Stability analyses of side-exposed backfill considering mine depth and extraction of adjacent stope

Abstract

Pillar recovery requires stable backfill upon side exposure in open stoping mining methods. Until now, the solutions used to estimate the required strength of side-exposed backfill are mainly based on a wedge model where the effect of rock-wall closure was neglected. In this paper, the influence of mine depth and adjacent extraction on the stability of side-exposed backfill is analyzed through numerical modeling with FLAC3D. The failure mechanism and cohesion at failure (cf) of backfill are investigated. Results show that the governing failure mechanism can be sliding or crushing, depending on the magnitude of rock-wall closure. When the mine depth and rock-wall closure are small, sliding failure is dominant and rock-wall closure has effect to improve the stability of exposed backfill. The values of cf can become even smaller than those obtained with immobile rock walls solutions. When the sliding failure is dominant, the cf decreases with the increase of mine depth, fill stiffness, rock pressure coefficient, and fill-rock interface strength (friction angle and adhesion). Increasing rock mass stiffness, stope height and width leads to an increase in cf. When mine depth and rock-wall closure are large, the crushing failure is dominant. The cf increases with the increase of mine depth, stope height and length, fill stiffness and rock pressure coefficient. It decreases with the increase of stope width and rock mass stiffness, and is insensitive to the variation of fill-rock interface strength. In all cases, the stability of side-exposed backfill is improved by increasing its internal frictional angle.