A numerical solution of coupling hydro-mechanical behavior for subsea tunnels in strain-softening rock masses: theory and case study

Most contemporary studies on subsea tunnels have failed to integrate the hydro-mechanical and strain-softening behaviors of rock masses. Additionally, these studies often consider the hydraulic parameters of rock masses as constants despite their nonlinear variation with plastic strain and confining pressure. This study proposed an updated numerical solution for coupling hydro-mechanical behavior of subsea tunnels in strain-softening rock masses. Using existing test data, the hydraulic parameters of rock masses, including the permeability coefficient, Biot's coefficient, Poisson's ratio, and elastic modulus, were characterized through fitting equations. These equations more accurately captured the influence of confining pressure and plastic shear strain on hydraulic parameters, aligning more closely with the actual rock mass behavior. The updated numerical procedure was derived from the governing equations, boundary conditions, seepage equations, and fitting equations, enabling solutions for stress, displacement, plastic region, and water inflow around subsea tunnels in strain-softening rock masses. The effects of varying the initial permeability coefficients, Biot's coefficients, and pore water pressures on tunnel stability were analysed. Finally, using finite difference simulation software, the distributions of the seepage, displacement, and stress fields for a practical case were examined.