Stress transfer law and its influencing factors of mesoscopic fracturing of coal rock mass

High stress is a common technical problem in many coal mines, and coal rock mass fracturing is an effective means to transfer stress. In this paper, the RFPA numerical simulation method is applied to investigate the stress transfer law under the various influence factors. The results show that coal rock mass with cracks produces a saddle-shaped stress profile that may be divided into three characteristic zones: a pressure relief zone, a pressure boost zone, and a primary rock stress zone. Shear slip deformation occurs along cracks and cracks are squeezed, forming an elliptical low-stress region around the cracks and a torsion plane in the displacement field. Increased mining-induced stress causes cracks to extend continuously into the bulk, which transfers the high stress at the original crack tip continuously to the new crack tip. This stress transfer phenomenon is enhanced monotonically with increasing crack length and decreasing angle between crack direction and minimum principal stress, thereby weakening the mechanical properties of the crack surface and increasing the number of crack groups. An analysis shows that, in each crack group, cracks oriented at small angles with respect to the minimum principal stress more strongly affect stress transfer, and the pressure relief area is a polygonal area defined by the crack tips. As crack spacing increases, the stress exhibits a low-pressure, high-pressure, low-pressure wave-shape distribution. Finally, with increasing burial depth, the crack pressure relief range becomes small.