MECHANISM AND PREVENTION OF TUNNEL COLLAPSE THROUGH WATER-RICH FAULT FRACTURE ZONE

Tunnels across mountain always go through fracture zones. With lack of knowledge of the mechanisms on rock faults, constructions on rock tunnels used to bring about quite an amount of collapse accidents with large deformations. This paper applied a combination of theoretical and numerical simulation with the on-site monitoring data. It considered the underground water in rock faults and examined the surrounded rock instability and collapse mechanism during the construction process. The result shows that the discontinuous structural plane is fully infilled with debris or clay when the tunnels going through water-rich fracture zones. Coupled with construction disturbances, the structural surfaces are prone to dislocation, causing groundwater flow with further damages. The formation of structural surface erosion reduces the integrity and mechanical strength of the surrounding rock. The lowers the shear strength of the fault fracture zone, the larger the range of loosening of the surrounding rock and the greater the probability and range of collapse. Based on the principle of "water resisting, drainage and strengthening surrounding rock", this paper proposes several measures letting tunnels go through fracture zones preventing collapse. These strategies can provide references for maintaining construction safety in upcoming project and include setting up detour pits, pre-reinforcement of the ground, increasing support strength, optimizing construction methods and strengthening monitoring measurement.