Temporary confined water responsible for triggering the landslide of a piedmont gentle slope in Ningzhen Area, China

Abstract. The traditional viewpoint is that a piedmont gentle slope is conducive to the overall stability of a mountain, which in turn has a counterpressure effect on the whole mountain. However, in recent years, with the increase in extreme heavy rainfall, some landslides have occurred in the piedmont gentle slopes in Ningzhen area. On July 6, 2016, a landslide occurred on the P0 slope of Paomashan Mountain, which is a typical piedmont gentle slope. After field investigation and analysis of monitoring data, we found that it was an intermittent creeping landslide, staged by initial deformation, isokinetic deformation and accelerated deformation. Survey data show that the slope has a very special stratum structure, that is, clay in the surface, coarse-grained soil or weathered rock in the middle, and bedrock in the bottom. In addition, the permeability of each layer is weak-strong-weak from top to bottom. According to the monitoring data, we found that temporary confined water (confined water formed and dissipated in a certain period of time that has never been encountered before) in the middle layer of the slope was the most important factor in inducing the landslide. Through numerical simulation, we analyzed the formation process and influencing factors of the temporary confined water. Finally, we propose effective control measures for this kind of landslide. The research results can be used in the treatment of similar piedmont gentle slope landslides in the Ningzhen area of China.