The discrete element method is adopted to investigate the failure process in punch-through shear tests. The numerical tests agree well with the laboratory tests on crack propagation sequence and the influence of confining stress on effective shear fracture toughness. More importantly, the numerical tests indicate that the increase in axial force first causes stress concentrations. When the stresses reach critical values, cracks initiate and the concentrated stresses dissipate. With further increase in axial displacement, the axial force may fluctuate, accompanied with crack development. In addition, the increase in confining stress promotes the critical values of the concentrated stresses before crack propagation. Thus, the numerical tests show that the increase in confining stress promotes the effective shear fracture toughness and restrains the propagation of tensile cracks.

采用离散单元法研究穿通剪切试验的破坏过程。数值测试与实验室测试在裂纹扩展顺序以及围压对有效剪切断裂韧性的影响方面吻合良好。更重要的是，数值测试表明，轴向力的增加首先导致应力集中。当应力达到临界值时，裂纹开始，集中的应力消失。随着轴向位移的进一步增加，轴向力可能会波动，并伴随裂纹的发展。另外，限制应力的增加促进了裂纹扩展之前集中应力的临界值。从而，