The reactivated mechanism of Aniangzhai ancient landslide in Danba County, China

Abstract

This study presents a catastrophic landslide that occurred on June 17, 2020, on the left bank of the Xiaojinchuan River in Danba County, Sichuan Province of China. This landslide was a large-scale reactivation of the Aniangzhai ancient landslide. The failure event blocked the Xiaojinchuan River, induced a landslide-outburst flood disaster chain, destroying a 6.6 km-long section of national road G350 and causing significant economic losses. Based on field investigations, unmanned aerial vehicle surveys, and geophysical prospecting, this study unravels the causing factors and reactivates the landslide mechanism. The results suggest that the topography and unconsolidated rock-soil mass are predisposing factors for reactivation. The hourly precipitation within three hours reached 61.80 mm and induced the Meilong debris flow. The debris flow rushed into the Xiaojinchuan River and converted it to flow along the foot of the Aniangzhai ancient landslide. The intense scouring of slope toe caused by the rise of river level is the inducing factor of the landslide. Based on the geometry and geomorphic parameters, the landslide can be divided into four areas: leading edge collapse area, middle bulging area, upstream cracking area, and downstream cracking area. The reactivated Aniangzhai landslide could be determined as a compound landslide involving incipient retrogressive failure and latter progressive slide. Several cracks had developed in the upper part of the slope due to the movement of the landslide, and the four areas of the reactivated landslide mass were still creeping. A detailed monitoring and mitigation measure should be paid to this reactivated deposit.