A rock mass rating system for evaluating stope stability on the Bushveld Platinum mines

摘要

Several large falls of ground occur annually in the narrow, tabular slopes mined in the Bushaveld Complex. These falls comprise safety risks and cause substantial production losses and compromise efforts to increase productivity. Underground observations in conjunction with instrumentation sites were used to establish the strategic parameters required to describe the rock mass behaviour of shallow-dipping stopes on the Bushveld platinum mines. Existing rock mass rating systems were evaluated using the observations and instrumentation results. None of the current systems adequately described all the relevant geotechnical conditions. Thus a hybrid of several current systems was developed, and the proposed system is discussed in the paper. The new rock mass rating system is termed the 'New Modified Stability Graph' system and follows the method originally described by Mathews et al. and revised by Hutchinson and Diederichs. Changes have been made to some of the tables provided by Barton and to the stress analysis suggested by Hutchinson and Diederichs. In addition, the logistical regression analysis has been applied to databases, formed using the suggested analyses, for three support resistances and risk levels established.