Page 30 - Rock Mechanics For Underground Mining

ROCK MECHANICS AND MINING ENGINEERING

pervasive structural features in the mine area. A comprehensive geological description
would also include the distribution of lithologies in and around the orebody, the
distribution of values throughout the orebody, and the groundwater hydrology of
the mine area. In the last case, the primary need is to identify aquifers in the zone
of possible influence of mining which might deliver groundwater into any part of
the mining domain. Finally, specific geological investigations would identify sources
of potential mining problems in the mine area. These include zones of shattered
ground, leached zones, cavernous ground (vughs), rocks and minerals with adverse
weathering properties, and major structural features such as faults and clay seams
which transgress the orebody and are expressed on the ground surface.
It is clear, from this specification of duties, that mine geological activity should
produce a major component of engineering geological data. It implies that successful
execution of the engineering exploration of an orebody and environs requires the
active co-operation of geologists and rock mechanics personnel. It may be necessary,
for example, for the latter to propose drilling programmes and targets to clarify site
conditions of particular mining consequence.

1.4.3 Planning
Mine planning and design engineers are responsible for the eventual definition of all
components of an engineering study of a prospective mining operation. Their role is
initiative as well as integrative. In their interaction with rock mechanics engineers,
their function is to contribute information which can usefully delineate the scope of
any geomechanical analysis. Thus they may be expected to define the general mining
strategy, such as one-pass stoping (no pillar recovery), or stoping and subsequent
pillar extraction, and other limitations on mining technique. Details of anticipated
production rates, economic sizes of stopes, and the number of required sources of
ore production, can be used to define the extent of the active mine structure at any
time. The possibility of using backfills of various types in the production operation
should be established. Finally, the constraints imposed on future mining by the current
location of mine accesses, stoping activity, permanent openings and exploration drives
should be specified.

1.4.4 Rock mechanics
It has been noted that the mine engineering contributions of a rock mechanics group
relate to design tasks concerned principally with permanent mine openings, mine
layout and sequencing, extraction design, support and reinforcement and operational
responses. Specific activities associated with each of these tasks are now detailed. De-
sign issues related to permanent mine openings include siting of service and ventila-
tion shafts, siting, dimensioning and support specification of level main development,
and detailed design of major excavations such as crusher excavations, interior shaft
hoist chambers, shaft bottom facilities and workshop installations. The demand for
these services is, of course, episodic, being mainly concentrated in the pre-production
phase of mine operations.
The majority of rock mechanics activity in mining operations is devoted to res-
olution of questions concerned with the evolutionary design of the mine structure.
These questions include: dimensions of stopes and pillars; layout of stopes and pillars
within the orebody, taking due account of their location and orientation relative to the
geological structure and the principal stress directions; the overall direction of mining
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