Engineering construction (e.g. water conservancy project, transportation engineering, and so on) in mountain areas bring mass of discarded soil and rock, whose stability is critical to the ecological environment and the safe operation of engineering facilities. For this reason, engineering assessment on stability and dynamic analysis after failure are important for the selection and design of landfills. The biggest Disposal site of Pumped Storage Power Station Project in Hunyuan County, Shanxi Province, China, with a volume of 7 million m3 and a maximum height of 240 m, is to be located at the upstream of Mahua Valley. To evaluate the impact of the slag dump on the buildings in the ditch, the kinematic process and the effect of the deposit mass on the engineering facilities were conducted by numerical simulation, utilizing PFC, depending on the depict of the engineering geological condition of the deposit area. Our simulation results clearly display scenario-based debris mass run-out paths and indicate that, considering the worst case scenario, the ground ventilation platform and ventilation tunnel exit might be rapidly destroyed by landslide debris. The results are useful information for decision support and future hazard assessment.