Investigations on the initiation mechanism of rainfall-induced loess landslides driven by sinkhole-assisted seepage: a case study in Qinghai, China

On 4 September 2024, a sudden loess landslide occurred in Henagou Village, Qinghai Province, China, after 19 h of rainfall (44.9 mm), causing three fatalities and one injury. Field investigation revealed that pre-existing sinkholes and their connected subsurface seepage pathways played a key role in slope failure. Rainwater was preferentially captured by sinkholes and rapidly conveyed toward the weak band, where wetting-induced softening and pore-water-pressure increase significantly reduced slope stability. To clarify this process, we combined field surveys, double-ring infiltration tests, laboratory shear tests, and FLAC 3D hydro-mechanical simulations. The results show that sinkholes acted as efficient preferential-flow conduits, accelerating infiltration and promoting localized pore-pressure build-up along the weak band. This led to concentrated shear-strain development and rapid displacement growth, with the simulated initiation time reaching 18.8 h after the onset of rainfall. Comparative simulations further indicate that sinkhole-assisted seepage substantially shortened the pre-failure period relative to the case without sinkholes. The study highlights the critical role of sinkhole-controlled preferential seepage in rainfall-induced loess landslides and provides a useful basis for hazard recognition and risk assessment in similar loess regions.