Support of excavations subjected to dynamic (rockburst) loading

摘要

Rockbursts are violent events that manifest in the ejection of rock from excavation walls, often at high velocity. Although attempts have been made to link the seismic source magnitude via peak particle velocities to predicted ejection velocities, back analyses of ejection velocities from rockburst damage indicate inexplicably large magnifications of the peak particle velocities obtained from seismic measurements. This indicates a lack of understanding of the mechanisms of rock mass behaviour in seismic conditions. There is an equal lack of understanding of the mechanisms of action and interaction of support elements in a rockbursting environment. The design of rock support for these conditions is therefore problematic, since neither the demand imposed on the support, nor the capacity of support systems under dynamic loading, can be defined. A conventional engineering design approach is therefore not possible owing to the design indeterminacy. Since testing of support has shown that both rockbolts and containment support systems such as wire mesh plus wire rope lacing can absorb large amounts of energy, an alternative philosophy is to specify the support conservatively. A very important requirement is that the containment support, and the connecting elements between this support and the retainment support, should not fail - they must ensure that the dynamic loading is passed fully into the rockbolts. The conservative specification approach may be perceived to be an expensive solution. However, if all costs of consequences are taken into account, containing rockburst damage is almost certain to create improved safety and increased value for the operation.