Elsevier Encyclopedia of Geology

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geology, soil mechanics, rock mechanics, hydrogeol-

ogy, and mining geomechanics. Examples of work

activities are as follows.

Geotechnics is concerned with the foundations of

any type of building or structure, such as dams and

bridges, and with excavations, slopes, embank-

ments, tunnels, and other underground openings.

The exploitation of natural resources involves sur-

face and underground mining, the extraction and

protection of groundwater, and the extraction of

natural materials for construction, hydrocarbons,

and geothermal energy.

Geo-environmental considerations include pro-

tection and conservation of the geological envir-

onment, rehabilitation of contaminated land

(soil and groundwater) and of mining areas,

waste disposal (domestic and toxic), and the sub-

surface emplacement of chemical and radioactive

waste.

Geo-risk is the process of mitigating geological

hazards (e.g. earthquakes, slope instabilities,

collapsible ground, gas) in land-use planning.

Ground engineering is of considerable economic

importance and benefit to society because it pro-

vides a means of building efficient structures and

facilitating the sustainable use of resources and

space. This is often not fully appreciated by the

general public. In stark contrast to other engineer-

ed structures, most geoengineered solutions are

hidden in the ground and so are not visible. Neverthe-

less, ground-engineered structures can present a

major challenge to engineering design and con-

struction and, if successfully completed, are test-

ament to substantial technological and intellectual

achievements.

The execution of such projects requires input

from a range of scientific and engineering specialties,

and the relevant specialists must be able to communi-

cate with each other in order to agree on conceptual

models and parameters to apply to the design and

must leave an audit trail to ensure quality and safety.

In addition, and perhaps even more importantly,

there is a need to communicate with other interested

parties, not least the owner of the project and the

general public. Subjects on which efficient communi-

cation is required include observations of the condi-

tion of the ground in and around the works and the

quality of that ground as revealed by physical records,

the logging of cores or exposures, and parameters

measured in field and laboratory tests. In order for

such communication to be possible, an internation-

ally agreed library of linguistic and scientific termin-

ology, test procedures, and overall investigation

processes needs to be available.

What are Codes in Engineering

Geology?

Before considering the trends and requirements in the

codification of the practice of engineering geology, it

is important to remind ourselves of the role of the

practitioner in this field. The fundamental role of an

engineering geologist is to observe and record evi-

dence of geological conditions at the site of proposed

or current engineering works and to communicate

these observations to other (non-geological) members

of the team. The evidence for the ground conditions

may be in the form of exposures, such as cliff or

quarry faces, or may be in the form of cores or

samples recovered from boreholes. It is almost uni-

versally the case that this geological information

comes from the proximity, but not the actual loca-

tion, of the proposed works. There may also be indir-

ect information, such as the results of geological

mapping or geophysical surveys or evidence from

previous engineering works in the same area or geo-

logical setting. The engineering geologist therefore

has to develop an understanding of the geology of

the area and make predictions about the geology

that will be encountered by, or will affect or be

affected by, the engineering works. It is rare for the

geologist to have sufficient information to understand

the ground conditions fully, and there is always a

point beyond which further investigation cannot be

justified by a further reduction in uncertainty. It is

therefore not uncommon for the geologist to have less

information than might be obtained from a small

number of boreholes. For instance, road and rail

tunnels driven at low level through mountains cannot

sensibly be investigated: borehole locations may not

be available, and the cost of drilling hundreds of

metres before reaching the zone of interest can be

prohibitive.

Notwithstanding the source and detail of the infor-

mation available, the engineering geologist has to

collate and interpret the geological information in

order to produce a realistic geological model that

includes realistic assessments of the degree of uncer-

tainty. The first stage is to create an essentially factual

model, before moving on to the interpretation phase.

The key aspect of the engineering geologist’s role then

comes into play: the communication of all aspects of

this conceptual model to other members of the design

team, the project owner or client, and, increasingly,

the public.

To some extent this communication of infor-

mation can be carried out using existing geological

nomenclature in a qualitative sense. However, such

an approach by geologists has often left listeners

confused. Usually, standard geological nomenclature

ENGINEERING GEOLOGY/Codes of Practice 449

is qualitatively, rather than quantitatively, defined, so

even other geologists can be left uncertain as to the

exact meaning intended. Over the years, a language

of better-defined terms has developed, which should

better enable geologists to communicate, not least

because there is now a core of standard terminology

with which the listeners will be familiar. It is the

derivation and definition of this standard termin-

ology that is one of the main reasons for recent

advances in the drafting and implementation of

codes in engineering geology.

The intention of the ISO and CEN in preparing

international standards is to help raise levels of

quality, safety, reliability, efficiency, compatibility,

and interchangeability, and to provide these benefits

economically. Standards contribute to making the

development, manufacturing, and supply of products

and services more efficient, safer, and cleaner. They

make trade between countries easier and fairer. ISO

and CEN standards also safeguard consumers, and

users in general, of products and services and make

their lives simpler.

The History of Codification in

Description

Prior to 1970, there was no international standard

terminology to allow the communication of descrip-

tions of geological materials or their properties, al-

though some of the larger contracting companies

had developed internal guides. The first British Code

of Practice (CP 2001) was published in the UK in

1957. This code laid down key underlying precepts

for the description of soils, in particular that soils

should be described in terms of their likely engineer-

ing behaviour. This basic need is often lost in today’s

welter of published guidance. However, CP 2001 did

not cover the description of rocks. Geological sci-

ences continued to develop an increasingly variable

use of terminology, but the increasing size of the

ground engineering industry made the terminology

increasingly irrelevant and no longer tenable. The

need for a defined and wide-ranging terminology

had arrived.

The use of undefined and narrow terminologies

caused confusion and ambiguity in communication

and, as a result, frequent contractual arguments

arose, often leading to claims based on ‘unforeseen

ground conditions’. This was hardly surprising as, if

the terminology is variable and undefined, there will

always be someone who could misread the ground

conditions being predicted. For instance, terms

such as ‘highly fissured’ and ‘moderately jointed’

were not defined and therefore meant different

things to different readers. This was addressed when

the Engineering Group of the Geological Society of

London published, in the early 1970s, a series of

Working Party Reports for guidance, for example on

core logging (in 1970) and the preparation of maps

and plans (in 1972). These reports formed the basis

of UK practice and, as it turned out, international

practice in many respects. Similar activities on the

international scene resulted, by 1981, in publications

from the International Association of Engineering

Geologists and the International Society of Rock

Mechanics on field investigation, geological map-

ping, and soil and rock description. In the UK, this

decade of guidance culminated with BS 5930 (pub-

lished in 1981), the seminal National Standard for

engineering geological activities. It is important to

note, however, that even at this stage BS 5930 was

designated as a code of practice, meaning that the

guidance was advisory rather than normative (i.e.

mandatory). This designation was maintained in

the updated version of BS 5930, published in 1999.

The reasons for this relate to the preference of

many geologists to not be given edicts on geological

terminology. However, the designation of codes as

advisory has little practical relevance. The codes are

referenced in contract specification documents and

thus become binding. In legal arguments about claims

or failures, the courts will expect the national

guidance to have been followed. Therefore, at least

by default, the codes of practice have become de facto

Standards.

The publication of international guidance has

continued, albeit at a slower pace, with individual

nations publishing national guidance documents.

The designation of such guidance as mandatory or

advisory varies, and it is this variance that is

now being resolved in the name of international

normalization.

Particular Problem Areas in

Combining National Codes

Despite the codifications in various countries pro-

ceeding independently, there are many cases where

the practices of one country have been adopted by

another. For this reason, the preparation of inter-

national codes by the ISO has not been as difficult

as might have been anticipated, at least as far as the

description of soils and rocks is concerned. There

have nevertheless been a few difficulties, as outlined

below. However, the historical development of local

codes has tended to reflect and emphasize local

450 ENGINEERING GEOLOGY/Codes of Practice

geological conditions, and the classifications were

rather more difficult to bring together into an all-

embracing international standard. This proved par-

ticularly difficult for the classification of soils and

resulted in the need for a simple and separate ISO

Standard on this topic.

The Scandinavian countries have different types of

soil (coarse glacial deposits and fine ‘quick’ clays)

from Italy (volcanic sands) and Japan (silts and

loose sands that are liable to liquefaction). National

practice has, for sound technical reasons, tended to

reflect the regional geological source materials, active

geological processes, and impacts of climate and time

of exposure, all of which vary across the world. The

work carried out by the ISO Technical Committees

has needed to incorporate these variations into

practice.

Fine-Grained Materials

The definition of the grain-size boundaries used to

classify soils and rocks for engineering purposes has,

by and large, developed along similar lines through-

out the world, as shown in Table 1. Exceptions to this

are the USA, where a range of definitions are avail-

able, and some Pacific Rim countries. The agreement

is wide ranging and complete except for the finer-

grained materials, specifically rocks, where terms

such as claystone, siltstone, mudstone, shale, and

slate are all variously used. The simplification of the

terminology to mirror the descriptive terms for soils is

proposed in the latest codes.

Weathering Classifications

Weathering classifications are provided in a number

of the existing national and international guidance

documents, but there is little commonality between

publications. The provision of such classifications

within a descriptive framework has proved unhelpful,

as weathering profiles are rarely amenable to global

classification (because they depend strongly on cli-

mate and local topography) and fail to embrace the

actual description of the weathering features that

are present. For this reason, UK practice, since the

1999 publication of BS 5930, requires the descrip-

tion of weathering profiles. Further classification

schemes are permitted only if relevant, available,

useful, and unambiguous. However, this practice is

not yet generally accepted at an international level.

Core Indices

Core indices such as Rock Quality Designation

(RQD) have been proposed for the logging of rock

not only from borehole cores but also from the map-

ping of exposures, in order to provide a ready indica-

tor of rock quality. A number of indices and a range of

definitions have been proposed, without much com-

monality. Recent International Standards have ad-

dressed this and provide unambiguous and clear

definitions of which fractures should and should not

be included in the quality assessment and of how the

index should be measured. Although the RQD is only

a crude indicator of rock quality, it is very widely

used, on its own and correlated with other properties,

Table 1 Particle size definitions

Soil name Soil fractions Dimensions Sedimentary rock name

Boulders over 200 mm

Cobbles 200–60 mm

Gravel Coarse 60–20 mm

Medium 20–6 mm Conglomerate (boulders, cobbles

and gravel)

Fine 6–2 mm

Sand Coarse 2–0.6 mm Coarse-grained sandstone

Medium 0.6–0.2 mm Medium-grained sandstone

Fine 0.2–0.06 mm Fine-grained sandstone

Silt Coarse 0.06–0.02 mm

Medium 0.02–0.006 mm Siltstone (coarse, medium and fine)

Fine 0.006–0.002 mm

Clay less than

0.002 mm

Mudstone or claystone

Few soils comprise merely a single principal size fraction. Soils usually include secondary constituents of a different size fraction

that could significantly influence their engineering behaviour. There are also minor constituents that can help in geological

identification but do not influence characteristic behaviour. Claystone is used in some countries to match the soil terms, but this can

be confused with nodular concretions. In these cases the term Mudstone is preferred.

ENGINEERING GEOLOGY/Codes of Practice 451

in rock-mass classification systems (e.g. compressibil-

ity, diggability, tunnel stand-up time). The lack of

consistency in the measurement of the index is not

widely appreciated, and so the international and nor-

mative standardization of the index is long overdue.

This neatly illustrates the need for standardization

wherever a property, however simple, is used to

communicate a measure of ground quality. It will be

valid only if the measurement process is consistently

applied and understood.

The ongoing evolution of the codification of ter-

minology and test procedures means that users need

to be aware of the date of data collection when con-

sidering the descriptive and measurement standards

that are likely to have been incorporated in borehole

logs, maps, and records. In particular, archival

records are likely to have been prepared according

to different, outdated, Standards and definitions.

History of the Codification of Field

and Laboratory Testing

The standardization of field and laboratory proced-

ures is as important as the standardization of the

description and includes forming the borehole or

describing the exposure, executing field tests, re-

covering samples, and carrying out laboratory tests.

If the results of any of these activities are to be applic-

able and relevant in the minds of others, the pro-

cedures used need to be clearly identifiable and

standardized.

The codification of laboratory test procedures for

soils commenced in the 1940s, when the first ma-

chines were developed. The procedures covered

everything from how to drill a borehole, conduct the

basic field tests, and take and describe samples, to

their storage, transport, and laboratory testing. In

fact, even the design of the testing machines had to

be specified as test procedures evolved. Work by the

ISO and CEN that is underway at the time of writing

will describe the procedures and concentrate on the

preparation of Technical Specifications (Table 2),

building on earlier test procedures drafted by the

International Society of Soil Mechanics.

The testing of rocks in commercial practice started

somewhat later, by which time the need for inter-

national cooperation was better appreciated. It has

therefore been possible for the rock-testing proced-

ures to be better established, under the auspices of

the International Society of Rock Mechanics, who

have published a series of suggested methods. As

there were no precedent procedures in place, these

suggested methods have been rapidly adopted by

the professional community and have become inter-

nationally recognized without the involvement of

national standards bodies. It would therefore be com-

paratively straightforward, but not necessarily easy,

to prepare normative international standards for

most rock tests.

Professional Qualifications

A further aspect of codification is the identification of

relevant qualifications and experience necessary for

those who plan, execute, and interpret ground inves-

tigations. The guidance documents and codes pre-

pared up to the end of the 1980s did not try to lay

down rules about the qualifications and experience

required by those working as specialists in engineer-

ing geology. In the very early days, this was felt to

be unnecessary; the number of practitioners was

small, and their capabilities and limitations were

known through reputation. This has become increas-

ingly less reliable, with even academic programmes

of training changing significantly from previously

accepted standards of coverage and achievement. It

is now necessary to define the roles and who may be

permitted to practice. It is interesting to consider who

benefits most from such codification. Is it the client,

who can feel better protected by the knowledge that

they have properly trained and experienced profes-

sional advisors, is it the insurers, who feel they have

lower exposure to risk, is it the individual practition-

ers, who feel this improves their status in society, is it

the employers, who can recognize a qualified practi-

tioner, or is it the companies, who can see a market

with fair competition? The truth is probably a com-

bination of all of these. The position taken by the

Standards Institutions is based on the latter view,

and ISO/CEN documents currently in preparation

include definitions of specialist practitioners. These

definitions will therefore become requirements in the

practice of ground engineering.

The development of such defined roles is closely

linked to the development of Directives in the Euro-

pean Union. In order to facilitate the mobility of

workers, the availability of internationally recog-

nized qualifications is essential. The Directive on

this subject is likely to be enacted by about 2005.

The requirement for practitioners to be able to prac-

tice, at least for limited periods, in any European

Union country is the holding of a recognized qualifi-

cation. This qualification is likely to be represented

by the common platform of the European Federation

titles of EurIng, awarded by the European Fede-

ration of Engineers, and EurGeol, awarded by the

452 ENGINEERING GEOLOGY/Codes of Practice

Table 2 Codes in preparation by CEN/TC 341 and ISO/TC 182/SC 1 concerning geotechnical investigation and testing

ISO

reference number Title Committee draft

Draft

International Standard

Final draft International

Standard

Publication

as EN/ISO standard Remarks

14688-1 Identification of soil 2002–March 2002–June ISO

14688-2 Classification of soil 2001–June 2002–September 2002–December ISO

14689 Identification of rock 2001–September 2002–September 2002–December ISO

22475-1 Sampling methods 2003–September 2004–September 2006–March 2006–June

22475-2 Sampling – Qualification criteria 2003–September 2004–September 2006–March 2006–June

22476-1 Cone penetration tests 2003–September 2004–September 2006–March 2006–June

22476-2 Dynamic probing 2001–December 2002–September 2004–September 2004–December

22476-3 Standard penetration test 2001–December 2002–September 2004–September 2004–December

22476-4 Menard pressuremeter test 2003–September 2004–September 2006–March 2006–June

22476-5 Flexible dilatometer test 2003–September 2004–September 2006–March 2006–June

22476-6 Self-boring pressuremeter test 2003–September 2004–September 2006–March 2006–June

22476-7 Borehole jack test 2003–September 2004–September 2006–March 2006–June

22476-8 Full displacement pressuremeter 2003–September 2004–September 2006–March 2006–June

22476-9 Field vane test 2003–September 2004–September 2006–March 2006–June

22476-10 Weight sounding test 2002–June 2002–December TS

22476-11 Flat dilatometer test 2002–June 2002–December TS

22477-1 Testing of piles 2003–September 2004–September 2006–March 2006–June

22477-2 Testing of anchorages 2003–September 2004–September 2006–March 2006–June

22477-3 Testing of shallow foundations 2003–September 2004–September 2006–March 2006–June

22477-4 Testing of nailing 2003–September 2004–September 2006–March 2006–June

22477-5 Testing of reinforced fill 2003–September 2004–September 2006–March 2006–June

17892-1 Water content 2002–December 2003–June TS

17892-2 Density of fine-grained soils 2002–December 2003–June TS

17892-3 Density of solid particles 2002–December 2003–June TS

17892-4 Particle size distribution 2002–December 2003–June TS

17892-5 Oedometer test 2002–December 2003–June TS

17892-6 Fall cone test 2002–December 2003–June TS

17892-7 Compression test 2002–December 2003–June TS

17892-8 Unconsolidated triaxial test 2002–December 2003–June TS

17892-9 Consolidated triaxial test 2002–December 2003–June TS

17892-10 Direct shear test 2002–December 2003–June TS

17892-11 Permeability test 2002–December 2003–June TS

17892-12 Atterberg limits 2002–December 2003–June TS

TS: technical specification, not initially normative.

All document-drafting committees are led by CEN except where noted to the contrary.

ENGINEERING GEOLOGY/Codes of Practice 453

European Federation of Geologists.These titles show

that the bearer has undertaken an appropriate course

of study, carried out appropriate training, and gained

sufficient experience to be able to act as a profes-

sional engineer or geologist, and that this record has

been submitted to the bearer’s peers for validation.

The holder of such a title agrees to work within the

code of conduct operated by the awarding Federation

and will be able to work in any European country, at

least for limited periods, without needing to qualify

separately in that country. These are major develop-

ments in providing commonality of professional

standards and represent development exactly as

hoped for by the ISO and CEN, but driven forward

by the European Commission.

Codification into the Twenty-First

Century

After 25 years in preparation, the suite of Eurocodes

is, in the early 2000’s, becoming a reality. These Euro-

codes bring together codes of practice for building

and civil engineering structures, and provide a

world-class standard for all aspects of construction.

Included in Eurocode 7 (geotechnical design) are

elements of codes on the description and class-

ification of soils and rocks, field investigation

methods, field and laboratory testing, assessment of

engineering parameters, and design procedures. For

the first time, engineering geologists throughout

Europe will be talking in a common language when

reporting the findings of their field observations.

This progress extends beyond Europe, as, in accord-

ance with the Vienna agreement, the standards drawn

up by CEN and ISO undergo parallel voting proced-

ures for common adoption. Thus, for example, the

proposals for the description of soils and rocks pre-

pared by the ISO in 2003 will also be incorporated

into Eurocode 7. Thus, engineering geologists around

the world will be able to pass on their geological

information without misunderstanding and ambigu-

ity. The Japanese ‘brown sandy clay’ will be the same

as the Swedish ‘brown sandy clay’. Similarly, the

results of field or laboratory testing will be transfer-

able around the world. Major exceptions to this rule

are China and the USA, who are not members of

either of these standards bodies and who have had

no input into the drafting of the codes.

A schedule of the codes and specifications being

prepared by the ISO and CEN in this area is given in

Table 2. The codes for the description and classifica-

tion of soils and rocks were prepared by a Technical

Committee of the ISO. The reason for this work item

being proposed initially was, in accordance with the

ISO mission, to encourage and allow international

communication in applied science and therefore to

allow more and fairer competition in international

trade. This enshrines the concept of engineering

geologists the world over sharing a single interpret-

ation of a conceptual ground model. They will there-

fore be able to compete equally for contracts and

cooperate more effectively on design briefs.

The primary benefit of such codes is that they

will standardize ground investigation, reporting, and

design approaches that are common over much of the

world. The market for investigation and design, and

thus the market for engineering geology, thus be-

comes both much larger and much more competitive,

but with a level playing field.

However, the Eurocodes do not completely sub-

sume the national practices, which have been built

up over the years and which are pertinent to local

situations. This is right and proper given that vari-

ations in engineering geological practice have their

base in the different geological conditions in different

countries. For instance the Scandinavian extensive

crystalline basement crust and soft ‘quick’ clays varies

significantly from the deep weathering profiles of the

tropics. These different conditions require different

approaches to investigation and testing. The descrip-

tion of the materials can nevertheless be based on a

single standardized approach.

The national differences in the approach required

can be incorporated into National Annexes, which

allow key safety and technical issues to remain a

national rather than a European responsibility and

allow geological and climatic variations to be taken

into account. However, these National Annexes are

enhancements of, rather than local rewrites of, the

overarching international codes.

Concluding Remarks

Over a remarkably short time-span, engineering

geology has developed from a situation where the

early professionals acted as individuals and managed

without codes to today’s world where teamwork pre-

dominates and there is an increasing need for ac-

countability. The codes coming into place in the

2000s define how we should drill holes, take and

test samples, and describe soils and rocks. Perhaps

the biggest change will be that we will have to carry

internationally recognized qualifications if we want

to be able to practice all over the world.

454 ENGINEERING GEOLOGY/Codes of Practice

Further Reading

Bonilla MG (1967) Historic surface faulting in continental

United States and adjacent parts of Mexico. Unnumbered

open file report to the US Atomic Energy Commission.

US Geological Survey. Menlo Park, California.

Bonilla MG (1973) Trench exposures across surface fault

ruptures associated with San Fernando Earthquake. In:

Murphy ML (ed.) San Fernando, California Earthquake

of February 9, 1971, pp. 173–182. Washington DC: US

Department of Commerce.

Bonilla MG, Mark RK, and Lienkaemper JJ (1984) Statis-

tical relations among earthquake magnitude, surface

rupture length, and surface fault displacement. Bulletin

of the Seismological Society of America 74: 2379–2412.

Brown RD Jr, Ward PL, and Plafker G (1973) Geologic

and Seismologic Aspects of the Managua, Nicaragua,

Earthquakes of December 23, 1972. USGS Professional

Paper 838. Washington DC: US Geological Survey.

Eckel EB (1964) The Alaska Earthquake, March 27, 1964:

Lessons and Conclusions. USGS Professional Paper 546.

Washington DC: US Geological Survey.

Hays WW (1981) Facing Geologic and Hydrologic

Hazards: Earth Science Considerations. USGS Profes-

sional Paper 1240-B. Washington DC: US Geological

Survey.

Krinitzsky EL (2003) How to combine deterministic and

probabilistic methods for assessing earthquake hazards.

Engineering Geology 70: 157–163.

Obermeier SF, Jacobson RB, Smoot JP, et al. (1990) Earth-

quake-Induced Liquefaction Features in the Coastal Set-

ting of South Carolina and in the Fluvial Setting of the

New Madrid Seismic Zones. USGS Professional Paper

1504. Washington DC: US Geological Survey.

Scott GR (1970) Quaternary Faulting and Potential Earth-

quakes in East-Central Colorado. USGS Professional

Paper 700-C. Washington DC: US Geological Survey.

Youd TL and Hoose SN (1978) Historic Ground Failures in

Northern California Associated with Earthquakes. USGS

Professional Paper 993. Washington DC: US Geological

Survey.

Wells DL and Coppersmith KJ (1994) New empirical rela-

tionships among magnitude, rupture length, rupture

width, rupture area, and surface displacement. Bulletin

of the Seismological Society of America 84: 974–1002.

Geological Maps

J S Griffiths, University of Plymouth, Plymouth, UK

Introduction

Engineering geological maps provide ground informa-

tion of relevance to civil engineering planning, design,

and construction. Given that geology and civil engin-

eering deal with three-dimensional structures and

how they behave through time, albeit usually on dif-

ferent time-scales (geology 10

–10

years; civil engin-

eering 10

–10

years), it is to be expected that the

preparation of maps and plans is a essential compon-

ent of both disciplines. Hence engineering geology

maps have been regarded as an effective means of

conveying information between geologists and engin-

eers from the earliest days of the emergence of engin-

eering geology as an identifiable subject. Indeed, the

first classic stratigraphic maps and sections of William

Smith (see Famous Geologists: Smith) in the late eight-

eenth and early nineteenth centuries arose out of his

work on canal construction and the need to anticipate

ground conditions.

An engineering geological map differs from the

standard geological map by not being limited to

scientific categories of bedrock and/or superficial

geology. The map may group materials according

to similar engineering characteristics and also pre-

sent relevant data on topography, hydrology, hydro-

geology, geomorphology (see Engineering Geology:

Geomorphology), and geotechnics, plus information

on man-made structures such as landfill sites or earth-

works. This additional ground information may be

shown on the map itself, or by using tables, charts,

and diagrams accompanying the map, as exemplified

by Table 1 from the Hong Kong Geotechnical Area

Studies Programme (GASP), and Figure 1 from the

Vı

a Inter-Ocea

nica, Quito, Ecuador. Whilst most

maps in the past were cartographically drafted

and produced as hardcopy, there is increasing use of

computer-based Geographical and Geoscience Infor-

mation Systems (GIS and GSIS) for compiling the

data in formats that can be readily updated and

analyzed.

The data for an engineering geological map will be

compiled from a wide range of data sources and will

ENGINEERING GEOLOGY/Geological Maps 463

Table 1 Example of an extended engineering geology legend based on bedrock data from the Hong Kong GASP programme

Material description Evaluation of material

Map unit Lithology Topography Weathering Material properties Engineering comment Uses/excavation

Lower

Cretaceous

Dolerite

(dyke rock)

Black to very dark

grey, fine to

medium-grained

rock. Smooth

joints normal to

boundaries

result of cooling

Generally occurs as linear

structural features transecting

the volcanic and granite units.

May be of slightly depressed

or elevated topographic form

due to variable resistance of

the country rocks. This

geological structure often

controls local surface runoff

and may act as a loci for

subsurface water

concentrations

Weathers deeply to a

dark red silty clay

Weathered mantle will

contain a high

proportion of clay and

iron oxides leading to

low Ø values. Intact

rock strength will be

very high, >100 Mpa

when fresh

Restricted extent

precludes detailed

comment. Weathered

mantle will have

relative low

permeability and will

affect groundwater

hydrology by forming

barriers, and variable

boundary conditions.

Sub-vertical dykes

may dam

groundwater leading

to unexpectedly high

groundwater levels.

Restricted extent

precludes deliberate

borrow or quarry

activities. Weathered

material would make

poor fill but fresh rock

would make suitable

high density

aggregate or railway

ballast.

Upper Jurassic

Hong Kong

Granite

Pink to grey

medium-grained

equigranular,

non-porphyritic

rock Mineral

include quartz,

potassium

feldspar,

plagioclase,

biotite and

muscovite.

Rough sheeting

joints and widely

spaced tectonic

joints

widespread

Forms extensive areas of

moderate to steep convexo-

concave slopes. High-level

infilled valeys are common.

Drainage pattern is often

dendritic in nature and is

commonly dislocated by major

tectonic discontinuities. These

units are characterised by

moderate to severe gully and

sheet erosion associated with

hillcrest and upper sidelong

terrain

Shallow to deep

residual soils over

weathered granite.

Local development

of less weathered

outcrops in stream

beds and occasional

cliff faces. Residual

core boulders

common on surface

of sidelong ground

and gullies.

Weathering depths

>20 m

Material properties vary

with depth within the

weathering profile.

For completely

weathered granite

typical values are c



0–25 kPa, Ø  31–43



;

permeablity  10

6

–

8

m/s; dry density

1500 kg m

. Moisture

content 15% near

surface, 30% at depth.

Fresh rock UCS 80–

150 MPa. Rock mass

strength dependent

on joint

characteristics.

Roughness angles for

tectonic joints 5–10



;

for sheet joints 10–15



;

basic friction

angle  39



Weathered mantle

subject to sheet and

gully erosion with

landslides in steep

slopes or if severely

undercut. Perched

water tables conform

with highly permeable

upper weathered

zones. Rock is prone

to discontinuity

controlled failures in

fresh to moderately

weathered state.

Stream and drainage

lines align with

geological weakness.

Large structures may

require deep

foundations. Cut slope

design may be

governed by the large

depths of weathered

material

Extensively quarried

and used as concrete

aggregate. Weathered

material widely used

as fill as it is easily

excavated by

machinery. Core

boulders can cause

problems during

excavation

464 ENGINEERING GEOLOGY/Geological Maps

Middle and

Lower

Jurassic Lok

Ma Chau

Formation

Metamorphosed

sedimentary and

volcanic rocks,

including schist,

phyllite, quarzite,

metasediments

and marble.

Forms hills of moderate to low

relief due to its low resistance

to erosion. Occurs extensively

beneath collluvial and alluvial

cover. Local areas of surface

boulders and occasional rock

outcrops on sidelong ground

and in gullies

Metasediments

generally weather to

produce moderately

deep (1–2 m),

uniform or

gradational red-

brown clay

Near-surface completely

weathered residual

soil acts as a silt with

a void ratio 0.25–0.33.

Gradings show 5–

15% clay, 40–60% silt,

20–30% fine sand. PL

25–35%; LL 34–40%.

Typical shear strength

 0–15 kPa, Ø  35



Weathered materials

dry density 1600–

1800 kg m

. Fresh

rock UCS 40–90 MPa.

Discontinuity strength

parameters c

0–

5 kPa, Ø  25–30



Considerable care is

required during

investigation, design,

and construction.

Bearing capacity

reasonable for low

and moderate loads.

Stability is dependent

on the very closely

spaced

discontinuities.

Discontinuity surveys

are essential for cut

slope design. Material

prone to failure along

discontinuities when

weathered and

saturated

Material can be used as

a source of bulk fill

but may break down

to silt if over-

compacted.

Excavation by

machine is relatively

easy

ENGINEERING GEOLOGY/Geological Maps 465

Elsevier Encyclopedia of Geology - vol I A-E

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