Analysis of step-path failure mechanisms in rock slopes with en-echelon joints based on FDEM simulation

In this study, an in-house combined finite-discrete element method (FDEM) is implemented to simulate and analyze the entire step-path failure process in rock slopes with en-echelon joints under natural conditions. Based on the Longmenqiao Reservoir slope in Chongqing, China, numerical models of the slope with and without en-echelon joints are established, and a comparative analysis is first conducted to explore the effects of the en-echelon joints on the slope failure mode. Then, to further investigate the slope failure mechanisms due to various influencing factors on site, a series of parametric analyses is conducted following an orthogonal experimental design with six factors at three levels. Through range and variance analyses of the computation results from 18 numerical models, the sensitivities of the slope stability to slope angle, slope height, joint angle, joint length, rock bridge angle, and rock bridge length are evaluated. Furthermore, a single-variable analysis method is adopted to build 24 numerical models with a focus on the aforementioned six key influencing factors to investigate the specific impacts of each factor on the slope stability, slope failure mode, and kinetic energy variation during the slope failure process. It is found that the fracture of the slopes with the en-echelon joints emerges sequentially along the joints and rock bridges from the bottom to top during the small deformation stage and reversals in shear stress direction are observed within the rock bridges during the detachment stage. The slope stability is found to be sensitive to the following six key influencing factors in descending order: joint angle, slope angle, slope height, joint length, rock bridge angle, and rock bridge length. A negative correlation is identified between the slope stability and the slope angle, slope height as well as joint angle while no clear linear relationship exists with the other three parameters. The numerical findings not only deepen the understanding of the mechanisms of step-path failure in rock slopes but also provide solid theoretical and data foundations for landslide risk assessment and prediction under complex environmental conditions.