Study On Rivival Mechanism And Prevention Measures Of Outang Landslide In The Three Goeges Reservoir

Since impoundment of the Three Gorges Reservoir,rainfall infiltration and periodic fluctuation of reservoir water level have induced many ancient landslides to resurrect and deform.The characteristics of the reactivation deformation of ancient landslides in reservoir area are mostly step-like,so it is difficult to predict the stability of such ancient landslides.A large number of cities and towns or enterprises and institutions in the TGR are located on the ancient landslide.The resurrection deformation of ancient landslide may bring huge economic losses or casualties.Therefore,the study of the resurrection mechanism and treatment of the ancient landslide is an urgent problem to be solved.Taking the Outang landslide in the TGR as the research object,the formation mechanism,resurrection deformation mechanism and treatment measures of the ancient landslide in the TGR are studied.Based on field investigation,geological survey data and field monitoring data analysis for six years,combined with numerical simulation method,the following aspects are mainly studied: based on the field investigation data,long-term monitoring data and topography of the study area,the historical formation mechanism of the outang landslide is inferred;the revival and deformation mechanism of the ancient landslide in the reservoir area is analyzed and compared according to the field monitoring data and numerical calculation results;and the mechanism and economic advantages of the new drainage anti-slide pile proposed by the author in the treatment of the ancient landslide are studied by numerical simulation method.The main achievements of this paper include the following parts:(1)Based on the analysis of geological conditions and deformation monitoring data,and combined with the results of ESR test of the rock-soil body,it is concluded that the outang landslide can be divided into three secondary sliding bodies,and there are independent sliding surfaces in each sliding mass.Each secondary slide mass were formed in different ages.The formation ages of the first,second and third slide masses are about 120-130 ka,65-68 ka and 47-51 ka.Based on the above research contents,the inferences of the graded formation and different processes of outang landslide are put forward.(2)By analyzing the relationship between groundwater level,deep displacement,surface displacement,rainfall infiltration and periodic fluctuation time of reservoir water level of each secondary slide mass of outang landslide,it is concluded that the outang landslide presents the law of step-like resurrection deformation,and the main controlling factors of resurrection deformation in different areas are different.The deformation of the first slide mass is mainly affected by periodic fluction of reservoir water level.The deformation of the middle and rear parts of outang landslide is mainly affected by rainfall infiltration.(3)The seepage field and deformation characteristics of outang landslide under the rainfall infiltration,periodic reservoir water fluction and rainfall-reservoir water coupling effect are obtained by numerical simulation.The mechanism of rainfall infiltration and reservoir water level fluction on revival deformation of ancient landslide is revealed.The influence of rainfall infiltration on slope can be summarized as two aspects: 1)hydrostatic pressure: the pore pressure of the secondary and tertiary slides increases dramatically and the effective stress of the slides decreases,which results in the decrease of the strength of the rock-soil mass;2)hydrodynamic pressure: the pore water flow rate in the middle and rear parts of the slides is obviously higher than that in the front of the slides in the seepage field caused by rainfall,and the pore water flow in the rear edges produces greater thrust on rock-soil mass.The thickness of the rear sliding body is smaller,so,the erosion of the rock-soil mass by pore water is more obvious.The above two reasons lead to the rapid deformation of the second and third slide mass of outang landslide under rainfall conditions.The long-term periodic fluctuation of reservoir water level makes the mechanical parameters of rock and soil in the position of the fluctuation zone decrease and the erosion of reservoir water makes the interior of the sliding mass of the fluctuation zone "hollow".The seepage force pointing to the foot of the slope is produced by the falling of reservoir water,which eventually leads to the revival deformation of the front edge of the lotus pond landslide,and the closer to the surface of the slope,the more obvious the deformation is.(4)A new type of semi-hollow drainage anti-slide pile is proposed.This type of pile could drain groundwater from the sliding mass,and reduce the static and dynamic effects of pore water under the conditions of rainfall and reservoir water fluctuation.This pile can fundamentally reduce the revival deformation speed of the reservoir-induced ancient landslide.Finally,the reinforcement mechanism of this type of drainage anti-slide pile slope is expounded by numerical simulation method.