Table Of ContentEngineering Geological
Mapping
W. R. Dearman Pho
Emeritus Professor of Engineering Geology,
Department of Geotectinical Engineering,
University of Newcastle upon Tyne, UK
L U T T E R W O R TH
Ĺ I Í Ĺ Ě A Í Í
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First pubhshed 1991
© Butterworth-Heinemann Ltd., 1991
British Library Cataloguing in Publication Data
Dearman, W. R.
Engineering geological mapping.
1. Geological maps
I. Title
551.8
ISBN 0-7506-1010-7
Library of Congress Cataloging-in Publication Data
Dearman, W. R.
Engineering geological mapping/W. R. Dearman.
p. cm.-(Butterworths advanced series in geotechnical engin
eering)
Includes bibliographical references.
ISBN 0-7506-1010-7:
I. Engineering geology. 2. Geological mapping. I. Title.
II. Series.
TA705.D33 1990
624.r51O223-dc20 90-1816
Filmset by Bath Typesetting Ltd, London Road, Bath, Avon
Printed and bound in Great Britain by Courier International Ltd,
Tiptree, Essex
Preface
This book grew from a perceived need to combine and The I AEG, conceived in December 1964 at the Inter
expand two reports on the preparation of engineering national Geological Congress in New Delhi, was offi
geological maps. Work on the first, The Preparation of cially constituted at Unesco headquarters in January
Maps and Plans in Terms of Engineering Geology' was 1967. The First Congress of the I AEG was held in Paris
begun in 1968 by a working party set up by the Engin in September 1970, with one of the themes 'Engineering
eering Group of the Geological Society (of London). geological mapping'. In his Presidential Address to the
The final report was published in late 1972 as Volume 5, General Assembly, Professor Quido Zaruba emphasized
No. 4, of the Quarterly Journal of Engineering Geology. that 'the necessity of submitting results to engineers in
It was intended as a guide to engineers and engineering an understandable form prompted engineering geolo
geologists as well as to geologists, but not a Code of gists to develop appropriate mapping techniques. The
Practice on the subject since it was recognized by the methods of presentation are diverse, but all aim at
working party that with the possible rapid evolution of making each map carry the maximum amount of infor
techniques of engineering geological mapping the re mation in the most intelligible way. Attempts are now
port would require revision from time to time. No being made to standardize the methods of presentation
revision has been undertaken, although a foothold for of information on engineering geological maps'. This
engineering geological mapping has been gained for the was a reference to the setting up by the Association of a
first time in the 'Code of Practice for Site Investigations': working group (later commission) for engineering geolo
BS 5930:1981 published by the British Standards Insti gical maps.
tution. A short section on geological mapping for I had been invited by Mr Rudolph Glossop, then
ground investigation is supplemented by a section deal Chairman of the Engineering Group of the Geological
ing with a 'Legend for engineering geological maps and Society, to be the UK member of the working group and
plans', with recommended symbols for soils and rocks, attend the first full meeting at the Congress. In fact, the
general planar structures, and geological structures and working group had been established in 1968 at the
boundaries. General Assembly of the lAEG on the occasion of the
A second report, 'Engineering Geological Maps. A International Geological Congress in Prague. The
Guide to Their Preparation', was published by Unesco Unesco guidebook was the first accomplishment of the
in 1976. For many years Unesco has been concerned commission in response to its stated aims.
with the preparation and publication of small-scale geo Members of the lAEG commission who took part in
logical maps of various kinds. This new booklet was the preparation of the guide were: Professor Milan
devoted to a particular aspect of this programme, Matula (Chairman), Czechoslovakia; Professor G.A.
namely engineering geological mapping. The purpose of Golodkovskaja, USSR; A. Peter, France; A. Pδhl, West
engineering geological maps is to show the distribution Germany; Mrs Dorothy H. Radbruch-Hall (Secretary),
of specific geological phenomena and characteristics of USA; and myself as Editor. We were driven and moti
rocks and soils affecting engineering use of different vated by the energy and enthusiasm of our Chairman,
terrains. The ever-growing demand for such maps has Milan Matula, at the first full working meeting arranged
revealed the need for the standardization of principles, by him in Bratislava, with the preparation of the guide
systems and methods. This is an urgent but at the same book quickly becoming our main aim. Later publi
time a difficult problem which can best be solved by cations by the commission in 1981 gave recommended
international co-operation - sensible comments for the symbols and rock and soil description and classification
preface to the guidebook, which had been prepared by for engineering geological mapping. After that the com
the Commission on Engineering Geological Maps of mission disbanded itself, a decision reluctantly accepted
the International Association of Engineering Geology by the lAEG as possibly a temporary measure.
(lAEG). Just how far-sighted Professor Zaruba was in 1970 is
vi Preface
borne out by his observation that 'Finally, there is the manuscript was prepared and revised within the year.
last group (field of study), very important nowadays, Remote sensing, close-up photogrammetry and the com
which is connected with the study of the human environ puter manipulation of data and images are now being
ment and the planning of land-use, called forth by the used more extensively to prepare environmental and
increasing pressure of population on space. The so- engineering geological maps and plans. Those develop
called environmental geology likewise includes the ments would appear to provide the most fruitful practi
examination of the effects of human works on existing cal applications for the future: at large scale during
geological conditions so as to prevent any disturbance of engineering construction, especially as a recording
the balance of nature. It also embraces the problem of medium for the design of remedial measures and the
protection of the natural environment. The speed with as-built conditions at engineering works, and at small
which man is changing his environment often makes him scales for environmental assessments.
forget that natural forces are still at work, and it is a
great challenge to engineering geologists, among other
natural scientists, to harness them to the profit of man\
After a decade of relative quiescence, a reformed Units
Mapping Commission of the lAEG is to consider new
developments in the field of environmental engineering Throughout the book, units are given in their original
geology, including hazards and the risks associated with published form, but where there has been a deliberate
them, some of which are touched on in the later chapters change, as for example when a diagram or plan has been
of this book. redrawn, preference has usually been given to the use of
Work on the book was begun in 1980, but for a SI units.
variety of personal reasons was stopped until I was
induced to start again in 1988 when a completely new W.R.D.
Introduction
In 1968 the Engineering Geological Mapping Commis The present book was started in 1980 by two members
sion of the International Association of Engineering of the international commission; active efforts towards
Geology was initiated. In 1970 guidelines for the work of completion, after a long period of quiescence, began late
the commission were proposed: in 1987. The aim was both to expand the rather con
densed exposition in the guide, and to consider later
• to clarify the present situation in engineering geologi
developments in mapping for both engineering and
cal mapping;
environmental purposes.
• to analyse the various types of maps called engineer
ing geological maps - maps which are to serve for
building construction and land-use planning; 1.1 Definition of engineering geology
• to outline the trends for the future development of
engineering geological cartography and to present
There is no difficulty in defining engineering geology. It
general recommendations on the information to be
is one branch of applied geology which, broadly, is the
provided by a complex engineering geological map;
application of geology to industry - not some special
• to contribute to international exchange of infor
type of geology but the whole spectrum of the science.
mation on this subject.
Engineering geology is the discipline of geology applied
A long-term programme of topics for discussion was to civil engineering, particularly to the design, construc
established, which effectively guided the work of the tion and performance of engineering structures inter
commission for a decade. Selected topics were: acting with the ground in, for example, foundations,
cuttings and other surface excavations, and tunnels.
1. What is an engineering geological map? This would
involve consideration of: the basic concepts and
methodological background of engineering geological 1.2 Recording the early applications of
mapping; classification of the various kinds of engin geology in engineering
eering geological maps according to their purpose,
scale and content; and the position of engineering
It is worth while recalling that engineering geology has
geological maps among other geological maps,
had a very long history, even though only in the past two
including environmental geological maps.
decades has it acquired a degree of sophistication and
2. What are the problems involved in three-dimensional
now stands as an independent subject. In the following
representation of subsurface conditions on engineer
brief review of the development of engineering geologi
ing geological maps?
cal mapping, attention is focused selectively on Euro
Six other topics were also selected, including the use of pean practice. A similar review could be written for
computers. North America.
To what extent this aim was achieved can be judged
from the UNESCO publication prepared by the com
mission (Anon., 1976): Engineering Geological Maps. A 1.2.1 Architects and foundation
Guide to their Preparation. mapping
In the early 1970s a Working Party of the Geological
Society of London Engineering Group had been set up John Smeaton (1724-1792), engineer and mechanic, was
to prepare a report on The preparation of maps and engaged as an architect to reconstruct the lighthouse on
plans in terms of engineering geology' (Anon., 1972). the Eddystone in the English Channel off Plymouth.
The theoretical approach of the commission report is Two former lighthouses, constructed mainly of wood,
very effectively complemented by the more pragmatic had been destroyed by storms. Smeaton decided that
working party report. stone was the proper material with which to rebuild the
Introduction
lighthouse. Having formulated detailed ideas on how to At a scale of 1 in = 100 ft, the plan is accompanied by 13
construct the building, he then visited the rock for the cross-sections at 1 in = 20 ft. The sections show the
first time on 26 April 1756, on his sixth attempt to land construction of the wall, profile of the river bed with the
(Smiles, 1861, p. 32). During this and subsequent visits, sand layer, ground level and fill behind the wall, and the
Smeaton spent 15 hours on the rock, taking dimensions tidal range in the river.
of all its parts to enable him to construct an accurate Part of the plan, including the location of Section
model of the foundation of the proposed building. He No. 5 and the positions of Boreholes No. 3 and 4, is
paid three more visits to the rock for the purpose of shown in Figure 1.2(a); Cross-section No. 5 forms
correcting his measurements, before constructing a com Figure 1.2(b).
plete model of the lighthouse with his own hands.
Smeaton had devised a simple method of surveying,
whereby he could determine the position and elevation 7.2.2 Nineteenth century recording of
of any point on the rock within a circle 32 ft in diameter, ground conditions at dam sites
centred on the highest point. The surface of the rock was
a stepped combination determined by bedding in the The early association of geology with practical prob
slate and jointing; the bedding dip was 26°W. He con lems, although maintained in both metalliferous and
trived a robust, three-legged wooden stool with a circu coal mining, soon died out in the field of civil engineer
lar seat. On this he mounted the base of a 12 in diameter ing, and from 1850 onwards geology became more and
theodolite to which was fixed a 16 ft long calibrated more neglected in civil engineering practice in the UK
wooden stick. With 35 primary locations marked on the (Glossop, 1969). Despite this, dam engineers and water
rock with the point of a jumper, each could be accurately engineers continued to be concerned with, and to record,
located using a graduated vertical stick to intersect the geological details of ground conditions encountered in
horizontal pole, the bearing being determined by the major engineering works; brief details of these were
theodolite base (Figure 1.1). Intermediate points often published.
between any two locations could be fixed by off'set
measurements taken from a string line stretched between Vyrnwy dam, Wales, UK
the two. Deacon (1896) described the foundation conditions at
16ft- the Vyrnwy dam in central Wales. Undertaking as an
Theodolite engineer his own geological investigations, he concluded
from his assessments of the form of the valley to be
dammed that a rock bar limited on the downstream side
the infilled glacial basin that was to form the Vyrnwy
reservoir. In a classic site investigation to determine the
highest part of the bar, hidden by alluvium, 177 borings
and probings, and 13 shafts, were sunk. By means of
these, actual contours were drawn (Figure 1.3) and a
model made of the rock surface. In the course of exca
Figure 1.1 Diagram of the method used for large-scale mapping of
vation. Deacon records that watertight rock was found
Eddystone rock, Plymouth, UK (After Smeaton, 1793)
to be 6-7 ft lower than the rock surface which the
contours had shown. Commenting on the foundation
The whole surface of the rock could be modelled by
conditions, he states that rock masses weighing
drilling down vertically from the plane upper surface of
hundreds of tons, broken from their beds and moved
the wood block to guide the depth for carving; this is the
some distance down the valley by the former glacier, or
method used in carving. Two copies were made, and on
only just detached, were met with.
the second the rock excavation (carving might be more
appropriate even in the slate) required to suit the build It is apparent that early papers on major engineering
ing was indicated. The intention was to remove as little projects occasionally dealt with geological aspects aff'ect-
of the rock as possible, while ensuring that the flat base ing the works. In the late nineteenth century these
of each building block was protected by at least a 3 in accounts would be illustrated by steel engravings on
upstand in the rock. which very considerable geological detail could be
shown. One such is the somewhat schematic cross-
Early in the nineteenth century, much of what would
section illustrating the geological conditions associated
now be regarded as major civil engineering construction
with driving the tunnel beneath the River Mersey as part
was still in the hands of architects. Occasionally their
of the Vyrnwy scheme for the Liverpool water supply.
plans indicated ground conditions determined by bor
The diagram (Figure 1.4) comprises four vertical sec
ing. An example from North-east England is the 'Gen
tions through the alluvium and boulder clay overlying
eral Plan for the Rebuilding and Extension of the Quay,
New Red Sandstone bedrock. Of particular interest is the
Newcastle Upon Tyne\ an ink and watercolour architec
disintegrated sandstone (Red Roche) underlying the
tural drawing prepared by John Dobson on 1 January
1836. The plan shows the location of five boreholes just boulder clay. There is a lack of realism in the represen
on the river side of the line of the new quay wall. Each tation of the bedding in the sandstone which should be
borehole is marked by a red dot and numbered, with a sensibly horizontal, although despite this the section is a
note alongside of the materials met with in boring. As realistic geological plan of the subsurface conditions
examples: encountered. Incidentally, the tunnel was driven through
the water-bearing alluvium rather than at a much
No. 1. 8 ft sand, gravel below. greater depth through the sandstone in order to reduce
No. 2. 4 ft sand into gravel 2 ft. water pressure in the siphon.
Recording the early applications of geology in engineering
(b)
Figure 1.2 Extract from General Plan for the Rebuilding and Exten
sion of the Quay, Newcastle Upon Tyne\ UK, by John Dobson,
showing the location of investigatory boreholes and a cross-section
through the proposed quay wall and the river bed (From Dobson,
1836)
Figure 1.3 Plan drawn at an
original scale of 1:1800 showing
contours on the rockhead bar
below the alluvium at the
Vyrnwy dam site, Wales, as
proved by borings and probings
(Redrawn from Lapworth, 1911,
Fig. 5)
Introduction
Figure 1.4 Geological cross-
section of the ground conditions
at the Vyrnwy tunnel-siphon
beneath the River Mersey, UK
Scale, 1 inch = 64 feet. (From Deacon, 1896, Fig. 10)
Burrator reservoir, Devon, UK were concerned) and the trench ended in solid granite
At the Burrator Works on Dartmoor, for the water rock.
supply of Plymouth in Devon, the site for the main The geological plan of the trench wall and bottom was
masonry dam proved to be entirely satisfactory on plotted as excavation proceeded, and affords a valuable
massive fresh granite. Such was not the case, however, record of the as-found engineering geological conditions
for the small earthwork dam across a subsidiary minor on this part of the site. Until quite recently some idea
col. The cut-off trench for the Sheepstor embankment of ground conditions in the trench could be gained
(Sandeman, 1901) was 680 ft long, whereas the embank from the road-cutting at the western end of the dam.
ment is only 470 ft long. Unexpected ground conditions Exposures left after road-widening (Figure 1.6a), now
account for the discrepancy (Figure 1.5). nearly completely grown over, were reasonably well
Several trial pits were sunk to ascertain the most exposed in 1959. Corestones, measuring 2 χ 1 m, are
advantageous line for the trench. In two of the trenches, only moderately weathered (grade III) internally with
rock was exposed at a depth of about 14 ft, in the event a the feldspars unaffected, but the outer skin some 15 cm
delusion because on opening the trench they were found thick is highly weathered and the feldspar megacrysts are
to have penetrated to pinnacles of rock which shelved kaolinized. There is an abrupt transition to the loose
away rapidly to considerable depths. The trench, which friable completely weathered granite (grade V) with
at the centre was 105 ft deep, was cut through an kaolinized feldspars which forms the matrix to the core-
extensive layer of decomposed granite crossed by stones. The line drawing (Figure 1.6b), with details of
quartz-tourmaline veins and minor intrusions of decom discontinuities in the corestones and veins in the grade V
posed fine-grained granite (elvan). The veins ranged granite still preserved, was made by drawing directly on
from 1 inch to 3 feet in thickness, and the larger had the the photograph in Indian ink and then bleaching out the
appearance which would be exhibited by the section of a photographic image (Fookes, Dearman and Franklin,
dry rubble wall of irregularly shaped stones fitting one 1971).
into another... these veins were the main reason for so
deep a trench being sunk.' Eventually, at depth the Pennine dams, Northern England
rotten granite disappeared, the veins became one with In 1911, Lapworth published many cross-sections of
the granite they traversed (so far as engineering purposes the foundation excavations, particularly the cut-off
Recording the early applications of geology in engineering 5
S=7
PLAN
WEST 100 200 EAST
SECTION ' SCALE-FEET
BJQ QUARTZ-TOURMALINE VEINS E3 DECOMPOSED GRANITE ^ WHITE CLAY I SOFT RED ELVAN I GRANITE
Figure 1.5 Geological plan and cross-section of the cut-off trench for
the Sheepstor embankment of the Burrator reservoir, Devon, UK
(Redrawn from Sandeman, 1901, Plate 1, Fig. 7)
sandstone (grit) were affected by landsliding before the
deposition of some 60 ft of alluvium partly infilling the
old valley (Lapworth, 1911).
Other cross-sections in similar settings, not repro
duced here, show examples of landslides, cambering and
valley bulging, and water-bearing wide-open joints in the
horizontal sandstones. Somewhat simplified from meti
culously engraved originals, Lapworth's drawings are
true engineering geological plans, affording a permanent
record of the as-found conditions in the walls of cut-off
trenches, the method favoured at the time for ensuring a
positive water barrier beneath a dam.
It is interesting to note Lapworth's recommendation
that the plans should not be drawn at a scale smaller
than 1 :2500.
(a)
Alterc^tipn vein in
the original granite
Grade 21 below soil 7.2.5 Deve/opment of engineering
geológica/ maps in Europe
Peter (1966), discussing geotechnical mapping, reviewed
the development of maps in Germany. It was at the
Exposition Technique de la Construction, held in Leip
zig in 1913, that plans were shown for the first time of
both the engineering structure and foundation con
ditions. These geotechnical plans were made for the
towns of Erfurt, Frankfurt on Oder, Danzig and several
others. Coloured dot patterns and conventional signs
Grade ΠΙ corestones
123 WEATHERING GRADE! . • 0 ; Metre showed areas prone to flooding, where the watertable
was less than 1 m deep - mines, quarries, etc. A descrip
(b)
tive memoir gave the results of boreholes put down for
Figure 1.6 Roadside cutting, Burrator reservoir, Sheepstor embank
ment, Devon, UK, in weathered Dartmoor granite: (a) photograph site investigation and in the search for water.
of the exposure in 1959; (b) drawing from the photograph showing In 1919, Moldenhauer produced a geotechnical map
the distribution of weathering grades in the granite (From Fookes, of Danzig from the geological map of the city, a tech
Dearman and Franklin, 1971, Plate IV, by permission)
nique of historical importance that is the basis of more
recent mapping methods. Although the maps have not
trenches, for dams. Many of the examples were from the been available for examination, it is understood that the
Pennines of Northern England. The one chosen for author divided the ground into a number of depth zones:
illustration (Figure 1.7) is the trench for the Yarrow 0-2 m, 2-4 m, 4-6 m and 6-10 m. Results were presented
reservoir of the Liverpool Waterworks at Rivington. in two sheets: a map of the location of boreholes (600
Sensibly, horizontal alternations of beds of shale and alone for Danzig) and a geotechnical map.
Introduction
TOP or BANK
old Rivr Cei//-i»
Figure 1.7 Large-scale plan of the wall of the foundation excavation
and cut-off trench of the Yarrow reservoir of the Liverpool Water
works, Rivington, UK (From Lapworth, 1911, Fig. 14)
Stremme in 1932 published a group of maps of Osten- Early maps purporting to show ground conditions
dorff dealing with geology and geotechnics. Three geolo were essentially pedological maps, with the main post
gical maps give details of useful rocks and soils, ground war advance coming from the acceptance of the prin
water and surface water, and construction conditions. ciple that the maps should be geologically based. The
For the latter, Moldenhauer's method of depth zones first geological maps for engineering practice were so-
was used with regard to the geotechnical map; details called maps of 'soil conditions' or 'ground conditions',
were given of estimated allovv^able bearing pressures, representing both the superficial soils and the pre-
moisture content, and probability of landshding. Quaternary rocks beneath.
By 1938, Muller had published maps of the parish of In 1947 Zebera, in a publication of the State Geologi
Marke with a very modern aspect. The series of maps cal Institute of the Czechoslovak Republic, outlined a
comprised: an outcrop map of soils; an interpretative standard form of geotechnical maps for planning that
map of construction conditions; a hydrological map; a had been developed in Czechoslovakia (Zebera, 1947a).
map of treatment for the improvement of soils; a map In another report published the same year, dealing with
for use in planning. Suitability for construction of vari the Bustehrad area, he described the strip method, an
ous types of ground was shown by colours: ingenious system for showing engineering geological
conditions in three dimensions (Zebera, 1947b). These
• green and yellow were used for ground suitable for
reports discussed the main geological rock units, flag
construction that would permit bearing pressures of
ging the factors that might cause difficulties in construc
not less than 2.5 bar;
tion, such as swelling clays and landslides; indicating
• orange indicated moderate ground;
which soils were most suitable for agriculture and
• orange cross-hatching indicated least favourable
forestry; and noting the places where scenic areas should
ground conditions in its present state, where variable
be preserved. In this respect the maps approach environ
hydrological conditions necessitated special attention
mental geological maps.
being paid to foundations - nevertheless, allowable
Zebera's description of the methods being used in
bearing pressures were subject to restriction;
preparing maps for planning presented a format that
• red corresponded to poor ground requiring costly
had been in the process of development since 1941, when
foundations - it comprised generally fill, marshy
a geological service for the planning of settlements was
ground, steep slopes, etc.
established under the administration of the State Geolo
On the soil map, each soil type is shown by a distinctive gical Institute of the Czechoslovak Republic. For this
colour. Black cross-hatching and coloured conventional purpose, the geologists of the institute worked out field
symbols are used to indicate the characteristic physical methods and map standards for the Survey Map of Soil
and chemical properties of each. Conditions in the Czechoslovak Republic at the scale of
By the 1930s, numerous detailed geological maps, 1:25 000 and Detailed Plans of the Foundation Soils of
including geotechnical maps, had been prepared essen Settlements in the Czechoslovak Republic at the scale of
tially for town and country planning in Germany. It 1:5000.
seems, however, that many of these maps were, accord Because of its historical importance in engineering
ing to Pfannschmidt (1939), pedological soil maps. As geological cartography, the first version of the strip (or
such, 'ground maps' at scales of 1:10 000 and 1:25 000 stripe) method deserves illustration here, even though it
had been prepared for many towns, including as one is dealt with in detail in Chapter 6. Originally a 'banding'
example Osnabrück. Brüning (1939) also mentions the method (Figure 1.8) was used to show the depth to
pedological atlas of Hannover, including a soil type bedrock beneath the surface. Deep colours represented
map, an economic/administrative/planning map, and a outcrops of bedrock at the surface, whereas pale colours
water map. depicted the soils. Where the depth to bedrock was 4 m
Preparation of maps of foundation soils in Warsaw, or less from the surface, the depth was shown by a band
on which the geological conditions at several levels were of colour appropriate to the rock. A broad band indi
plotted, was a pioneering work in urban geology cated bedrock down to 1 m depth, a narrow band the
(Sujkowski and Rozycki, 1936). depth range 1-2 m, and an interrupted band showed that
