Analysis On The Reliability Of Anti-seepage Curtain Based On Isotope-Hydrogeochemistry Method

Anti-seepage curtain is the key project of hydropower engineering in karst area.As an underground concealed works,working on the complex hydrogeochemical environment of high pressure permeability for a long time,its anti-seepage performance is of great importantce.This paper analyzes and studies the operation reliability of a typical representative hydropower project anti-seepage curtain in karst area of Guizhou from two aspects.On the one hand,white calcium precipitates,the main conponent is Ca CO3,is a common material in curtain grouting corridors of hydropower engineering in karst area.On the basis of existing research of precipitates,using the control variable thinking,the calcareous precipitation simulation test in indoor and curtain corridor,indoor anti-seepage curtain simulated penetration test and on-site sampling test on the curtain corridor were carried out,according to the relationship between the carbon in nature and the carbon component in engineering facilites,different physical state,chemical form and specific isotopic composition of carbon.According to the interrelation between solid-liquid-gas three-phase material,four types of tests and their samples were compared and analyzed by using carbon stable isotope assay.And according to the theory of carbonate balance and isotope fractionation,to research the sources,formation and evolution mechanism of white calcium precipitatesand and the relationship between them and the curtain seepage prevention performance of hydropower engineering in karst areas.On the other hand,the hydrogeochemical model of the dam foundation of hydropower station is reasonably generalized,on this basis,the combination of chemical thermodynamics,chemical kinetics,groundwater dynamics,mineral dissolution dynamics and hydrogeology multidisciplinary theory is developed a new method of hydrogeochemistry for solving hydrogeological parameters,namely,contacted Darcy's law and used water chemical indicators to express the analytical formula of hydraulic conductivity.Combined with the actual geological-water environment characteristics,fully consider the type and content of each component in the seepage water,the saturation index of mineral calcite,dolomite and gypsum in the water environment of dam site were calculated,runoff conditions were determined,and to divide the mineral solution-precipitation zone,which is shown by hydrogeochemical reaction-migration and differentiation in the seepage field of the dam site.In the different partitions,selection of corresponding analytical formula to calculate the permeability coefficient of Hydropower station foundation curtain,the calculation results are compared with the field pump-in test value and grouting curtain anti-seepage control value,then analyze the applicability and rationality of the method on the curtain.Based on this,the permeability of the anti-seepage curtain of a hydropower station was analyzed.Based on the above two aspects related research results,according to the engineering geological conditions,hydrogeochemical environment features of hydropower station,and in the running of phenomenon,such as water penetration,high pressure and calcium deposit,etc.Comprehensive analysis and evaluation curtain anti-seepage reliability under the operation condition of D hydropower station in karst,and provides reliable evaluation basis for subsequent research and reservoir safety.Through the study,the following main results are obtained.(1)The visible white calcium precipitates in the curtain grouting gallery of hydropower station in the karst are mainly derived from the hydration product Ca(OH)2 of the curtain cement grouting material.(2)The white calcium precipitates appearing in the gallery of hydropower project in the karst are the manifestation of the dissolution erosion of the curtain cement grouting.Its formation mechanism is the hydration products Ca(OH)2 dissolved under the action of seepage water,formed alkaline seepage water excretion in grouting gallery,and then react with CO2 from the air forming Ca CO3 precipitation,The chemical equation indicates that the process is: Ca(OH)2 + CO2(g)+ n H2 O ? Ca CO3?+(n+1)H2O(3)Using hydrogeochemistry to calculate the permeability coefficient of the curtain ground mass of the Karst area D hydropower station,and comparing with the result of the field pump-in test corresponding to the location,the results obtained by the two methods are in the same order of magnitude,the difference between the two results is very small,it is in good agreement with the field environmental index.The results show that the new method for calculating hydrogeology parameters is feasible for calculate the permeability coefficient of dam foundation seepage curtain,and the operation status of dam foundation anti-seepage curtain can be analyzed by using the calculated data.(4)According to the results of the comprehensive analysis,the curtains in each abnormal area on the anti-seepage line of the D hydropower station in the karst zone showed erosion and weakening in different degrees,and the performance attenuation of the curtain in individual abnormal areas is moreserious,monitoring and preventive treatment must be strengthened.the curtain and geology body of the left bank of the hydropower project were mainly mechanical erosion that caused by geologic structure,with mild dissolution erosion.The dam foundation is slightly dissolution erosion.Under the possibility of mechanical erosion caused by geological tectonics,the right bank plant area is mainly dissolving-erosion.Under the adverse geological structure condition,the right bank reservoir area is currently dissolving type erosion.There are no obvious abnormality in other parts of grouting gallery,anti-seepage reliability is good.The comprehensive evaluation suggested that The overall anti-seepage reliability of the curtain is good,which is in the "middle age period",it can meet the requirements of anti-seepage and the normal operation of the reservoir.