Research on Crack Propagation and Failure of Concrete Cutoff Walls Based on the Coupling of Plastic Damage and XFEM

Under complex loads, the stiffness mismatch between the cutoff wall and the overburden layer may result in damage or even cracking in certain parts of the wall. Unfortunately, as an underground concealed structure, it is difficult to detect the location and propagation of cracks in cutoff walls. In this paper, a coupling method combining plastic damage and the extended finite-element method (XFEM) was proposed to simulate the cracking behavior of cutoff walls without prefabricated cracks. This method, on the basis of the plastic damage model that can accurately simulate the stress state of structures, further employs the maximum principal stress fracture criterion of XFEM to simulate the propagation of cracks. Therefore, it significantly improved the accuracy of the crack propagation simulation. Moreover, a displacement equivalent load fitting equation was established to address the issue of nonconvergence in XFEM simulations of crack propagation in large concealed structures. Subsequently, the proposed method was applied to simulate the cracking behavior of a 186-m-deep cutoff wall without an initial crack in an earth-rock dam, serving as a case study. The results indicate that cracks are primarily distributed around the interface between the overburden and the bedrock, forming two main cracks along the contour of the cutoff wall, with several smaller microcracks developing between them. This crack distribution pattern corresponds to areas of high stress concentration and severe damage in the cutoff wall. In conclusion, the displacement-equivalent load strategy proposed in this paper significantly improves the efficiency and convergence of numerical simulations. The plastic damage-XFEM coupling method provides a novel approach for optimizing the design and maintenance of large-scale concealed structures.