| Baihetan Hydropower Station is located in the lower reaches of Jinsha River.The dam site is about 45 km away from Qiaojia County,Yunnan Province.Its design water level is 765 m and its maximum water level is 825 m.The project will be completed in 2022.It is the second largest hydropower station in China after the Three Gorges hydropower station.About one third of Qiaojia County will be submerged under the normal storage level of Baihetan Reservoir.Qiaojia giant ancient landslide is located in the rear of Qiaojia County,where the regional geological structure background is complex and the neotectonic movement is strong.It is located in the seismic intensity_area.There are strong earthquake records in modern times,and it has the possibility of strong earthquake recurrence.Earthquake,heavy rainfall and reservoir water fluctuation will be the key factors affecting the stability of Qiaojia landslide.Therefore,it is of great significance to study the stability of Qiaojia giant ancient landslide under earthquake,heavy rainfall and high water level.On the basis of collecting and sorting out the geological and hydrogeological data of the study area,combined with remote sensing images and field survey results,this paper analyzed the distribution characteristics and causes of Qiaojia giant ancient landslide.By using limit equilibrium method and particle flow simulation software,the deformation and failure characteristics and stability of ancient landslide under the conditions of current situation,heavy rainfall,strong earthquake and reservoir impoundment are analyzed.The main conclusions are as follows:(1)Qiaojia giant ancient landslide is located in the triangle zone where Jinsha River and Niulan River meet.Its accumulation body is 5.5 km long,9 km wide,and its average thickness is about 250 m.Its coverage area is about 80 km 2,and its overall volume is about 1.2 billion m3.Its main sliding direction is about 260°?280°.There are five large-scale active fault zones nearby.The overall strike of the main fault wall behind the landslide is consistent with the regional tectonic line,and the receiving area is the same.The influence of geological structure is obvious,and the development of landslide steps is obvious.The front of landslide body protrudes to the opposite bank of Jinsha River,forcing the abnormal bending of Jinsha River.(2)The formation of ancient landslides is mainly influenced by faults,neotectonic movements,earthquakes and water.The geological structure in this area is complex,and the faults and folds are well developed.The eastern,southern and western regions are surrounded by a large number of deep faults and their derivative faults.The crustal uplift caused by Himalayan movement provides the basic conditions for the formation of Qiaojia giant ancient landslide.The ancient landslide is located in the area of degree earthquake intensity and is very vulnerable to strong earthquakes.The climate vertical change in Qiaojia area is dramatic.Intense rainfall destroys the underlying strata and produces creep zones,which leads to landslides.(3)The calculation results of limit equilibrium method show that the ancient landslide is in a stable state under natural dead weight condition,while the stability is reduced under saturated condition,it is still in a basic stable state,and the landslide is in an unstable state under strong earthquake condition.(4)The stability of landslide under different working conditions was studied by using the numerical simulation software of particle flow.The simulation results show that the landslide will lose stability under strong earthquakes;the ancient landslide is more likely to be damaged in the middle of the landslide under the condition of strong earthquake coupled rainfall;if the reservoir is impounded and then strong earthquake occurs,the part under the influence of seepage field will be damaged first. |
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