Influence mechanism of tunnel excavation on adjacent fault based on FDM-DEM coupling method
YU Haitao1, CHEN Zhiwei2
1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China; 2. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China
Abstract: Tunneling usually causes the dislocation of adjacent faults and further induces disasters such as earthquakes, but the physical mechanism is still not clear. A numerical model of near fault tunnel excavation was established by coupling mechanics of continuous media with mechanics of discrete medium. The discrete element method(DEM)was used to simulate the meso-mechanical behavior of the fault fracture zone, and the finite difference method(FDM)was used to describe the macro-dynamic characteristics of the upper and lower walls of the fault. Based on the multi-factor influence analysis, the physical mechanism of the near-fault dislocation induced by tunnel excavation was explored. The analysis results showed that the fault dislocation caused by tunnel excavation could be divided into four stages: incubation stage, acceleration stage, slowing stage and stability stage. The interaction between the fracture zone and the upper and lower walls was weak, and the rock mass deformation caused by excavation was difficult to propagate through the fracture zone to the other side. The discontinuity and disharmony of the deformation of the upper and lower walls were the main reasons for the fault dislocation. When the tunnel was located in the hanging wall, the fault displacement above the tunnel depth was positive, showing the form of positive fault, while the fault displacement below the tunnel depth was negative, showing the form of reverse fault. When the tunnel was located in the footwall, the result was opposite. The farther the tunnel was from the fault, the smaller the fault displacement caused by tunnel excavation was, and the fault displacement at different depths finally approached to 0. The increase of distance might also lead to the change of fault dislocation form below the tunnel depth. When the tunnel was located in the hanging wall, the fault displacement decreased with the increase of dip angle. When the tunnel was located at the footwall, the fault displacement above the buried depth of the tunnel increased with the increase of dip angle. The fault displacement under the buried depth of the tunnel decreased continuously. The fault displacement at the buried depth of the tunnel first decreased to 0 with the increase of dip angle, and then the dislocation form changed, and the displacement continued to increase.
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2021, Vol. 3 
