ABSTRACT Soft‐hard interbedded rock formations present significant challenges to tunnel stability due to their pronounced lithological heterogeneity and complex coupled hydro‐mechanical behaviors. This study develops a coupled hydro‐mechanical phase field model to investigate damage evolution and seepage behavior in porous elastoplastic geomaterials. The plastic deformation of the solid skeleton is described using the Drucker–Prager yield criterion, and an improved volumetric‐deviatoric strain energy decomposition that accounts for initial geostress is introduced to prevent spurious damage under high compressive stress states. The model is implemented in ABAQUS through user‐defined element (UEL) and user‐defined material (UMAT) subroutines, utilizing a staggered solution scheme. The proposed framework is validated against analytical solutions and experimental benchmarks. It is subsequently applied to tunnel excavation in soft‐hard interbedded formations with varying bedding angles. The results demonstrate that excavation‐induced damage localizes preferentially along soft interbeds and is primarily governed by plastic deformation, leading to a permeability enhancement of several orders of magnitude and a strongly coupled evolution of pore pressure. The bedding angle significantly influences the spatial distribution of damage, displacement, and pore pressure, inducing asymmetric mechanical and hydraulic responses that intensify with increasing bedding inclination. Maximum tunnel deformation and lining tensile stress occur at a bedding angle of 45°. Furthermore, the pore water pressure in the tunnel near‐field exhibits a two‐stage evolution characterized by rapid post‐excavation dissipation followed by gradual stabilization, with the direction of dissipation governed by bedding‐controlled permeability anisotropy.
Lan et al. (Thu,) studied this question.