A Study On Engineering Geology Of Chaoqian Reservoir And Suitability Of Dam Construction

Chaoqian reservoir is located in the Southwest Prefecture of Guizhou Province,which belongs to the karst area. The regional engineering geological conditions are socomplex that the engineer geological problems about them can have an adverse effecton reservoir construction. Given this, the system analysis of the regional engineeringgeological conditions will be done through formation lithology, geological structureand hydrology condition in this dissertation. Based on these analyses, the engineergeological problems of reservoir and the suitability of dam construction will bediscussed with the leakage of reservoir and the dam foundation stability. By the aboveresearch, this paper draws conclusions as follows:(1)The basic seismic intensity of reservoir region is Ⅵ; theregional stability isfine; the probability of the reservoir induced seismicity is very small.(2)The valley of main impoundment area is a cross valley, it’s U-curve andasymmetric. Tianjia valley is a consequent valley. The reservoir region is manly ofdissolution landform and denudation landform. The karst caves and spring aredeveloped. The continuity of rock formation is good. The rock mass in both side ofdam site are stable. In total, there are few poor geological phenomenon and enoughfactors for building reservoir in reservoir region.(3) There is a fault through dam site. The width of fault is5meters. Contrastwith the right bank, the left bank has worse rock masses quality, higher waterpermeability and stronger dissolution landform. In consideration of the short ofBaishi valley and the connection of Tianjia valley, the region of optional dam site isvery small. Additionally, there is a hydraulic drop at lower reaches, so the option ofdam site is only one.(4)The altitude of ground-water divide and most the karst caves and spring arehigher than normal pool level; the hydraulic connection between ground water andsurface water is well; so the possibility of the leakage between two valleys is small. (5)The dissolution landform of both side bank are strongly developed, the leftbank is stronger than the right. The left bank has worse rock masses quality. The leftbank is more severely influenced than the right by the fault. There are lots of jointsurfaces in both sides. So the leakage of dam abutment is possible, and the left bankhas more possibility.(6)The fault, bedrock fissure, and karst pipe in dam foundation may causeleakage of dam foundation. The leakage depth may generally reach twenty-fivemeters. Imperious curtain is an useful suggestion.(7) Synthesizes all of engineering geology conditions, gravity dam is the bestoption. The weakly weathered dolomite can be used as the foundation rock holdinglayer. The excavation depth of dam foundation should larger than five meters.(8) The global stability of dam is studied with overload method, strengthreduction method and partial coefficient method respectively by FLAC3D. Theoverload coefficient is3.5. The strength reserve coefficient is3.7, both of them largerthan stability coefficient, which number is3. The overload coefficient of partialcoefficient method is1.15. The strength reserve coefficient of partial coefficientmethod is1.25, both of them larger than stability coefficient of partial coefficientmethod, which number is1.08. These results show that the dam has a certain overloadability and strength reserve, it’s safe.