FORMATIONG MECHANISM OF LARGE-SCALE LOOSE SEDIMENT AT THE RELOCATION SITES OF WUSHAN COUNTY ON THE THREE-GORGES

Investigation, identification and evaluation of the large scale loose deposits sediments at the relocation sites of Wushan County on the Three Gorges are discussed . A large number of the excavated sections show a complex accumulation of the sediments formed by tectonic process and karstification, and reveal a sliding zone between the loose deposit and bed rock. The sediments consist of landslidemass, rockfall,debris,karst collapse mass, etc. The thickness of the sediments determined by high resolution shallow seismic detection is 40m to 60m and can be divided into three wave velocity layers. A comprehensive conceptul model is set up and UDEC method is applied to simulated it. The formation and evolution process of the loose sediments can be divided into four stages geologic energy accumulation, fault system formation, rebound deformation and unload fracture, and epigenic reworking. Karstification is important to control the whole process.