Numerical Study on the Path-Dependent Evolution of the Excavation Damage Zone under Transient Unloading

Excavation and unloading of deep rock mass under varying in-situ stress levels is a typical non-linear geomechanical process, Specifically, in the context of the widely used drilling and blasting (D&B) method, the excavation damage zone (EDZ) around underground opening induced by transient unloading represents a dynamic response problem governed by multiple factors. While the exact theoretical solution of stress state in surrounding rock during transient excavation can describe the stress state and eventually converge to the Kirsch solution after rock mass excavation completed, it cannot fully capture the dynamic damage process. Therefore, a circular tunnel model for transient excavation was established in this study using a dynamic finite element code LS-DYNA. An equivalent released nodal force method was implemented to stably control the transient unloading path under non-hydrostatic in-situ stress conditions after stress initiation, which realizing the synchronous release of radial and tangential stresses in the excavated zone. Moreover, the validity of the linear elastic transient excavation model was verified through comparison with an analytical solution. Then the dynamic stress redistribution, as well as the EDZ evolution process were numerically simulated under various stress unloading paths and lateral pressure coefficients, utilizing an elastoplastic constitutive model. This study provides a basis for simulating transient excavation under various paths and understanding failure of surrounding rock in non-hydrostatic stress states.