Rainstorm?induced large?scale landslides in Northeastern Chongqing, China, August 31 to September 2, 2014

摘要

From August 31 to September 2, 2014, a 50-year heavy rainstorm hit the Northeastern Chongqing area, China, and caused 2340 landslides, including 80 large-scale landslides with volumes greater than 10 x 10(5) m(3). The distribution, characteristics, and conditions contributing to the formation of these large-scale landslides are still unclear. We conducted a comprehensive analysis based on collected rainfall data, field investigations, and remote-sensing data. The results show that the distribution of these large-scale landslides coincided with variations in the rainfall intensity, with the rainfall threshold for landslide formation inferred to be 200 mm. Most of these large-scale landslides occurred in areas with low-angle slopes formed of Mesozoic interbedded sandstones and mudstones. Three representative landslides of different types were selected for detailed assessment: the Laoyaopu landslide, which is a bedding rockslide; the Xianchi Reservoir landslide, which is a bedding rockslide-debris flow; and the Wushanping landslide, which is a rotated bedding rockslide-debris flow. The leading causes of these landslides are the topographical, geological, geotechnical, and rainfall conditions. The dip-slopes with large heights are naturally conducive to the formation of large-scale rockslides. The existence of interbedded sandstones and mudstones, and the presence of extensional tensile cracks at the trailing edges of slopes, facilitates the rock fracturing and separation required to induce landslides. Aided by these conditions, rainstorms are a crucial driver for the formation of regional large-scale landslides. These findings are essential for future disaster prevention and mitigation in this area and other areas that experience similar conditions.