Mining‐Induced Redistribution of the Abnormal Stress under the Close Bearing Coal Pillar for Entry Design

Abstract

Underground space is vulnerable to large deformation influenced by the abnormal stress induced by the bearing coal pillar. A numerical simulation model was established to determine the redistribution of the abnormal stress induced by the mining activities. The double-yield model, the strain softening model, the interface model, and the Mohr–Coulomb model were determined to simulate the gob compaction effect, the pillar strength reduction effect, the structure plane discontinuity effect, and the rock mechanical behavior, respectively. This numerical simulation model is reliable to predict the abnormal stress under the bearing coal pillar by the comparison of the abutment stress from this model and the existing theoretical model as well as the entry roof surface displacement from this model and the field measuring method. The results from the validated numerical model indicate that the abnormal stress including stress concentration coefficient, stress gradient, and lateral pressure coefficient will redistribute to another state that the stress concentration coefficient and stress gradient increase gradually and then decrease, and the lateral pressure coefficient decreases gradually, then increases, and finally decreases sharply with the approach of the mining working face. Their maximum increasing rates are calculated as 121.05%, 198.56%, and 236.82%, respectively. This predicted mining-induced redistribution of the abnormal stress is available for designing the underground entry layout in the determination of the entry position, determination of the driving operation time, mining disturbing range warning, and the prediction of the strengthening support area.

Numerical Investigation on the Yield Pillar Bearing Capacity under the Two-End-Type Cable Reinforcement

“…One salient feature of coal is its pronounced strain-softening behavior. This perspective is echoed by Liu and Shen [16] who discerned that the failure of coal samples can be compartmentalized into three distinct regions: the residual, strain-softening, and elastic areas. From a practical standpoint, a pillar undergoes a sequence of phases prior to failure, encompassing elasticity, followed by plastic-softening, and finally reaching the residual phase.…”

“…Despite the effective use of the gob-side entry driving (GED) technique that retains slender coal pillars, several challenges remain. One significant concern is the need to Energies 2023, 16, 6418 2 of 17 delay excavation of roadways in subsequent mining areas until the overlying strata in the neighboring goaf stabilize, in order to counteract dynamic pressures. This delay spans an extended period, typically 6 to 8 months, post-extraction.…”