Research on the Mechanism of Fault Activation and Water Inrush Across Variable Coal Pillar Widths

Abstract

During coal mining operations, the activation of geological faults induced by mining activities, leading to sudden water inrush, presents a significant technical challenge to safe extraction. This study uses the Wugou Coal Mine as a case example to analyze the characteristics of fault activation under deep-seated high stress and high confined water pressures, as well as to determine the optimal dimensions for the implementation of waterproof coal pillars. This study employs a combination of numerical simulation and indoor model experiments to establish a fracture–permeability coupled computational model. The dynamics of fault-induced water inrush and the adequacy of waterproof coal pillar widths are evaluated through laboratory experiments. Results demonstrate that as the mining face progresses near the fault zone, fracture development within the fault increases, and the stresses in the coal seam’s roof and floor escalate, reaching a peak before experiencing unloading. This intensification in fracture development, driven by the dual impacts of mining activity and subfloor hydrostatic pressures, leads to the formation of interconnected fractures through the fault zone. Numerical simulations provide insights into the changes in overburden stress, the characteristics of plastic deformation in the surrounding rock and fault zones, and the permeability traits of the faults at various coal pillar widths. The findings indicate that as the width of the waterproof coal pillars decreases, stress concentration at the interaction points between the fault and the mining layer becomes significantly pronounced. The plastic deformation in the roof shifts from an “elliptical arch” shape to a “saddleback” shape, while the floor displays extensive planar failure. Particularly when the width of the waterproof coal pillars is less than 20 m, there is a substantial increase in the pore water pressure within the fault zone, greatly increasing the probability of fault activation and subsequent water inrush.