Page 19 - Rock Mechanics For Underground Mining

1 Rock mechanics and

mining engineering

1.1 General concepts

The engineering mechanics problem posed in all structural design is the prediction
of the performance of the structure under the loads imposed on it during its pre-
scribed functional operation. The subject of engineering rock mechanics, as applied
in mining engineering practice, is concerned with the application of the principles
of engineering mechanics to the design of the rock structures generated by mining
activity. The discipline is closely related to the main streams of classical mechanics
and continuum mechanics, but several specific factors identify it as a distinct and
coherent field of engineering.
A widely accepted definition of rock mechanics is that first offered by the US
National Committee on Rock Mechanics in 1964, and subsequently modified in 1974:

Rock mechanics is the theoretical and applied science of the mechanical behaviour
of rock and rock masses; it is that branch of mechanics concerned with the response
of rock and rock masses to the force fields of their physical environment.

Clearly, the subject as defined is of fundamental relevance to mining engineering
because the act of creating mining excavations changes the force fields of the rock’s
physical environment. As will be demonstrated throughout this text, the study of the
response of the rock to these changes requires the application of analytical techniques
developed specifically for the purpose, and which now form part of the corpus of the
subject. Rock mechanics itself forms part of the broader subject of geomechan-
ics which is concerned with the mechanical responses of all geological materials,
including soils. The learned society for geomechanics in Australia, the Australian
Geomechanics Society, defines geomechanics as “the application of engineering and
geological principles to the behaviour of the ground and ground water and the use
of these principles in civil, mining, offshore and environmental engineering in the
widest sense”.
This definition of geomechanics is almost synonymous with the term geotechni-
cal engineering, which has been defined as “the application of the sciences of soil
mechanics and rock mechanics, engineering geology and other related disciplines
to civil engineering construction, the extractive industries and the preservation and
enhancement of the environment” (Anon, 1999). The term geotechnical engineering
and the adjective geotechnical will be used in this sense in this text.
Application of rock mechanics principles in underground mine engineering is based
on simple and, perhaps, self-evident premises. First, it is postulated that a rock mass
can be ascribed a set of mechanical properties which can be measured in standard
tests or estimated using well-established techniques. Second, it is asserted that the
process of underground mining generates a rock structure consisting of voids, support
elements and abutments, and that the mechanical performance of the structure is
amenable to analysis using the principles of classical mechanics. The third proposition
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