| The engineering of Xinji reservoir is located in the Daxi river of Lingtai county in Gansu province, which is located in valley gully area of the southern edge of the Longdong loess plateau, growthing many gullys and covering a large loess areas, baring many bedrocks around the two sides of bank slope, the engineering geological conditions are more complex, and the engineering geological problems will have an adverse impact to the construction and operation of the Xinji reservoir. In this paper, based on the field investigation and indoor physical and mechanical test data, from the aspects of topography, lithology, geological structure and hydrogeological conditions, making a detailed analysis of the engineering geological conditions of the reservoir area and the dam area, and on this basis,making the in-depth analysis and research of the main engineering geological problems of reservoir leakage,seepage stability of dam, reservoir bank stability and bank collapse and the dam area of loess collapsibility, thus making a comparison of the upper damsite and the lower damsite from the two aspects of the engineering geological conditions and engineering geological problems, through the above research, this paper reached the following conclusions and understanding:(1) The Xinji reservoir is located at the southern margin of the Longdong loess plateau, the southwest margin of Ordos platform, main landform are valley mountains area and low mountain gully area, the river valley of the damsite area is relatively narrow, the left slope is steeply erosion coast, bedrock exposed, and right is slowly accumulation of land, covering a large loess areas, the stability of regional structure is good and have basic conditions for dam construction.(2) The dam abutment seepage and dam foundation seepage problems are existed in upper and lower damsite, the result of the test shows that from the slope belt of weathering to below the bedrock surface, the permeability changes in the range of 0.15～33.4Lu, it has certain influence on the stability of the dam abutment if there are not seepage preventions, the permeability q>3Lu of dam foundation rock surface under the range of 6m, q<3Lu below 6m.(3) The results from the three different seepage conditions shows that water level changes have influence on the dam seepage, especially in maximum flood level conditions, the location of the phreatic line is relatively more higher, the seepage water pressure of upstream dam is more higher and has obvious effect on dam safety, the location of the phreatic line of the case of normal water level and dropped dead water level conditions is significantly lower, less impact on the dam.(4) The analysis of the stability of the dam of three kinds of different working conditions shows that the stability safety coefficient of upstream dam slope are 2.641, 2.472,1.642, lowerstream dam slope are 1.957,2.023,2.269, the stability safety coefficient is less than the standard allows range and the slope of dam is basically stable.(5) The stability of bank slope will be destroyed when the reservoir is filled water, the major bank slope failure mode are erosion type, slip type, collapse type, landslide type, making a prediction to typical slope section of bank collapse through the graphic method, the result is that the reservoir bank collapse is larger, and lower damsite reservoir is larger than upper, it has certain effect on the reservoir normal operation, so taking control measures is necessary before reservoir filling.(6) Through the analysis of soil sampling, the loess collapsibility degree is more serious of upper and lower damsites on the left and right bank, so taking certain measures on the dam abutment soil before construction, the soil can be used as the dam abulment.(7) Through comparative analysis of the engineering geological conditions and decision evaluation of the main engineering geological problems, the Xinji reservoir upper damsite conditions better than lower damsite conditions, so determine the upper damsite as the proposeed damsite. |
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