Reliability Analysis of Rock Supports in Underground Mine Drifts: A Case Study

Support failures in mine drifts represent potential hazards that threaten underground mine safety and productivity. The aim of this study is to determine the reliability index associated with the rock supporting elements used in Ridder-Sokolny mine, an underground mine located in East Kazakhstan. Numerical simulations of the drift support and the First Order Reliability Method (FORM) were employed to carry out the analysis. Several support cases were considered including: shotcrete, bolting, concrete, bolting combined with concrete and unsupported drift case. For each support case, the Factors of Safety (FS), the reliability index (β) and the Probability of Failure (P_F) were determined in accordance with the corresponding rock mass quality and the excavation geometry. The results indicate a slight variation of the average FS values for the different support cases (except for shotcrete) while β and P_F vary more significantly between 0.62–3.25 and 0.05–27 (× 10³%) factor depending on the rock conditions and the installed support. The probability of failure of the rock support increases with a decrease in the rock mass quality. Similar trends are observed with an increase of the width/height ratio of the excavations for the same rock domain. These results illustrate that a single FS value obtained from a deterministic method may not always provide a sufficient indication of safety. This is in agreement with the field observations which have indicated a poor performance of the supports. Hence, on the basis of the reliability index of the supports, the requirement in terms of coefficient of variability of the rock mass quality to meet the target performance level is proposed. It is concluded that the results of this study could help improving the drift support design in Ridder-Sokolny mine.