ELASTIC-PLASTIC SOLUTION FOR SUBSEA CIRCULAR TUNNEL UNDER THE INFLUENCE OF SEEPAGE FIELD

Subsea tunnels are different from the overground mountain tunnels. Due to the high seepage pressure, the effective stress of wall rocks would be reduced, which results in lower stratum stability. In this paper, the subsea circular tunnel with liner is simplified as axially symmetrical and the effect of seepage field is simplified as seepage volume force acting on the stress fields. Elastic-plastic analytical solutions of stress and displacement are obtained respectively for two cases: the elastic-plastic interface locates in the liner or in the surrounding rock. Based on the results of a practical example, the effects of sea depth and rock cover thickness on the stress fields are analyzed with the consideration of seepage fields. Some conclusions are as follows: 1) The maximum radial stress and tangent stress occur at the elastic-plastic interface. 2) No matter the elastic-plastic interface locates in the liner or in the rock, sea depth variations have little influence on the normal contact pressure at the liner-rock interface. 3) For a tunnel structure with determinate rock cover thickness, if the elastic-plastic interface locates in the liner, sea depth variations have little influence on the radius of the plastic region and on the normal contact pressure at the elastic-plastic interface. But, if the plastic region expands into the rock, the plastic region expands linearly and the radial stress at the elastic-plastic interface increases linearly as the sea depth increases.