Modeling progressive failure in steep rock slopes using the combined finite-discrete element method

Steep rock slopes are vulnerable to failure under complex geological and environmental conditions, posing serious risks to infrastructure and human safety. Conventional numerical techniques of slope stability, including the limit equilibrium method (LEM), the finite element method (FEM), and the discrete element method (DEM). They often struggle to simulate progressive failure involving the rock transition from a continuous to a discontinuous state. To overcome these limitations, this study proposes an integrated finite-discrete element method combined with the gravity increase method (FDEM-GIM). Unlike conventional approaches, this framework automatically identifies the critical failure surface and calculates the corresponding factor of safety (FoS), while explicitly simulating the full progressive failure process. In a case study from the upper Lancang River region, the simulations showed a clear progressive failure sequence characterized by slope toe cracking, upward crack propagation, tensile deformation, and eventual global instability and rock mass accumulation. Comparisons with LEM and DEM produced similar FoS values, but only the FDEM-GIM framework reproduced the full spatial and temporal evolution of damage and movement. Overall, this research indicates that the FDEM-GIM framework is effective for long-term stability assessment of steep rock slopes in complex geological settings and can support reinforcement design and safety management.