The Deformation and Failure Analysis of Rock Mass Around Tunnel by Coupling Finite Difference Method and Discrete Element Method
The deformation and failure mechanics of the rock mass around tunnel after excavation are very important for design and construction. Simulation is always difficult when using either the finite difference method (FDM) or discrete element method (DEM). Consequently, a two-dimensional (2D) coupling analysis method was introduced by employing the commercial codes FLAC for FDM and PFC for DEM simultaneously. The developed 2D coupled method was applied to analyze the mechanical response of Tongluoshan tunnel which is the longest interval railway tunnel in China. By comparison with theoretical method, the displacement by numerical simulation shows good agreements with analytical equation for cases with different ground stress ratios. The reasonable dimension for DEM model should be 4 times of tunnel radius to assure reliable results in terms of efficiency and accuracy of calculation. Generally, the maximum of vertical displacement will increase according to the increase in stress ratio. Fracture of rock mass initiates and visible collapse of tunnel happens when ground stress is over 4 MPa (54% of uniaxial compressive strength) and 6 MPa (81% of uniaxial compressive strength), respectively. Both fracture and collapse predominantly concentrate above tunnel crown.
Keywords: Rock mass around tunnel, Numerical simulation, Multi-scale coupling, Deformation and failure