RESEARCH ON STRESS FIELD OF SURROUNDING ROCK AND LINING STRUCTURE OF DEEP-BURIED SUBSEA TUNNEL CONSIDERING SEEPAGE EFFECT

Deep-buried subsea tunnels are often under high water pressure condition and therefore groundwater seepage exerts a great impact on the surrounding rock and lining structure safety. In this paper, a mechanical model of deep-buried subsea tunnel with lining is proposed to study the influence mechanism of groundwater seepage on the surrounding rock and lining structure stability during the service stage of subsea tunnel. Firstly, a conformal mapping method is adopted to map the semi-infinite domain which includes seawater and surrounding rock elastic zone into an annular domain, and the seepage equation in polar coordinates between interfaces is established according to the seepage boundary conditions. Thus, the analytical solution of the seepage field of the subsea tunnel is obtained. Secondly, the seepage field is applied to the stress field in the form of volume force, the stress balance equation is established according to the stress boundary conditions, and based on the Drucker-Prager (D-P) criterion which takes account of the effect of the intermediate principal stress, an elastoplastic analytical solution is derived for the surrounding rock and lining structure under the influence of seepage effect. Finally, taking Shenzhen Mawan Sea-Crossing Passage as an engineering example, the analytical solution is compared with the finite element numerical solution, which verifies the accuracy of the theoretical solution in this paper, the influence law of seepage effect on the stress field of tunnel surrounding rock and lining structure is studied, and the factors influencing the radius of surrounding rock plastic zone are analyzed. The results show that: the seepage effect has a significant influence on the hoop stress in surrounding rock and lining structure, and the radial stress increases nonlinearly with the increase of \rho . As the seawater goes deeper, the water pressure on tunnel continues to increase, and the surrounding rock plastic zone increases significantly. An increase in the internal water head can effectively limit the development of the surrounding rock plastic zone, with the initial limiting effect being obvious while the subsequent effect being gradually weakened.