The Extenics Studying On The Bank Caving Prediction Of Changshou Area Along Three Gorges Reservoir

The type of Three Gorges Reservoir is a typical river valley, the reservoir area submerged include twenty six county (city or section) of Hubei province and Chongqing city , the water level is raised about 100m .The reservoir adopts method of impounding in winter and venting in summer after built , according to the initial designed report of the hydro-junction of Three Gorges reservoir, after the Three Gorges reservoir to be set up, the water level of dam will reach 175m, but the water level will keep 145m from the middle ten days of June to the end of September, from October to the beginning of April of the second year the water level will keep between 145m and 175m, the water level changes 30m .With the coming of impounding of the reservoir , the bank stability of the reservoir area becomes more important. The Changshou canton belongs to one of the 13 important towns of Three Gorges Reservoir area, the Changjiang River cross from the south of the area, and the length of drainage basin is about 20km. The Changshou canton, having more than 20 large and medium-sized industry business enterprises, is an important city of chemical industry, the main industry and the factory distribute in the slope of the left bank of the Changjiang River and the slope of Longxi river and Taohua brook .When the water level of Three Gorges Reservoir is 175m, the water level of surveying area will attain between about 175.3-179.60m .The high water level and higher water level changes, will effect on the bank stability, and induct the problem of bank caving. The eight surveying bank slopes of Changshou canton assemble residents, street, town, the industry area and factory area .After reservoir impounded, these bank slopes may be submerged, causing bank slopes caved, hazarding the safety of littoral residents, town and industry. Therefore, researching bank caving has important meaning. The paper ,taking a great deal of data as the foundation, detailed analysis the stability of the bank slope in Changshou canton, and carry on the prediction study about the problem of bank caving of each shore segment. Obtained the results of the following: 1. The 8 segments of Changshou surveying bank slope long 16.6km together, and is divided into 21 second segments totally, and two kinds: the soil bank slope and the rock. And the rock bank slope accounts for 64.3% of all, which mainly distributes to the left bank in the Changjiang River. The soil bank slope mainly distributes to the right bank of the Changjiang River, the left little, 2.9% only. The soil bank slope constituted mainly the loess form soil and the silty clay, and commonly the loess form soil in the right, silty clay the left and also the peach blossom river. While the rock bank slope constituted mainly the sandstone and the mudstone. And the structure of the bank slope mainly includes four kinds of: inclined to the layer inside, inclined to the layer outside, even slow layer outside and horizontal slope. Among them, the rock slope of inclining to the layer inside form is most widely, length for 4738m, and occupied 28.5% of a total length of shore. And the second is the horizontal slope, length for 3395m, occupies 20.5% of the total length, and the inclining to the layer inside, its length account for 1567m, 9.4% of the total length, while the least is the even slow layer outside, 967m only, occupies 5.8%.And the even slow layer outside slope all distributes to the right of the Changjiang River, and others mostly distributes to the left. 2. The bank caving of Changshou canton mainly has three kinds of modes: Erosion to abrasion type, slumping type and whole slipping type. The main mode is slumping, there is 14, accounting for 66.7% of the total; then the second is the type of Erosion to abrasion, there is 7, accounting for 33.3%; And the whole slipping type main appears in the front of Taohua brook~ cement works, the scale is not very big. 3. When predict the width of the bank caving with the method of numeration, the soil bank slope has bigger width, general above 40m, and most arrive to 60m, and the affecting altitude of the bank caving is about 181-190m, major exceeded the lowest baseline altitude(182m).The soil bank slopes most cave violently and two pieces compares mighty, and slightly only 1. Totally, the rock bank slope has stronger ability to resist the caving. The caving width of the rock bank slope is less compared with the soil bank slope, but the affecting altitude is higher. The width of the rock slope is majority below 58 m, only one exceeds, that is a 75m, the fifth segment of the Shantuo field. The affecting altitude lowest is a 183m, all exceeding the lowest baseline altitude (182m), highest is a 191m. The rock slope is caved stronger, 12 segments were caved strong, mightiness of 4, and compared with the soil slope, it is better. This is related with the slope property. Totally analysis, the rock bank slope has stronger ability to resist the caving. 4. The stability of the bank slope of Three Gorges can be divided into 4 classes: Stability good, the better, the worse, and the bad. Use extenics to evaluate the stability, can discover the stability of the Changshou canton is better .The stability classes is mainly the better with a litter worse, the second is the worse but with a little better. The stability of the soil bank slope commonly is the worse with a little better, and the second is the better with a little worse; but the stability of rock bank slope is better comparing with the soil slope.