Mesoscopic evolution of coal containing gas's shear fracture

With the self-developed meso-shear test equipment for coal and rock shear fracture tests on coal containing gas were carried out under different molding pressures. The rules of the cracks' initiation, evolution and transfixion were studied at a mesoscopic level. Also different molding pressure impacts on shear strength and the final shear fracture were analyzed. The results suggest that the coal density and the shear strength increase with the increase of molding pressure. The speed of crack propagation is related to the distance between the predetermined shear plane and the cracking position. On predetermined shear plane the shearing stress is high and the speed is fast, and the propagation crack force decreases as it is away from the predetermined shearing plane, even cannot be transfixed. The crack morphology is related to molding pressure of gas-filled coal. The crack propagation is easy with low molding pressure, low density and shear strength. The crack propagation is difficult with high molding pressure, high density and shear strength. Because the left of the coal is fixed and the right is loaded during the shear fracture process, it is easy to form echelon crack. Eventually the tension cracks will be developed between echelon cracks.