Page 15 - Rock Mechanics For Underground Mining

Preface to the first edition

Rock mechanics is a field of applied science which has become recognised as a
coherent engineering discipline within the last two decades. It consists of a body of
knowledge of the mechanical properties of rock, various techniques for the analysis of
rock stress under some imposed perturbation, a set of established principles express-
ing rock mass response to load, and a logical scheme for applying these notions and
techniques to real physical problems. Some of the areas where application of rock me-
chanics concepts have been demonstrated to be of industrial value include surface and
subsurface construction, mining and other methods of mineral recovery, geothermal
energy recovery and subsurface hazardous waste isolation. In many cases, The pres-
sures of industrial demand for rigour and precision in project or process design have
led to rapid evolution of the engineering discipline, and general improvement in its
basis in both the geosciences and engineering mechanics. An intellectual commitment
in some outstanding research centres to the proper development of rock mechanics
has now resulted in a capacity for engineering design in rock not conceivable two
decades ago.
Mining engineering in an obvious candidate for application of rock mechanics
principles in the design of excavations generated by mineral extraction. A primary
concern in mining operations, either on surface or underground, is loosely termed
‘ground control’, i.e. control of the displacement of rock surrounding the various
excavations generated by, and required to service, mining activity. The particular
concern of this text is with the rock mechanics aspects of underground mining engi-
neering, since it is in underground mining that many of the more interesting modes of
rock mass behaviour are expressed. Realisation of the maximum economic potential
of a mineral deposit frequently involves loading rock beyond the state where intact
behaviour can be sustained. Therefore, underground mines frequently represent ideal
sites at which to observe the limiting behabiour of the various elements of a rock
mass. It should then be clear why the earliest practitioners and researchers in rock
mechanics were actively pursuing its mining engineering applications.
Underground mining continues to provide strong motivation for the advancement
of rock mechanics. Mining activity is now conducted at depths greater than 4000 m,
although not without some difficulty. At shallower depths, single mine excavations
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greater than 350 m in height, and exceeding 500 000 m in volume, are not uncommon.
In any engineering terms, these are significant accomplishments, and the natural
pressure is to build on them. Such advances are undoubtedly possible. Both the
knowledge of the mechanical properties of rock, and the analytical capacity to predict
rock mass performance under load, improve as observations are made of in-situ
rock behaviour, and as analytical techniques evolve and are verified by practical
application.
This text is intended to address many of the rock mechanics issues arising in under-
ground mining engineering, although it is not exclusively a text on mining applica-
tions. It consists of four general sections, viz. general engineering mechanics relevant
to rock mechanics; mechanical properties of rock and rock masses; underground

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