Numerical Analysis of the Effect of Bedding Plane Strength on Laminated Roof Failure in Underground Entries Using Coupled FDM-DEM

Numerical simulations have been used to investigate roof fall in the past decades. When compared to the continuum-based methods, the discrete element method has been well recognized for its excellent performance in simulating large strain problems and the fracturing processes in the rock mass. However, the discrete element method has its limitations. When simulating a large-scale problem, a large number of particles are required, which consumes significant computational resources. In the present study, a 3D numerical model coupled with the finite difference method (FDM) and the discrete element method (DEM) was created to simulate the laminated roof failure in an eastern coal mine in the USA. In the FDM-DEM coupled model, the laminated roof of the entry is represented by an assembly of bonded particles using PFC3D. The laminated roof is simulated by adding parallel discontinuities. The discontinuities are given certain stiffness and strength parameters in the model. The rest of the surrounding rock, including ribs and floor, is represented by continuum zones using FLAC3D. The strength of the discontinuities is varied sequentially and the fracturing of the laminated roof was analyzed with respect to entry advance. The results showed that the laminated roof fractures along the discontinuities, while an intact roof fractures in a dome shape. Increasing the strength of the discontinuity could enlarge the tensile zone inside the laminated roof and hence change the crack distribution. In addition, the number of cracks in the laminated roof behind the advancing face decreases with the increment of discontinuity strength while this trend is not occurring ahead of the advancing face. The simulation demonstrated that the coupled method using PFC3D/FLAC3D can reproduce the laminated roof failure in underground coal mines.