Environmental Effects of Shuanghe Giant Landslide in Jiuzhai, Sichuan, China

Abstract

The Jiuzhai county is located in the northwest of Sichuan Province, China with high seismic intensity. There were a series of huge landslide damming events in the geological history resulting in beautiful lake or a wide valley in the reservoir. Shuanghe landslide is one of such landslides. Understanding of the mechanism of this landslide is the key to the future similar slope stability in the region of the similar slope. Based on a geological survey at a large scale, borehole drilling and core sample dating, it reveals that the landslide is located in the right bank of Baishui River, its source region is characterized by the high slope with counter-tilt structure, and the regional maximum geo-stress is perpendicular to the flow direction of Baishui River. Since the middle of Pleistocene, the river has incised intensively, causing the intensive unloading and stress field adjustment. As obvious toppling deformation of the high slope, a huge rock landslide was triggered by a strong earthquake that occurred about 30,000 years ago. The landslide overlapped the second Terrace, the accumulation is composed of huge block with a volume estimated at 250 million m³. The barrier dam existed for a long time until it broke, leaving a wide valley in the front of the barrier dam. Though the main part of Shuanghe landslide is stable, the front part can suffer from the river lateral erosion in the toe of the landslide accumulation. The environmental benefit includes a wide valley in the ever-reservoir area, providing the people with a satisfied site for construction of a new township. As the lacustrine silt sediments lie beneath the new county town, the bearing capacity and sand liquefaction could exist. A road construction cutting in the narrow valley at the toe of the landslide may dam the river again which could threaten the new county town.