Stochastic assessment of hard rock pillar stability based on the geological strength index system

Abstract: Hard rock pillar is a crucial rock mass structure to maintain the stability of underground mine. It needs of special attention to analyze its stability from the point of rock mass quality. In this paper, the geological strength index (GSI) representing the rock mass quality of the hard rock pillar is examined as a new influence factor of stability, and combined with the conventional parameters (uniaxial compressive strength (UCS) of intact rock mass, width of pillar (w), height of pillar (h), the ratio of pillar width to its height (w/h)) to complete the stochastic assessment of the stability of hard rock pillar. The 47 actual cases of hard rock pillar improved by numerical simulation software Flac^3D. An empirical formula fitted by the Least Square method and artificial intelligence prediction models are used to estimate the pillar strength combining with the pillar stress to conduct the probability and reliability analysis in the Monte Carlo simulation. The result of stochastic assessment showed that UCS and w still play a vital role in maintaining pillar stability, but the influence of GSI cannot be ignored. It found that the GSI has a greater influence on the sloughing pillars in comparison with stable and failed hard rock pillars. Concluding remarks is that GSI has crucial effects on the stability of hard rock pillars as well as UCS of the rock mass and shape of pillars (w and h). Thus, the GSI should be considered as one of input parameter for pillar design and stability assessment in underground mines. Article highlights: A new empirical formula and artificial intelligence models considering five parameters(GSI, UCS, w, h and H) are developed with the improved 47 actual cases of hard rock pillar to estimate the pillar strength.Two pillar performance functions are determined by the Monte Carlo Simulation technique to complete the stochastic assessment based on the probability and reliability analysis of stability conditions of hard rock pillars.The probability of different conditions of pillars can well indicate the relationship between the new (GSI) and traditional influencing factors (UCS, w, h and H) and the stability of pillars.The GSI index has a greater influence on the sloughing pillars in comparison with stable and failed hard rock pillars.