Study On Deformation Mechanism And Evolution Trend Of Muyubao Landslide In Three Gorges Reservoir Area

After the water storage in the Three Gorges Reservoir area,the Muyubao landslide has begun to slowly regenerate and deform.Since the professional monitoring was carried out in September 2006,it has been in the creeping deformation phase.There are 140 villagers and 500 people and more than 140 houses in the landslide area.Once the landslide is affected,it will pose a threat to people's lives and property in the region,and endanger the shipping safety of the Yangtze River.Based on the collection and analysis of landslide-related survey results,this paper conducts field investigations and indoor finishing analysis work.Based on the actual geological environment characteristics of the landslide area,combined with the actual deformation monitoring results of the landslide,the in-depth analysis of the landslide deformation influencing factors and mechanical mechanisms is conducted.On this basis,a centrifugal generalized model of the landslide is established,and a test loading operation scheme is designed according to the water level regulation of the Three Gorges Reservoir area and hydrometeorological data of the landslide area to reproduce the entire process of landslide deformation under reservoir water fluctuations,rainfall,and coupling conditions.Analyze the response mechanism and deformation mechanism of the landslide in each period.Finally,Flac3 D and Geo-studio software were used to simulate the long-term effects of reservoir water on the landslide deformation evolution trend and increase the reservoir water decline rate.The following conclusions were obtained:(1)The Muyubao landslide is a rocky ancient landslide.The typical circle-chairshaped groove topography,the lower part is a convex gently inclined platform,and the middle and upper part is a circle-chair-like steep slope.Both sides are divided by Dalegou and cobblestone ditch.After the reservoir area is stored and maintained at 145?175?145m,the landslide will undergo periodic creep deformation.The leading edge and the borders on both sides are mainly local landslides.Many tensile cracks are developed near the trailing edge of the landslide.And accompanied by shallow soil collapse.(2)Based on the comparative analysis of long-term deformation monitoring data,it is clear that reservoir water level change is the primary cause of landslide deformation,and rainfall is only a secondary cause.The impact on the deformation and stability of the landslide is most significant during the first impoundment period.With the increase of the number of up and down cycles of the reservoir water cycle,the annual amount of deformation shows a decreasing trend as a whole.Based on the correlation between the water level changes in the reservoir area,rainfall and landslide displacement,the landslide period deformation is divided into four periods: the low-speed deformation stage of the landslide in the flood season ? the deceleration deformation stage of the reservoir water uplift landslide ? the landslide increase rate during the high water level and slight decline period Deformation stage ? landslide deceleration and deformation stage in the period of reservoir water disappearance.(3)The large geotechnical centrifuge test was used to simulate the entire process of the reservoir water ups and downslope deformation.By adjusting different reservoir water lifting rates in the test,the effects of reservoir water buoyancy,dynamic water pressure,and hydrostatic pressure on the deformation of the landslide during the reservoir water level change process are clear,that is,when the reservoir water lifting rate is small,the slope body The internal water level is basically synchronized with the reservoir water level change,the head difference between the inside and outside of the slope is very small,and the reservoir water buoyancy force controls the deformation of the landslide.After the rise and fall of the reservoir water rate,the water level in the slope lags behind,and the increase of the head difference between the inside and outside of the slope leads to an increase in the dynamic water pressure,which promotes the deformation of the landslide to be weakened during the rise of the reservoir,and the deformation obtained during the decline of the reservoir strengthen.(4)The landslide geological environment data,deformation monitoring results and centrifuge physical simulation test results summarize the deformation mechanism of Muyubao landslide as follows: the up-sloping and down-sloping chair-like topography controls the sliding deformation of the landslide,and the periodic reservoir water lifting process The buoyancy force of the reservoir water in the middle has the most significant influence on the stability of the landslide.The hydrodynamic pressure and the static water pressure at the leading edge during the same period will also restrict the deformation of the landslide.(5)Based on the deterioration law of the shear strength of sandstone under different dry-wet cycles,considering that the reservoir bank is subjected to a large drywet cycle every year,Flac3 D software was used to simulate and calculate the stability change law of the long-term reservoir landslide.Within 20 years of simulation calculations,creep deformation occurred on the whole landslide,the stability was reduced but it was still in a stable state,and no large-scale slip occurred.The east side of the back of the landslide is a strong deformation area of the slope body,and the deformation growth on the west side of the front edge is more obvious.Due to its good vacancy conditions,local bank collapse may occur.(6)Geo-studio software was used to study the stability of the landslide that increased the rate of decline of the reservoir water.It was found that with the increase of the rate of decline of the reservoir water,the internal wetting line of the slope body lags behind the reservoir water level.The stability at the beginning of the decline is the lowest.By changing the rate of descent in different periods during the decline of the reservoir water,it was found that moderately reducing the initial rate of the reservoir water level and increasing the rate of the later stage of the decline can help increase the overall benefit of the reservoir and reduce the impact on landslide stability.