Hydrogeology of Dongfeng Hydropower Station

The drainage area above the dam site is 18 16 1 km2, and the once-in-a-millennium design flood flow is14200m3 per second. The normal water level of the reservoir is 970 meters, and the corresponding storage capacity is 65.438+0.25 billion cubic meters. The dead water level is 936 meters, with a corresponding storage capacity of 535 million cubic meters. The regulating capacity is 490 million cubic meters, which is an incomplete annual regulating reservoir. The reservoir flooded 564 hectares of cultivated land, and the immigrant population was 80 18. When the normal water level of the reservoir is 970 meters, the regulated storage capacity is 490 million cubic meters. The inundation of the reservoir area involves Qingzhen, Zhijin and Qianxi counties. According to the preliminary investigation of 198 1, the population needs to move to 808 1, 8454 mu of cultivated land (including paddy field 1954 mu) and 2 124 mu of forest land is flooded. The site is a slightly asymmetrical U-shaped valley with narrow riverbed and steep bank slope. There are 75 ~ 85 cliffs along the river bank, and the water surface is only 50 ~ 60 meters wide in dry season. The dam site area is structurally stable, the basic earthquake intensity is lower than ⅵ, and the dam base is limestone of Yongningzhen Formation of Lower Triassic, with hard, dense and complete lithology and monoclinic structure. There are no large structures passing through the dam area, which is suitable for building high arch dams and large underground caverns. Both the dam foundation and the reservoir head are limestone strata with karst development, and shale with a depth of about 100 m and a thickness of about 40 m under the dam foundation is used as the water-resisting layer. The chord length of the river bend on the right bank is 2.5 kilometers, and there are two karst systems, fish cave and cool wind cave, which are connected at the height of 9 15 meters to 930 meters. In order to prevent karst leakage after reservoir impoundment, concrete sealing and curtain grouting are used to prevent seepage. The curtain is 3,664m long, the impervious area is 550,000m, the curtain grouting is 32 1.5m, and the maximum hole depth is1.20m. The principle of "reducing, slowing and avoiding" is adopted to treat the leakage zone in the reservoir area by stages. The curtain is 1 row ~ 2 rows of holes, and the hole spacing is 2 ~ 3 meters. Grouting adopts high-pressure grouting with closed orifice from top to bottom, and the maximum grouting pressure is 5MPa. 1995 except for the curtain of about 20,000m in the upper layer of the reservoir area, the rest is basically completed. Since the operation of 1994, the normal water level has reached more than 970 meters. The patrol inspection results show that the curtain seepage control effect is good, no abnormality is found on the downstream banks, the rock mass of the two abutments is dry, the seepage of the underground powerhouse has no obvious change before and after water storage, and the total seepage of the 40 main drainage holes in the dam foundation corridor is less than 40 liters/minute.