The Centrifuge Modeling Test Of Mechanics And Stability Analysis Under The Normal Operation Of Reservoir For Sanma Mountain Landslide In New Main Site Of Fengjie County

The new Fengji County in Chongqing Province locates at the Sanma mountainwhose west boundary is Lijia gully, east boundary is Dahe gully and the south boundaryis yangtze river. The new re-constructive area of the new county is92.41hetares. Withyears’ construction and development, the district has became the political, economical,and cultural center of Fengjie county and had significant meaning for the economicaldevelopment and long-term stability of Fengjie county.After the site selecting and some geotechnical investigations, the SanmaMountain, where the main county locates at, is defined as a geotechnical anomaly,which has complicate geotechnical condition and broken rock structure. Whether thetectonism (fault) or deep slide (landslide) causes current situation and how about itsstability haven’t reach a consensus in the geological engineering sector of our country.Because of the lack of understanding to the mechanics of this landslide, we must facemuch confusion and many problems during the process of treatments for Sanmamountain landslide and new county developments. Furthermore, with the Three Gorgeshydropower project is built and put into use, the hydro-geological condition of Sanmamountain landslide, which affected by the cyclical fluctuations of the reservoir waterlevel, has tremendous changes. In such external factors, the change rules of seepagefield and the development trend of stability of Sanma mountain landslide become thepoint people focus on.So on the basis of the results of previous studies, this paper mainly focuses on thefollowing two aspects:1.Using the method of centrifuge modeling test to simulate themechanics and re-produce the process of how Sanma mountain landslide becomes,during the historical period of Yangzte River cutting down.2.On the basic of correct mechanics and structural characteristics of Sanma mountain landslide, we use theGeo-studio numerical modeling software to analyse the development trend of seepagefield and stability of this landslide, when the reservoir water level fluctuates from145m-175m at different rates. In summary, the main research results shows as follows:1. Firstly we Baseon the Detailed informations of site investigation, we ascertaininternal structure and the spatial distribution of the Sanma mountain landslide andestablish the appropriate geotechnical model and on the basic of the work mentionedupon, we built up the conceptual model and appropriate centrifuge test model correctly.Secondly, after understanding the core ideas of centrifuge modeling test, we do ratiotest and deduce the physical and mechanical parameters of materials we need during thetest, according to the similarity theory and multiple of model scale down andaccelerating multiple of centrifugal. Finally we complete the production of the model,according to the production process. During the test process of three times cutting downof Yangzte River, we completely record the deformation characteristics and put forwardthe mechanics of Sanma mountain landslide.2. The characteristics of Sanma mountain landslide seepage field affected by thecyclical fluctuations of the reservoir water level are in line with the law of the loose soilseepage field changes.(1).Seepage field of Sanma mountain landslide changed most obviously locates inthe leading edge of the landslide. For the reason of constant head supply, the seepagefields locate in the middle and back are in a state of dynamic equilibrium.(2).Although the water table of landslide affected by the drawdowm rate of waterlevel, the trend is consistent(3).When reservoir water level rises from the low water level to high water level,the soil infiltration rate of the leading edge of the slope is less than the rate of reservoirwater level rising, the increasing gradient of outside water head is greater thanincreasing gradient of internal water head, the outside pressure is greater than thelandslide internal water pressure, water infiltrates into the landslide, the Phreaticsurface of saturated seepage field of leading edge of landslide is concave and graduallystabilizes with the infiltration of groundwater.(4).When reservoir water level falls from the high water level to low water level,the soil infiltration rate of the leading edge of the slope is less than the rate of reservoirwater level falling, the decreasing gradient of outside water head is greater thandecreasing gradient of internal water head, the outside pressure is lower than thelandslide internal water pressure, water infiltrates out the landslide, the Phreatic surface of saturated seepage field of leading edge of landslide is convex and graduallystabilizes with the infiltration of groundwater.(5).During the process of Cyclic fluctuation of the reservoir level, the change ofgroundwater level of Sanma mountain landslide compared to change of the externalreservoir level has a significant hysteresis.(6).The lasting rainfall has little effect on the groundwater seepage field of Sanmamountain landslide.3. By two-dimensional stability analysis of three representative cross-section ofSanma mountain landslide, the results showes that:(1).Landslide stability factor shows a trend of increase with the drawdown ratedecreasing.(2).During the process of reservoir level dropping from175m to145m, if withouttaking into account any measures, the less stable state of the HouZishilandslide,LaoFangzi landslide and ZhiWuyouchang landslide locating at the leadingedge of Sanma mountain landslide appears at the lowest water level.(3).The stability of Sanma mountain landslide is mainly controlled by the changeof the reservoir water level, the Infiltration caused by the rainfall has less impact on thestability.