Elastoplastic damage evolution constitutive model of saturated rock with respect to volumetric strain in rock and its engineering application

Hydro-mechanical (HM) coupling analysis is of tremendous importance in numerous engineering applications crucial to the stability of strata when tunneling in deep underground engineering. In this study, based on the relation between the evolving permeability and porosity and the volumetric strain, a damage evolution model with respect to the volumetric strain and a differential elastoplastic constitutive equation are developed. The evolution model can consider the effect of rock dilatancy when the volumetric strain in a rock becomes negative. Subsequent to being introduced into a commercial software package through user-defined subroutines, the damage evolution model is applied to a large hydropower station with four diversion tunnels. The performance of the developed model is compared with that of field monitoring and the traditional HM coupling calculation in terms of the pore pressure and displacement in the surrounding rock, and the former is verified to be reasonable and reliable. The stability analyses of the four diversion tunnels indicate that the rock dilatancy (negative volumetric strain) and permeability variation around the tunnel distribute dominantly in the vertical direction. The damage and plastic zone disperse over only a small scope around the tunnel surface. Thus, the four diversion tunnels are far away to connect to each other; after draining the water, the tensile stress in the lining continuously increases to 1.82 MPa and is considered to be within safety limits.