Simulation of the Q 2 loess slope with seepage fissure failure and seismic response via discrete element method

The Loess Plateau has a history of frequent landslides. Considering the Xiangning landslide that occurred on March 15, 2019, in Shanxi Province, China, a numerical slope model was constructed using the PFC 3D discrete element software. A tension fissure and building load were set on the top of the slope to elucidate the slope instability mechanism and failure evolution process under the condition of surface water infiltration. The failure process and dynamic response of the loess slope in this area were analyzed by a seismic wave load input into the model. The results show that the instability process of the loess slope under water infiltration into the fissure can be divided into four stages: subsidence, extrusion, failure, and stability. Under earthquake motion, the slope began to suffer damage from the shoulder and toe of the slope, with a final sliding crack surface occurring near the fissure. Additionally, the failure surface of the slope top changed at 25 m from the free surface to 22 m, while the accumulation body at the toe of the slope changed from a length of 80 m in the direction of the gully to a length of 280 m. The peak ground acceleration (PGA) amplification factors (PAF) of the loess slope are as follows: free face (range: 1.73–4.5), elevation (range: 1.01–1.72), and fissure face (range: 1.40–1.55). The results provide a theoretical basis for reducing the instability risk of loess slope in this area.