M du Plessis and S Liebenberg
The geology intersected by a mining excavation dictate the rockmass condition and stability of the excavation. The general geologic structure of the UG2 Reef horizon with regard to rock type, jointing and potential parting planes are well understood. Mining layouts and support applications are applied to control the anticipated rockmass behaviour. Case studies conducted at several instability sites have, however, revealed that in most cases the rockmass behaviour is controlled by the geologic structure which may appear as intact joints visible from scanline or borehole core mapping. The significance of these structures within the hangingwall is mostly not visible in a 3-dimensional space. The prominent structure is related to deformation processes which crosscut the strata and ramp to areas with strength competent contrasts (i.e. stringers or alteration layers). As a result large-scale instabilities may occur. The extent of these structures are only realised following large-scale instability. At the study site a combination of visual observations, scanline and borehole mapping, ground penetrating radar and high definition 3-dimentional laser scans were used to interrogate the geologic structure intersected along the hangingwall of a stope contributing to the instability experienced. The intent was to identify the precursors of these “unidentifiable” structures present in the unexposed hangingwall. The paper discusses the findings of the investigation conducted.
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