Table Of ContentEngineering Geology
and Geotechnics
F.G. BELL
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First published 1980
© Butterworth & Co (Publishers) Ltd, 1980
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ISBN 0 408 00355 3 (cased)
British Library Cataloguing in Publication Data
Bell, Frederic Gladstone
Engineering geology and geotechnics.
1. Engineering geology
I. Title
624'.151 TA705 79-40875
ISBN 0-408-00355-3
Typeset by Scribe Design, Gillingham, Kent
Printed in England by Billing & Sons Limited,
Guildford, London and Worcester
Preface
Geology is an essential study for anyone entering the professions of civil
engineering and mining engineering, as both of these involve working on or
within the ground. Accordingly engineering geology and geotechnics have
together become an accepted discipline studied by civil and mining engineers as
well as geologists, and this book attempts to show how the relevant aspects of
the geological sciences are applied to engineering practice. Geological factors will
obviously affect the location of engineering works, their design, construction
and subsequent maintenance.
Within the last two decades significant advances have been made in
engineering geology and geotechnics. Unfortunately this has inevitably meant
that the gap between the researcher on the one hand and the student and
practitioner on the other has widened. In such situations textbooks which
provide a general survey of the subject are a vital necessity, providing a much
needed bridge between the two groups. This book attempts to provide such a
survey which incorporates recent developments, but it is realised that, although
every effort has been made to include relevant, up-to-date material, certain items
may have been omitted whilst others may have been superceded. The reader is
therefore advised to supplement the information provided, with material
obtainable from the many journals now available in this field, the titles of which
can be found in the references given at the end of each chapter.
The text assumes a basic knowledge of geology which, for example, the
undergraduate is likely to obtain in his first year at college, and also assumes that
the reader has some knowledge of rock and soil mechanics. As far as the student
is concerned the text therefore is aimed primarily at the two final years of an
undergraduate course in engineering geology or civil or mining engineering.
However, it is hoped that the text will be of some service to those in related
professions such as building and planning.
Because the solution to every problem created by ground conditions is more
or less unique, the study of individual case histories is obviously important.
However, because of the limitation placed on the size of the book, case histories
have not been mentioned as extensively as one would have wished. This short
coming is to some extent compensated for in the extensive lists of references
given at the end of each chapter.
Many concerns have supplied material, especially for illustration, and due
acknowledgement has been given in the text, but the author wishes to offer his
thanks to all those concerned. If any person or body inadvertently has not been
afforded due acknowledgement then apologies are accordingly expressed. In
particular the author would like to note his appreciation of the kind help given
by Mr. Robert Lane who reviewed chapter eleven and made several useful
suggestions. The author is also indebted to Dr. J.M. Coulthard who read the
proofs.
F.G. Bell
Chapter 1
Site Investigation
1.1 INTRODUCTION
Site investigation involves exploring the ground conditions at and below the
surface, it is a prerequisite for the successful and economic design of engineering
structures and earthworks. Insufficient or inadequate information with respect
to the character of the ground can lead to the production of an unsatisfactory
design which may subsequently result in serious damage or even failure of the
structure concerned. Any attempt to save on costs by having a low budget for an
investigation may cause additional expenditure later if unfavourable ground
conditions, previously undiscovered, are found during the construction stage. In
fact the cost of site investigation is relatively small, it usually being less than
1% of the total cost of the entire work. Economic considerations should be
regarded as a secondary matter as far as safety is concerned.
The general objective of a site investigation is to assess the suitability of a
site for the proposed structure. A site investigation also should attempt to
foresee and provide against difficulties that may arise during construction due
to ground and/or other local conditions. Indeed investigation should not cease
once construction begins. It is essential that the prediction of ground conditions
which constitute the basic design assumption, are checked as construction
proceeds and designs should be modified accordingly if conditions are revealed
which differ from those predicted.
Usually a site investigation consists of a map and literature survey, a pre
liminary reconnaissance of the site and then the site exploration programme,
Figure 1.1 (see CP 2001:19571, Fookes, 1967)2.
An investigation of a site for an important structure requires the exploration
and sampling of all strata likely to be significantly affected by the structural
load. Data appertaining to the ground water conditions, the extent of weathering
and durability of newly exposed rocks, and the discontinuity pattern in rocks,
affect the ease with which material can be removed and the stability of the
sides of an excavation. They are also significant controlling factors as far as earth
pressures and the bearing capacity of the foundation rocks are concerned.
In some areas there are special problems, for example, potential subsidence in
mining areas (see Bell, 1975)3. In mining areas old maps and plans may prove
useful as they may show old mine workings which are absent from the latest
editions of the same areas. Changes in topography between different editions
1
s
Subsurface investigation Boring Hand Digging augers Pits Adit ary Percussion Trenches Screw Butterfly Log and sample tests in-situ Sample Log and sample urbed) (disturbed) In-situ tests (permeability, etc.) 2 after Fookes, 1967J
Rot es ndist on (
cor (u ati
vestigation Geophysical techniques Log netic Gravity a site investig
Site in nvestigation In-situ observations pling esting In-situ tests Seismic Sonic Mag Electrical Electrical resistivity logging Figure 1.1 Organisation of
i mt
ace Saand hers
Surf Geological mapping (also topographical if required) Air photography Field sampling Index tests Otin field or laboratory Strength tests in laboratory
Site Investigation 3
may indicate the presence of fill if the surface is higher whilst if it is lower then
this may indicate that subsidence has taken place. Also the presence of old
shallow mine workings tends to alter subsurface drainage regimes. In built-up
areas an investigation must also consider the influence of the proposed
construction on existing structures. Some site investigations will also include a
search for suitable construction materials.
1.2 LITERATURE AND MAP SURVEY, AND PRELIMINARY
RECONNAISSANCE
The effort expended in any data search and literature review depends on the
complexity and size of the proposed project, and on the nature of the expected
ground conditions. Detailed searches for information can be extremely time
consuming and may not be justified for small schemes at sites where the ground
conditions are relatively simple or well known. In such cases a study of the
relevant topographical and geological maps and memoirs, and possibly aerial
photographs may suffice. On large projects literature and map surveys may save
time and thereby reduce the cost of the site investigations.
Sources of information for site investigations are summarised in Table 1.1 and
are provided by Dumbleton and West (1971)5. The data obtained during such
searches should help the planning of the subsequent site exploration and should
prevent duplication of effort. In some parts of the world little or no literature,
or maps are available. However, in the UK this is not the case, as work on similar
sites may have been carried out, and the details may be available.
In the UK the Ordnance Survey supply topographical, geological and soil
maps (Table 1.1). Geological maps afford a generalised picture of the geology of
an area and generally the stratum boundaries and positions of the structural
features, especially faults, are interpolated. As a consequence their accuracy
cannot always be trusted. Fortunately map memoirs accompany many 1:63360
maps, and these provide a detailed survey of the geology of the area in question.
The amount of useful information which can be obtained from aerial
photographs varies with the nature of the terrain, the type and quality of the
photographs and the ability of the interpreter. Generally the technique will be of
most use in the feasibility stage, that is, during the site selection and
investigation planning stage. It is an inexpensive way of providing information
for a preliminary appraisal of a large area and airphotos may sometimes reveal
features which cannot be detected easily from the ground. Aerial photographs
can be taken rapidly for any locality and have proved particularly important
where the ground terrain was difficult and therefore impeded access. In the UK
there are several collections of air photos (see Dumbleton and West, 19706 and
Table 1.1). For most engineering purposes a scale of 1:10000 is suitable. Colour
photographs may prove useful where the ground is covered with vegetation.
In this context infra-red colour is even better and it can also be used for
delineating water masses. Stereoscopic examination of aerial photographs allows
the relief of the terrain to be observed and, if required, contour maps can be
drawn from these. Aerial photographs can also be used to study drainage
patterns and river development, landslip areas, coastal features, soil and rock
boundaries, geological structures, subsidence areas and the location of con
struction materials (see Table 1.2). Indeed geological maps can be produced
V
^
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Remarks Ordnance Survey will provide up-to-date survey information control data, maps on microfilm, magnetic tape or transparent material, enlargements and reductions. Material may be copie^for professional use subject to copyright licensing terms. One-inch' Ordnance Survey maps date back to 1805-1840. Initial 1:10 560 maps (6" to 1 mile) issued 1840-1895. Initial 1:2 500 maps (25" to 1 mile) issued 1842-1875.
CES OF DATA IN THE UK 4 w, 1975) Location of information Small scale maps and plans published by Ordnance Survey of Great Britain. Information and lists from: England and Wales: Ordnance Survey, Romsey Road Maybush, Southampton S09 4DH Scotland: 43 Rose Street, Edinburgh 2 N. Ireland: Ladas Drive, Belfast BT6 9FJ Published maps available from approved dealers. Complete sets of earlier editions of Ordnance Survey maps may be consulted at: British Museum Library Bloomsbury, London WCL National Library of Wales, Aberystwyth. National Library of Scotland, Edinburgh Local collections may be available at: County Libraries County Record Offices County Engineers Departments
Table 1.1 PRELIMINARY SOUR(After Chaplo Nature of in formation contained All topographical maps may be interpreted to yield information on: Landforms, especially specific hazards such as landslides, steep slopes, mineral workings etc. Geology: interpretation of landforms gives indirect information on the geology of an area. Supplementary information obtained on access and location of structures adjacent to site. Information on previous land usage and changes in ground conditions, e.g. subsidence, erosion, deposition, previous mineral workings, areas of redevelopment, changes in water courses, onset of instability.
Source of data Modern topographical maps and plans (a) Small scale maps: 1:50 000 (replaces 1" to 1 ml) 1:25 000 (replaces 2Yi" to 1 ml) 1:10 000 (replaces 6" to 1 ml) (b) Large scale plans: 1:2 500 (about 25" to 1 ml) 1:1250 (c) Others: Numerous maps at other scales are also available. ^Topographical maps and plans
-
7
Remarks 1:10 560 maps published for the coalfields, London and a few other mining areas. 1:63 360 maps are published for much of the UK. Significant amounts of unpublished data are available for inspection at the IGS. Other useful IGS publications include Water Supply Memoirs and Well Catalogue Series published by HMSO. Enquiries on groundwater problems should be addressed to: Hydro-geological Dept. IGS, London SW7.
ble ds,
Location of information Lists of published information, enquiries, and for consultation of 1:10 560 manuscript maps: England and Wales: Soil Survey of England & Wales, Rothamstead Experimental Station Harpenden, Herts. Scotland: Soil Survey of Scotland, Macaulay Institute of Soil Research, Craigie-buckler, Aberdeen AB9 2QJ List of publications from Ordnance Survey. Published maps and lists from: Institute of Geological Sciences, Exhibition Road, London SW7. HMSO Bookshops Published and manuscript data availafor inspection at IGS in London, LeeExeter, Edinburgh and Belfast. &*** w*
Nature of in formation contained Limited information on geology, landforms, drainage, chemical and physical properties of soils. Many serve as good supplement to older geological maps where information on nature of drift deposits is limited. Information on geological structure of area. Details of lithologies and thickness of superficial deposits may be very limited. On more recent maps areas of ground instability may be mapped. /Memoirs describe the geology of individual maps. \J
Source of data Pedo logical maps Many parts of UK covered by maps of scale: 1:63360 1:25 000 Some memoirs also available. Geological maps and memoirs (a) Institute of Geological Sciences Maps are available at the following scales: 1:10 560/1:63 360* They provide coverage of much of the UK 1:25 000-Limited number available, some with explanatory booklets. 1:253 440/1:625 000/1:1000 000-Available for regional planning exercises (b) Other sources: Assorted maps may be available in journals and papers *Being replaced by 1:50 000
,
ώ
*
*
Os >
5
ontinued Location of information Remarks Published maps, lists, enquiries and for consultation of manuscript 1:10 560 maps: The Director, Land Utilisation Survey, Kings College, Strand, London WC2 Published maps from: E Stanford Ltd, 12/14 Long Acre, London WC2. Consultation of manuscript maps for Scotland: National Library of Scotland, Edinburgh. Information is available as follows: Many old records of mineral Coal Mines: in the Plans Record workings are incomplete and the Office of the National Coal Board absence of records should not Area in which the mine was located. be taken as indicative of the For general information contact absence of workings at any site National Coal Board, Hobart House, in an area of previous mining. Grosvenor Place, London SW1. Information on current mineral For information on opencast mines: working is contained in the following annual publications. NCB Opencast Executive, Harrow, .Guide to the coalfields pubMiddlesex. lished by Colliery Guardian, 17/ For information on oil shale mines: 19 John Adam Street, London Plans Record Office, Edinburgh SW1 for information on coal, shale, stratified iron stone and fire clay mines All other mines (except in Cornwall): Directory of quarries and pits Plans Records Office, Safety and published by Quarry Managers Health Commission, Thames House, North Millbank, London SW1. T nndnn Wt for details of For Cornish mines: County Records quarries in operation. Office, Truro.
c
Table 1.1 Nature of information contained Present land usage. Information on likely presence and nature of mineral workings both recent and ancient. (See also comments relating to the use of old maps, plans and aerial photographs).
Source of data Land utilisation maps Published maps at 1:25 000 scale cover much of England Records of mines and mineral deposits.
