An enhanced numerical model for considering coupled strain-softening and seepage effects on rock masses surrounding a submarine tunnel

The seepage of groundwater and the strain-softening of rock mass in a submarine tunnel expand the plastic region of rock, thereby affecting its overall stability. It is therefore essential to study the stress and strain fields in the rocks surrounding the submarine tunnel by considering the coupled effect of strain-softening and seepage. However, the evolution equation for the hydro-mechanical parameters in the existing fully coupled solution is a uniform equation that is unable to reproduce the characteristics of rock mass in practice. In this study, an updated numerical procedure for the submarine tunnel is derived by coupling strain-softening and seepage effect based on the experimental results. According to the hydro-mechanical coupling theory, the hydro-mechanical parameters such as elastic modulus, Poisson's ratio, Biot's coefficient and permeability coefficient of rocks are characterized by the fitting equations derived from the experimental data. Then, the updated numerical procedure is deduced with the governing equations, boundary conditions, seepage equations and fitting equations. The updated numerical procedure is verified accurately compared with the previous analytical solution. By utilizing the updated numerical procedure, the characteristics of stress field and the influences of initial pore water pressure, Biot's coefficient, and permeability coefficient on the stress, displacement and water-inflow of the surrounding rocks are discussed. Regardless of the variations in hydro-mechanical parameters, the stress distribution has a similar trend. The initial permeability coefficient exerts the most significant influence on the stress field. With the increases in initial pore water pressure and Biot's coefficient, the plastic region expands, and the water-inflow and displacement increase accordingly. Given the fact that the stability of the tunnel is more sensitive to the seepage force controlled by the hydraulic parameters, it is suggested to dewater the ground above the submarine tunnel to control the initial pore water pressure.