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Quarterly Journal of Engineering Geology and Hydrogeology
doi: 10.1144/1470-9236/08-0032010, v.43; p321-331.Quarterly Journal of Engineering Geology and Hydrogeology
F.J. BaynesSources of geotechnical risk
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The Geological Society of London 2014
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Sources of geotechnical risk
F.J. BaynesBaynes Geologic Pty. Ltd., 9 Chester Street, Subiaco, WA 6008, Australia
(e-mail: [email protected])
Abstract: The geotechnical risks that can affect projects result from a range of hazards associated
with geological conditions and geological processes, but also from hazards associated with the
geo-engineering process. For example, active faults identified during pre-feasibility studies will pose
one type of hazard, whereas a management decision to limit the extent of a site investigation to save
money will pose another type of hazard. A systematic assessment of the nature and the source of the
various hazards may be used to differentiate the types of geotechnical risk. Examples from projects are
provided and some statistics are presented, to indicate the rates of occurrence of the various types of
geotechnical risks in projects. Some established approaches to managing geotechnical risks in projects
are noted.
Effective management of geotechnical risks is supremely
important in many projects. In an authoritative publica-
tion, geotechnical risk has been described as the risk tobuilding and construction work created by the site
ground conditions (Clayton 2001). At first reading, this
might suggest that the ground conditions are the only
source of geotechnical risk. However, the publication
went on to describe how geotechnical risk is created by
both the ground conditions and the geo-engineering
process. This is an important distinction, because the
management of geotechnical risks created by the site
ground conditions (essentially the geological conditions)
may require a very different approach compared with the
management of geotechnical risks created by the geo-
engineering process (essentially a human endeavour).
The terms geotechnical risk and geotechnical hazard
are used in different ways by different researchers and it
is difficult to find an unequivocal definition. In this
paper the terms are used with the following meanings. A
geotechnical risk is something associated with the
ground that might happen and that would have adverse
consequences for the project. The something . . . that
might happen may also be called a geotechnical hazard.
The geotechnical risk may be measured as the product of
the likelihood of the geotechnical hazard occurring and
the consequences to the project. The sources of geotech-
nical risks are thus geotechnical hazards, in the broader
sense of the word. It should be noted that an identifiedgeotechnical risk, like all risks, is not an inherent prop-
erty of the ground or of an engineering process, rather it
represents a subjective belief of the probability of a
hazard with given consequences occurring, on the part
of those charged with assessing the risks (Harr 1987).
The premise of this paper is that to effectively manage
geotechnical risks, those involved in geo-engineering
must both appreciate the subtleties of the various types
of geotechnical risks and understand how, where and
why these types of geotechnical risks occur within
projects; that is, they must understand the sources of
geotechnical risks. This knowledge is particularlyimportant to practitioners of engineering geology, as
they are responsible for developing the geological model
(Fookes 1997) and they are increasingly charged with a
responsibility for using the geological model as a funda-mental tool to assist in geotechnical risk management
(Morgenstern 2000; Knill 2003).
Types of geotechnical risk
Various types of geotechnical risk have been described in
the prolific and ever-increasing literature on the subject.
The matter has been discussed for many years by many
experts and the intent of this paper is not to attempt to
review these studies but instead to provide a brief
glimpse of three of the more incisive contributions.
McMahon (1985) identified three main types of geo-technical uncertainty associated with geotechnical
design, which he described as the risk of encountering
an unknown geological condition, the risk of using the
wrong geotechnical design criteria, and the risk of bias
and/or variation in the design parameters being greater
than estimated. He also identified other uncertainties
that can affect projects, including human error, design
changes and over-conservatism.
Clayton (2001) noted that geotechnical risks have
three components or impacts, which he divided into
technical, contractual and project management. Techni-
cal risks arise from the particular problems on the site
such as soft ground or contaminated land, contract riskis associated with the type of contract that the developer
adopts, and project management risks are determined by
the way the project manager or his advisors elect to
manage the project.
Trenter (2003) also divided geotechnical risk into
three interrelated categories, which are equivalent to
Claytons three components:
(1) design risk (equivalent to Claytons technical risk),
which was further divided into three areas of
uncertainty (which are somewhat equivalent to
McMahons three main types of geotechnical
uncertainty): uncertainty associated with the geo-logical framework (taken to be equivalent to the
Quarterly Journal of Engineering Geology and Hydrogeology, 43, 321331 1470-9236/10 $15.00 2010 Geological Society of LondonDOI 10.1144/1470-9236/08-003
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geological model); the appropriateness of the engi-
neering analysis; the reliability and representabilityof the engineering properties used in design;
(2) the below-ground contract risk, because contracts
fundamentally involve transfer of risk.
(3) project management risk, because project managers
are ultimately responsible for the successful man-
agement of all of the geotechnical risks in a project.
The basic types of geotechnical risk outlined by these
researchers are clearly a well-accepted and useful frame-
work and have been adopted in this paper. This frame-
work is used to consider the relationships between the
various types of geotechnical risk and the most likely
sources of these types of geotechnical risk. By under-standing the sources of geotechnical risks it is possible to
appreciate the reasons why these geotechnical risks arise.
Discussion of types of geotechnicalrisk
A suggested schematic relationship between the basic
types of geotechnical risk that form the accepted frame-
work identified in the literature is portrayed in Figure 1,
which could be thought of as a project organizational
structure that indicates responsibility for the manage-
ment of the various types of geotechnical risk.In Figure 1 specific geotechnical risks form one
obvious category of project risks and may be divided
into technical and contractual. The term technical is
preferred to design because some of the geotechnical
risks in this category are associated with activities other
than design. Technical risks can be subdivided into those
associated with the geological model, those associated
with the engineering analysis and those associated with
the engineering properties used in the analysis. Each of
these subcategories could be the responsibility of some-
one within an organization. There are usually many
other project risks and line management usually carriesthe responsibility for them. However, some types of
more general geotechnical risks that relate to overall
project implementation are the sole responsibility of
project management, and have been indicated as such in
Figure 1. The types of geotechnical risk portrayed in
Figure 1 and the geotechnical hazards that are the
sources of the risks are discussed in more detail below.
Project management
Identifying and managing geotechnical risks, in a general-
ized way, is a fundamental project management activity in
any project with a geo-engineering content. Project staff
are responsible during both the pre-project planning phase
and the main works construction stage for managing
specific types of geotechnical risks, but also for managing
the broader aspects of the project that can incur or
mitigate geotechnical risk (e.g. overall project planning,
construction planning, the choice of project procurement
model, information acquisition for decision making, the
preparation of a risk register and the responses to any
risks that happen). Potent geotechnical risks often develop
at a very early stage if appropriate project-wide geotech-
nical risk mitigation measures are not implemented.
When these risks develop it is usually because high-level
decisions have been made by people who are over-
worked and under-resourced and/or who do not appre-
ciate the importance of geotechnical risks, through a
lack of experience, education or training; those people,
unwittingly, become the source of the geotechnical risk.
Contractual
Geotechnical risks are associated with contracts that
relate to the ground conditions. Contracts involve the
transfer of risk and, in many projects, geotechnical risks
are transferred against some form of site investigation
report on the basis of the information presented therein.
Thus the quality of the site investigation report, and how
it is communicated, plays a pivotal role in the way
contractual geotechnical risks can develop in projects,
particularly in respect of claims based on unforeseen
ground conditions. Contracts usually refer to designs,
quantities and specifications, and can also include
measures to allocate risk and resolve disputes, so the
quality of these aspects of the geo-engineering, and howthey are communicated, is often equally important. The
contract will also reflect the risk allocation model for
project procurement that has been chosen by project
management (Eddlestonet al. 1995) (e.g. lump sum, bill
of quantities, cost plus, etc.). When the contract and
accompanying documentation is inadequate, the source
of the risk must be the project staff responsible for
managing the procurement and production of the docu-
mentation. The reason that this occurs is usually an
inadequate understanding of the importance of the
geo-engineering aspects of the contract on the part of the
project staff, or a limitation placed on those staffby ahigher-level project management decision.
Fig 1. The relationship between the types of geotechnical riskidentified in the literature.
F.J. BAYNES322
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Analytical
The engineering analysis that is adopted may not reflect
the actual failure mechanisms that occur or may be
based on unreasonable assumptions about the system
being analysed. If the engineering analysis is not appro-
priate, then the source of this risk is usually the projectstaff, who are responsible for electing to use the par-
ticular analytical method. It may be that they have
an inadequate understanding of what would constitute
an appropriate engineering analysis for the particu-
lar project and ground conditions. Of course, it is
also possible that the project staff are acting under
instructions from project management.
Properties
The engineering properties used in design may not be
reliable and may not be representative. For example,
they may be chosen from test results which may beaffected by sample disturbance, a limited sampling pro-
gramme, sampling or testing bias, etc. If the engineering
properties chosen for use in design are not reliable or not
representative, then the source of this risk is usually the
project staff, who are responsible for the choice, and
who probably have an inadequate understanding of
what would constitute reliable or representative engi-
neering properties for the particular analytical approach
and ground conditions. Again, it is also possible that the
project staffare acting under instructions from project
management.
Geological
Geotechnical risks associated with the geological and
geomorphological conditions are somewhat different
from those associated with the geo-engineering process,
as the latter is essentially a human endeavour. Uncer-
tainty is part of geological knowledge and is best con-
sidered relative to the concept of the geological model
(Fookes 1997; Fookes et al. 2000; Knill 2003). It is
suggested that within any geological model three sources
of uncertainty can be identified. These create different
types of geotechnical hazard that could lead to adverse
project consequences and hence are the source of differ-ent types of geotechnical risk. The three sources of
geotechnical risk are as follows.
(1) Variability in the 3D distribution of geological
units and variability in the geological characteris-
tics of each of the units, which could be caused by
facies changes, unconformities, folds and faults,
weathering profiles, soil fabric, rock structure, the
groundwater regime, etc. The potential geotechni-
cal hazard to the project results from shortcomings
in knowledge of what each and every part of the
ground consists of; boreholes, test pits, mapping,
etc. can only ever acquire information about a verysmall proportion of the total volume of ground
being investigated. The hazard results from the
presence of geological detail that is unforeseeable
within the practical limits of an investigation, and
differences between the scale of the project, the
scale of the investigation and the scale of the
geological features will have a profound influence
on the extent to which this source of risk is allowed
to develop.
(2) The occurrence of actual hazardous geological
conditions or processes within the ground. There
may be uncertainty about the spatial distribution
of some hazards; for example, a seam of asbesti-
form mineral may be known to exist on a site and
to be a significant health hazard if it is comminuted
and the dust inhaled, but the exact location of that
seam may not be known. Alternatively, there may
be uncertainty about the temporal occurrence of
some hazards; for example, a landslide may be
known to exist at a certain location or an activefault might have been identified but the precise
timing of the next movement of the landslide or the
fault will not be known. Of course, there can be
both spatial and temporal uncertainty with some
hazards.
(3) When there is an absence of knowledge of what
might be in the ground in which the project is
being built (and this happens regularly on major
projects around the world), a hazard to the project
is created because of the possibility of encounter-
ing an unforeseen ground condition that might
adversely aff
ect the project.
Unforeseen versus unforeseeable
An important distinction exists between unforeseen
conditions and unforeseeable ground conditions.
Fookes (1997) and Fookes et al. (2000) have argued as
follows.
(1) There is very little geology or geomorphology that
will be unforeseen on a site if the investigation is
carried out properly. This means that if a project is
managed in a way that implements all of the
established techniques developed to mitigate geo-
technical risk, and the work that is carried out is ofhigh quality, then the probability of an unforeseen
condition being encountered during construction
should be reduced to negligible proportions.
(2) Nevertheless, there are some geological conditions
that are unforeseeable, and when those con-
ditions are encountered (they will have been antici-
pated) there will inevitably be some undetectable
variations in the geology that can never be com-
pletely investigated within practical limits; for
example, cavernous ground as a result of karst
may be recognized but it may be impractical to
attempt to investigate the details of every singlecavity; the details are unforeseeable.
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Types of unforeseen ground conditions
The concept of unforeseen ground conditions is associ-
ated with two types of geotechnical risk, as follows.
(1) Technical risk. A truly technically unforeseen
ground condition would be a ground condition
encountered during construction that was not rec-ognized or anticipated at all during site investi-
gation. An example might be if the presence of
faulting was not anticipated and then an adversely
oriented fault that was not identified during the
site investigation was unexpectedly encountered in
an excavation and caused instability, which in turn
gave rise to cost and time over-runs. It should be
noted that this is not the same as an unforeseeable
condition, where the condition is anticipated but
the detail can never be investigated.
(2) Contractual risk. Unforeseen ground conditions
can be those ground conditions that one party to a
contractual dispute claim to have encountered
when contractual geotechnical risks happen; for
example, an adversely oriented fault may be
encountered in an excavation and lead to instabil-
ity, which in turn gives rise to cost and time
over-runs, which are then the subject of a contrac-
tual dispute. Typically in such a dispute one party
will argue that the instability was caused by a
ground condition that could not have been fore-
seen and the other party will argue that it could
have been foreseen. It would be naive to think that
such disputes are settled solely on the basis of
scientific facts, as a range of commercial, legal andpersonal factors will come into play. Thus, where
unforeseen ground conditions are claimed within a
contractual setting, they should be thought of as a
special case of unforeseen ground conditions that
may or may not have a basis in scientific facts.
They can be distinguished by referring to them as
contractually unforeseen ground conditions and
represent a link between technical geotechnical
risks and contractual geotechnical risks.
Sources of geotechnical riskLike all risks, the various types of geotechnical risks are
the product of hazard and consequence. The consequences
to projects are similar for each type of geotechnical risk
and consist of significant cost or time over-runs and/or
physical failure of the facility. The hazards are any con-
dition or process that is associated with the geology and
geomorphology that may have adverse consequences for
the project, and are different for each type of geotechnical
risk. Each hazard has a primary source, which may relate
to the geological conditions and geological processes, or
to various aspects of the geo-engineering process.
The types of geotechnical risks that have been dis-cussed above, the hazards that they are associated with,
and the primary source of these hazards, are summa-
rized in Table 1. It should be noted that because the
various risks are interrelated, the sources are also inter-
related. Table 1 suggests that within the three types of
geotechnical risk identified by Clayton (2001) and
Trenter (2003) there are only two ultimate sources of
geotechnical risk, as follows.
(1) Project staff responsible for the geo-engineering
process who have an inadequate understanding of
the ground conditions and/or who do not appreci-
ate the importance of ground conditions. Often
this deficit of knowledge is compounded by that of
high-level decision makers: politicians, financiers
and promoters who determine funding and timing
and who probably have never even heard of geo-
technical risk.
(2) Geological conditions or geological processes
that are difficult to investigate or inherently
hazardous.
Examples of geotechnical risks inprojects
Examples are presented below of projects from the last
two decades that the author has been involved in and
that have been affected by many of the types of geotech-
nical risks that are identified in Table 1. The authors
role varied from project to project and the examples are
presented anonymously, and have been modified to
make them difficult to identify, for reasons that are fairly
obvious.
Project management
A major industrial facility was being designed and built
by a contractor. The site had been investigated by over
300 boreholes but the work had been carried out with a
tick the box when the geotechnical work is done
mentality; there was no geological map or sections, no
understanding of the geology, no awareness of the active
geological processes and no appreciation of the geotech-
nical risks that the project faced. Consequently, despite
the huge amounts of information available, the follow-
ing problems developed during construction.(1) Granular construction materials that could have
been used in wet weather were neither identified
nor preserved, and consequently construction
ground to a halt during the rainy season as the
haul roads had no pavement; construction plan-
ning did not take into account the ground con-
ditions.
(2) Although noted in early investigations, the pres-
ence of acid sulphate generating soils was not
anticipated during design and late-stage changes
had to be made, including protecting footings and
treating runoff; an unreasonable analytical modelwas chosen for footing design.
F.J. BAYNES324
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(3) Landslides were present in many parts of the site,
reducing soil strengths to residual values and lead-
ing to unstable cuts and fills; optimistic strength
values were initially chosen for slope design.
(4) Faulting affected parts of the site, resulting in deep
weathering and low strengths requiring over-
excavation and replacement of foundation soils;
optimistic strength values were initially chosen for
foundation design.
(5) Coastal erosion occurring at rates that would
affect facilities within their design life required
changes to the design of port facilities; inherently
hazardous ground conditions existed and were notrecognized.
All of these problems affected the construction pro-
gramme, leading to significant cost and time over-runs,
although the facility was eventually successfully con-
structed. Many specific geotechnical risks were encoun-
tered on this project, but the fundamental source of the
risk was poor project management: the significance of
the specific geotechnical risks was not appreciated until
too late.
Contractual
A contractor tendered for work that involved road cuts,a tunnel and embankment construction using clean,
strong, durable angular rockfill won from the excava-
tion. The total amount of rockfill available from exca-
vation was enough to build the embankments but
because of the complex sequencing of the construction
and restricted access, the rockfill required double han-
dling and longer than anticipated haul distances, and a
claim resulted. Upon independent review of the tender
documents, the following conclusion was drawn. The
limited availability of rockfill from excavations could
have been anticipated from consideration of the docu-
mentation, site inspection and the viewing of the cores.
However, the precise extent to which rockfill availability
would be limited was difficult to evaluate as thedocumentation did not include geological sections or
maps relating the proposed structure to the observed
and interpreted geology on a chainage basis. The
as-encountered limitations on the availability of rockfill
could have been anticipated only with great difficulty by
the contractor during the tender period. The claim was
partially successful and the contractor obtained some
financial relief.
This is an example of contractual geotechnical risk
caused by a well-planned and well-executed site investi-
gation that was poorly documented and poorly pre-
sented, and this deficiency led to difficulties in thecommunication of the ground conditions. It also
Table 1. Sources of geotechnical risk
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reflected poor project management, as the documenta-
tion could have been better prepared if the project
manager had appreciated the importance of getting it
right and had allocated sufficient resources to the task.
Analytical
A tunnel was to be built by a design and construct
contractor that involved excavation through rock
beneath a palaeochannel containing permeable gravels.
During bid preparation, the tunnel was designed to be
drained; that is, flow of water into the tunnel was
considered to be of no great consequence. However, softcompressible sediments occurred in the palaeochannel
overlying the permeable gravels downstream of the
tunnel (Fig. 2), and to prevent settlement damage occur-
ring during construction the tunnel lining had to be
redesigned to be less permeable and the dewatering
effects of the tunnel had to be compensated for by
injection wells, and large delays and costs were incurred.
In this case an unreasonable engineering analysis was
initially adopted that did not allow for the potential
settlement problems associated with the geological con-
ditions along the palaeochannel. The other type of
geotechnical risk that occurred was associated with
project management: the significance of the geotechnical
risk to the project was not recognized and was not
allowed for in the bid, and consequently the construction
cost was underestimated. The matter ended in litigation.
Properties
A road involving a large amount of earthworks was
being designed and built by a contractor. Very stiff,
low-plasticity clays and silts had been identified and
characterized by laboratory testing along the route, and
earthworks with cut batters at 2h:1v were designed,
based on average measured properties. When construc-tion started it was realized that the clays and silts were
deeply weathered, more plastic and had softened over
the top several metres, and that the lower shear strengths
exhibited by only a small proportion of the tested
samples would have to be adopted for cut batter design.
The cut batters were flattened to 4h:1v, resulting in a
larger volume of excavation, increased spoil requiring
disposal and increased construction time.
Prior to construction all of the information was avail-
able to make the correct choice of parameters but the
significance of the range of measured strengths was not
appreciated and unreasonable design values were chosen.
The unreasonable design values were chosen because the
understanding of the ground conditions contained in the
simple geological model illustrated by Figure 3 was not
communicated amongst the project staff.
Unforeseeable geological details
A dam was being built by a government utility with
well-developed in-house design and construction capa-
bility. The dam was to be founded on karstic limestone
and extensive investigations were carried out in four
phases that involved regional mapping, aerial photo-
graph interpretation, detailed geological mapping, hun-
dreds of boreholes and test pits, seismic refraction
survey, an extensive laboratory testing programme,
grouting trials, and external review. The last phase of the
investigation was carried out after construction was
temporarily halted, to relocate the dam to a less hazard-
ous position.
Despite the amount of investigation, and the late-
stage relocation, the utility was of the view that thereremained too many unforeseeable details of the ground
conditions, and that this presented a significant geotech-
nical risk (Fig. 4). A very conservative belt and braces
design was adopted, the observational method was used
when construction recommenced, and an extensive pro-
gramme of monitoring and maintenance was put in
place and continues to this day. The dam functions
acceptably. However, there were significant cost and
time over-runs when compared with the original cost
estimate and schedule.
Other types of geotechnical risks also affected the
project. The dam was founded on an inherently hazard-ous geological condition consisting of karst limestone,
and project management risks occurred because design
and construction of the dam commenced before the
investigation had been completed and before the opti-
mum dam location had been identified.
Inherently hazardous geological conditions
A pipeline being built under a design and construct
contract was located within a route corridor determined
largely by the availability of land that could be pur-
chased. Route options past a village included some
poorly drained ground to the west and some gravel hillsforming a series of low linear escarpments to the east.
Fig. 2. Block model of geological conditions in thepalaeochannel.
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After the pipeline corridor was fixed within the east-
ern option, a site investigation was carried out and
major active regional thrust faults were identified (Fig.
5). Five fault crossings had to be designed and built, and
this caused significant delays to construction.
This geotechnical risk was an inherently hazardousground condition that was ultimately catered for in
design. However, other types of geotechnical risks affected
this part of the project: the lack of timely site investigation
resulted from poor project management and led to an
unforeseen ground condition being encountered.
Unforeseen ground conditions
A hydroelectric project being built using a traditional
ownerengineercontractor approach was designed with
an unlined pressure tunnel that required sufficient in situ
stress to ensure high-pressure water containment(Fig. 6). It was assumed that the in situ stress at depth
would include both a gravity and a compressive tectonic
component. The site investigation included a range of
boreholes and pressure tests that suggested that the
tunnel configuration would achieve the design objective.
However, because of the depth of the tunnel and the
remote location, drilling did not extend down to the levelof the proposed downstream limit of the unlined tunnel
(the upstream limit of the steel liner). During construc-
tion, confirmatory testing in the vicinity of the power
station indicated that the in situstresses were a lot lower
than expected and the power station was moved several
hundred metres further into the hillside, where the
stresses were marginally higher. Even after the move, the
as-constructed tunnel configuration required further
remedial treatment to prevent leakage because the in situ
stresses clearly did not include a sufficient compressive
tectonic component.
This unforeseen ground condition resulted in signifi-cant delays and increased costs to the project. With
Fig. 3. A simple geological model illustrating the distribution of weathered and softened clays.
Fig. 4. Dam on karstic foundations resulting in unforeseeable geological details. MFL, . . .; NMOL, . . .
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hindsight, the geological model for the area should
have placed greater emphasis on the regional faulting
pattern, which included normal faults, suggesting tensile
regional tectonic stresses. Other types of geotechnical
risks associated with project management affected the
project. The design of the underground works was based
on a poor understanding of the geological condition,
and recognition of the criticality of this aspect of thedesign and the significance of the risk at an early stage
might have alerted the project manager to the need to
carry out more thorough investigations, and create a
more flexible contract arrangement that allowed changes
to the power station location.
Rates of occurrence of geotechnicalrisk
It is instructive to consider the rates of occurrence of
geotechnical risks, but there is very little publishedinformation available, presumably because of a natural
disinclination to discuss failures. Projects involving a
significant proportion of geo-engineering can be divided
into those where there were no significant geotechnical
risks involved, those where significant geotechnical haz-
ards were present but where the risks were effectively
managed and consequences such as significant cost and
time over-runs and physical failures did not happen, and
those that were affected by significant cost and time
over-runs and/or physical failures.
Stapledon (1983) quoted studies by the International
Commission on Large Dams that indicated that 1% of
all major dams built between 1900 and 1965 failed
during operation. Stapledon also estimated, based on his
personal experience, that 20% of recently built dams had
significant cost and time over-runs during construction
(Stapledon 1983). Whitman (1984) indicated an annual
probability of failure of about 220% for mine pit
slopes and about 0.11% for foundations; presumably
this meant physical failure, as opposed to cost and timeover-runs. McMahon (1985) collected information on
130 major civil and mining projects developed between
1955 and 1985 in the Australasian region and concluded
that 36% of the projects were affected by significant
geotechnical problems and 5% were affected by failure
during operation. Hoek & Palmieri (1998) presented a
review of 64 thermal and 71 hydroelectric plants and
concluded that actual construction costs were, on aver-
age, 27% above estimated costs and schedules were 28%
longer than estimated. A large proportion, but not all of
these time and cost over-runs, were attributed to geo-
technical factors. Clayton (2001) presented a survey ofroad construction that suggested that of 49 road
projects, 55% had a greater than 20% cost over-run. This
author reviewed 70 geo-engineering projects that he
was involved in and concluded that 31% had involved
some form of significant time or cost over-run and that
about 1% had been affected by physical failure during
operation.
This information suggests that geotechnical risks
might occur at the following rates.
(1) Physical failures of geo-engineering projects might
occur in around 0.11% of civil projects and up to
20% of mining projects. Presumably this illustrates
a greater appetite for risk on the part of themanagers of mining projects.
(2) Significant cost and time over-runs might occur in
2050% of all projects.
There is even less information regarding the rates of
occurrence of specific types of geotechnical risk.
McMahon (1985) differentiated the 47 projects that
had been affected by significant geotechnical problems
into his three types of technical risk and another cat-
egory, which is taken to be akin to project management
risk. Stapledon (1983) described 13 failures of water-
works and Duncan (1988) described 13 personal lessons
in what not to do from the perspective of a designengineer. The information provided by Duncan (1988)
Fig. 5. Pipeline route options and fault trace.
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mainly concerned engineering design because he was a
geotechnical engineer. Fookes et al. (2000) described 31
case histories of geo-engineering failures that illustrated
how understanding the geological model could have
helped anticipate the cause of the failure. This author
reviewed 70 geo-engineering projects that he was
involved in and attempted to identify the specific type ofgeotechnical risks involved in the 22 that had had some
form of significant time or cost over-run or physical
failure. In the case of Fookes et al. (2000) and this
author, a large proportion of the projects that were
categorized involved inherently hazardous ground con-
ditions, because they are the source of many commis-
sions for consultant engineering geologists.
From this information an interpretation of the rates
of occurrence of the various types of geotechnical risk in
projects is provided in Table 2. The information in Table
2 does not provide a clear picture of the distribution of
the types of geotechnical risk but suggests that both the
ground conditions and the project staff responsible forthe geo-engineering process are a significant source of
geotechnical risk, and that the project staffmay actually
be the largest source. The reason why project staffare a
significant source of geotechnical risk has been explored
by Stapledon (1983), who identified 15 factors that
contributed to failures. Of the 15 factors, it is of interest
to note that most relate to people management such as
a lack of training or knowledge on the part of project
staff, poor project management, communication prob-
lems, not asking the right questions, excessive work
loads and poor quality work, and only a few relate to the
engineering design function. Sowers (1993) reviewedapproximately 500 geotechnical failures and concluded
that 88% reflected human shortcomings, and that this
was a factor that could be reduced by addressing people
management issues.
Management of geotechnical riskwithin projects
The implementation of projects can generally be divided
into the idealized stages illustrated in Figure 7. Depend-
ing upon the method of project procurement, differentparties may be responsible for different stages and the
stages might occur in a different order. For example, if
the project is being implemented through a traditional
ownerengineercontractor relationship, the responsi-
bilities for the stages will be different from if project
implementation is through a design and construct con-
tractor. Probably more importantly, in the case of a
design and construct tender, the contract stage and theall-important agreement of the price of the project often
occurs after only a preliminary investigation and hence
the bid price is fixed when only limited information is
available, a classic way in which a project management
decision can generate geotechnical risk.
The idealized project stages can usually be identified
even when different project procurement methods are
employed, and the literature on geotechnical risk clearly
describes the established techniques that are available to
manage the risks during each of the idealized project
stages. These include the following.
(1) The use of risk registers for overall management of
the geotechnical risks (Clayton 2001; Trenter 2003).
(2) An adequate and comprehensive site investigation
(Stapledon 1983; Fookes 1997).
(3) A multistage approach to the site investigation and
an experienced multidisciplinary team to carry out
the work (Stapledon 1983; Fookes 1997; Fookes
et al. 2000).
(4) The use of different types of reports to systemati-
cally convey the findings of the site investigation to
the contractor (Knill 2003; van Staveren & Knoeff
2004).
(5) Peer review at critical hold points for the project
(Stapledon 1983; Baynes et al. 2005).(6) The adoption of the observational method during
construction (Fookes 1997; Fookes et al. 2000;
Knill 2003).
(7) Contract flexibility that allows the contractor to be
paid for work that needs to be done (Fookes et al.
2000; Clayton 2001).
(8) The use of a contract that fairly allocates geotech-
nical risk between the owner and the contractor
(Eddlestonet al. 1995).
(9) The use of residual risk registers to manage risks
during operation (Clayton 2001; Knill 2003).
(10) The adoption of a total engineering geologyapproach, where a lot of effort is applied to
Fig. 6. Cross-section showing underground arrangement and topography; no vertical exaggeration; elevation in metres.
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understanding the geology and defining and docu-
menting baseline or reference conditions at the
earliest possible opportunity (Knill 2003; van
Staveren & Knoeff, 2004; Baynes et al. 2005).
The relationship in time between when these estab-
lished techniques should be used and the idealized
project stages is illustrated in Figure 7.
Unfortunately, the established techniques are seldom
fully adopted in practice, because of cost and time
pressures and inept or inexperienced management. The
consequence of not fully adopting the established tech-
niques is the manifestation of uncontrolled geotechnical
risk.
Conclusions
(1) If past performance can provide a guide to what
will happen in the future, then the likelihood of
experiencing a significant geotechnical risk in the
form of a cost or time over-run on a major projectis somewhere between 20 and 50%.
(2) Similarly, the likelihood of a physical failure is
much less, maybe less than 1 or 2% for civil
projects and up to 20% for mining projects.
(3) Geotechnical risks can be divided into those
associated with project management and those
that relate to technical and contractual matters.
Technical risks can be subdivided into those
associated with the geological model, those associ-
ated with the engineering analysis and those
associated with the engineering properties used in
analysis. The risks associated with the geologicalmodel can be divided into those associated with
unforeseeable geological details, those associated
with inherently hazardous ground conditions and
those associated with unforeseen ground con-
ditions.
(4) Available information suggests that the ground
conditions and the project staffresponsible for the
geo-engineering process are both significant
sources of geotechnical risk and that the project
staffmay actually be the largest source.
(5) Project staffcan be educated and trained to man-
age and mitigate the geotechnical risks, rather than
generate them.
(6) The ground conditions cannot be changed, but
competent engineering geologists can advise how
projects can be engineered to overcome risks
associated with the geological model.
(7) Effective geotechnical risk management techniques
for different project stages are clearly described in
the literature. The single greatest challenge is to
manage the project in a way that incorporates all
of these established techniques and obtains the
maximum benefit from their use.
Acknowledgements.I am grateful to A. Moon and P. Fookesfor their many thoughtful comments and contributions to thisT
ab
le2.Ratesofoccurrence(givenasperc
entages)oftypesofgeotechnicalriskinprojects
Ultimatesource,andhazard
McMahon(1985);47
projectswith
problems*
Stapledon(1983);13
failuresofwaterworks
Duncan(1988);
13
personallesson
s
Fookesetal.(2000);
31casehistories
illustratinggeological
models*
Autho
rsrecordsof22
p
rojectswith
problems*
Proj
ectstaff
Poormanagementofentiregroundengine
ering
process
25
38
95
Poormanagementofsiteinvestigationand
co
ntract
n.a.
46
73
Unr
easonableanalyticalmodelchosen
22
62
46
64
Unr
easonabledesignvalueschosen
58
15
46
6
32
Groundconditions
Unforeseeabledetailsofgroundconditions
n.a.
59
Inherentlyhazardousgroundconditions
n.a.
7
68
73
Unforeseengroundconditions
33
8
29
73
n.a.,
thiscategorywasnotusedbyMcMahon.
*Th
efrequenciesadduptomorethan100%becausesomeprojectsencounteredmoretha
nonetypeofproblem.
Itshouldbenotedthat18%oftheprojectsin
volvedallofthetypesofrisk.
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paper, and also to two anonymous reviewers who took the
time to comment on this paper so constructively. The views
expressed here are my own.
References
B, F.J., F, P.G. & K,J.F. 2005. The totalengineering geology approach applied to railways in thePilbara, Western Australia. Bulletin of EngineeringGeology and the Environment, 64, 6794.
C,C.R.I.2001.Managing Geotechnical Risk: ImprovingProductivity in UK Building and Construction. ThomasTelford, London.
D, J.M. 1988. Prediction, design and performance ingeotechnical engineering.In: Fifth AustraliaNew ZealandConference on Geomechanics,Sydney. Institution of Engi-neers Australia, Canberra, 112.
E,M., M, R.E.& W,S.1995. The roleof the engineering geologist in construction. In:E,M., W,S., C,J.C.& C,M.G.(eds)Engineering Geology of Construction. Geologi-cal Society, London, Engineering Geology Special Publi-
cations, 10, 389401.F, P.G. 1997. The First Glossop Lecture, geology forengineers: the geological model, prediction and perform-ance. Quarterly Journal of Engineering Geology, 30, 293424.
F, P.G., B, F.J. & H, J.N. 2000. Totalgeological history: a model approach to the anticipation,observation and understanding of site conditions. In:GeoEng 2000 Conference, Melbourne Australia, Vol. 1.Technomic, Lancaster, PA, 370460.
H,M.E.1987.Reliability-based Design in Civil Engineering.Dover, New York.
H,E.& P,A.1998. Geotechnical risks on large civilengineering projects.In: M,D.P.& H,O.(eds)Proceedings of the 8th Congress of the InternationalAssociation for Engineering Geology and the Environment,Vancouver, Vol. 1. Balkema, Rotterdam, 7988.
K, J.L. 2003. Core values: the First Hans Cloos lecture.Bulletin of Engineering Geology and the Environment, 62,134.
MM, B.K. 1985. Geotechnical design in the face ofuncertainty. Journal of the Australian GeomechanicsSociety, 10, 719.
M,N.R.2000. Common ground.In: GeoEng 2000Conference, Melbourne Australia, Vol. 1. Technomic,Lancaster, PA, 120.
S, D.H. 1983. Towards successful waterworks. In:Proceedings of the Symposium on Engineering for Damsand Canals. Institution of Professional Engineers, NewZealand, 1.31.15.
S, G.F. 1993. Human factors in civil and geotechnicalfailures. ASCE Journal of Geotechnical Engineering, 119,238256.
T,N.2003. Understanding and containing geotechnicalrisk.Proceedings of the Institution of Civil Engineers: CivilEngineering, 156, 4248, Paper 12706.
S,M.T. & K, J.G. 2004. The geotechnicalbaseline report as a risk allocation tool. In: H, R.,A, R. & C, R. (eds) Engineering Geology
for Infrastructure Planning in Europe. Springer, Berlin,777785.
W, R.V. 1984. Evaluating calculated risk in geo-technical engineering. ASCE Journal of GeotechnicalEngineering, 110, 145188.
Received 4 March 2008; accepted 3 March 2010.
Fig. 7.The management of geotechnical risk at the various project stages (indicated at the top of the figure and progressing in timefrom left to right).
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