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

摘要

The Jiuzhai county is located in area of the northwest of Sichuan Province with high seismic intensity.There were a series of huge landslide damming events in the geological history, providing beautiful lake or a wide valley in the reservoir.Shuanghe landslide is one among them.The mechanism study of the landslide is the key to the future similar slope stability in the region.Based on the large scale geological survey, drilling and time dating, it reveals that the landslide is located in the right bank of Heishuijiang River, its source region is the high slope with counter-tilt structure, the regional maximum geostress is perpendicular to the flow direction of Heishuijiang River, since the middle Pleistocene, the river has cut intensively, the intensive unloading and the stress field adjustment resulted in obvious toppling deformation in the high slope, and a huge rock landslide was triggered by a strong earthquake in 30000years ago, it overlapped over the second terrace, the accumulation is composed of huge block with a volume about 250 million m3, it dammed the river for a long time, forming a reservoir and then it broke, then left a wide valley in the reservoir.The main part of Shuanghe landslide is stable and the front part can reactive as the river lateral erosion in the toe of the landslide accumulation.The environmental effects can be concluded: there is a wide valley in the everreservoir area, providing the people with a satisfied site for new county town construction;as the lacustrine silt sediments beneath the new county town, the bearing capacity and sand liquefaction exist;the narrow valley in the front of the landslide, as the road construction cutting at the toe, the front part of the landslide can survive in the future, which may dam the river again which could threaten the new county town.