Study On Environmental Hydrogeological Characteristics And Variation Regularity Of Karst Reservoir Dam Foundation

As the main carrier of dam seepage control,cement grouting curtain is inevitably influenced by high water pressure after dam impoundment,and the construction of dam will cause the original stress readjustment of the dam site area,which will complicate the environmental characteristics of the dam area.Combining with the environmental hydrogeological situation and the thought of "field" in engineering geology,this paper firstly summarizes the characteristics of seepage field in the dam site area on macroscopic and reasoning analysis,including the original seepage characteristics of both sides of the dam and the groundwater level in the early stage and the current two sides of the dam.The leakage of the corridor,dam foundation seepage,deep karst leakage,and so on,using the reservoir water,seepage of dam foundation,seepage of each elevation corridor,water temperature and temperature field of the dam body,such as the total dissolved solids,conductivity,ph value,constant ionic components,etc.The chemical field information of the chemical type,water-rock-curtain body,the change of calcium content and the transfer,to achieve the microscopic analysis on the environmental hydrogeological characteristics of the dam site,and use the relevant software to illustrate the variation characteristics and trend of seepage field,temperature field and chemical field,as well as the plotting of hydrogeological anomaly area.On this basis,according to the transfer of characteristic ions in the water environment,the main chemical reactions,the changes of the physical properties of the carriers and the degree of calcium loss,the seepage control performance and effectiveness of the curtain are evaluated.Finally,the following main conclusions are obtained:?The main vertical confluence of groundwater on both sides of the dam site drains,partly through the underground river system into the dam site downstream to the Wujiang River.?the construction of the ground water level due to curtain wall at the right bank end and the left shore curtain along the downstream side of the stable high water level,on the left side of the curtain line upstream of the stable low water level,the overall stability of water level,affected by the change of the reservoir water level is very small.?The influence of the reservoir water level change on the elevation Corridor,dam Foundation and deep karst leakage is not remarkable,in which the influence of the dam Foundation and deep karst seepage can be neglected,and the influence of the leakage of the elevation corridor shows a weakening trend.And with the elevation decrease the leakage of the phenomenon,the current corridor leakage is maintained under the 4L/min,the Dam Foundation total leakage is about 2.16L/min,the Dam Foundation Piezometric the water level is less than 1.5m,each dam foundation of the pressure strength coefficient is mostly less than 0.1,The measured uplift pressure is much smaller than the design value.?The dam site area amounted to four hydrogeological anomalies.The scope is small,each other is relatively isolated,the characteristic indicator shows partial coincidence;dam body temperature and Dam Foundation,dam Corridor seepage temperature is more stable,and the bottom reservoir to maintain about 2 ? between the temperature difference,indicating that the reservoir water and dam seepage in the temperature is not directly connected.?Seepage is the carrier of occurrence and transfer of hydrologic geochemistry anomaly.The increase or decrease of the characteristic ion content is the objective manifestation of the reaction between water-rock-curtain body,especially the dissolution of the curtain body;the high ph value,low percolation quantity and dry hole phenomena of the seepage point are the manifestations of the obstruction of runoff pathway.?The change and transfer of calcium content in curtain body can not only cause the decrease of seepage control performance,but also enhance the seepage control performance,the main chemical reaction equations have two,respectively Ca?OH?₂+H₂CO₃=H₂O+CaCO₃?s?,CaCO₃+ H₂O+CO₂?Ca?HCO₃?₂;With the loss of calcium and potassium sodium as the calculating indicator,the cement content of the curtain body is the failure criterion,and the cement content in the curtain body can dissolve about 1000 years in years.?The water chemical type is mainly HCO₃^-,followed by OH-and K⁺+Na⁺ type,and the reservoir water is consistent with the groundwater type.The normal seepage of corridor is basically consistent with the reservoir water or groundwater type,and the abnormal seepage is different from the type;the seepage of deep karst fault zone is different from that of reservoir water or groundwater type,far away from the influence zone of deep karst faults,and the deep karst seepage of dam Foundation differs from the type.?The dam working condition is good,there is no obvious and persistent or regular anomaly occurrence,is still in "young adulthood period",the impervious function of curtain body is still effective and reliable.