The Three Gorges Reservoir Fengdu-fuling Area Landslide Stability Evaluation And Prediction

To increase the storage capacity of the Three Gorges Reservoir,the Three Gorges Corporation intends to reduce the original non-flood season water level from 0.6m/d to 1.2m/d.After the increase in the decline is bound to change the reservoir area along the old landslides geological conditions and hydraulic conditions,may induce some of the old landslide resurrection or local resurrection.Therefore,it is urgent to evaluate the stability and risk prediction of the Fengdu-Fuling section of the Three Gorges Reservoir area,which is of great theoretical and practical significance for the disaster prevention and mitigation,forecast and early warning of the landslide in the reservoir area.Based on the geological environment conditions and landslide site investigation in three gorges reservoir Fengdu-Fuling area,through the field research,theoretical research,field test and numerical simulation and other means,the characteristics and regularity of landslide development in the study area are analyzed.According to the development characteristics of landslide accumulation and the interaction type between reservoir and reservoir,the reservoir landslide is divided into three types:rapid response of reservoir water,medium response of reservoir water,and hysteresisresponse of reservoir water.Study of landslide deformation mechanism,and evaluatethe stability of landslide under the condition of increasing daily drop.At the same time,the risk prediction model of landslide in the study area is established,for nocontrollandslidethe risk of the landslide under the condition of increasing the daily fall is predicted by site investigation decision method,AHP and the unascertained measure theory.The main results are as follows:(1)The total length of the study area is about 134 km,39 of which are not controlled,and 27 of which are controlled.According to the geological environment conditions,thereservoir bank is divided into two types: rock slope and soil slope.According to the lithology,the rock slope is divided into the slope of the carbonate rock group(I)and the slope of the clastic rock group(II).The soil bank slope is mainly composed of loose bulk deposits(III).There are 5 types of rock slope:nearly horizontal layered slope,inclined forward layered slope,inclined reverse layered slope,oblique layered slope and transverse layered slope;reservoir bankslope failure mode mainly has four kinds:sliding fracturing,slip bending,Creep sliding crack and collapse landslide compound deformation.(2)The right bank.Landslide is mainly distributed in the Jurassic middle shaxi temple ? class rock group.50% of the landslide is distributed ininclined forward layered slope,early deformation mainly with sliding fracturing and creep sliding crack.Landslide plane formmainly forshaft type,sliding surface morphology is mainly straight and curve shape,the average slope are more concentrated in the 10°<??20°.(3)Through the analysis of groundwater and landslide physical and chemical effect,mechanical effect and time effect,The results of the landslide accumulation are as follows:wading degree(?1<30%?30%??2?60%?60%<?3),overall form(leading edge thick margin thin?middle thick both ends thin and leading edge thin edge margin thick),material composition(pieceof gravel soil deposit,layered deposit and contain fragment stone silty claydeposit)and different depositpermeability(weakly permeable?permeability is Weak ~medium?permeability is medium~Strong).Based on the above research,the reservoir landslide is divided into three types:rapid response of reservoir water,medium response of reservoir water,and hysteresis response of reservoir water.At the same time,comparative analysis of different types of landslide deformation characteristics and deformation mechanism.The results show that the landslide of Tang Yakou is the most affected by reservoir water,followed by Xiang lutan landslide(?)and Hu Jiatuo landslide.(4)Based on SEEP/W,SLOPE/W modulecouplingin simulation software GeoStudio,simulation of seepage field and stability evaluation result shows that: 1)withreservoir water drop landslide gradually decline of groundwater,landslidewith rapid response of reservoir water underground water level descending velocity and water level drop rate basic synchronization,there is no hysteresis phenomenon;Landslide with hysteresis response of reservoir water there is a significant lag in the phreatic line,with the increase of water level drop rate,infiltrating online convex tendency is obvious;Landslide withmedium response of reservoir waterresponse speed somewhere in between.2)library during water levels from 175 m to 145 m,the overall stability of the landslide with the water level drop showed a trend of gradual decline,declining rate increase after the drop on landslide stability are increased.When the reservoir water level dropped from 175 m to 145 m,the overall stability of the landslide decreased gradually with the decrease of the reservoir water level,and the landslide stabilitydeclining rate increase after the dailydecline are increased.(5)Through the study of the effect of the landslide control project,the evaluation index system shows that:1)Have controlled landslide under the currentcondition,most of the landslide are basically stable to stable,with the increase of the daily drop,most of the landslide will remain basically stable to stable.2)No controlledlandslideunder the current condition,most of them arewhole stable to stable,a few of them are in the overall basic stability,local unstable;After the increase of the daily drop,most of the landslide is in the stable state.Most of the landslide in the overall basic stability to stable,part of the landslide leading edge appears local unstable and instability.(6)Landslide stability coefficient sensitivity calculation and analysis results show that:1)different day drop,the landslide stability influence coefficient?n=((Kn-K1)/K1)value has the following relations:?3>?2>?1,shows that with the increase of drop water,the stability of landslide is reduced greatly.2)Landslide stability influence degree by reservoir water day drop increases fastest decline for landslide with medium response of reservoir water,landslide with rapid response of reservoir water is second,and landslide with hysteresis response of reservoir water is small.3)Landslide with medium response of reservoir water ?1>(?2-?1)>(?3-?2);landslide with rapid response of reservoir water(?2-?1)>(?3-?2)>?1;landslide with hysteresis response of reservoir water ?1>(?2-?1)>(?3-?2).(7)By site investigation decision method,AHP,and the unascertained measure theorythe,select 10 correlation factors,such as landslide volume,engineering rock group,bank structure,wading degree,reservoir water response type,hazard in the study area is predicted under the condition of increasing the daily drop.The results show that the calculation results of the unascertained measure theory model based on the field investigation are more consistent with the actual situation,and the evaluation result has 94.8% guarantee rate,the prediction results are superior to the AHP evaluation model.The unascertained measure risk assessment model can determine the risk grade of the landslide disaster point,sort the risk,and calculate the reliability of the result has a high guarantee rate.