Mining-induced fault slip: Assessment model and method for determining fault instability ranges

Objective Faults are highly susceptible to activation and slip instability under the influence of mining. This might trigger many disasters such as mine earthquakes, posing serious threats to mine safety. Therefore, it is necessary to analyze the mechanical mechanisms behind mining-induced fault activation and determine the ranges of mutual feedback between mining and fault activation in advance. Methods With the 213B mining face of the Xinzhi coal mine as the engineering background, this study analyzed the fault activation process induced by mining and created an elastic mechanical model for the impacts of mining on the surrounding rocks of faults. Accordingly, this study elucidated the mechanical mechanisms of the impacts of mining on fault stability from the perspective of stress changes and constructed an assessment model for fault slip tendency. Using the FLAC3D software, this study simulated the variation trends of the slip tendency indices of faults’ hanging and foot walls during mining. Based on the relationship between the slip tendency index and friction coefficient of faults, this study determined the critical value of fault activation, identified the spatial range of fault instability, and analyzed the hazardous spatial range of fault activation-induced strong mine earthquakes. Results and ConclusionsThe results indicate that the slip tendency indices of faults significantly increased when the mining face gradually approached the faults. Under the influence of mining, faults F1478 and F1477 underwent local slip and displacement. Regarding the slip tendency, both faults showed a trend of mutual displacement between their hanging and foot walls, leading to vibration waves in the slip tendency indices. Under the numerical simulation of a mining face with dual faults, the mutual feedback between mining-induced slip instability of faults and mining was identified at 32‒200 m from fault F1478 in the advancing direction of the mining face, and fault slip and displacement were concentrated primarily within 12 m above the coal seam floor. On-site microseismic monitoring data suggested that the slip instability of faults occurred at 30‒200 m from fault F1478 in the advancing direction of the mining face, consistent with the numerical simulation results. This demonstrates that the assessment model of fault slip tendency is accurate and reliable and that the mutual feedback range determined by numerical simulation analysis is rational. The method developed in this study can provide a technical reference for assessing fault activation of the mining face with similar geological conditions, thus ensuring safe and efficient coal mining.