## 5 Discussion  
The proposed elastoplastic phase field model offers a novel framework for simulating rock failure under compressive-shear conditions by explicitly coupling plastic deformation with crack evolution. This study bridges critical gaps between classical plasticity theory and phase field fracture mechanics, providing a more realistic description of energy dissipation mechanisms and failure modes in rock engineering applications. While the model demonstrates significant advancements in capturing elastoplastic damage and crack propagation, its assumptions, limitations, and broader implications must be carefully contextualized within both theoretical and practical domains. 1. Advantages and Contributions: The model's primary strength lies in its ability to overcome the limitations of purely elastic phase field approaches. Traditional models often neglect plastic deformation mechanisms such as shear band localization and residual strength, leading to overly brittle predictions. By integrating plastic strain energy and non-associated flow rules, this work quantifies the reduction in crack propagation resistance caused by plastic slip, enabling a seamless transition from elastic loading to plastic damage accumulation and unstable fracture. Numerical validation through single-edge notch tension and uniaxial compression tests confirms the model's accuracy, with load-displacement curves exhibiting less than 5% error in elastic stiffness and a 1.2% deviation in peak load compared to experimental benchmarks. These results highlight its potential for predicting residual strength in underground engineering structures, where stress redistribution and long-term stability are paramount. 2. However, the model's reliance on small-deformation theory and isotropic hardening assumptions introduces constraints. Scenarios involving large rotations, such as shear band widening or rockbursts, may require extensions to finite-deformation frameworks to account for geometric nonlinearity. Additionally, the omission of crack interaction mechanisms--such as coalescence or branching--limits its applicability to multi-fracture systems. Furthermore, while key parameters (e.g., critical energy release rates, regularization length scale, and residual strength coefficient) are calibrated through benchmark tests, their sensitivity to crack propagation behavior and energy dissipation remains to be systematically quantified. A comprehensive parametric sensitivity analysis would refine calibration protocols for heterogeneous rock masses, though such an exploration is deferred to future work to maintain focus on the foundational coupling framework proposed here. Figure 9: Load–displacement curve of uniaxial compression test for rock with prefabricated cracks. 3. Comparison with Existing Studies: When compared to existing studies, the proposed model distinguishes itself through its explicit integration of plasticity and fracture mechanics. Prior hydromechanical phase field models, such as those by [PERSON] et al. [15] and [PERSON] et al. [16], omitted plastic energy dissipation, while cohesive zone approaches employed by [PERSON] et al. [14] relied on predefined crack paths. In contrast, this work eliminates such constraints, enabling autonomous crack initiation and propagation through a unified energy functional. This theoretical innovation not only enhances computational flexibility but also provides a more holistic representation of rock behavior under compressive-shear loading, as evidenced by its alignment with classical experimental observations. 4. Future Directions: Future research should focus on expanding the model's scope to address multifield coupling and dynamic loading scenarios. Incorporating thermo-hydro-mechanical (THM) interactions would improve predictions for saturated or thermally altered rock masses, where pore pressure and temperature gradients significantly influence fracture behavior.