Confining pressure effect of fault unloading and slippage induced by deep coal seam mining

With the continuous advancement of deep coal resource extraction in China, the issue of dynamic disasters induced by geological structures has become increasingly prominent. Among them, fault unloading slip, as a typical instability form under mining-induced stress disturbances, poses a serious threat to the safe production of mines. This study takes a series of high-energy seismic events triggered during the mining of a working face crossing a fault in a mine in Gansu Province as the background. By employing a biaxial unloading slip test method, the process and mechanism of fault unloading slip induced by deep mining disturbances were revealed, and differentiated prevention and control strategies for deep fault slips were proposed. The research results show that fault slip can be divided into three stages: stress accumulation stage, critical slip stage, and instability slip stage, with distinct slip characteristics in each stage. Fault slip is primarily caused by changes in normal shear stress on the fault plane, where shear stress governs the fault slip. Once the shear stress on the fault plane exceeds the maximum shear strength of the fault, slip will occur. Normal stress mainly affects the stability of the fault, with high confining pressure increasing fault stability. However, once slip occurs under high confining pressure, it can lead to more significant dynamic disasters. This study provides guidance for fault stability evaluation and disaster prevention in deep coal mining.