Multi-objective Dynamic Inversion Of Seepage Based On BP-GA And Safety Study Of Dam Seepage

Aiming at the uniqueness problem of inversion results of dam permeability coefficient and characteristics of dynamic changes of seepage field,this paper takes the Shuikou concrete dam as the research object,and establishes the seepage multi-objective dynamic inversion analysis model based on the orthogonal design,finite element positive analysis,BP neural network and genetic algorithm.Based on the numerical calculation software,the three-dimensional finite element model of the diversion dam section of the Shuikou concrete dam is established.The paper takes monitoring environmental quantities and effects amount as data basis for parameter inversion and takes seepage multi-objective dynamic inversion analysis model as technical basis of parameter inversion and conducts the research of inversion of permeability coefficient of dam body,anti-seepage curtain and dam foundation of Shuikou dam.Based on this,the seepage safety status of the Shuikou Dam is analyzed and the optimization suggestions for seepage monitoring are proposed.The main research results are as follows:(1)Aiming at the unique problem of stable seepage inversion results,a multi-objective dynamic inversion analysis model based on orthogonal design,finite element positive analysis,BP neural network and genetic algorithm was established.The feasibility of the established inversion model is verified by an example of earth-rock dam.The influence degree of different monitoring effect quantities on the seepage inversion results is discussed,and the optimal weight in the mathematical model of the inverse flow problem is determined.The multi-objective dynamic inversion analysis model established in this paper can better solve the defects of single-objective inversion.The obtained inversion parameters are absolute permeability coefficient,and the inversion results are unique.(2)Based on the general situation of Shuikou concrete dam and the design plan of seepage monitoring,the data of the dam foundation pressure and seepage flow were obtained,and the variation law of the pressure and seepage flow was analyzed,which provides a reference for the safe management of Shuikou concrete dam.Aiming at the sudden change of pressure and seepage flow in some measuring points,the main causes of abnormal changes are analyzed,and the influencing factors that threaten the safety of dams are excluded.In view of the accuracy of the inversion results,the data available for seepage inversion are screened out,which reduces the error of the inversion results to a certain extent and ensures the accuracy of the inversion results.(3)Based on the finite element numerical simulation software,a three-dimensional finite element model of the diversion dam section of the Shuikou dam is established.Combined with the hydrogeological conditions of Shuikou concrete dam,the parameters involved in seepage inversion are determined.Through the multi-objective dynamic inversion analysis model of seepage in this paper,the inversion permeability coefficients of the dam body,dam foundation(strongly weathered granite and weakly weathered granite)and anti-seepage curtain are obtained.The relative errors between the inversion permeability coefficient and the theoretical value of the dam body,anti-seepage curtain,strong weathered granite and weakly weathered granite are 17.41%,9.2%,-18.11% and 15.3%,respectively.In general,the relative error of the inversion permeability coefficient is controlled within 20%.In order to verify the accuracy of the inversion permeability coefficient,the reliability of the inversion results is analyzed by comparing the measured values of the pressure and the single wide seepage flow with the simulated values.The relative error of the pressure of the three osmometers is controlled within the range of-0.40% ~ 0.92%,-9.92% ~ 8.75%,and-22.03% ~ 22.7%,respectively.The relative error of single-wide seepage flow is controlled within the range of-17.50%~26.92%,and the inversion results are reliable.The permeability coefficient inferred in this paper reflects the parameters of the Shuikou dam under real working conditions.The inversion permeability coefficient can be used for the safety analysis of the seepage of the Shuikou dam.(4)The safety analysis of the seepage of the Shuikou dam under the normal water storage level and the check flood position is carried out.The distribution law of the seepage field of the Shuikou dam under two working conditions is basically the same.Under the two working conditions,the anti-seepage curtain bears about 82% and 80% of the water head,and the osmosis slope value of the dam foundation is basically controlled within the range of 0~2 and 0~2.15.The maximum osmosis slope value at the anti-seepage curtain is close to 18.5 and 19.4,both of which are less than the design allowable slope value of 25.By comparing the distribution law of the total head of the dam under the two working conditions,it can be known that the upstream water level change has little influence on the water head value of the downstream side of the dam foundation anti-seepage curtain,indicating that the anti-seepage curtain and drainage hole of the Shuikou dam have a good effect of “front blocking and rear row” and the dam is in a safe operating state.Combined with the analysis results of seepage field,it is suggested to arrange a longitudinal pressure monitoring section along the axis of the dam in the upstream side of the anti-seepage curtain of the 4#~39# section of Shuikou dam to monitor the dynamic change of the forward pressure before the anti-seepage curtain.At the same time,it is suggested to close the osmometer in the horizontal corridor of the 11#,17#,25#,29#,and 32# dam sections.