Failure mechanism and dynamic characteristics of the Kuayanzi rockslide at the Qutang Gorge, the Three Gorges Reservoir, China

On August 14, 2025, the Kuayanzi rockslide occurred in Pingcao Village, Wushan County, within the Three Gorges Reservoir Area (TGRA). Although the rockslide was successfully mitigated by an early warning system with zero casualties, its complex failure mode and distinct dynamic characteristics present a highly valuable case study for geohazard research. To systematically elucidate its failure mechanism and dynamic evolution, this study integrates field geological surveys, close-range unmanned aerial vehicle (UAV) photogrammetry, physico-mechanical testing, and RAMMS numerical modeling. The failure was fundamentally controlled by a competent-over-incompetent lithological structure, comprising dolomitic limestone overlying thin-bedded argillaceous limestone. Long-term water-rock interactions progressively weakened the basal layer, while a funnel-shaped topographic catchment concentrated rainfall runoff into rear tension fissures, driving rapid pore-pressure accumulation during extreme precipitation. Calibrated via back-analysis, the RAMMS simulation accurately reproduced the entire initiation-entrainment-deposition sequence. The results reveal that the rockslide reached a peak velocity of 26.4 m/s and a maximum impact pressure of 1820 kPa. These findings underscore the coupled influence of lithological contrast, basal degradation, and topographic runoff concentration on rockslide initiation. Furthermore, this study demonstrates the robust utility of combining UAV-derived topography with dynamic simulations for comprehensive hazard assessment.