Hydraulic and Displacement Response Analysis of Shield Tunnel in Gassy Seabed under Wave Action

The gas in the seabed sediment exists in the seabed soil as discontinuous gas phase, existing theoretical studies seldom consider the gassy seabed environment, and there are few studies on the additional deformation of the tunnel lining caused by the seepage force induced by the wave dynamic pressure. Firstly, the control equation of gas-water mixed flow is obtained by Biot consolidation equation, and the pore water pressure response around the tunnel lining is obtained by combining with Stokes second-order nonlinear wave theory suitable for shallow water. Secondly, the superposition method is used to consider the oscillatory pore pressure and cumulative pore pressure in the seabed soil caused by waves, and the maximum pore water pressure and seepage force that may appear around the lining are taken as the most unfavorable load cases. The displacement variation law of the tunnel lining during service under the action of wave seepage force is obtained in combination with the exponential decay model to describe the lining deterioration effect. Finally, accuracy of the theoretical analysis in this paper is verified by the experimental monitoring data and numerical simulation. Parameter analyses are made on the wave period, water depth, seabed shear modulus, seabed gas content, tunnel radius, burial depth and lining deterioration. The cumulative effect of wave pressure propagating into the seabed and excess pore water pressure can be weakened when the seabed gas content increases. The extreme pore pressure around the tunnel lining decreases and the phase lag occurs with the increase of the gas content in the seabed. The external seepage force and the radial displacement of the lining decrease significantly with increasing the gas content in the seabed. Larger wave period and shallower seawater depth can significantly increase the wave pressure on the seabed surface, and induce greater seepage force around the tunnel lining, resulting in greater radial displacement. Reducing the radius and depth of the tunnel can effectively weaken the influence of the seepage force caused by the accumulated pore water pressure. When the lining deterioration coefficient is constant, the influence of excess pore water pressure caused by waves in the seabed with lower gas content is more significant, and the lining produces large radial displacement, which is not conducive to the normal service of the tunnel.