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

To protect the environment and reduce the water pressure on tunnel lining as far as possible,the controlled drainage design principle is generally adopted in deep mountain tunnels below high water table.The mechanical character of tunnel supports and linings under coupling of seepage and stress are studied by using numerical method and model test based on tunnel mechanics and seepage mechanics.The result shows that(1) the water pressure on the primary supports will not change notably when drainage conditions are transformed even though the mountain tunnels are impacted by drainage conditions;(2) the pore water pressure on primary supports would divert to tunnel linings when the drainage channels transferred from the interface between rock mass and primary supports to the interface between primary supports and secondary linings,and the primary supports would be unloaded and moves outwards to rock mass;(3) the water pressure on tunnel linings could be neglected when the ground water could be discharged smoothly;(4) the underground flow gradient would be decrease,the effective radial stress would be decrease,the radial flow toward tunnel would be decrease and the ground deformations would be decrease while the water pressure on secondary lining would be increase when the tunnel drainage system degenerats gradually.This research provided a rational approach for a preliminary design of the primary supports and secondary linings in deep mountain tunnels below high water table,and contributed to identify the load-transfer mechanisms between ground,water and support.