Analysis of External Water Pressure on the Support and Lining of Deep Mountain Tunnels below High Water Tables

To protect the environment and to minimize the water pressure on a tunnel lining, the controlled drainage principle is proposed for deep mountain tunnels below high water tables. The mechanical characteristics of tunnel supports and linings with respect to seepage and pressure are studied by using numerical methods and a test model based on the tunnel mechanics and seepage mechanics. The results show that the pressure exerted on primary supports is unrelated to surrounding drainage conditions. The pore water pressure on primary supports diverts to tunnel linings when the drainage system moves from the interface between rock mass and primary supports to the interface between primary supports and tunnel linings, and the primary supports are unloaded and the pressure moves outwards to the rock mass. The water pressure on tunnel linings can be neglected if the ground water can be discharged smoothly. When a tunnel drainage system malfunctions and leads to poor drainage, the flow gradient in the ground decreases, the effective radial stresses decrease, the radial flow of tunnel decreases and the ground deformations decrease.