| The geological abnormal of Da sanmashan lied in Fengjie county in which the relocation of immigrants from the main city, located in the left bank of the Yangtze River. It is begin from the west of Lijia Gully, east to Dahe Gully, with an area of 92.41 hectares. The district has developed into economic and cultural center of Fengjie County with great significance of economic development. If deformation and failure,of the Dasanmashan Geological Abnormal occurred ,It will be a direct threat to the lives and property of thousands population, and cause very serious social implications.Therefore, we carried out an analysis of the overall and local stability in different states and different water level based on the identification of structure characteristics and formation mechanism. According to this, we can make a comprehensive evaluation by predicting the deformation. The result has an important theoretical and practical significance for the urban development, security risk assessment, prevention engineering measures, structural type and engineering design.In this paper, we treated the Dasanmashan geological anomaly as a research object. Based on the field survey and the early research results, we had identified geological environment, the basic characteristics and genetic mechanism combined with additional exploration drilling data at present. Qualitative analysis and limit equilibrium method had been used to make an evaluation of the whole body, and then we had got the local potential landslide stability of water level in the current situation; Additionally, the paper determine the reservoir water level fluctuation and rainfall seepage field conditions based on the the SEEP / W program of Geostudio. The main research contents and research results are as follows:(1)Dasanmashan geological anomaly is a giant ancient landslide which is deprive from the north edge of Kuizhou, south to Yangtze River, east to Sunjiagou, and developed from the Poyangping ditch in the west side. The front elevation is 100m, and the posterior elevation is 310m, the length from north-south is about 482 ~ 676m, and east to west is 745 ~ 936m. The area of the body is about 0.56km2. Landslide thickness is approximately 69 ~ 171m, the average thickness is 125m and the total volume is nearly 7500×104m3.(2)According to the field survey and monitoring data, the entire San-ma-shan abnormal geological body is in stable state. As the three edging secondary landslides have no evident deformation, so they are also in stable state.(3)We carried out slope stability calculation based on the limit equilibrium method for the Dasanmashan abnormal body and its potential secondary landslide.The results are as follows:①The overall stability coefficient is 1.735 ~ 1.84, and the coefficient of local secondary potential landslide is1.25 ~ 1.37. Therefore, all the landslide is in the stable condition.②The overall stability coefficient had dropped to 1.68 ~ 1.76 in the rainfall condition with a good stability; The secondary potential slope is also in a steady state with the stability factor of1.17 and 1.36. Rainfall has a greater impact which is compared to its nature condition. The rain has no effect on its stability as theⅡ-Ⅱ'profile of potential landslides are all located under the water level.(4)We constructed the model and studied the change of water level status and the regulation of the changes of groundwater seepage field, the results of the stability trend are as follows:①In the conditions of the water level sudden rise or sudden drop , seepage changed in the front of the sliding body significantly, while the flow field which is away from the reservoir banks will take some time to respond to these changes.②As the water level rising, the variation trend of stability presents the downward-upward style. The stability declines sharply at the beginning and it increases slowly and gradually after it reaches its lowest point. The overall and local stable coefficients are reduced to 1.58~1.61 and 1.17~1.22 respectively when the water level increases from 154 to 175 without rainfall, but they are still in stable state; the overall and local stable coefficients are reduced to 1.49～1.512 and 1.12～1.145 respectively when the water level increase from 154 to 175 with strong rainfall, but they are still in stable state.③The water level dropped in the process of evolution trend of decreasing its stability type, start O'clock decrease stability factor greater critical water level the lowest point in the post, its decline significantly slowing down, its stability was basically stable. Decline in water level (175 ~ 145m) and no rainfall, its overall and local stability of the coefficients were reduced to 1.29～1.32,1.065 ~ 1.082, in a stable ~ basically stable. Decline in water level (175 ~ 145m) and there is heavy rainfall cases, the overall and local stability of the coefficients were 1.251 ~ 1.28, 1.052 ~ 1.065, in stable condition.④we can draw a conclusion that the decline of water level has a greater impact on its stability and the it has dropped at 13% through contrast of during the change water level stability.⑤The heavy rainfall had an significantly affected on its stability when the water level changes. At first, the rainstorm had little effect on its stability, while its stability decreased with the time increase. Therefore, the infiltration of heavy rainfall may be the main factors of instability.
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