| Through the field geological investigation from Xichang to Puge alonge Zemuhe fault zone, several catastrophic landslides of tens of million in volume distribute in Qiaowo town. The region along Zemuhe river is important areas for the local economy development, and there is an unique path there from Xichang to Ningnan. Also, there will be 4~6 cascade hydropower stations builded at the downstream in Heisuihe river. Daqing fault and Chechejie fault are the most active sections of Zemuhe fault zone, and landslides are the main reasons of blocking the Xining highway. There happened high-magnitude earthequakes of many times with seismic geological condition. The magnitude of this area is estimated to be 7.2~7.7, and its Dangerous urgency is A class. Under the background of the above, the investigation and study of development characteristics in this area and the research of the genetic mechanism of the huge landslides have theoretical and practical significance.the author uses the methods such as: collection of the existing research achivements, field investigation, statistical analysis, semi-qualitative analysis and numerical simulation of 3DEC, to study the development characteristics and the genetic mechanism of the huge landslides. We have got several following conclusions.(1)Huge landslides distribute on the right bank of the Zemuhe river, and concentrate in the area of about 12 km upstream and downstream of Dacaohe river. large-scale landslides distribute on the driving plate of Zemuhe fault zone,and concentrate in the overlap of the Daqing fault and Chechejie fault. Landslides develop in the strong-cutting area of the tributary and the most elevation range is 1750~2700m. The development of landslides is controlled by the structure of the slope, and they distribute in the slopes of angle in 39°~55°. No large-scale landslide deposit are found in other areas.(2)The typical plane form of landslides are tonguelike, striplike, calabash-shaped, irregular shapes, and so on, but not chair-shape in gravity environment. And it has the properties like that the length of the landslide scope is longer than the width, the deposits of the landslides spread uniformly. The slope shape of present and foregone is roughly “concave-convex-concave”, and the landslide surface pass through the slope crest, also, the deposits are primiarly in the form of low-angle platform. In the aspect of material composition and structures, the deposits are disordered, unstratified, different along the main slide direction and from upstream to downstream.(3)In the aspect of movement characteristics, the main slide orientation are about in the azimuth of 55°~71°. In other words, the deposits interest the falut zone in large angle. The displacement of the landslides are more than 1000 m, and the longest distance of the landslides is evaluated about 2100 m. The huge landslides present the characteristics of high-impetus and long-ran debris flow, and its movement characteristic value is about 0.3582~0.4.(4)The landslides along the Zemuhe fault zone formed before 11.7~1.26 thousand years, and this period is the most active epoch in the development of the Zemuhe fault zone.(5)Large-scale landslides is controlled by the large-magnitude earthquake, slope structure, micreorelief of three facing empty. The typical genetic mechanism of the landslides can be generalized to “Shaking loose-slip along bedding-joint tracking-Collapse sliding- depositting and compacting ”.(6)Through the 3DEC model simulation, this paper studied features of the seismic dynamic response, deformation, failure, long-run movement of the typical landslide of this area. And the results of the simulation is consistent with the field investigation. |
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