Abstract: The construction of Daxiang mountain tunnel in water-rich fault has great risks of causing water bursting and mud gushing easily. High-position drainage can reduce water pressure ahead of working face effectively. By using field test and numerical simulation, under different water-level conditions, the interrelation between method of high-position drainage and stability of tunnel is studied; and the optimal plan of arrangement of high-position drainage pipes is put forward. Studies show that: maximum water pressure of Daxiang mountain tunnel in fault is up to 1.98 MPa. The tunnel can be constructed securely after drainage and the maximum water head is only 10 meters. Therefore, prevention of water bursting is mainly concentrated in the period of tunnel face excavation. The drain volume of drain pipes at vault is maximum. The closer drain pipes and arch foot are, the more poor drainage capacity is; and the density of drain pipes at vault should be higher than that at arch foot. In actual construction, for faster to reach drain effect, drain pipes at vault should be first to arranged, then at arch foot. Interrelation between number of drain pipes, drain volume and extrusion deformation of tunnel face is studied. According to economy and effect of hydrophobic reinforcement, reasonable drainage scheme is put forward.

Key words: fault, water-rich, mountain tunnel, high-position drainage, working face stability