Hydrological and failure process of loess-bedrock fill slopes under continuous heavy rainfall

During extensive gully land consolidation projects on China's Loess Plateau, many loess-bedrock fill slopes were formed, which frequently experience shallow landslides induced by rainfall. However, studies on loess-bedrock slope failure triggered by continuous heavy rainfall are limited, and the role of the soil–rock interface between the original bedrock slope and fill slope in the hydrological and failure process of the slope remains unclear. In this study, we conducted a continuous rainfall model test on a loess-bedrock fill slope. During the test, the responses of volume water content, pore pressure, micro deformation, and movement of the infiltration front were observed. The hydrological process and failure mechanism were then analysed. The findings suggest that the soil–rock interface is a predominant infiltration surface within the slope. Rainfall infiltration rates at the interface reach 1.24–2.80 times those of the fill slope, with peak interfacial pore water pressure exceeding that of the loess fill. Furthermore, the infiltration front moves rapidly along the interface toward the bottom of the slope, reducing interfacial cohesion between bedrock and loess. The slope failure modes are summarised into three phases: local failure→flow slide and crack penetration→multistage block retrogressive slides. The cracks generated at the slope surface serve as key determinants of the geometry and scale of shallow landslides. Therefore, we recommend targeted engineering interventions to mitigate the instability and erosion of loess–bedrock fill slopes.