Back analysis of a debris landslide based on a real-time video recording: sliding process and post-slide investigation

A real-time video recording of the 2008 landslide in Nanmu, China is analyzed to reveal information regarding the format, velocity, post-failure characteristics and destructiveness of the slide. This recording indicates that the failure proceeded in three stages. Back analysis has found that colluvial deposits (residual slope deposits and cemented colluvial deposits) in a weakly cemented form were the internal factor that contributed to the failure, and that damage resulting from the Wenchuan earthquake in 2008 and focused rainstorms were the external contributing factors. A field investigation showed that the destructiveness of the slide involved integral pushing damage to the base of man-made structures and damage to buildings from the impact of rolling gravel. In the 5 years following the Nanmu landslide, the local landscape has evolved further with sporadic individual rock falls or local collapses along the sliding bed and boundary. Corresponding prevention practices for the secondary disasters have demonstrated that the combined measures, including the removal of accumulated gravel, installation of a passive prevention net on the sliding bed, construction of an underground diversion culvert and a retaining wall, have been extremely effective and economical during the past 5 years.