Fracture initiation and propagation from a wellbore within a rock formation exhibit nonlinear and inelastic behaviors. When the rock material undergoes plastic deformation prior to failure, the classical Griffith theory is no longer valid. In this study, a variational phase-field approach is applied to model the inelastic behavior of granite rock in a punch through shear test. The rock failure and the fracture initiation and propagation during the loading was simulated and compared to the corresponding experimental investigations. In this numerical approach, the total local free energy is fully coupled with solid deformation and computes the plastic strain rate. The code is scripted in Multiphysics Object Oriented Simulation Environment (MOOSE). The model is shown capable of reproducing the evidenced phenomena from Punch Through Shear (PTS) test encompassing mixed mode fracture pattern Mode I, and Mode II. The numerical results show a good agreement in the stress–displacement curve with experimental data for the critical energy release rate of \({G}_{c}=600\mathrm{N}/\mathrm{m}\). Therefore, the granite sample’s fracture toughness for Mode II is calculated to be 4.85 \(\mathrm{MPa}\sqrt{\mathrm{m}}\) at no confining pressure.

岩层内井筒的破裂萌生和传播表现出非线性和非弹性行为。当岩石材料在破裂前经历塑性变形时，经典的格里菲斯理论不再有效。在这项研究中，采用变分相场方法对通过冲剪的花岗岩岩石在冲头中的非弹性行为进行建模。模拟了岩石破坏以及在加载过程中裂缝的萌生和扩展，并将其与相应的实验研究进行了比较。在这种数值方法中，总的局部自由能与固体变形完全耦合，并计算塑性应变率。该代码在Multiphysics面向对象的仿真环境（MOOSE）中编写了脚本。所显示的模型能够重现“穿剪剪切”（PTS）测试中包含的混合现象，包括混合模式I和模式II。数值结果表明，应力-位移曲线与实验数据的临界能量释放速率吻合良好。\（{G} _ {c} = 600 \ mathrm {N} / \ mathrm {m} \）。因此，在无围压的情况下，花岗岩样品在模式II下的断裂韧度经计算为4.85 \（\ mathrm {MPa} \ sqrt {\ mathrm {m}} \）。