The Research On Karst Formation Of Yangqu Dam Site In The Upper Reaches Of The Yellow River

Yangqu Hydro-power station on yellow river which will be built on the canyon river reach 3 kilometers downstream far from Yangqu village and towns of Xinghai country in Qinghai province, the length of canyon is 3 kilometers. The dam area locates in the north of Tibetan plateau, with dry weather and less rainfall in northwest area. The stratu is lower permain system, limestone with huge thickness layers, dissolution pore and karst cave developed. This condition is unfavorable to the base of dam, which can also bring the bad effect after water storage of reservoir. So , there is great need to make a research for genesis mechanism and dissolution distribution law on semiarid zones on relatively higher altitude, and make services for engineering construction.On the basis of geological investigation data of statistic of Yangqu hydro-power station, togethered with geological environment of dam area and other study fruit of higher elevation and dry dissolution, geo-chemical measures are utilized to solve the question of dissolution evolution of this area. Many fruit are as follow:(1) Research of geological environment in upperstream of yellow river: This point contains geology background in upperstream area of yellow river, and topography and geomorphology, stratum lithology, geological structures, climat conditions, hydrology conditions, and modern history of geology evolution. These materials provide a foundation for the study of dissolution mechanism. In the process of geology evolution, Tibetan plateau uplifting and evolution of yellow river water system are discussed.(2) Study of dissolution distribution law in the dam area of Yangqu hydropower station: According to the field survey and boleholes data, togethered with fruit of Northwest institut materials, dissolution distribution law are summarized up systematicly. According to the surfacial geological investigation, geological data of drilling and drift, there exist dissolution area in area of downstream dam in both banks, and karst cave with size more than 20 centimeters amount to 30 places, 20 places out of 30 can be seen on the ground surface, exposed by drillings and drift amount to more than 10 places. The distribution features of dissolution area can be summed up heterogeneity and zonation along vertical and horizontal direction. In the horizontal direction, the dissolution area mostly distribute on the ground surface period 500 meters from the canyon to the downstream area or on the rock layer 30-70 meters far from the bank. Relatively, dissolution development scale features on the left bank is more than on the right bank. From the gound surface and drift investigation, most dissolution zones are along the faults zones and crack zones, take on moniliform distribution. The stretch orientation of dissolution zones is consistent with the tectonic face occurrence. So, they are controlled by the tectonic face. Karst caves are independent each other, and no dissolution pipes formed. According to the surfacial geological investigation, geological data of drilling and drift, there exist dissolution area in area of downstream dam in both banks, and karst cave with size more than 20 centimeters amount to 30 places, 20 places out of 30 can be seen on the ground surface, exposed by drillings and drift amount to more than 10 places. The distribution features of dissolution area can be summed up heterogeneity and zonation along vertical and horizontal direction.(3) Study of dissolution phenomena of Yangqu hydropower station: this paper divide the dissolution phenomena into 2 types, they are lake type and yellow river type(here is the lake type, that is before the formation of yellow river in this area, only under the effect of lake, dissolution is formed. Yellow river type dissolution is formed after the period of formation of yellow river in this area). According to the study of distribution features of dissolution, scale features, and characteristic of these 2 types of dissolution, history of dissolution evolution can be judged.(4) Formation mechanism of dissolution in yangqu hydropower station: dissolution formed is in the process of development of geology background and topography, and formation of dissolution phenomena of yangqu hydropower station also experienced long geological edge. According to the study of evolution history of 2 types dissolution of yangqu hydropower station, recognition of formation mechanism of dissolution in yangqu hydropower station will be deepened.