A new elasto-plastic solution for analysis of underwater tunnels considering strain-dependent permeability

An analytical-numerical solution is proposed in this paper for calculating the mechanical and hydraulic characteristics of underwater tunnels, excavated in an elasto-plastic strain-softening and Hoek-Brown rock material considering strain-dependent permeability. The problem is considered with axial-symmetry condition and thus, the initial stress state is assumed to be hydrostatic. Hydraulic and mechanical differential equations governing the plastic and the elastic rock mass around the tunnel are derived. As the derived equations do not have closed-form solutions, a computer program has been prepared, in order to solve the corresponding equations numerically and to examine the analysis. The results obtained are compared with the results obtained using a commercial finite difference code for investigating the effects of utilised simplifying assumptions. The proposed approach is also used to analyse the response of tunnels under different hydro-mechanical conditions. The results show that the proposed solution can be used for the actual design of underwater tunnels, hydraulically and mechanically.