| From 1950s to 1960s,a large number of new dam projects were built in China.However,in recent years,some dams located in karst areas began to experience different degrees of leakage,instability and other dangers under the coupling effect of seepage pressure of dam foundation and chemical erosion of karst water.After a lot of investigation and analysis,it was found that the continuous attenuation of seepage control and reinforcement performance of dam grouting curtain was an important cause of the danger.Therefore,this thesis relies on the national natural science foundation(NO.52108389),the doctoral postgraduate foundation(NO.2022M713654),the natural science foundation of hunan province(2021JJ41086),the outstanding youth project of hunan provincial education department(20B596)and other research methods,such as theoretical analysis,laboratory experiments and numerical simulation.This thesis reveals the deterioration mechanism of dam grouting curtain in karst area under seepage and ion erosion,finds out the performance deterioration law of dam grouting curtain in karst area,and puts forward a life prediction method and optimization design method suitable for dam grouting curtain in karst area.The main research contents and conclusions are as follows:(1)By exploring the influence of seepage flow and aggressive ions on the internal structure and material composition of grouting curtain,the seepage erosion mechanism and ion erosion mechanism of grouting curtain in karst water environment are revealed.Based on the theory of transmission,the mass balance equation between calcium ions dissolved by curtain and aggressive ions mainly existing in karst water environment and the concentration balance equation in a certain mass transfer direction are deduced.The results show that the diffusion characteristics of erosive ions in karst water are influenced by both seepage pressure and ion reaction rate,and the second derivative of calcium ion concentration and the second derivative of each erosive ion concentration are linearly combined in a certain mass transfer direction.(2)A set of sample preparation device suitable for grouted stones in karst area was developed,and the laws of compressive strength,porosity,mass loss and micro-morphology deterioration of cement grouted stones and cement clay grouted stones in karst water erosion environment were obtained through accelerated erosion tests.The results show that within 120d after curing in karst water,the strength of stone body in group A is reduced from 32.89MPa to 20.03MPa,and the porosity is increased from 26.06%to 33.91%,while the compressive strength of stone body in group B is reduced from 3.89MPa to 2.03Mpa,and the porosity is increased from 58.04%to 77.01%,which indicates that karst water environment will accelerate the deterioration of stone body and make the strength of stone body increase.Under the action of karst water,the quality and micro-morphology of the two groups of stone bodies have changed,and the cement clay grouting stone body is more affected by karst water erosion than the cement grouting stone body.(3)Based on the deterioration law of grouting stone body obtained from the test,the failure control standard of grouting curtain for dams in karst area is put forward.Based on the grey prediction theory,the deterioration law model of compressive strength and porosity of grouting stones with service time is established,and the calculation formula of grouting curtain life under different control indexes is derived.Considering the service effect and service performance requirements of grouting curtain,a set of life prediction process of grouting curtain for dams in karst area is proposed.After testing,the variance ratios of the four prediction models are 0.1805,0.1816,0.2471 and 0.1386(all less than 0.35),that is,the prediction accurac y of the deterioration law model is good;According to the requirements of seepage control and reinforcement,the service life of grouting curtain A is about 70.59 years,and that of grouting curtain is about 58.36 years.The comparison of the service life prediction results of the two groups of grouting curtains is consistent with the law obtained from the deterioration test,which also shows that the proposed prediction method of the service life of grouting curtain for dams in karst area is feasible.(4)A numerical model of seepage and dissolution of dam grouting curtain in karst area is established by using finite element software,and based on the numerical simulation results,a regression model between permeability coefficient K,height H,width D and dissolution rate of Ca(OH)2 in curtain in karst area is established by response surface experiment design.In the regression model,the P value of parameter K is less than 0.0001,and the P values of parameters D and H are 0.0022 and 0.0001,respectively,which shows that K,H and D all have significant influence on curtain serviceability,and the degree of influence from big to small is K>H>D.Based on the established regression model,an optimization method of grouting curtain design parameters in karst area is proposed,and the optimization method is applied to curtain design of a dangerous dam in karst area.The optimal combination of design parameters of grouting curtain is H=15.80m and D=4.51m,and the service quality of grouting curtain under the optimal combination of design parameters is better. |
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