Study of Seismic Dynamic Response and Instability Failure Patterns of Fractured, Loosened, Unloaded Slopes at a Hydropower Station on the Lancang River

In high-altitude, frigid regions, the coupled effects of permafrost thaw-freeze cycles and weathering erosion are pronounced. These areas develop extensive fractured, loosened rock masses with pronounced relaxation characteristics and poor stability. Under seismic loading, such formations are highly susceptible to instability and failure, posing significant threats to hydropower project construction and operation. To this end, this paper takes the slope of a hydropower station on the Lancang River as a case study. Using UAV aerial surveying and interpreting three-dimensional point cloud data, the dominant structural planes within the fractured and loosened rock mass were identified. A 3DEC discrete element model—a true three-dimensional numerical model—was established for the slope. The study investigates the response patterns of acceleration, velocity, and displacement, as well as the failure modes of the fractured and loosened rock mass slope under seismic loading. Results indicate that the acceleration response of fractured and loosened rock slopes to seismic loads exhibits distinct elevation amplification and surface-oriented effects. Under seismic loading, slope failure initiates as near-surface overturning deformations, triggering stepwise sliding-and-shearing failure of the upper fractured and loosened rock mass. This process is accompanied by localized overturning and toppling of fractured and loosened rock blocks.