Trials of the garford hybrid dynamic bolt reinforcement system at a deep-level gold mine in South Africa

Abstract

Efficient dynamic bolt reinforcement is crucial in deep-level gold mines prone to rockbursts. Deep-level gold mining in South Africa is approaching 4000 m, so appropriate support designs need to be implemented to manage ground stability challenges associated with these great depths. In order to extract the orebody, both novel mining methods and massive mining techniques have to be applied. Currently, massive mining techniques are used and destressing is imperative. Destressing is accomplished by cutting a series of overlapping, 5 m high horizontal slots across the reef. Although the minor span of each slot is about 100 m, stresses are extremely high due to presence of abutments. In order to protect workers from the effects of small seismic events, a yielding support system consisting of weld mesh (100 mm apertures and 5 mm strands) and 2.5 m long Garford hybrid bolts has been developed. The support system allows installation to be made at 0.5 m from the advancing face without significant damage by the blast. A tendon pretension of 49.3 kN ensures an active support system at installation, with 29 kJ/m2 energy absorption capacity during seismic events, and static tensile capacity of 147 kN. The effectiveness of the Garford hybrid bolt is discussed in this paper.