Research On Three Dimensional Electric Field Distribution And The Leakage Diagnosis Technology Of Earth-rock Dam

Investigation and treatment of earth-rock dams leakage is one of the hot issues in the field of hydraulic engineering.At present,electrical resistivity tomography is widely used to diagnose the leakage of earth-rock dams both at home and abroad.However,due to lacking of in-depth and systematic research on both the three-dimensional electric field distribution law of earth-rock dam and it’s three-dimensional electric field variation law in the evolution process of seepage field,the diagnostic method is limited to the qualitative determination of resistivity.Furthermore,the relationship between the seepage field and the electric field has not been established,leading to the deficiency in accuracy and comprehensiveness of the diagnosis of the hidden danger of the earth dam by the resistivity method.Therefore,relying on the projects of National Natural Science Foundation of China(51279219,51879017),this paper systematically studies the three-dimensional electric field distribution law and leakage diagnosis technology of earth-rock dam by means of theoretical analysis,physical experiment,numerical simulation,and digital image processing.The main research contents and results are as follows:(1)Research on mathematical model of three-dimensional electric field distribution of earth-rock dams in point source fieldBased on the recent research,the hidden dangers and characteristics of earth-rock dams were summarized.Then the generalized models of different types of hidden dangers in nonhomogeneous earth-rock dams were established.Furthermore,cracks,caves and leakage channels in the point source field were derived through the generalized model.(2)Research on numerical simulation of three-dimensional electric field distribution of earth-rock dams in point source fieldBased on the finite element method,the forward modeling of the electric field of the three-dimensional earth-rock dam structure was studied.Begin with the basic equations satisfied by the forward electric field simulation,the infinite domain of the three-dimensional problem was transformed into a finite field by the equation discretization approaches and the required boundary conditions.The analysis program for three-dimensional resistivity was based on Delphi language,accelerated by the R language and SQLite database processing.The results show that,after optimization,the overall speed of the forward calculation is increased by 7% and the memory consumption is reduced by 20%.By calling Surfer imaging software to present the three-dimensional electric field distribution images of different types of hidden dangers,the electric field response of different hidden types in the point source field was obtained.Based on the continuous theoretical analysis of electric field strength and current,the causes of the change of electric field were discussed,which provides a basis for the diagnosis of heterogeneous dam type of resistivity image by resistivity image.(3)Analysis of seepage field of earth-rock dam based on three-dimensional electric field distribution lawThrough the experimental study,the change law of resistivity during self-water absorption saturation of different earth-rock ratio specimens under different compaction conditions was determined,and the dynamic stability process of resistivity after the water-saturation of earth-rock dam material was found.The resistivity-saturation relationship of earth-rock was fitted by using the unsaturated model with favorable result.Based on experimental results of porosity and saturation,the osmotic head and hydraulic ratio drop at different positions during the infiltration process of homogeneous dams were obtained by COMSOL numerical simulation software.Then,through the comparison of the hydraulic ratio drop and the critical ratio drop of the dam material during seepage deformation,the problem of whether the material of the dam at a certain position is damaged can be solved.Based on the coupling of the seepage field and the electric field,the range of resistivity change at the point source of electric field was obtained,which provides a diagnostic basis for the resistivity image comparison.At the same time,the potential,charge and resistivity distributions of different types of hidden dangers at the point source field of heterogeneous dam were obtained,which provides a basis for the prediction of real-time monitoring of hazard types by resistivity.(4)Research on leakage image recognition and diagnosis technology based on edge detection algorithmMassive pictures are automatically screened for hidden pictures through the convolutional neural network,then the pictures with hidden dangers are marked.Based on the resistivity image comparison,the Canny edge detection algorithm and the image centroid algorithm code were used to obtain the change of pigment threshold value for the resistivity image.By comparing the change of pigment threshold with the change rate of resistivity in the electric field corresponding to the osmotic failure of the dam material in the seepage field,a diagnosis method for leakage damage of earth dam was formed.(5)Research on leakage diagnosis of earth-rock dam based on electric field distributionTaking the earth-rock dam of Shangxishan Reservoir in Qujing,Yunnan as the research object,the resistivity images at the same position with different times were obtained through real-time monitoring.Through the comparison of images in different time periods,the diagnosis feasibility of leakage in application based on resistivity image contrast theory was verified.