Peridynamic Simulation Method for Excavation Damage of Surrounding Rock in Water-Rich Fractured Strata Tunnels

Groundwater seepage and engineering excavation are among the primary causes of rock mass strength degradation and damage failure during tunnel construction. In natural strata, the groundwater seepage field and the rock stress field exist in a state of natural equilibrium. Tunnel excavation disrupts this equilibrium, inducing sudden changes in the original groundwater recharge–migration–discharge system. This may trigger shear slip along internal structural planes and the initiation and propagation of hydraulic fractures, exacerbating the damage and failure of the surrounding rock, and eventually leading to surrounding rock instability or water inrush disasters. Peridynamics (PD) can simulate the damage and failure behavior of rock masses under in situ stress and can also characterize the seepage of groundwater in porous–fractured media. This paper integrates peridynamics for discontinuous deformation and failure of solid materials with groundwater seepage modeling. Based on the effective stress principle, a simulation method is developed for the damage and failure of water-rich fractured rock masses under fluid pressure-driven conditions, in which the conductivity of each fluid bond is controlled by the state of the corresponding solid bond. Furthermore, the material point dormancy method (MPDM), which represents the unloading effect of tunnel excavation, is extended to the fluid field, so that excavation unloading and a drained tunnel surface are treated within one framework. The propagation of hydraulic fractures is simulated for different natural fracture dip angles and stress states and for a random fracture network, and the results are compared with RFPA simulations computed by the authors (a code-to-code consistency check). Tunnel excavation in water-rich jointed strata is then simulated for different joint counts and seepage pressures, and the resulting excavation damage zones and pore water pressure distributions are analyzed. The results are limited to the two-dimensional, homogeneous-matrix cases examined and have not been validated against experimental or field data; they provide a numerical reference for the analysis of excavation-induced damage in surrounding rock of tunnels situated in water-rich fractured strata.