Spatial–temporal evolution of gas migration pathways in coal during shear loading

Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures. The spatial–temporal evolution of gas migration pathways in the coal during shear loading was also researched. The results show that gas pressure can hasten crack growth at the shear fracture surface, can reduce the shear strength of gassy coal, and can accelerate the shear failure process. Shear failure in gassy coal exhibits five stages: the pre-crack stage; the stable crack growth stage; the unsteady crack growth stage; the fracture stage; and, finally, the friction crack stage. The shear breaking creates two kinds of crack, shear cracks and tensile cracks. Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms. The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°–10°.