Research On Integrity Inspection Method Of Vertical Curtain In Landfill

Landfill is an effective measure for the centralized disposal of domestic waste and industrial solid waste at present,and also an important means for the environmentally friendly development in the future.In the long-term operation process of landfill,especially after the landfill is closed,it is difficult to maintain the horizontal High Density Polyethylene（HDPE）impervious curtain,and leachate diffusion will lead to a wider range of pollution after the failure of the impervious system.In order to prevent or prevent the diffusion of leachate,vertical anti-seepage curtain is often built in the middle and later period of landfill operation.At present,there are few researches on the integrity detection of vertical impermeable curtain in China,and the corresponding seepage treatment methods are backward.Vertical seepage prevention is the last line of defense to ensure the operation of landfill sites.Once seepage occurs,leachate will spread to farmland,groundwater and other areas,which will seriously threaten the health of surrounding residents and increase the burden of environmental management.Therefore,it is urgent to carry out research on the integrity detection method of vertical curtain in landfill site,accurately identify and locate the leakage area,and provide scientific reference for the vertical seepage prevention and restoration project.Aiming at the problem of integrity detection of vertical HDPE anti-seepage curtain,this paper combines the method of high-density resistivity detection device and the electric field distribution characteristics of vertical curtain site to develop a double-array highdensity detection system.On this basis,the forward and inversion of resistivity is carried out.Research on data processing methods,simulate different vertical curtain vulnerability models,analyze the characteristics of leakage anomalies generated by them,verify the accuracy of the algorithm,and finally conduct field experiments on the detection method in this paper,the main research contents and conclusions as follows:（1）The basic principle,device method and applicability of the high-density resistivity method are expounded,the electric field distribution characteristics of the semi-infinite space under the vertical curtain are analyzed,and a double-array high-density detection system is designed.Design and development of software functions,complete the integration of hardware modules of the detection system,and realize the development and testing of the vertical anti-seepage curtain detection system.（2）Based on the research and verification of the subsequent data processing method based on the detection system,the algorithm research was carried out in combination with the forward modeling theory of traditional geophysical exploration,and the solution of large-scale sparse linear equations was optimized.Numerical simulations were carried out and verified by comparison with COMSOL numerical solutions.The results show that,except for the fitting error near the power supply electrode,which is within 1%,the other node errors are almost 0,which verifies the accuracy of the forward modeling 3D finite element method numerical simulation.（3）Combined with inversion theory,the objective function with added constraints and the solution technology of Jacobian-free Krylov subspace are used to improve the accuracy and speed of Gauss-Newton parameter optimization inversion.The Gauss-Newton inversion is used to optimize the parameters of the models of the position,size and number of holes with different holes,and the abnormal situation of the vertical curtain when different holes exist is compared and analyzed.The results show that the potential of the detection electrode measuring line will be larger due to the influence of the power supply electrode,and the shallower the hole and the larger the size,the higher the potential near the hole.If the vulnerability is within 6m,the location of the vulnerability can be accurately determined through the low resistance area.The shallower the depth is,the larger the vulnerability size is,the smaller the inversion error is,which can verify the accuracy of the inversion algorithm.（4）In a landfill site in Jiangsu,a double-arranged high-density detection system was used to conduct a simulated loophole group detection experiment on its vertical anti-seepage curtain.Block and locate loopholes;single loophole simulation experiment,the loophole depth is within 8m,and the coordinate error range does not exceed 0.3m,which can better reflect the position of the loophole.The vertical curtain double loophole simulation experiment can well reflect the position of the loophole near the shallow 3m.The double loophole is between 3m～6m due to the uneven distribution of the electric field and the different dielectric resistivity,resulting in an abnormal location error of around 3m.In conclusion,the results show that the integrity detection method studied in this paper has a certain reference value in practical engineering application.