Prediction of limit support pressure for face stability of deep tunnels buried beneath sea/water

An upper bound analysis procedure was presented in this paper to investigate the face stability of a deep-buried tunnel excavated beneath water/sea. By constructing a kinematic velocity field, the kinematic solution of support pressure required for tunnel face stability was formulated, considering a uniform and a linearly increased soil cohesion profile. A uniform and a linearly increased distribution of support pressure was considered in this study. The consistency of the proposed procedure was well substantiated through comparing with FLAC3D and spatial discretization technique combined with the upper bound analysis. The required support pressure and critical failure mode were discussed, considering the effects of soil strength parameters and pore water pressure. For the ease of practical use, some design charts were presented in terms of normalised quantities, and an empirical formula was proposed to calculate the required support pressure. This study aids to provide a quick estimate of effective support pressure required for tunnel face stability.