Elsevier Encyclopedia of Geology

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Further Reading

British Geological Survey (2003) World Mineral Statistics

1997–2001. Minerals Programme Publication 13, Key-

worth.

Davis GR (1978) Geology in the minerals industry. In: Knill

JL (ed.) Industrial Geology, pp. 78–110. Oxford: Oxford

University Press.

Dixon CJ (1979) Atlas of Economic Mineral Deposits.

London: Chapman & Hall.

Evans AM (1997) An Introduction to Economic Geology

and its Environmental Impact. Oxford: Blackwell

Scientific.

Evans AM (ed.) (1995) Introduction to Mineral Explor-

ation. Oxford: Blackwell Science.

Hartman L (1987) Introductory Mining Engineering. New

York: Wiley.

Holland HD and Petersen U (1995) Living Dangerously:

The Earth, its Resources and the Environment. New

York: Princeton University Press.

Jones MP (1978) Applied Mineralogy – A Quantitative

Approach. London: Graham & Trotman.

Manning DAC (1995) Introduction to Industrial Minerals.

London: Chapman & Hall.

Wills BA (1997) Minerals Processing Technology, 6th edn.

Oxford: Pergamon Press.

a0005 ENGINEERING GEOLOGY

Contents

Overview

Codes of Practice

Aspects of Earthquakes

Geological Maps

Geomorphology

Geophysics

Seismology

Natural and Anthropogenic Geohazards

Liquefaction

Made Ground

Problematic Rocks

Problematic Soils

Rock Properties and Their Assessment

Site and Ground Investigation

Site Classification

Subsidence

Ground Water Monitoring at Solid Waste Landfills

Overview

M S Rosenbaum, Twickenham, UK

Engineering geology embraces the whole of geo-

science, gathering information pertinent to the

(infra-)structure of society, preservation and en-

hancement of the environment, and sustainable

development. The engineering geologist interprets

this information with the relevant application of

knowledge and judgement to support the engineer-

ing profession, and to protect the public and the

environment.

An engineering geologist in essence reads the

ground like a book, anticipating where adverse

conditions might arise. The primary concern is with

defining the likelihood of a geological hazard

(‘geohazard’) occurring, whose existence may be

predicted from an appropriate consideration of the

444 ENGINEERING GEOLOGY/Overview

Aspects of Earthquakes

A W Hatheway, Rolla, MO and Big Arm, MT, USA

Introduction

The main product arising from the work of engineer-

ing geologists is their site characterizations for engin-

eered works. In terms of the impact of earthquakes

and their mitigation, design engineers, architects, and

planners need to both accommodate people and pro-

vide functionality. With these goals in mind, engineer-

ing geologists develop three-dimensional descriptions

of the ground to the depth that will be affected by the

static loads resulting from the engineered works and

by the expected levels of earthquake-induced ground

motion.

The damaging effects of earthquakes can be miti-

gated, but the earthquakes themselves cannot yet be

controlled or stopped. Engineering geology can be ap-

plied in a variety of ways to assist in mitigating the

effects of earthquakes; for instance by

recommending the avoidance of sites that are likely

to experience ground displacement as a result of

fault movement;

grading the site to a configuration that promotes

stability of the ground mass;

improving the engineering characteristics of the

ground so as to resist damaging deformation;

controlling groundwater that is likely to experi-

ence excess pore pressure leading to ground failure

under the involved structural loads; and

creating green space to isolate active faults and

possible seismically induced slope failures.

Engineering geologists also record details of and

analyse the damage done by earthquakes (Figure 1).

In this context, the role of the geologist is expanded

from considering the known structural-loading condi-

tions imposed by the designers to considering the un-

known, but anticipated, ground motion during a

hypothetical earthquake felt to be appropriate to the

role and function of the project. Worst-case-earthquake

design predictions are appropriate for critical facilities

or for projects housing dependent populations. Critical

facilities are those projects for which the consequences

of failure are intolerable.

Worst-case-earthquake design is based on the con-

cept of the maximum credible earthquake (MCE),

which is the greatest magnitude and duration of strong

motion that can reasonably be expected to occur.

Ancillary to this concept is risk analysis to define

magnitudes and durations of strong motion for which

there are cost benefits and for which damage can be

tolerated.

Figure 1 Engineering geological mapping records evidence of earthquake motion such as this railroad deformation indicating

north-to-south shortening of the ground along the rail right of way. Most evidence of earthquake damage is fragile and likely to be

destroyed by human activity within hours or days. (Photographed by Richard J. Proctor, then Chief Engineering Geologist, Metropol-

itan Water District of Southern California, at San Fernando Valley, California, February 1971.)

456 ENGINEERING GEOLOGY/Aspects of Earthquakes

Why Ground Fails During

an Earthquake

The behaviour of the ground during an earthquake

depends not only on the character of the incidental

ground motion but also on the properties of the site

subsurface. Engineering geology is used in this con-

text to detect and delimit bodies of ground that

are most susceptible to earthquake damage and to

identify, where possible, the interfaces between geo-

logical units where shaking displacements may be

concentrated or otherwise focused.

Engineering geological investigation looks for

horizons and pockets of damage-susceptible soil and

potential surfaces of failure (displacement, created

where differential stress is greatest and exceeds

in situ shear strength). For rock masses, the failures

representing displacements generally occur along

pre-existing discontinuities.

p0040 Geometry plays a strong role in the development

of earthquake-induced failure conditions. In the

worst case, the gross motion vector generally

enters a hillside mass and leaves at a hillside or some

form of cut slope where there is no restraint to the

passing, outward-bound ground motion, hence

leading to failure. River banks and incised stream

valleys are very susceptible to such conditions.

Added to this basic geometry, if rainfall has been

heavy for a week or more, the earth media have

been infiltrated by rain or snowmelt, or, for reser-

voirs, drawdown has been recent and of some mag-

nitude (a few metres or more) then a significantly

unstable situation will result.

Where soil masses serve as the foundation and have

little or no lateral ground support, new soil failure

surfaces can be created leading to a condition of

lateral spreading, where the foundation shifts in the

direction of least lateral support, generally causing

considerable damage to the affected component of

the engineered structure.

Another poor geological situation is where major

open rock joints strike at an oblique angle to the face

of a hillside or cut, dipping towards the face at a dip

angle greater than that of the internal friction of the

failure surfaces, which themselves form a wedge of

rock pointing out of the hillside.

Little warning of impending failure is given (per-

haps just a couple of seconds in which audible grind-

ing noises are heard) before the accelerated mass of

debris, separated from the hill by the surfaces of the

geometric wedge, begins to move.

Earthquake strong motion typically lasts between

10 and 30 seconds, which, given the presence of the

instability factors listed above, is long enough to

create a failure motion.

Linking Earthquakes to

Ground Effects

As already noted, engineering geologists assess the

likelihood of earthquakes occurring, based on data

from observed and historic earthquakes in the same

seismotectonic zone. Geological observation becomes

the basis for predicting the potential occurrence of

various ground effects.

Near-region geological evidence indicates the gen-

eral seismogenic character of the site. Relevant factors

include seismic history (magnitude and frequency

of recurrence), palaeoseismic patterns, geomorpho-

logical evidence, fault sources, and the delimitation

of seismogenic zones within which individual capable

faults occur.

Displacement effects occur when bodies of earth

materials are displaced along curvilinear failure sur-

faces (in soil) or along pre-existing discontinuities (in

weak rock). Normally the displacement occurs in the

direction of least lateral constraint.

Slope failures may affect unstable masses, defined

by hillside geometry, valley walls, river banks, and cut

slopes, when the arriving earthquake ground motion

acts momentarily within the up-gradient mass to

reactivate pre-existing rock discontinuities or newly

formed curvilinear failure surfaces. Gravitational ac-

celeration moves the disequilibrated earth mass down

the slope.

Liquefaction is a dynamic process that mainly

affects cohesionless unconsolidated soil in the pres-

ence of near-surface groundwater. Earthquake strong

motion raises pore-water pressure in such strata,

mobilizing the soil, often upward along linear or

pipe-like channels, which may reach the surface

to generate a fountain, leaving geomorphological

evidence in the form of sand blows.

Geologically Based Mitigation

One of the most successful methods of mitigating

potential earthquake damage is to employ engineer-

ing geological studies to devise methods by which

human development can be governed or designed so

as to be less susceptible to seismic damage.

Avoiding Damage-Prone Areas

Development projects should avoid damage-prone

areas, and site characterization should be employed

to discover and delimit ground at an unacceptably high

risk. This is naturally difficult to accomplish where

land development is governed by commercial interests

and imperatives. There are two basic means by which

development can be limited; both have been success-

fully employed in the State of California using local

ENGINEERING GEOLOGY/Aspects of Earthquakes 457

laws (generally enacted as city or county ordinances)

and State laws.

The first measure is the creation of a greenbelt,

whereby ground felt to be prone to damage is assigned

to park or promenade use, thereby remaining land-

scaped but available for use by residents rather than

being given over to the construction of residential

housing or commercial buildings.

The second measure is the zonation of capable

(active) faults. This was devised by the California

legislature in 1969. Named after its politician pro-

moters, State Senator Alquist and State Assemblyman

Priolo, the Alquist–Priolo Act requires the California

Geological Survey to define exclusion zones (440 m

wide) bounding the most likely central-axis location

of the subject fault and also designed in band-width

to meet the usual California alluvial fault-rupture

situation in which repetitions of historic ground rup-

tures often occur with positional variance. The maps

are updated regularly and are available for public

inspection.

Improving Ground Conditions

For engineered works that must be built in seismically

active regions, but not within or adjacent to active

faults, there remains a variety of geotechnical methods

that can improve the ability of the foundation or

the surrounding ground to resist the expected MCE

ground shaking. Such geotechnical methods generally

fall into one of the following categories, all of which

require engineering geological input in order to be

successfully designed and emplaced.

Dewatering avoids the pore-pressure build-up that

may cause liquefaction or other forms of ground

failure. Measures can be passive (e.g. French drains

and vertical gravel-packed columns, wick drains and

subhorizontal drain pipes) or active (e.g. dewatering

points or wells).

Retention generally uses iron or steel tiebacks and

ground anchors to counter vectoral earthquake

motion acting outwards from the foundation mass

towards unconfined ground (such as hillsides and

cuts) and upward acceleration towards the ground

surface itself.

Densification of the ground is usually achieved by

dynamic compaction using falling weights (e.g. a

demolition ball dropped from a crane).

Less stable layers, pockets, or zones may be ex-

cavated and replaced. Selection of this option is

generally controlled on the basis of (low) cost.

Predicting Collateral Damage

Earthquake-induced ground motion can dislodge or

otherwise set in motion boulders, joint blocks, and

slope masses. These situations generally can be identi-

fied from photogeological interpretation and confir-

med by geological mapping. Each situation will have

a slightly different nature, but is likely to fit into one of

the following categories.

Boulder dislodgment is the displacement of boul-

ders by long-term geological processes (mainly

slope erosion) or earthquake excitation. Much has

been done by the Utah Geological and Mineral-

ogical Survey to mitigate this hazard by educating

land developers and home buyers. The situation is

perhaps worst along the front of the Wasatch

Mountains, at Salt Lake, and in Utah cities between

Provo and Ogden.

Rockfall is perhaps the most prevalent and dan-

gerous of the slope-motion earthquake threats,

recognizable mainly along major transportation

routes through rugged mountain terrain, especi-

ally in areas and at elevations not supporting

dense vegetation that would obstruct the passage

of debris. The leader in the mitigation of individ-

ual-event rockfall is the Colorado Geological

Survey.

Slope failure has been noted primarily in the South

American Andes and in the Coast Range immedi-

ately south of San Francisco, California. The South

American slope failures have been particularly spec-

tacular and perhaps the most devastating in terms

of loss of life. Here, the dominant geological fac-

tors have been extreme topographical relief, narrow

mountain-front valleys, concentrated human occu-

pation in valley-sited towns, and, of course, the

general position on the actively subducting Nazca

tectonic plate. It is probable that each large earth-

quake in the greater Andean region will kill hundreds

or thousands of people in these mountain-front

towns, because huge masses of ground, often sup-

ported on naturally compressed air masses, will be

dislodged so rapidly that the use of alarm sounds and

evacuation principles will be impractical.

Engineering geological evidence relies on the re-

cognition of the topographical circumstances that

will lead to the occurrence of tsunamis in coastal

regions. Palaeoseismic evidence of tsunami inunda-

tion has been observed along the coast of Oregon.

In continental interiors, vertical components of

earthquake-induced ground rupture can create a

similar inundation effect alongside lakes. All that

is required is instantaneous displacement of the

down-thrown side of a fault or an associated

above-lake slope failure. Either case would displace

masses of soil or rock into the body of the lake.

This situation is very difficult to mitigate in terms

of public rights and awareness.

458 ENGINEERING GEOLOGY/Aspects of Earthquakes

Seismotectonic Zonation

Zonation is a technique whereby known and predicted

earthquake damage can be assigned to areas for plan-

ning, zoning, and regulatory purposes. A number of

concepts apply to zoning. Each determination should

be made on site-specific needs.

Active Faults

Where ground rupture or the associated effects of

surficial damage have been noted it is appropriate to

assign a status of ‘active’ faulting. State-of-the-art

determination is represented by the Alquist–Priolo

Active Fault Zones, legislatively mandated in 1969

by the California Legislature. These zones are named,

delineated, and maintained by the California Geo-

logical Survey and constitute 400 m wide strips centred

along the best-identified trace or centre line of the

subject fault. Zones are plotted on 1 : 24 000 US Geo-

logical Survey topographical quadrangle bases and

are available for reference on the world wide web.

Credible Faults

The definition of credible faults was an innovation of

the nuclear power plant safety programme of the US

Nuclear Regulatory Commission (USNRC); credible

faults are known faults or areas where there is strong

geomorphological or structural geological evidence

of fault displacement at least once during the Holo-

cene and more than once in the past 500 000 years.

The half-million-year bracket is an artefact of the

fusilinid age determination resolution affinity of

California marine seashore terraces, and was applied

to the Diablo Canyon Nuclear Power Station (NPS) in

the early 1960s. The concept, however, is not applic-

able elsewhere, though it is frequently specified.

Credible faults are considered capable of experien-

cing ground rupture and propagation of ground

motion along their entire known length. Bonilla was

the first to associate ground-rupture length with the

magnitude of the causative event.

Deterministic Design Input

Design-level input by engineering geologists forms

the basis for carrying actual earth science evidence

into ‘seismic withstand’ design by civil and other

engineers. This geological input consists of the fol-

lowing process of analysis and evaluation. First, the

area around the project is seismically zoned, and

credible faults are identified or a most likely epicentre

for a candidate earthquake is assigned for each seis-

mogenic zone identified. Then, where active faults

are defined, the design-input ground motion is con-

sidered to occur at the location closest (measured

perpendicular to the fault trace) to the site. Where

an active fault has not been identified, a most likely

location is selected for each seismogenic zone; the

expected ground motion is attenuated from the hypo-

centre to the site. This becomes the MCE for each

of the candidate source faults or zones. Finally, the

style of earthquake to be represented for each of the

candidates is evaluated, in terms of vector displace-

ment, duration of strong motion, and peak ground

acceleration.

Attenuation

This assessment looks at the ground motion from the

hypocentre to the project. Waves of ground motion

move through the earth media, are concentrated in

the bedrock, and there suffer the physical effects of

trying to displace the surfaces of innumerable rock

discontinuities encountered during the passage to the

site. This infinite number of surface-to-surface grind-

ing processes consumes much of the energy of the

earthquake.

Attenuation curves have been developed empirically

for a variety of geological terranes and are published in

the literature, particularly in the reports of the former

US Army Waterways Experiment Station (now Engin-

eer Research and Development Command, Vicksburg,

MS, USA).

Each geological terrane has its own directional

effect on attenuation. The greatest effect is generally

exerted perpendicular to strongly foliated older meta-

morphic terranes, such as the north-east-foliated

Lower Palaeozoic sequence of New England, USA.

Comparison of Candidate Design Earthquakes

A selection of potentially impacting design earth-

quakes are defined in terms of the parameters listed

above. Each candidate is moved through a defined

scenario and attenuated from each stipulated source

to the site. The worst cases are then declared the

MCEs, and their characteristics are used as input in

seismic-withstand design.

Engineering Geological Mapping

A primary method for addressing and meeting seismic

threats uses engineering geological mapping, which

records the evidence of past earthquake damage and

uses this alongside geological conditions.

Earthquake damage was generally not mapped in

detail until the Alaskan ‘Good Friday’ earthquake of

1964. The former (regrettably now defunct) Branch

of Engineering Geology responded to this event under

the constructive leadership of its Director, the late

Edwin B. Eckel, also later the Executive Director of

the Geological Society of America. Eckel’s lobbying in

Washington DC was immediate, and the Survey

ENGINEERING GEOLOGY/Aspects of Earthquakes 459

mounted a field effort to observe and map the damage

of the magnitude 8.3 event as a long series of Profes-

sional Papers, the content of which has served as the

ongoing model for the application of engineering

geology to earthquake mitigation learning.

Subsequent American earthquakes have been given

similar, yet lesser overall, attention, for instance the San

Fernando (California) earthquake of 9 February 1971

(magnitude 6.6) and the Loma Prieta event of 17 Octo-

ber 1989 (magnitude 7.1) located just south of San

Francisco (California) on a San Andreas splinter fault.

Purpose

Strictly speaking, the purpose of engineering geological

mapping in this context is to record the physical nature

of ground-rupture earthquakes and to elucidate the

related types of motion-induced damage (Table 1).

Once defined, these can be applied on a worldwide

basis, wherever similar conditions of tectonics and

near-field geology and topography occur.

Engineering geological mapping for earthquake miti-

gation (Table 2) determines how engineered works and

human safety can be protected by judicious design con-

siderations, most of which are governed by geological

conditions related to the site characterization.

Geological Profile (or Ground Profile)

This term geological profile has taken over in engin-

eering geology from ‘geological section’ and considers

only the depth of influence of engineering works

(generally less than 15 m; Table 3).

Exploration Trenches and Trench Logging

During the peak of nuclear power-plant siting and

construction in the 1970s considerable effort was

made to confirm the absence of active faults within

the footprint of the power block (i.e. the location of

the reactor and the critical cooling linkage). The con-

cept of avoiding active fault traces was promoted so

that the risk of damage to the reactor and its contain-

ment as a result of rupture-type earthquake ground

motion could be minimized. As a result, the technique

of exploratory trenching advanced from the original

method of observation from hand-dug pits (Table 4).

Site Characterization

As an integral part of site characterization in seismo-

genic regions, attention should be given to identify-

ing geological conditions that may make the site

susceptible to physical damage from strong motion

(Table 5).

Post-Event Surveys

Certain elements of the earth media are particu-

larly susceptible to being lifted, shifted, toppled, or

cracked by earthquake strong motion. The patterns

of damage reveal much about the frequency charac-

teristics of the incident ground motion and the rela-

tive duration of the strong motion. Particularly

affected are fine soils, boulders on slopes, blocks of

rock defined by joints, overly steep stream and shore

banks and cliffs, and hillside masses saturated with

groundwater.

Geologists have but hours to locate, photograph,

and map these features before they are destroyed, first

by human visitors and soon after by rainfall and other

natural erosive agents (Table 6).

Cultural features within the built environment (in-

cluding engineered works) offer additional potential

Table 1 Engineering geological mapping of earthquake effects

Elements Purpose Important considerations

Stratigraphy Identify and describe the geological

formational units to be expected in design

and construction

Individual engineering geological units

Groundwater regime Define character of groundwater, as it is

affected by ground motion and diminishes

the shear strength of earth media to

resist dynamic deformation

Perched water

Vadose zone and fluctuations

Peizometric surface

Potentiometric surface

Rock-mass characterization Delimit observable or likely subsurface

bounds of each detectable hard rock unit

Identify bodies of discontinuity-bounded

rock masses that may become unstable

from shaking

Presence of weak rock Basis of definition, including why the

rock is determined to be weak

Recommendations as to how and why such

weak rock may pose problems to design

and/or construction, operation, and

maintenance

Potential problems related to

sedimentological, structural,

or geomorphological

conditions

Portions of surface or subsurface that

appear to be related to mapped

patterns of earthquake damage

Use special map symbols to portray these

features; the Geological Society of

London Engineering Geomorphological

map symbols are ideal for this purpose

460 ENGINEERING GEOLOGY/Aspects of Earthquakes

evidence to the discerning eye of the engineering

geologist. Relatively tall and thin objects (such as

gravestones, lamp standards, free-standing walls,

plate window glass, roadway signboards, and utility

poles and towers) tend to register a deformational

response to ground motion. In addition to reveal-

ing much about the character of the underlying

ground, such damage also gives an insight into the

vector, acceleration, and duration of local ground

motion.

Table 2 Engineering geological mapping for earthquake mitigation

Elements Purpose Important considerations

Before earthquake

Conceptual site geological model Forms the basis for expectation and

detection of geological features critical

to the mission of defining geological

controls over site-specific earthquake

threats

Define the presence and interrelationships

between site geology and topographical

configuration, to include hydrogeological

conditions, as well as the character of

existing or planned development

Existing evidence of presence of

active or credible faults in near

proximity to the project

Provide maximum means for avoidance

of ground-rupture potential to the

project works

Regional geological maps

Known active or credible faults

Site explorations to preclude the presence

of active or credible faults

Geomorphological evidence

of past displacements or

earthquake-induced

ground failure

Generally high potential for recurrence

of failure or displacement in the future

Image interpretation of aerial photographs,

especially those executed at low sun

angle with shadows

After earthquake

Ground deformational evidence basis for reconstruction, lessons learned

for basic knowledge

Map evidence immediately before it

is destroyed

Locate and plot evidence of ground rupture

from activated faults

Provides felt-intensity information useful in

meisoseismal mapping for quantification

of attenuation

Groundwater perturbation Establish fluctuation in groundwater

surface from existing water wells and

observation wells (if such are present)

Instructive as basis for pore-pressure effects

in deformation as well as liquefactions

Evidence of dislodgement Helps to establish ground acceleration

magnitude and vector of ground motion

Sometimes possible to locate fresh slope debris

and to establish provenance of dislodgment

Displacements Traces of offset pavement, curbs and

traffic-control lines

Establishes ground-motion vectors and possible

ground rupture

Fracture pattern and offsets in sidewalks

and retaining and structural walls

Distortion of infrastructure Collapsed power lines, broken water and

sewer pipes, deformed railroad rails

Facility may need significant improvement in

replacement, if design or location is faulty in

terms of future earthquake motion

Water displacement Wave-motion characteristics and indication

of tsunami or seiche character

Evidence will persist for only a few days, even

without human intervention

Survey triangulation Establishes bounds of displaced ground May indicate tilting of ground masses from

ground shaking

Table 3 Ground profiles for earthquake mitigation

Elements Purpose Important Considerations

Primary profile Placed perpendicular to known or most likely

trace (strike) of active or credible fault

The profile integrates the Site Conceptual

Model with actual site conditions and

sets the stage for exploration trenching and

logging

Display geological conditions

related to expected worst-

case site response to and

damage from the MCE

Promotes rational consideration of all

geological site conditions that could

conceivably affect performance of the

planned works, in the context of earthquake

threat

Generally means that one or more exploratory

trenches will be placed and logged

perpendicular to secondary geotechnical

profiles

Secondary profile(s) Examination of potential failure scenarios other

than perpendicular to nearby active or

credible fault

Prime example would be to construct a

geotechnical profile perpendicular to

the face of a slope or other face thought

to be susceptible to earthquake damage

ENGINEERING GEOLOGY/Aspects of Earthquakes 461

Summary

The engineering geologist’s expertise in characteriz-

ing ground for all manner of engineered works can

be extended to seismogenic zones. Engineering

geologists can detect and describe geological, hydro-

geological, and topographical conditions, defining

the potential hazard at sites that are at risk of damage

from earthquakes.

The description of fresh earthquake damage

improves the ground model, helping to mitigate

the adverse effects of future earthquakes. These

analyses can be applied more widely to assist civil

Table 4 Exploration trenches and trench logging for earthquake mitigation

Elements Purpose Important considerations

Orientation of trench Perpendicular to suspected fault trace (strike)

or related geomorphological feature

Maximum exposure of displacement and

age-determination

Trench log True-scale representation as a hand-drawn

graphic image

Show running horizontal scale and repetitive

vertical scale

Observation and recording Capture dimensional relationships in true scale

and position

Establish vertical and horizontal control

Locate sample and photographic locations

Graphic scale Faithful representation Generally at 1 : 3 to 1 : 5, for detail

Sampling Mainly for purposes of age determination of

horizons and faulting displacements

Show location of samples on the graphical log

Labelling Viewer identification of key geological features

related to the nature and age determination

of faulting

Mark also on the archival photograph and/or

video image record of both faces of

the trench

Faces The surface portrays interrelationships of

stratigraphy and relative ages of elements;

normally only one of the two opposing faces

is logged

Carbon-14 samples give minimum ages of

offset strata; other techniques (e.g. fluid-

inclusion analysis) refine minimum age of

displacement of trench-intercepted faults

Table 5 Site characterization for earthquake mitigation

Elements Purpose Important considerations

Stratigraphy Define horizons, zones, or pockets that may be

improved by engineering to withstand

earthquake induced failures or movement

Engineers to consider methods of improvement of

the geotechnical characteristics of the critical

slope-failure mass

Displacement surfaces Defines source and magnitude of ground rupture

as input to design accommodation of future

displacement on known faults

Generally applied only to earth-fill dam

embankments where it is deemed worth the

effort, cost, and risk to attempt withstand design

Palaeoseismic

evidence

Sand blows, as well as geomorphological evidence

of ground displacements as seen in exploratory

trenches, sand and gravel pits, and stream

banks

Evidence mainly occurs as stratigraphical

displacement or cross-cutting relationships

Table 6 Post-event geological mapping

Elements Purpose Important considerations

Ground rupture Define nature of displacements from activation of

a causative active fault

Displacement on active fault; displacement from

ground heaving; tensile failures of lateral

spreading

Liquefaction Locates ground below which to excavate

exploratory trenches

Need to define structural and stratigraphical locus

of liquefaction

Lateral deformation Define how cultural features have been affected Transportation features, towers, pipelines, walls,

gravestones, and many other thin and/or spindly

objects that are moved in a bodily fashion

Ground failure Delimit the failed ground then excavate, observe,

sample, and define causes of damage

Forms more bases for lessons learned and then

applied elsewhere

462 ENGINEERING GEOLOGY/Aspects of Earthquakes

engineers in the development of effective measures

to withstand future events.

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.

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Survey.

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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

of the death of Hans Cloos. Bulletin of the International

Association of Engineering Geology 13: 35–36.

Paige S (ed.) (1950) Application of Geology to Engineering

Practice. Berkey Volume. New York: Geological Society

of America.

Rosenbaum MS and Culshaw MG (2003) Communicating

the risks arising from geohazards. Journal of the Royal

Statistical Society, Series A 166(2): 261–270.

Terzaghi K (1925) Erdbaumechanik auf Bodenphysika-

lischer. Grundlage. Vienna: Franz Deuticke.

Codes of Practice

D Norbury, CL Associates, Wokingham, UK

Introduction

The practice of engineering geology requires effective

communication of observations, test results, and a

conceptual model of the ground. This communication

has to be unambiguous and clearly understood if

the works are to proceed smoothly. Engineering pro-

jects have become increasingly international, increas-

ing the importance of clear communication. National

codification of descriptive terminology and field and

laboratory test procedures has been appearing over

the last 30 years; the next step is for these national

standards to be subsumed within international

standards.

The History of Codification

Engineering geology as an established professional

practice has been in existence for some 70 years,

although some may argue that the practice has been

around for as long as man has been carrying out

engineering works in and on the ground. As the indus-

try grew it became increasingly clear that the mean-

ings of words, observations, and results were too

often being misunderstood, making effective work

increasingly difficult.

Initially there was no published guidance, but a

range of publications aiming to standardize practice

have emerged in two distinct areas. The procedures

to be used in the field and in the laboratory have

become standardized: guidelines have been prepared

at a national level but with limited coordination be-

tween countries. However, the description of soils

and rocks, which is arguably the basis of all engin-

eering geological studies, has not seen the same rapid

progress. Most of the guidance in this area has

been advisory rather than compulsory, possibly be-

cause geologists tend to be independently minded

practitioners.

As construction projects and engineering geology

have become increasingly international, the need for

common procedures and practices has increased. One

of the primary aspirations of the International Organ-

ization for Standardization (ISO) is to provide such

commonality, leading to better communication and

fairer competitive tendering for work.

The development of standards essentially takes

place in committee and is coordinated by the Comite

Europe

en de Normalisation (CEN) and the ISO.

This article outlines the history of the development

of codes in the practice of engineering geology,

largely by reference to publications in the UK, which

is the author’s base of experience. Developments in

other countries have been along similar lines at simi-

lar times, so the example of the UK situation is a

useful illustration of the general picture. Examples

of standards from other countries are included in

the list of Further Reading. We are looking at a pro-

fession where the guidance is moving from national

and advisory to international and normative.

What is the Role of Engineering

Geology?

Engineering geology is a core component of the pro-

fession of ground engineering, which concerns engin-

eering practice with, on, or in geological materials.

Ground engineering is concerned with the well-being

and advancement of society, including

the safety of residential, commercial, and industrial

structures,

the essential supply of energy and mineral

resources,

the mitigation of geological hazards,

the alleviation of human-induced hazards,

the efficient functioning of the engineering infra-

structure, and

contributing towards a sustainable environment.

Ground engineering is based on the professional

input of geologists and engineers, and specifically

includes the scientific disciplines of engineering

448 ENGINEERING GEOLOGY/Codes of Practice

Elsevier Encyclopedia of Geology - vol I A-E

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