| The planned Gushui hydropower station is located at the eastern edge of the Qinghai-Tibet Plateau, the upstream of the Lancang River. Research area belongs to high canyon landscape, where toppling deformation of layered rock mass at the bank slopes is strong.There are many large landslides evolved from toppling displaced mass, and Zhenggang landslide which is located at the right bank of the downstream of the hydropower station dam of about 1km is one of them. Zhenggang landslide is a giant rock ancient landslide which the average thickness of it is about 37.11 m, the area is about 128×104m2, the volume is 4750×104m3.The landslide deformation with many signs of revival is obvious recently, which constitutes a serious threat to the engineering construction and the safe operation of Gushui hydropower station.According to the survey, in the range of 20 km of the river downstream, the rock mass toppling deformation is strong with 4 large landslides. There are three problems to be studied as followed: the reasons of development of this kind of huge landslide with such a high frequency in such a short section, the formation mechanism of the strong toppling deformation and the process developing to a landslide, and the process of the giant landslide cutting out from the front hard basalt with 400 m thick in the front of Zhenggang landslide.Based on the mass of the research of Zhenggang landslide's basic characteristics,formation mechanism, evolution process and the stability evaluation and the toppling deformation characteristics of slope rock, Zhenggang landslide was studied. The main achievements obtained in the following the knowledge and research achievements:(1)The strong toppling deformation of slope rock mass is the result of multi factors, while the main internal cause is the special rock slope steep dip layered structure. Since the Quaternary Pleistocene, the high and steep valley free surface caused by strong, fast cut of Lancang River Valley provides a good space conditions for toppling deformation, and the strong unloading of slope rock mass caused by loading along with the quick valley cutting provides a further power source for toppling deformation in deep.(2)In this river reach, the main types of rock mass dumping deformation are toppling falling nappe,toppling creep and toppling-break?Its failure mechanism are mainly classified into four kinds of forms, namely shear rupture in the lay,shear rupture among the lay,tensile rupture in the lay and tensile- shear rupture.(3)Multi strip weak structural planes outward of the slope and two groups of the lower unloading fissure were developed in the basalt of the landslide. The formation mechanism of the landslide can be Summarized as two parts,namely the middle trailing edge of the anti dumping rock formations slip in the direction of the valley through dumping the broken section,under the load of upper rock mass and gravity,leading edge basalt is shearing-slipping along its internal slope to the weak structural plane and the low angle unloading fissure.(4)The evolution process of Zhenggang giant landslide can be divided into four stages:(1) Micro(not) deformation stage;(2) The stage of trailing edge dumping-bending creep and leading edge shearing-slip deformation;(3)The stage of trailing edge dumping and leading edge shearing-slip surface linking up;(4) Slide destabilization stages.( 5) Based on FLAC3 Dand GeoStudio, the present stability and the future evolution trend of Zhenggang landslide are studied. The results show that the stability of the landslide is better under the natural state. under the rainfall state, the middle and trailing edges of section?landslide accumulation bodys,the middle and leading edges of section?are likely to slip. |
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