acquisitions, general and local regu-
lations and rights of way.
● Approaches and access.
● Climate, i.e. temperature, rainfall, seasons etc.
● Ground conditions, i.e. geology, soil and vegetation, maps and reports and
hydrogeology.
● 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 flooding,
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
● Aerial photography.
● Ground conditions.
● Hydrogeology and hydrography.
● Climate.
● Sources of materials for construction.
● Disposal of waste and surplus materials.
● Adjacent properties and services.
Site reconnaissance prior to ground investi-
gations is of paramount importance.

9Chapter 2
Geotechnique
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 Ground investigations
2.2.1 Purpose 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 Project stages
Engineering construction projects are usually carried out through different
stages, normally identified 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 final design
or more commonly come in after the final design.
2.2.3 Requirements
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 profile.
● Establish the ground water profile.
● 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 Procedures
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. Define the objective of the investigation.
2. Decide the extent of the investigation.
3. Decide the method of investigation.
4. Carry out field and laboratory work, possibly by stages.
5. Reinstate all pits etc. by carefully backfilled, and any pits that have to be
left open and unattended should be fenced off or properly secured with
other appropriate methods.
The results should be continuously evaluated
to see if the objectives are met, and plans and
methods should be corrected if necessary.

10 Chapter 2
Geotechnique
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 financial side.
The extent of investigation conducted at the various planning stages may vary
widely. Some feasibility studies may not require a detailed ground investigation
at 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:
● Trial pits, shafts and headings.
● Soundings, borings. Tests in boreholes.
● Other in situ or field tests.
● Sampling, laboratory tests.
● Geophysical methods.
● Remote sensing.
The method of investigation to be used is decided by the:
● Character of the ground.
● Technical requirements.
● Character of the site.
● Availability of equipment and personnel.
● Cost.
2.2.6 Extent of ground investigations
General
The 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 field
assessment to locate areas affected by the works that are not obvious at first
sight. An example of such a situation is illustrated in Figure 2.1. Some general
guidelines are given below.
Figure 2.1: Example of areas influencing the works at a far distance from the site.
Mass influencing the worksMass influencing the works
Mass influenced by
the works
Drill rig in position on site.

11Chapter 2
Geotechnique
Location
The exploration points pits or boreholes should be located such that the general
conditions of the site are established, at the same time ensuring that sufficient
detailed information is obtained. Consequently, the greater the ground variations
the greater the number of exploration points required. For ordinary structures a
grid pattern of spacing 10 to 30 metres is often used. Minor structures covering
a 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-
fere with the proposed construction by disturbing the ground at the foundation
level or by opening up for water from deep aquifers.
Depth of investigation
The 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 half
times the loaded area, measured below the base of the foundation. In the case of
light structures the project may influence 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 has
to be decided and revised on the basis of results of the investigations in each
individual case. Sufficient 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 sufficient to check possible
shear failures through the foundation strata, evaluate settlements and, in the case
of dams, check seepage conditions. Cuts and excavations should be investigated
to a depth sufficient to evaluate the deformation and stability conditions, giving
due 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
for 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 don’t.
2.2.8 Personnel
Ground investigations should be planned and directed by a senior engineer or
geologist also responsible for assessing and interpreting the results. The supervi-
sion of field work may be delegated to qualified engineers or geologists assisted
by trained senior field technicians or drilling supervisors. This personnel should
be conversant with field description and classification of soils and rock and the
investigation methods used.
Borehole/test pits logging and field material descriptions are normally the respon-
sibility of the driller/technician and should be checked by the field supervisor.
Investigation of ground water level by
simple methods.

12 Chapter 2
Geotechnique
2.3 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 confident
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:
● Dynamic soundings.
● Static soundings.
● Weight- 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 the
shaft 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 soundings
The 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 identification.
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 when
using the percussion drill, is recorded. The resistance to penetration depends on
the soil type, and experienced drillers may be able to distinguish cohesive and

13Chapter 2
Geotechnique
frictional materials by the feel and sound of the drill steel. The dynamic sound-
ing method has limited penetration in firm 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 the
use 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 filling 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 Boring 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 flight 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.

14 Chapter 2
Geotechnique
A disadvantage with samples from mechanical augers is that the material
brought up becomes mixed, layering is thus difficult 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 borings
Percussion 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 the
ground water level. Other tools used are a clay cutter.
The clay cutter and shell bring up disturbed material that are sufficiently 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 ground
water 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 difficult 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 fitted with a
hydraulic power unit and attachments for mechanical augering, rotary core drill-
ing and cone penetration testing.
Rotary drilling
Rotary 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 bit
to break down all the material within the diameter of the hole. Water or mud is
used to flush 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 samples
to 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 drilling
fluid. Typical core diameters are 41 mm, 54 mm and 76 mm, but can range up to
165 mm. The larger diameters are used in difficult 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 samplers
Rotary 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 best
results in weak, watered or fractured rock.A core size of 76 mm is usually satisfactory,
but 100 to 150 mm and the triple barrel
technique gives the best results in weak,
watered or fractured rock.

15Chapter 2
Geotechnique
Wash boring
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 finer soils. Casing or drilling mud is
used 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 fine 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 five disturbance classes for samples depending on the degree to which
they have been disturbed by the process of sampling, handling and transport
until finally laboratory testing:
Class 1 Classification, moisture content, density, strength, deformation
and consolidation characteristics.
Class 2 Classification, moisture content, density.
Class 3 Classification, moisture content.
Class 4 Classification.
Class 5 None – sequence of strata only.
Within the five classes there are two main categories for practically denoting the
samples:
● Disturbed samples.
● Undisturbed samples.
Class 1
Class 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-
The principal types of tube samplers are:
● Open tube samplers
● Stationary piston samplers
● Continuous sampler
● Compressed air sampler
● Rotary core sampler

16 Chapter 2
Geotechnique
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 2
Class 2 is taking of disturbed samples with additional requirements to obtain
field/bulk density of the soils. Determination of the field density may be ex-
ecuted by:
● Block sampling.
● Core cutter method (shoe cutter).
● Split spoon sampler.
Classes 3 to 5
Classes 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 in
the laboratory.
2.5.3 Disturbed samples
Objectives
Disturbed samples, which are used mainly for soil classification tests, visual
classification and compaction tests. Disturbed samples have the following fea-
tures:
● Τhe same particle size distribution (grading) as the in-situ soil.
● Τhe soil structure has been significantly damaged.
● Τhe water content may be different from that of the in-situ soil.
Sampling methods
Disturbed samples can be excavated from trial pits or obtained from the tools
used 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 deficient in fines 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 soil
fabric.
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 in
permeable soils will require dewatering, and the safe excavation depth is very
limited.
Shafts and headings
Shafts 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 frequently
used for the investigation of rock or soil/rock in the case of dam abutments.
Safety precautions must be observed, esecially
sloping or supporting of the sides of deep pits be-
fore personnel are allowed to enter trial pits. Sam-
pling and inspection should be done immediately
upon excavation of unsupported pits.

17Chapter 2
Geotechnique
2.5.4 Un-disturbed samples
Objectives
Undisturbed 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 methods
Undisturbed 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 sampling
U4, 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, fine 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 U4
Other 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 samplers
The 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 classification 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
The highest quality samples are obtained by block
sampling.
U4 core sample.

18 Chapter 2
Geotechnique
Soil type, rock Samplers, tests Classification, comments
Non-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 in
ground with boulders and cobbles, but are
useful in gravel and sandSand
• CPT tests are preferable to SPT below GWL.
• Test pits or augers are useful, with casing or
hollow stem below GWL.
• Piston samplers or U4 tubes with core catcher.
Silt
Thin walled piston sampler Class 2 sample
U4 tubes without core catcher Class 3 sample
Vane test Un-drained shear strength of clayey silt
CPT tests are preferable to SPT. Below GWL
Hard, weathered tropical,
or over-consolidated clay
Augers or cable percussion methods can be used. -
Thin walled piston sampler Class 1 to 2
U4 tubes Class 1 to 3
Sample pit, cut block sampling Well suited
Core drilling equipment
In very stiff materials (sample is affected by
drilling water).
Soft clay
Augers or cable percussion methods can be used. -
Thin walled piston sampler Class 1
U4 tubes Class 2
Vane test or CPT In-situ shear strength.
Clays with gravel, cobbles
or boulders
Test pit is preferable. -
Rock
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-
sifications.
2.5.6 Field classification and sample size
Classification of samples in the field should follow the method after Brinks and
Jennings as described in Appendix 2.
Determination of the field density as part of the classification may be executed
by:
● Block sampling.
● Core cutter method (shoe cutter).
● Split spoon sampler.
The required size of sample for indicator and compaction tests in the laboratory
tests are given in Chapter 5.2.3 - Sampling for various types of soils. MinimumChapter 5.2.3 - Sampling for various types of soils. MinimumChapter 5.2.3 - Sampling
sample sizes are specified in the Laboratory Testing Manual - 2000 for each
geotechnical laboratory test.

19Chapter 2
Geotechnique
2.6 Handling, transport and storage of
samples
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 the
sample 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 Field recording
Sample description
Field sample description and classification 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 field 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.
Recording
Proper field procedures include accurate setting out with reference to an identifi-
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 identification including:
1. Project name.
2. Date.
3. Location and elevation of borehole.
4. Depth.
5. Method of sampling.
6. Description.
7. Remarks etc.
2.7.2 Reporting
General
All field 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 shipment
of core samples.

20 Chapter 2
Geotechnique
Soils and materials distribution maps
In 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.
● Εxisting borrow pits.
● Κnown areas of clay.
● Rock outcrops etc.
The technique of compiling data on maps is particularly useful for feasibility-
or preliminary studies, but will also aid the efficient 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 methods
Field Tests
F2.01 Soundings Cone penetration - CPT BS1377: Part 9: 1990
BS5930: 1999
F2.02 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
F2.04 Boring U100 (U4) sampling, undisturbed samples BS5930: 1999
F2.05 Ground water Pore pressure, ground water level 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

21Chapter 2
Geotechnique
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 probing
systems, 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
fixed 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 rods together to the next test depth. The resistance when advancing the
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 profile, 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
rock or cobbles may break the point.
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 firm ground of the dynamic penetration test.
Without friction sleeve
Witht friction sleeve
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Field investigations
Central Materials Laboratory2 Geotechnique
Test Method no F 2.01
Soundings:
Cone Penetration Test - CPT
CPT test assembly.

22 Chapter 2
Geotechnique
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 identification 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 identification 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).
CCPT
The 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.
● The soil strength parameters which can be inferred are approximate, but
may give a useful guide in ground conditions where it may not be possible
to 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
ferred are approximate.
● When the test is carried out in granular soils below groundwater level, the
soil may become loosened.
No disturbance may be impossible to achieve in
granular soils below the ground water level, which
may be loosened by flow towards the borehole. In
such conditions, in-situ tests performed indepen-
dently of a borehole should be considered, e.g.
the CPT test.
BS 1377 : Part 9 : 1990 denotes the CCPT test
SPT(C).
The test is sometimes carried out in boreholes
considerably larger in diameter than those used for
ground investigation work, e.g. in the construction
of bored piles. The result of the SPT is dependent
upon the diameter of the borehole. Tests should
not be regarded as SPT when performed in
boreholes with diameter larger than 150 mm.
Boreholes with reduced diameter shall continue
for min. 1m before SPT commences.
In conditions where the quality of the “undisturbed”
sample is suspect, e.g. very silty or very sandy
clays, or hard clays, it is often advantageous to
alternate the sampling with standard penetration
tests to check the strength.
Central Materials Laboratory
2 Geotechnique
Soundings:
Standard penetration test - SPT and
Continuous Cone Penetration Test - CCPT
SPT sampler.

23Chapter 2
Geotechnique
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 influence the result and consequently the borehole diameter shall
always be reported.
Split barrel sampler assembly
The sampler assembly shall have the shape and dimensions shown in the
figure 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 replaced
when 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 orifice 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 rods
The 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 deflections shall not be greater
than 1 in 1000 when measured over the whole length of each rod.
Drive assembly
The 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 a
free fall of 760 + 20 mm, and shall not influence 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 minimal
resistance 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 borehole
Clean 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 table maintain at all times the water or mud level in the borehole at a
sufficient distance above the groundwater level to minimize disturbance of the
Periodic checks for rod straightness shall be
made on site, including the threaded connections
between consecutive rods.
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SPT slip barrel sampler assembly.

24 Chapter 2
Geotechnique
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 test
Lower the sampler assembly to the bottom of the borehole on the drive rods
with 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:
1. Seating drive: Using standard blows the seating drive shall be a penetration
of 150 mm or 25 blows whichever is first 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-
tration 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-
tration of 300 mm has not been achieved.
Interpretation
Interpretation 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
● Review of relevant literature:
CLAYTON, C.R.I. The standard penetration test (SPT): Methods and use.
CIRIA Report no. 143. London: CIRIA 1995.
Withdraw the drilling tools slowly from the ground
and up the borehole (when filled with water) to pre-
vent suction and consequent loosening of the soil
to be tested. When casing is used, do not drive it
below the level at which the test is to commence.
The rate of application of hammer blows shall not
be excessive such that there is the possibility of
not achieving the standard drop or preventing
equilibrium conditions prevailing between succes-
sive blows.

25Chapter 2
Geotechnique
Soundings:
Vane test
Objectives
Vane 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.
A steel vane at the end of a high tensile steel rod is pushed into the clay below
the 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 influence laboratory results. It has little
applicability to partly saturated and cemented soils.
Advantages
A 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.
Limitations
If the test is carried out in soil that is not uniform and contains only thin layers
of laminations of sand or dense silt, the torque may be misleadingly high.
Results are unreliable in materials with significant coarse silt or sand content.
The results are questionable in stronger clays or if the soil tends to dilate on
shearing or is fissured. The presence of rootlets in organic soils, and also of
coarse particles, may lead to erroneous results.
Small hand operated vane test instruments
are available for use in the sides or bottom
of an excavation.
The un-drained shear strength determined by
an in-situ vane test is normally not equal to the
average value measured at failure in the field,
e.g. in the failure of an embankment on soft clay.
The discrepancy between field and vane shear
strengths is found to vary with the plasticity of the
clay and other factors.
Vane.

26 Chapter 2
Geotechnique
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Apparatus
The vane test apparatus shall be either the borehole or penetration type, as
illustrated. Small hand held equipment is only suitable as indicator tests.
Principle of vane testing.

27Chapter 2
Geotechnique
Vane
The vane of cruciform shape, should be of preferably of high grade stainless
steel with the following measurements, (reference to illustration).
Length (H): Shall be twice the overall blade width D
The design of the vane shall be such that it causes as little remoulding and
disturbance as possible when inserted into the ground for a test. The blades
shall be as thin as possible, consistent with the strength requirements, and
have a cutting edge at the lower end. The rod on which the vane is mounted,
normally of high tensile steel, shall preferably not exceed 13 mm in diameter.
Rods
The vane rod shall be enclosed by a suitably designed sleeve from just above
the blades and throughout the length it penetrates the soil to exclude soil
particles and the effects of soil adhesion. The sleeve shall be packed with
grease. This sleeve shall commence above the blades at a distance equivalent
to about two diameters of the vane rod.
Extension rods about 1 m in length. These shall be sufficiently strong to be able
to stand axial thrust, allow a reasonable amount of lack of linearity, and be fitted
with a coupling which makes it impossible for the rods to tighten or twist relative
to each other.
Instrument
Calibrated torque measuring instrument preferably with height adjustment and
capable of being clamped in the required position. The base of the instrument
shall be capable of being fixed to the ground. The instrument shall have a
torque capacity of approximately 100 Nm and an accuracy of 1 % or better of
the indicated torque from 10 Nm to the instrument’s maximum reading.
Procedure
The following is specified for performing the test.
● Place steady bearing minimum every 3 m in the case of tests in a borehole.
● Rotate the torque head throughout the test at a rate within the range 0.10°/
second to 0.20°/second (equal to 6° /minute to 12° /minute).
● Rotate the torque head until the soil is sheared by the vane. Read the
gauge at maximum deflection, thus indicating the torque required to shear
the soil.
Remoulding
Test of re-moulded strength of soils is done by removing the torque-measuring
instrument from the extension rods and turning the vane through six complete
rotations. A period of 5 min is permitted to elapse after which the vane test is
repeated in the normal way.
Shear strength of soil Suitable vane size, approximately
< 50 kPa 150 mm long by 75 mm
50 - 100 kPa 100 mm long by 50 mm wide

28 Chapter 2
Geotechnique
Calculations and reporting
The shear strength of the soil, (kPa) is calculated from the following equation:
S =
M
K
where
M is the torque to shear in the soil (in Nm);
K is a constant depending on dimensions and shape of the vane.
Assuming the distribution of the shear strength is uniform across the ends of a
cylinder and around the perimeter then:
K = � D2
H
(1+
D
)10-6
�� 2 ((1+1+
3H
where
D is the measured width of vane (mm)
H is the measured height of vane (mm)
As the ratio of length to width of the vane is 2 to 1 the value of K may be
simplified in terms of the diameter so that it becomes:
K = 3.66D3
X 10 –6
The test report shall contain the following information:
(a) The method of test used.
(b) The vane shear strength (in kPa) to two significant figures.
(c) The type of vane test apparatus.
References
• BS 5930 : 1999
• BS 1377 : Part 9 : 1990

29Chapter 2
Geotechnique
Objectives
Undisturbed 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.
Description of method and equipment
Open tube samplers: U100 core sampling
Open-tube samplers consist essentially of a tube that is open and made
sharp at one end and fitted at the other end with means for attachment to the
drill rods. General purpose 100 mm U100 (also called U4 after the imperial
measurements) 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 U100 sampler may
either be forced down in one continuous movement or be hammered down.
When forced down, samples of non-sensitive, fine cohesive 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.
Other open tube samplers of varying diameters, but of the same general
working principle as the U100 type, are also in use. Special thin walled
samplers have been developed to improve the sample quality, but piston
samplers are preferable.
Piston samplers
The 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 classification 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.
Refer to Chapter 2.5.2 for definition of disturbance
classes:
Class 1 (undisturbed)
Class 2 (classification, moisture, density)
Class 3 (classification, moisture)
Class 4 (classification only)
Class 5 (none, sequence of strata only)
Piston samplers are currently not commonly used
in the country and for further detail refer to relevant
literature and BS 5930:1999.
Boring:
U100 (U4) sampling, undisturbed samples
U100 (U4) core sampler with extracted core.

30 Chapter 2
Geotechnique
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References
● BS 5930:1999
U100 (U4) core sampler assembly.

31Chapter 2
Geotechnique
Objective
One of the most important parts of any ground investigation is the determination
of ground water levels or ground water pressures. In layered ground, permeable
layers separated by impermeable stratum may have different ground water
pressures and some may be artesian. Seasonal variations in the ground water
pressures should also be determined or evaluated.
Description of methods
General
The ground water conditions should always be observed as part of any borehole
operation. However, borehole observations may not be correct due to the time
required for the water level to stabilize, particularly in ground of low permeability.
Furthermore, it may not be possible to determine the levels or strata from which
the water is entering the borehole. Use of casings or mud may also interfere
with the results.
Piezometers - general
To measure ground water pressures accurately it is generally necessary to install
special measuring devices called piezometers. Piezometers may be installed to
different depths in the same location to study pressures in various layers. There
are several types of piezometers in the market as described below. Piezometers
are important parts of pumping tests, and the standpipe and hydraulic type may
also be used for in-situ permeability tests as described for boreholes.
Standpipe piezometers
Standpipe piezometers consist of a porous filter tip sealed into the ground at the
appropriate level and with an open tube (standpipe) to the surface for plumbing
the water level. The response time of this type of piezometer is long in soils of
low permeability due to the large volumes of water in the system. Some piezo-
meters (e.g. type BAT) are designed to facilitate sampling.
Hydraulic piezometers
Hydraulic piezometers are closed systems where the pressure is measured by
a manometer, having a short response time.
Electrical and pneumatic piezometers
Electrical and pneumatic piezometers also have rapid response time. These
systems use a porous element in which the water pressure is detected by an
electrical transducer or balanced by air pressure, respectively.
Electrical level detector
Electrical equipment is available for lowering into boreholes or standpipes, and
thereby detect the surface of free water level in the well (picture).
References
● BS 5930:1999
Groundwater:
Pore pressure, ground water level
Electrial ground water level detector.

32 Chapter 2
Geotechnique
Objective
Permeability tests are carried out for the purpose of measuring underground
flow characteristics of ground water through in-situ soils or rock. Pumping
tests may be carried out to study the permeability, transmissivity and storage
of an area of several square kilometres, as may be required in the evaluation
of ground water resources or the design of subterrain cut-off barriers in dam
design.
Of the variety of in-situ permeability tests in boreholes the common tests are:
A. Permeability of soils below the ground water level by the variable head
methods.
B. Permeability of soils below the ground water level by the constant head
methods.
C. Permeability of soils or rock by pumping tests.
D. Permeability of rock subjected to water pressure, Packer test.
Tests A and B both apply a hydraulic pressure in the borehole different from that
in the ground and observe the effect in the borehole.
Test C - pumping test for the permeability of the ground - involves a steady
flow pumping from a well and observation of the drawdown effect on ground
water levels in inspection wells (piezometers), at some distance away from the
pumped well. The drawdown in ground water level thus created is termed the
“cone of depression”.
Some particular problems encountered in in-situ permeability testing are:
● High test pressures may fracture, open up, the ground.
● Layers/fissures in the ground, and water tightness of the complete test
system greatly affects the results.
● Test holes may erode, use of filters, screens etc. may be required.
● Results are affected by the effective stress which in turn will be effected by
the test, in the case of compressible soils.
● The influence of partial saturation on permeability needs to be taken into
account in interpreting results as long term inflow tests are likely to give
permeabilities which are close to those for the saturated soil.
References
● BS 5930:1999
In-situ permeability testing is generally more
reliable than tests performed on samples in
the laboratory due to the large mass of ground
involved and the lack of sample disturbance.
However, permeability testing requires expert
knowledge both to select the correct method and
to evaluate the results.
As a rule, constant head borehole tests are likely
to give more accurate results than variable head
tests, but variable head tests are simpler to per-
form. The more elaborate and expensive pumping
tests with observation of the drawdown levels, give
the most reliable results.
2 Geotechnique
Groundwater:
Permeability tests for soils and rock

33Chapter 2
Geotechnique
Objective
Ground water sampling is carried out for the purpose of chemical analysis, either
for evaluation as a water source for consumption or use in the works. Water for
earthworks, layerworks or concrete requires testing against deleterious matter
such as e.g. soluble salts or other substances causing damage.
A sample should be taken immediately the water bearing stratum is reached
during boring. It is preferable to obtain samples from the standpipe piezometers
if these have been installed. It is important to ensure that samples are not cont-
aminated or diluted.
References
● BS 5930:1999
Groundwater:
Ground water sampling
Some piezometers (e.g. type BAT) are designed to
facilitate sampling.

34 Chapter 2
Geotechnique
2 Geotechnique
Deformation test:
Plate loading test
Objectives
The plate loading method is used for determination of the vertical deformation
and strength characteristics of soil, primarily for foundation footings, but may
also be requested for determination of in-situ E-modulus of pavement layers of
for support of the pavement.
The test is conducted by penetrating a rigid, circular, plate into the soil in-
situ and measuring the force and deformation strength of density of soils and
compacted layers of primarily clay and soft materials. Core cutting gives volume
by predetermining the size of the excavated hole with a calibrated core of
known volume.
Advantages
The method is a simple way of determining foundation support at shallow
levels for smaller structures or for investigation of small areas. The test may be
useful on construction sites during establishment of method specifications for
compaction control of earthworks.
Limitations
● The test is slow to perform and requires a considerable input of resources.
The method is therefore not well suited for investigations of large areas.
● The results are only valid for the site conditions under which the test is
performed, e.g. with regards to moisture conditions.
Apparatus
General
The apparatus for determining penetration is normally the same as used for
Benkelman beam testing. A hydraulic jack is used for applying the force, that
is measured by aid of a calibrated manometer on the jack. Support to the jack
may be a truck or other heavy equipment. Quick-setting plaster is required for
preparation of the test site. Equipment for sampling and field density measurement
is required if such tests are requested at the same location as the plate loading
test.
The test plate
The plate shall be circular and the diameter normally ranges between 150 and
300 mm. The plate diameter should be larger than five times the diameter of the
larges particles normally found in the soil. In case of measurement of fissured
clay the plate diameter should be larger than five times the spacing between the
fissures, and have a diameter of minimum 300 mm.
The depth to which the measurement has effect is
approximately1,5 times the diameter of the plate,
as a rule of thumb.

Tanzania field testing manual (2003)

Tanzania field testing manual (2003)

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