Dynamical process of the Hongshiyan landslide induced by the 2014 Ludian earthquake and stability evaluation of the back scarp of the remnant slope

Reinforcing a landslide dam and converting a landslide-dammed lake to a hydraulically engineered lake is a sound means to address this natural disaster. The Hongshiyan landslide-dammed lake reconstruction project provides an excellent example. However, the stability of the remnant slope is crucial to the reconstruction of this project. It is essential to analyse the formation failure mechanisms of the Hongshiyan landslide and evaluate the stability of the remnant slope. Combined with field investigations and unmanned aerial vehicle (UAV) 3D image technologies, the failure mechanisms of the Hongshiyan landslide and the stability of the remnant slope were qualitatively studied and discussed. The dynamic process and failure mechanism of the Hongshiyan landslide are significantly different to conventional landslides. The dynamic process of the Hongshiyan landslide can be divided into three stages: time-dependent deformation stage, earthquake-induced failure stage and an unloading recovery stage. The failure mechanism can be summarised as follows: tension–crush–shattering–sliding. The stability conditions of the remnant slope are worse than those of conventional landslides under the same conditions. Toppling and small collapse are possibly occurring at the back scarp of the remnant slope because of the steep slope gradient, well-developed tension fractures and frequent occurrence of aftershocks and rainstorms. Based on the density, opening degree, porosity and connectivity of the cracks, as well as instability risk probabilities, the rock mass of the back scarp of the remnant slope can be divided into three zones: the seismically damaged zone, the unloading damaged zone and the stable zone. To guarantee the safety of the remnant slope and reduce secondary earthquake or rainstorm disasters, corresponding comprehensive treatment measures must be taken to ensure long-term stability.