Page 27 - Rock Mechanics For Underground Mining

FUNCTIONAL INTERACTIONS IN MINE ENGINEERING

useful in that it conveys the major mechanical ramifications in any change of mining
strategy.
Irrespective of the mining technique adopted for ore extraction, it is possible to
specify four common rock mechanics objectives for the performance of a mine struc-
ture, and the three different types of mine openings described previously. These are:

(a) to ensure the overall stability of the complete mine structure, defined by the main
ore sources and mined voids, ore remnants and adjacent country rock;
(b) to protect the major service openings throughout their designed duty life;
(c) to provide secure access to safe working places in and around the centres of ore
production;
(d) to preserve the mineable condition of unmined ore reserves.
These objectives are not mutually independent. Also, the typical mine planning
and design problem is to find a stope or ore block excavation sequence that satisfies
these objectives simultaneously, as well as fulfilling other operational and economic
requirements. The realisation of the rock mechanics objectives requires a knowledge
of the geotechnical conditions in the mine area, and a capacity for analysis of the
mechanical consequences of the various mining options. An appreciation is also
required of the broad management policies, and general mining concepts, which have
been adopted for the exploitation of the particular mineral resource.
It is instructive to define the significant difference in operational constraints be-
tween underground excavations designed for civil engineering purposes, and those
types of excavations involved in mining engineering practice subject to entry by mine
personnel. In the latter case, the use of any opening is entirely in the control of the
mine operator, and during its active utilisation the surfaces of an excavation are subject
to virtually continuous inspection by mine personnel. Work to maintain or reinstate
secure conditions around an opening, ranging from surface scaling (barring down) to
support and reinforcement emplacement, can be undertaken at any stage, at the direc-
tion of the mine management. These conditions rarely apply to excavations subject
to civil engineering operating practice. Another major difference is that most mine
excavations have duty lives that are significantly less than those of excavations used
for civil purposes. It is not surprising, therefore, that mine excavation design reflects
the degree of immediate control over opening utilisation, inspection, maintenance
and support emplacement afforded the mine operator.
In addition to the different operating constraints for mining and civil excavations,
there are marked differences in the nature of the structures generated and these directly
affect the design philosophy. The principal difference is that a civil engineering rock
structureisessentiallyfixed,whereasaminestructurecontinuestodevelopthroughout
the life of the mine. In the latter case, stope or ore block extraction sequences assume
great importance. Decisions made early in the mine life can limit the options, and
the success of mining, when seeking to establish an orderly and effective extraction
strategy, or to recover remnant ore.

1.4 Functional interactions in mine engineering

The purpose of this section is to explore the roles of various engineering disciplines
in the planning, design and operation of an underground mine. The particular concern
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