Mechanism Analysis of Zulongding Landslide on Piedmont Slope: a Creeping Landslide Triggered by Rainfall

Abstract Due to increasing extreme heavy rainfall events, landslides have increased significantly on Piedmont slopes in Jiangsu Province, China, in recent years. The Zulongding landslide is a creeping landslide at the northeastern toe of Fangshan Hill, Nanjing City, Jiangsu Province, representing a typical slide on Piedmont slope. In July 2016, tension cracks appeared on roads near Zulongding due to rainfall, posing potential safety risks to the scenic area. Although the road cracks were sealed and repaired in time, the Zulongding area has experienced slow sliding, and the cracks are expanding slowly. On October 25, 2016, Zulongding experienced a large-scale, rapid slide caused by continuous heavy rainfall for 16-day as a result of the 2015–2016 EI Nino event. Field investigations, drilling holes, groundwater level monitoring, surface displacement monitoring, and numerical simulation were carried out to determine the geological features, deformation characteristics, sliding mechanism, and failure mode. An analysis of the monitoring data and the simulation results indicated the main reason for the landslide was a rise in pore pressure in the stratigraphic structure. As a result, the uplift pressure increased due to the confined water, decreasing the strength in the silty clay layer above the gravel layer and causing a slide. The deformation consisted of initial deformation, isokinetic deformation, and accelerated deformation. The seepage deformation and pressure balance theories are used to discuss the failure mode of the landslide. The results of this study contribute to safety evaluations and the prevention of similar landslide geological hazards.