| Dagang Mountain power station will be built as one of the recent developed largehydropower projects for Dadu River.It was located in the middle canyon area of Daduriver in Shimian country, Sichuan province. The power station control drainage areawas62700km2, which occupy81%of the whole river and whose average dischargeflow rate is about1000m3/s for several years. The normal storage level of the dam was1130m, the back-water height of the dam was180~190m.And the storage capacitywas about742million m3, the installed capacity was2600MW.The early research suggested that: DaGang mountain region had complicatedbackground of geological structure, developed various geological structure of theproject district,many structure surface groups, large density, large scale, and poorintegrity of rock mass.Especially, the fault in the rock mass of the dam foundation andinvaded fai green dikes developed well, the rock fracture network brought by the faultfracture zone and its influenced zone and fai green dikes was complex, which madethe groundwater migration channel more changeful, brought difficult for damfoundation seepage control and the safe operation of the project.This paper, from the research area’s geological environment conditions,investigated the hydrogeological conditions and fill diameter row features of thegroundwater system in the dam site area. On the basis of finding out the crackdeveloping degree and scale in the rock mass of the dam foundation this paperregarded the rock foundation surface of the Dagang Mountain power station as theresearch object, deeply analyzed the space combination characteristics andpermeability of the crack in fractured rock, got the permeability coefficient ofdifferent space position in rock mass, and then used the Modflow software tocompared and evaluated the seepage field in the dam site area before and afterimpounding, and discussed the leakage of the dam foundation and abutment underdifferent working conditions.The main research conclusions of this paper were as follows:（1）Comprehensively analyzed hydrological, geological conditions of the damsite and also analyzed the groundwater types, filling size row conditions and dynamiccharacteristics.The major types of the dam’s groundwater was bedrock fissure water,according to the different buried conditions, which can be divided into the bedrockfissure diving and confined water; Bedrock diving mainly accepted the precipitationsupply, drained into the Dadu river and the surrounding valleys,which was affected by the climate. Bedrock fissure confined water not only can accept the surface watersupplies of atmospheric precipitation collection, but also can get far atmosphericprecipitation supply source, it drained in the form of the ground springs point in theform, whose groundwater dynamic was more stable and less affected by the climate.（2） Deeply analyzed the types and features of the rock mass permeability of thedam foundation. According to the space combination characteristics of the crackdevelopment, the rock mass permeate structure in the research zone can be divided intonetwork form and ribbon form. The network form was mainly composited by fractureof different matrix, and the ribbon was mainly formed by the fault fracture zone and itsinfluenced belt and injected dike. Combining with the fracture linear density, roughdegree, filling features and characteristics of permeability of the structure, the networkform were further divided into four grades. Due to the complex and changeablehydrological geology characteristics of the fault fracture zone and its influenced andinjected dike, it was included as a single grade in the hierarchical process.（3）On the basis of analyzing and calculating the pressing water test andpermeability tensor of the rock mass of the dam foundation rock, the paper evaluatedthe permeability of different rock mass permeate structure, the conclusion was that: thecomprehensive permeate coefficient of the rock mass of the left bank of dam foundationwas2.39x10-5cm/s, the comprehensive permeate coefficient of the rock mass of theright bank of dam foundation was5.58x10-5cm/s, permeability coefficient of the faigreen rock was1.05x10-4cm/s, and the permeability coefficient of the fault fracturezone was9.7x10-5cm/s.（4） Forecasted and evaluated the groundwater seepage field of the dam site areaunder different working conditions and the leakage of the dam foundation and abutmentby using Visual Modflow three dimensional numerical simulation software.On thebasis of simulation,this paper analyzed the groundwater seepage field and the change ofgroundwater under pressure in high water head;And forecasted the leakage of the damsite by simulating the balance module in the software.After storing water, the leakagequantity of the dam foundation was9836m3/d, the leakage quantity of the damabutment was1604.3m3/d, the total amount was11440.3m3/d.After adding thewatertight screen, the leakage quantity of the dam foundation was7244.7m3/d, heleakage quantity of the dam abutment was423.7m3/d.The above situation was causedby the penetrating fault fracture zone and its influenced zone and fai green dikebecoming into advantaged water channel after storing water.（5） Basing on the above results of the crack development characteristics in thedam site area, the penetration of rock mass and the simulation results of seepage fieldunder different working conditions, the paper had the idea that the fracture of the damsite area in Dagang Mountain power station developed well, which largely influencedthe project. And the paper suggested that we can reduce the leakage of the fracturedrock mass by taking the engineering measures of combining anti-seepage curtain withdale, and reduced the leakage of the ribbon permeate structure by rock massreplacement. |
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