Practical rock-engineering-chapter-1-the-development-of-rock-engineering

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The development of rock engineering
Introduction
We tend to think of rock engineering as a modern discipline and yet, as early as 1773,
Coulomb included results of tests on rocks from Bordeaux in a paper read before the French
Academy in Paris (Coulomb, 1776, Heyman, 1972). French engineers started construction
of the Panama Canal in 1884 and this task was taken over by the US Army Corps of
Engineers in 1908. In the half century between 1910 and 1964, 60 slides were recorded in
cuts along the canal and, although these slides were not analysed in rock mechanics terms,
recent work by the US Corps of Engineers (Lutton et al, 1979) shows that these slides were
predominantly controlled by structural discontinuities and that modern rock mechanics
concepts are fully applicable to the analysis of these failures. In discussing the Panama
Canal slides in his Presidential Address to the first international conference on Soil
Mechanics and Foundation Engineering in 1936, Karl Terzaghi (Terzaghi, 1936, Terzaghi
and Voight, 1979) said ‘The catastrophic descent of the slopes of the deepest cut of the
Panama Canal issued a warning that we were overstepping the limits of our ability to
predict the consequences of our actions ....’.
In 1920 Josef Stini started teaching ‘Technical Geology’ at the Vienna Technical
University and before he died in 1958 he had published 333 papers and books (Müller,
1979). He founded the journal Geologie und Bauwesen, the forerunner of today’s journal
Rock Mechanics, and was probably the first to emphasise the importance of structural
discontinuities on the engineering behaviour of rock masses.
Other notable scientists and engineers from a variety of disciplines did some interesting
work on rock behaviour during the early part of this century. von Karman (1911), King
(1912), Griggs (1936), Ide (1936), and Terzaghi (1945) all worked on the failure of rock
materials. In 1921 Griffith proposed his theory of brittle material failure and, in 1931
Bucky started using a centrifuge to study the failure of mine models under simulated
gravity loading.
None of these persons would have classified themselves as rock engineers or rock
mechanics engineers - the title had not been invented at that time - but all of them made
significant contributions to the fundamental basis of the subject as we know it today. I have
made no attempt to provide an exhaustive list of papers related to rock mechanics which
were published before 1960 but the references given above will show that important
developments in the subject were taking place well before that date.
The early 1960s were very important in the general development of rock engineering
world-wide because a number of catastrophic failures occurred which clearly demonstrated
that, in rock as well as in soil, ‘we were over-stepping the limits of our ability to predict
the consequences of our actions’ (Terzaghi and Voight, 1979).

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In December 1959 the foundation of the Malpasset concrete arch dam in France failed and
the resulting flood killed about 450 people (Figure 1). In October 1963 about 2500 people
in the Italian town of Longarone were killed as a result of a landslide generated wave which
overtopped the Vajont dam (Figure 2). These two disasters had a major impact on rock
mechanics in civil engineering and a large number of papers were written on the possible
causes of the failures (Jaeger, 1972).
Figure 2a: The Vajont dam during impounding of the reservoir. In the middle distance, in
the centre of the picture, is Mount Toc with the unstable slope visible as a white scar on
the mountain side above the waterline.
Figure 1: Remains of the
Malpasset Dam as seen
today. Photograph by
Mark Diederichs, 2003.

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Figure 2b: During the filling of the Vajont reservoir the toe of the slope on Mount Toc was
submerged and this precipitated a slide. The mound of debris from the slide is visible in
the central part of the photograph. The very rapid descent of the slide material displaced
the water in the reservoir causing a 100 m high wave to overtop the dam wall. The dam
itself, visible in the foreground, was largely undamaged.
Figure 2c: The town of Longarone, located downstream of the Vajont dam, before the
Mount Toc failure in October 1963.

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Figure 2d: The remains of the town of Longarone after the flood caused by the overtopping
of the Vajont dam as a result of the Mount Toc failure. More than 2000 persons were killed
in this flood.
Figure 2e: The remains of the Vajont
dam perched above the present town of
Longarone. Photograph by Mark
Diederichs, 2003.

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In 1960 a coal mine at Coalbrook in South Africa collapsed with the loss of 432 lives. This
event was responsible for the initiation of an intensive research programme which resulted
in major advances in the methods used for designing coal pillars (Salamon and Munro,
1967).
The formal development of rock engineering or rock mechanics, as it was originally
known, as an engineering discipline in its own right dates from this period in the early
1960s and I will attempt to review these developments in the following chapters of these
notes. I consider myself extremely fortunate to have been intimately involved in the subject
since 1958. I have also been fortunate to have been in positions which required extensive
travel and which have brought me into personal contact with most of the persons with
whom the development of modern rock engineering is associated.
Rockbursts and elastic theory
Rockbursts are explosive failures of rock which occur when very high stress concentrations
are induced around underground openings. The problem is particularly acute in deep level
mining in hard brittle rock. Figure 3 shows the damage resulting from a rockburst in an
underground mine. The deep level gold mines in the Witwatersrand area in South Africa,
the Kolar gold mines in India, the nickel mines centred on Sudbury in Canada, the mines
in the Coeur d’Alene area in Idaho in the USA and the gold mines in the Kalgoorlie area
in Australia, are amongst the mines which have suffered from rockburst problems.
Figure 3: The results of a rockburst in an underground mine in brittle rock subjected to
very high stresses.

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As early as 1935 the deep level nickel mines near Sudbury were experiencing rockburst
problems and a report on these problems was prepared by Morrison in 1942. Morrison also
worked on rockburst problems in the Kolar gold fields in India and describes some of these
problems in his book, A Philosophy of Ground Control (1976).
Early work on rockbursts in South African gold mines was reported by Gane et al (1946)
and a summary of rockburst research up to 1966 was presented by Cook et al (1966). Work
on the seismic location of rockbursts by Cook (1963) resulted in a significant improvement
of our understanding of the mechanics of rockbursting and laid the foundations for the
microseismic monitoring systems which are now common in mines with rockburst
problems.
A characteristic of almost all rockbursts is that they occur in highly stressed, brittle rock.
Consequently, the analysis of stresses induced around underground mining excavations, a
key in the generation of rockbursts, can be dealt with by means of the theory of elasticity.
Much of the early work in rock mechanics applied to mining was focused on the problem
of rockbursts and this work is dominated by theoretical solutions which assume isotropic
elastic rock and which make no provision for the role of structural discontinuities. In the
first edition of Jaeger and Cook’s book, Fundamentals of Rock Mechanics (1969), mention
of structural discontinuities occurs on about a dozen of the 500 pages of the book. This
comment does not imply criticism of this outstanding book but it illustrates the dominance
of elastic theory in the approach to rock mechanics associated with deep-level mining
problems. Books by Coates (1966) and by Obert and Duvall (1967) reflect the same
emphasis on elastic theory.
This emphasis on the use of elastic theory for the study of rock mechanics problems was
particularly strong in the English speaking world and it had both advantages and
disadvantages. The disadvantage was that it ignored the critical role of structural features.
The advantage was that the tremendous concentration of effort on this approach resulted in
advances which may not have occurred if the approach had been more general.
Many mines and large civil engineering projects have benefited from this early work in the
application of elastic theory and most of the modern underground excavation design
methods have their origins in this work.
Discontinuous rock masses
Stini was one of the pioneers of rock mechanics in Europe and he emphasised the
importance of structural discontinuities in controlling the behaviour of rock masses
(Müller, 1979). Stini was involved in a wide range of near-surface civil engineering works
and it is not surprising that his emphasis was on the role of discontinuities since this was
obviously the dominant problem in all his work. Similarly, the text book by Talobre (1957),
reflecting the French approach to rock mechanics, recognised the role of structure to a
much greater extent than did the texts of Jaeger and Cook, Coates and Obert and Duvall.

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A major impetus was given to this work by the Malpasset dam failure and the Vajont
disaster mentioned earlier. The outstanding work by Londe and his co-workers in France
(Londe, 1965, Londe et al, 1969, 1970) and by Wittke (1965) and John (1968) in Germany
laid the foundation for the three-dimensional structural analyses which we have available
today. Figure 4 shows a wedge failure controlled by two intersecting structural features in
the bench of an open pit mine.
Figure 4: A wedge failure controlled by intersecting structural features in the rock mass
forming the bench of an open pit mine.

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Rock Engineering
Civil and mining engineers have been building structures on or in rock for centuries (Figure
5) and the principles of rock engineering have been understood for a long time. Rock
mechanics is merely a formal expression of some of these principles and it is only during
the past few decades that the theory and practice in this subject have come together in the
discipline which we know today as rock engineering. A particularly important event in the
development of the subject was the merging of elastic theory, which dominated the English
language literature on the subject, with the discontinuum approach of the Europeans. The
gradual recognition that rock could act both as an elastic material and a discontinuous mass
resulted in a much more mature approach to the subject than had previously been the case.
At the same time, the subject borrowed techniques for dealing with soft rocks and clays
from soil mechanics and recognised the importance of viscoelastic and rheological
behaviour in materials such as salt and potash.
Figure 5: The 1036 m long
Eupalinos water supply tunnel
was built in 530 BC on the Greek
island of Samos. This is the first
known tunnel to have been built
from two portals and the two
drives met with a very small
error.
The photograph was provided by
Professor Paul Marinos of the
National Technical University of
Athens.

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I should point out that significant work on rock mechanics was being carried out in
countries such as Russia, Japan and China during the 25 years covered by this review but,
due to language differences, this work was almost unknown in the English language and
European rock mechanics centres and almost none of it was incorporated into the literature
produced by these centres.
Geological data collection
The corner-stone of any practical rock mechanics analysis is the geological model and the
geological data base upon which the definition of rock types, structural discontinuities and
material properties is based. Even the most sophisticated analysis can become a
meaningless exercise if the geological model upon which it is based is inadequate or
inaccurate.
Methods for the collection of geological data have not changed a great deal over the past
25 years and there is still no acceptable substitute for the field mapping and core logging.
There have been some advances in the equipment used for such logging and a typical
example is the electronic compass illustrated in Figure 6. The emergence of geological
engineering or engineering geology as recognised university degree courses has been an
important step in the development of rock engineering. These courses train geologists to
be specialists in the recognition and interpretation of geological information which is
significant in engineering design. These geological engineers, following in the tradition
started by Stini in the 1920s, play an increasingly important role in modern rock
engineering.
Figure 6: A Clar electronic geological compass manufactured by F.W. Breihapt in
Germany.

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Figure 7: Plot of structural features using the program DIPS.
Once the geological data have been collected, computer processing of this data can be of
considerable assistance in plotting the information and in the interpretation of statistically
significant trends. Figure 7 illustrates a plot of contoured pole concentrations and
corresponding great circles produced by the program DIPS developed at the University of
Toronto and now available from Rocscience Inc.
Surface and down-hole geophysical tools and devices such as borehole cameras have been
available for several years and their reliability and usefulness has gradually improved as
electronic components and manufacturing techniques have advanced. However, current
capital and operating costs of these tools are high and these factors, together with
uncertainties associated with the interpretation of the information obtained from them, have
tended to restrict their use in rock engineering. It is probable that the use of these tools will
become more widespread in years to come as further developments occur.
Laboratory testing of rock
There has always been a tendency to equate rock mechanics with laboratory testing of rock
specimens and hence laboratory testing has played a disproportionately large role in the
subject. This does not imply that laboratory testing is not important but I would suggest
that only about 10 percent of a well balanced rock mechanics program should be allocated
to laboratory testing.

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Laboratory testing techniques have been borrowed from civil and mechanical engineering
and have remained largely unaltered for the past 25 years. An exception has been the
development of servo-controlled stiff testing machines which permit the determination of
the complete stress-strain curve for rocks. This information is important in the design of
underground excavations since the properties of the failed rock surrounding the
excavations have a significant influence upon the stability of the excavations.
Rock mass classification
A major deficiency of laboratory testing of rock specimens is that the specimens are limited
in size and therefore represent a very small and highly selective sample of the rock mass
from which they were removed. In a typical engineering project, the samples tested in the
laboratory represent only a very small fraction of one percent of the volume of the rock
mass. In addition, since only those specimens which survive the collection and preparation
process are tested, the results of these tests represent a highly biased sample. How then can
these results be used to estimate the properties of the in situ rock mass?
In an attempt to provide guidance on the properties of rock masses a number of rock mass
classification systems have been developed. In Japan, for example, there are 7 rock mass
classification systems, each one developed to meet a particular set of needs.
Probably the most widely known classifications, at least in the English speaking world, are
the RMR system of Bieniawski (1973, 1974) and the Q system of Barton, Lien and Lunde
(1974). The classifications include information on the strength of the intact rock material,
the spacing, number and surface properties of the structural discontinuities as well as
allowances for the influence of subsurface groundwater, in situ stresses and the orientation
and inclination of dominant discontinuities. These classifications were developed primarily
for the estimation of the support requirements in tunnels but their use has been expanded
to cover many other fields.
Provided that they are used within the limits within which they were developed, as
discussed by Palmstrom and Broch (2006), these rock mass classification systems can be
very useful practical engineering tools, not only because they provide a starting point for
the design of tunnel support but also because they force users to examine the properties of
the rock mass in a very systematic manner.
Rock mass strength
One of the major problems confronting designers of engineering structures in rock is that
of estimating the strength of the rock mass. This rock mass is usually made up of an
interlocking matrix of discrete blocks. These blocks may have been weathered or altered
to varying degrees and the contact surfaces between the blocks may vary from clean and
fresh to clay covered and slickensided.

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Determination of the strength of an in situ rock mass by laboratory type testing is generally
not practical. Hence this strength must be estimated from geological observations and from
test results on individual rock pieces or rock surfaces which have been removed from the
rock mass. This question has been discussed extensively by Hoek and Brown (1980) who
used the results of theoretical (Hoek, 1968) and model studies (Brown, 1970, Ladanyi and
Archambault, 1970) and the limited amount of available strength data, to develop an
empirical failure criterion for jointed rock masses. Hoek (1983) also proposed that the rock
mass classification system of Bieniawski could be used for estimating the rock mass
constants required for this empirical failure criterion. This classification proved to be
adequate for better quality rock masses but it soon became obvious that a new classification
was required for the very weak tectonically disturbed rock masses associated with the
major mountain chains of the Alps, the Himalayas and the Andes.
The Geological Strength Index (GSI) was introduced by Hoek in 1994 and this Index was
subsequently modified and expanded as experience was gained on its application to
practical rock engineering problems. Marinos and Hoek (2000, 2001) published the chart
reproduced in Figure 8 for use in estimating the properties of heterogeneous rock masses
such as flysch (Figure 9).
Figure 8: Geological Strength Index for heterogeneous rock masses such as flysch from
Marinos and Hoek 2000.

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Figure 9: Various grades of flysch in an exposure in the Pindos mountains of northern
Greece.
Practical application of the GSI system and the Hoek-Brown failure criterion in a number
of engineering projects around the world have shown that the system gives reasonable
estimates of the strength of a wide variety of rock masses. These estimates have to be
refined and adjusted for individual conditions, usually based upon back analysis of tunnel
or slope behaviour, but they provide a sound basis for design analyses. The most recent
version of the Hoek-Brown criterion has been published by Hoek, Carranza-Torres and
Corkum (2002) and this paper, together with a program called RocLab for implementing
the criterion, can be downloaded from the Internet at www.rocscience.com.
In situ stress measurements
The stability of deep underground excavations depends upon the strength of the rock mass
surrounding the excavations and upon the stresses induced in this rock. These induced
stresses are a function of the shape of the excavations and the in situ stresses which existed
before the creation of the excavations. The magnitudes of pre-existing in situ stresses have
been found to vary widely, depending upon the geological history of the rock mass in which
they are measured (Hoek and Brown, 1980). Theoretical predictions of these stresses are
considered to be unreliable and, hence, measurement of the actual in situ stresses is
necessary for major underground excavation design. A phenomenon which is frequently
observed in massive rock subjected to high in situ stresses is ‘core disking’, illustrated in
Figure 10.

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Figure 10: Disking of a 150 mm core of granite as a result of high in situ stresses.
Figure 11: Typical sequence of over-coring stress measurements.

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During early site investigations, when no underground access is available, the only
practical method for measuring in situ stresses is by hydrofracturing (Haimson, 1978) in
which the hydraulic pressure required to open existing cracks is used to estimate in situ
stress levels. Once underground access is available, over-coring techniques for in situ stress
measurement (Leeman and Hayes, 1966, Worotnicki and Walton, 1976) can be used and,
provided that sufficient care is taken in executing the measurements, the results are usually
adequate for design purposes. A typical over-coring sequence for in situ stress
measurement is illustrated in Figure 11 and one of the instruments used for such
measurement is illustrated in Figure 12.
Groundwater problems
The presence of large volumes of groundwater is an operational problem in tunnelling but
water pressures are generally not too serious a problem in underground excavation
engineering. Exceptions are pressure tunnels associated with hydroelectric projects. In
these cases, inadequate confining stresses due to insufficient depth of burial of the tunnel
can cause serious problems in the tunnel and in the adjacent slopes. The steel linings for
these tunnels can cost several thousand dollars per metre and are frequently a critical factor
in the design of a hydroelectric project. The installation of a steel tunnel lining is illustrated
in Figure 13.
Figure 12: A cell for measuring the in situ
triaxial stress field in a rock mass,
developed in Australia (Worotnicki and
Walton 1976). The hollow cylinder (on
the left) is filled with adhesive which is
extruded when the piston (on the right) is
forced into the cylinder.

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Figure 13: Installation of
steel lining in a pressure
tunnel in a hydroelectric
project.
Groundwater pressures are a major factor in all slope stability problems and an
understanding of the role of subsurface groundwater is an essential requirement for any
meaningful slope design (Hoek and Bray, 1981, Brown, 1982).
While the actual distributions of water pressures in rock slopes are probably much more
complex than the simple distributions normally assumed in slope stability analyses (Freeze
and Cherry, 1979), sensitivity studies based upon these simple assumptions are generally
adequate for the design of drainage systems (Masur and Kaufman, 1962). Monitoring of
groundwater pressures by means of piezometers (Brown, 1982) is the most reliable means
of establishing the input parameters for these groundwater models and for checking upon
the effectiveness of drainage measures.
In the case of dams, forces generated by the water acting on the upstream face of the dam
and water pressures generated in the foundations are critical in the assessment of the
stability of the dam. Estimates of the water pressure distribution in the foundations and of

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the influence of grout and drainage curtains upon this distribution have to be made with
care since they have a significant impact upon the overall dam and foundation design (Soos,
1979).
The major advances that have been made in the groundwater field during the past decades
have been in the understanding of the transport of pollutants by groundwater. Because of
the urgency associated with nuclear and toxic waste disposal in industrialised countries,
there has been a concentration of research effort in this field and advances have been
impressive. The results of this research do not have a direct impact on conventional
geotechnical engineering but there have been many indirect benefits from the development
of instrumentation and computer software which can be applied to both waste disposal and
geotechnical problems.
Rock reinforcement and support design
Safety during construction and long term stability are factors that have to be considered by
the designers of excavations in rock. It is not unusual for these requirements to lead to a
need for the installation of some form of rock reinforcement or support. Fortunately,
practical developments in this field have been significant during the past 25 years and
today’s rock engineer has a wide choice of reinforcement systems and tunnel lining
techniques. In particular, the development of shotcrete has made a major contribution to
modern underground construction.
There has been considerable confusion in the use of the terms “reinforcement” and
“support” in rock engineering and it is important for the reader to understand the different
roles of these two important systems.
Rock reinforcement, as the name implies, is used to improve the strength and/or
deformational behaviour of a rock mass in much the same way that steel bars are used to
improve the performance of reinforced concrete. The reinforcement generally consists of
bolts or cables that are placed in the rock mass in such a way that they provide confinement
or restraint to counteract loosening and movement of the rock blocks. They may or may
not be tensioned, depending upon the sequence of installation, and they may or may not be
grouted, depending upon whether they are temporary or permanent. In general, rock
reinforcement is only fully effective in reasonably frictional rock masses of moderate to
high strength. Such rock masses permit effective anchoring of the reinforcement and they
also develop the interlocking required to benefit from the confinement provided by the
reinforcement. In reinforced rock masses, mesh and/or shotcrete play an important role in
bridging the gap between adjacent bolt or anchor heads and in preventing progressive
ravelling of small pieces of rock that are not confined by the reinforcement.
For weak to very weak rock masses that are more cohesive than frictional, reinforcement
is less effective and, in the case of extremely weak materials, may not work at all. In these
cases it is more appropriate to use support rather than reinforcement. This support, which
generally consists of steel sets and shotcrete or concrete linings in different combinations,
must act as a load bearing structural shell to be fully effective in failing weak ground. The

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primary function of the support is to limit deformation of the rock or soil mass surrounding
the tunnel and the sequence of installation, in relation to the advance of the tunnel face, is
critically important. The capacity of the structural shell must be calculated on the basis of
the bending moments and axial thrusts that are generated in the support elements and
connections. In the case of large tunnels in very weak, highly stressed ground, where top
heading and bench or multiple headings are used, temporary internal support shells may be
required in order to prevent collapse of the temporary excavation boundaries. The
development of shotcrete has been extremely important in weak ground tunnelling since it
permits the rapid installation of a temporary or permanent load bearing lining with
embedded reinforcement as required.
The use of long untensioned grouted cables in underground hard rock mining (Clifford,
1974, Fuller, 1983, Hunt and Askew, 1977, Brady and Brown, 1985) has been a particularly
important innovation which has resulted in significant improvements in safety and mining
costs in massive ore bodies. The lessons learned from these mining systems have been
applied with considerable success in civil engineering and the use of untensioned dowels,
installed as close as possible to the advancing face, has many advantages in high speed
tunnel construction. The use of untensioned grouted cables or reinforcing bars has also
proved to be a very effective and economical technique in rock slope stabilisation. This
reinforcement is installed progressively as the slope is benched downward and it is very
effective in knitting the rock mass together and preventing the initiation of ravelling.
The design of both rock reinforcement and support have benefited greatly from the
evolution of personal computers and the development of very powerful and user-friendly
software. Whereas, in the past, these designs were based on empirical rules or classification
schemes derived from experience, it is now possible to study a wide range of excavation
geometries, excavation sequences, rock mass properties and reinforcement or support
options by means of numerical models. This does not imply that every metre of every
excavation has to be subjected to such analyses but it does mean that, once a reliable
geological model has been established, the designer can choose a few reinforcement or
support systems and optimize these for the typical conditions anticipated.
Excavation methods in rock
As pointed out earlier, the strength of jointed rock masses is very dependent upon the
interlocking between individual rock pieces. This interlocking is easily destroyed and
careless blasting during excavation is one of the most common causes of underground
excavation instability. The following quotation is taken from a paper by Holmberg and
Persson (1980):
The innocent rock mass is often blamed for insufficient stability that is actually the result
of rough and careless blasting. Where no precautions have been taken to avoid blasting
damage, no knowledge of the real stability of the undisturbed rock can be gained from
looking at the remaining rock wall. What one sees are the sad remains of what could have
been a perfectly safe and stable rock face.

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Techniques for controlling blast damage in rock are well-known (Svanholm et al, 1977,
Langefors and Kihlstrom, 1963, Hagan, 1980) but it is sometimes difficult to persuade
owners and contractors that the application of these techniques is worthwhile. Experience
in projects in which carefully controlled blasting has been used generally shows that the
amount of reinforcement can be reduced significantly and that the overall cost of
excavation and support is lower than in the case of poorly blasted excavations (Hoek,
1982). Examples of poor and good quality blasting in tunnels are illustrated in Figures 1.10
and 1.11.
Machine excavation is a technique which causes very little disturbance to the rock
surrounding an underground excavation. A wide range of tunnelling machines have been
developed over the past 25 years and these machines are now capable of working in almost
all rock types (Robbins, 1976, McFeat-Smith, 1982). Further development of these
machines can be expected and it is probable that machine excavation will play a much more
important role in future tunnelling than it does today.
Analytical tools
Analytical models have always played an important role in rock mechanics. The earliest
models date back to closed form solutions such as that for calculating the stresses
surrounding a circular hole in a stressed plate published by Kirsch in 1898. The
development of the computer in the early 1960s made possible the use of iterative
numerical techniques such as finite element (Clough, 1960), boundary element (Crouch
and Starfield, 1983), discrete element (Cundall, 1971) and combinations of these methods
(von Kimmelmann et al, 1984, Lorig and Brady, 1984). These have become almost
universal tools in rock mechanics.
The computer has also made it much more convenient to use powerful limit equilibrium
methods (Sarma, 1979, Brown and Ferguson, 1979, Shi and Goodman, 1981, Warburton,
1981) and probabilistic approaches (McMahon, 1971, Morriss and Stoter, 1983, Priest and
Brown, 1982, Read and Lye, 1983) for rock mechanics studies.
The advent of the micro-computer and the rapid developments which have taken place in
inexpensive hardware have brought us to the era of a computer on every professional’s
desk. The power of these machines is transforming our approach to rock mechanics
analysis since it is now possible to perform a large number of sensitivity or probabilistic
studies in a fraction of the time which was required for a single analysis a few years ago.
Given the inherently inhomogeneous nature of rock masses, such sensitivity studies enable
us to explore the influence of variations in the value of each input parameter and to base
our engineering judgements upon the rate of change in the calculated value rather than on
a single answer.

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Figure 1.10: An example of poor blasting in a tunnel.
Figure 1.11: An example of good blasting in a tunnel.

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Conclusions
Over the past 25 years, rock mechanics has developed into a mature subject which is built
on a solid foundation of geology and engineering mechanics. Individuals drawn from many
different disciplines have contributed to this subject and have developed a wide range of
practical tools and techniques. There is still a great deal of room for development,
innovation and improvement in almost every aspect of the subject and it is a field which
will continue to provide exciting challenges for many years to come.
References
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the design of tunnel support. Rock Mech. 6(4), 189-239.
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Bieniawski, Z.T. 1974. Geomechanics classification of rock masses and its application in
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