Comparative Analysis of Gas–Solid–Liquid Coupling Behavior in Front of the Working Face Before and After Water Injection During Coal Mining

Abstract

Coal seam water injection is a critical measure for the prevention of coal-and-gas outbursts. However, the gas–solid–liquid coupling effect in front of the working face before and after water injection during coal mining is scarcely investigated. This issue was explored in this study by (a) numerical simulation of stress, gas pressure, and water saturability distribution as well as their coupling effect in front of the working face via the proposed multi-field coupling model run in the COMSOL software and (b) comparative analysis of the above parameters before and after water injection. During coal mining, stress in front of the working face first increased and then dropped to the initial value as the distance from the coal wall increased, while gas pressure exhibited a similar distribution pattern. After water injection, the stress distribution pattern remained almost unchanged, but the stress peak shifted forward, the stress relief zone broadened, while the gas pressure around the borehole dropped. In particular, the gas pressure in front of the borehole increased slightly at the beginning of water injection. As water was permanently injected, the gas pressure in front of the borehole decreased, while that around the borehole further decreased. Meanwhile, the water saturability of the coal seam around each borehole increased, with a ring-shaped distribution pattern. Due to the interaction of water injection among multiple boreholes, the contour lines of water saturability showed semi-circular distribution patterns around multiple boreholes.