Page 32 - Rock Mechanics For Underground Mining

ROCK MECHANICS AND MINING ENGINEERING

Figure 1.7 Components and logic of
a rock mechanics programme.

multi-pass loop. There are two main reasons for this. First, the site characterisation
phase never generates a sufficiently comprehensive data base from which to develop
a unique plan for the complete life of the mine. Second, mine design is itself an
evolutionary process in which engineering responses are formulated to reflect the
observed performance of the mine structure under actual operating conditions. For
these reasons, the process may not proceed in the linear manner implied by Figure 1.7.
At times, some of the activities, or parts of those activities, may proceed in parallel.
These issues are clarified in the following discussion of the component phases of the
programme.

1.5.1 Site characterisation
The objective of this phase, in the first pass through the loop, is to define the me-
chanical properties and state of the medium in which mining is to occur. It involves
determination of the strength and deformation properties of the various lithological
units represented in and around the orebody, definition of the geometric and mechan-
ical properties of pervasive jointing, and location and description of the properties of
discrete structural features. An estimate of the in situ strength of the medium may then
be made from the properties of the constituent elements of the mass. This phase also
includes determination of the in situ state of stress in the mine area, and investigation
of the hydrogeology of the orebody and environs.
The difficulty in site characterisation lies in achieving representative data defining
geomechanical conditions throughout the rock medium. Under conditions of limited
physical access, yielding small numbers of small rock specimens, with no unifying
theorytorelatethespecimenpropertieswiththoseofthehostrockmedium,afirst-pass
site characterisation is intrinsically deficient.
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