Surface Rock Support Code Practice for Underground Mines
Rock falls are an ever-present hazard in underground mining, especially in unsupported ground. They are primarily caused by discontinuities and/or high or low adverse stresses in the rock mass. The intersection of three or more joints or fractures with the back, face or side wall of an excavation may create unstable blocks of rock. These blocks may fall or be ejected into the excavation with little or no prior warning, and pose a serious risk of injury or death. Ground support is installed to ensure the stability of the excavation and minimise the risk of injury. Ground support must match the ground conditions and the excavation geometry for
the life of the excavation and must take into account both inherent and mining-induced stresses.
The presence of ground support however does not necessarily guarantee that there will be no rock falls. While an excavation can be stable in terms of its overall structure it may not necessarily be safe. Localised surface failure can present serious risks. A combination of one or more of the following may result in unexpected rock falls:
· Deteriorating ground conditions;
· Inappropriate ground support;
· Inadequately installed ground support;
· Ground support that has deteriorated (corroded) over time; and
· Mining-induced or natural seismicity.
Ongoing check-scaling is a critical step in the ground control program to maintain the integrity of the excavation. In low profile headings, that is, those nominally less than 3.5m high, with adequate and correctly installed ground support, a person can readily visually check for localised surface rock failure and make safe the heading or excavation with the use of a scaling bar. However, in headings higher than 3.5m it becomes increasingly difficult to check and scale safely without the use of equipment to access the high backs and side walls. In addition, cap lamp illumination is inadequate for high headings. In high headings where surface rock support is installed the need for regular checking is reduced and the integrity of the excavation is greatly increased.
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