Ground Support Observations at Xstrata's Craig and Onaping Mines

Rick W. Deredin,
Abstract The theoretical capacity of various ground support components can be misleading, especially in bursting
ground where the failure mode is often in the retainment system. Wire mesh screen seams often peel
open rather than breaking the wire strands, fractured rock often un-ravels around the bolts rather than
breaking the bars. If a weak link(s) in the system fails prematurely, then the potential capacity of the
system may never be fully realized.
Underground observations are used to show how some support systems behave in the field. Various
combinations of wire mesh screen with friction bolts, rebar, modified conebolts, cablebolts, shotcrete and
mechanical rockbolts are considered. A short case history is used to contrast the performance of “just-intime”
development in a high stress faulted area versus a tunnel subjected to multiple stress changes in a
similar environment. The latter proved to be a serious ground support problem when the well developed
fracture zone around the opening was subjected to dynamic loading from a large seismic event causing a
severe rockburst. In such cases an improved mining strategy may be more relevant than higher capacity
support systems.
Keywords: Mine design, Ground support
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