Study On Causation And Stability Of Temi Large-scale Ancient Landslide In The Upper Jinsha River

Severl large hydropower stations will be built in the upper Jinsha River, where is the hydropower stations rather concentrated area of China, due to it with large gap terrain, abundant water resources. A large number of ancient landslides are distributed in the area, and most of them along the Jinsha River valley. It is very significant to study the forming ages and formation mechanism of ancient landslides for the water projects in the region. Conducting the back analyse of the ancient seismic parameters of ancient landslides is an effective way to obtain the ancient seismic parameters and provide reference for today’s seismic hazard assessment and large-scale construction projects, since there is some relevance between the large ancient landslides and ancient seismics. The stability evaluation to the residual accumulation body has become a urgent problem to the construction of the reservoir, since the stability of the residual landslide accumulation body of ancient landslide will decrease after the water level rising.Located in the upper Jinsha River, at the border of Sichuan Batang and Tibet Mangkang, the Temi landslide is one of the typical ancient landslide in the upper Jinsha River, the scale of which is huge and it is about 12 km away to Batang county. In this paper, the formation mechanism, the back analysis of the ancient seismic parameters and the stability of the residue accumulation body of the Temi landslide is analysed based on the detailed field geological survey, the remote sensing interpretation, the laboratory experiments, numerical simulation and analogy analysis. The conclusions are as followings.(1) The Temi landslide occurred about 7,200 yr BP, which is an enormous ancient rock landslide about 2,110×104 m3, dammed the Jinsha River and formed a large area of landslide lake. The now existing of the landslide are the residual landslide accumulation body in the two sides of the Jinsha River.(2) It can be inferred that the Temi landslide may have been triggered by the special geological environmental conditions in the region and a paleoearthquake events. The paleoseismic events was about MS 7.0-7.6, and the epicenter was located on Xiongsong-Suwalong fault, about 8-30 km, roughly in the belt Shuimogou to Jili that the coast of Jinsha River downstream Temi landslide.(3) The process of Temi landslide formed and dammed the Jinsha River is divided into the following five stages: ?the rocks has loosed after the former seismic effectâ†'? the back edge crack and leading edge shearâ†'?high speed sliding â†'?the leading edge cross the riverbeds and was blocked by the other side and then climbedâ†'?the slope material accumulation and dammed the Jinsha river.(4) The Temi landslide residual accumulation body is stable under the natural condition and seismic condition(the earthquake intensity is used in this paper numerical simulation, similarly hereinafter) at present. When Batang hydropower station is completed and rich the normal water level, the residual accumulation body may local instability under natural condition, and the front body will failure under seismic condition, but the residual accumulation body will not overall failure. Some treatment measures must be taken in order to ensure the Batang hydropower station construction smoothly and operation normally.