Research On Hydrogeological Conditions Of Leakage In Qianwei Hydropower Station Dam Site

The leakage problem of dam site area is one of the most frequent problems in the hydropower engineering. This paper is based on the proposed Qianwei hydropower station of Minjiang Avionics. Through field hydrogeological survey in detail, analysis of the geological environmental condition in the dam site area, groundwater pumping test of unsteady seepage, consecutive test, dissolution experiment, hydrochemistry analysis and microscopic test, this paper mastered detailed first-hand data. On this basis, it focus on the hydrogeological conditions on leakage, finds out the underground water system in the dam site area, and discusses the semi-karst erosion in the study area, and initially evaluatethe influence of semi-karst development to the construction of Qianwei hydropower project. In addition, leakage control measures are put forward by prelimilary. Paper main results are as follows:(1) The Qianwei hydropower station dam site area's physiognomy belongs to the low mountain landform. The exposed stratums are Quaternary overburden, Shaximiao Fm and Ziliujing Fm of Jurassic system, Xvjiahe Fm of Triassic system. Geological structure is simple. And semi-karst calcium sand (gravel) of phenomenon exists in the dam site area.(2) According to the aquifer medium type, groundwater in dam site area can be divided into: loose rocks of pore water; clastic rocks of fracture pore water; and bedrock fissure water which is the most main types.(3) Groundwater contain relatively high free CO2 in the study area. And pH value is partial neutral, salinity and conductivity value are on the high side. The major groundwater chemical types are HCO3-Ca and HCO3-SO4-Ca.(4) The groundwater in the dam site area is largely recharged by precipitation, running through the fissure channel and discharge to the lower part of reservoir. (5) The results of a test on several factors influencing corrosion rate of calcium sand (gravel) semi-karst show that: the calcium sand (gravel) semi-karst corrosion speed is slow in simulation of the actual hydrological conditions, and speculate that: in the natural conditions after the hydropower station impoundment, the calcium sand (gravel) semi-karst dissolution reaction is slow, and the calcium sand (gravel) semi-karst couldn't produce large leakage passages in limited time. In other words the calcium sand (gravel) semi-karst have small influence on the reservoir leakage.(6) The analysis results of the consecutive test show: Including of these water spots, 68 drill hole, 01 well, ditch-water beyond Zheng family bamboo grove, 47 drill hole, 59 spring and 12 spring, they belong to the same underground water system. The other water spots of 55 well and 56 well belong to another underground water system.(7) The underground water system in dam site area could be divided into five underground water systems: there are Shima River underground water system and Mindong Commune - Shunjiang Bridge underground water system in left bank; and Jiujiao Hole– Shipanshang underground water systems, Tangba Commune underground water systems, Hongshatui– Lanjia Dam underground water systems in right bank.(8) The reservoir impoundment will lead to the leakage of dam foundation and bypass seepage. The measure has been given to prevent leakage of the dam base and abutment in the dam site area.