Detection Of Lining Diseases And Global Numerical Boundary Finite Element Simulation

Ground penetrating radar(GPR)is widely used in tunnel lining quality inspection because of its nondestructive and high efficiency.However,the key and difficult point of GPR nondestructive testing lies in the interpretation of radar spectrum.At present,the disease detection of tunnel lining is mostly based on two-dimensional technology,which is difficult to provide more accurate and vivid information for us,and is not conducive to our interpretation of radar spectrum.In numerical simulation,different calculation methods and boundary conditions will directly affect the simulation results.In this paper,the diseases of tunnel lining are studied by combining physical model and numerical simulation model.Firstly,SIR GPR was used to collect data of the physical model,and then RADAN7 software was used for signal processing of the collected data.Finally,the single-channel waveform,two-dimensional radar profile and three-dimensional radar map were obtained and explained.Aiming at the shortcomings of the transmission boundary conditions,a more optimized boundary condition,namely the second type of global numerical boundary conditions,is introduced and applied to the numerical simulation of ground penetrating radar.Based on MATLAB,the finite element forward modeling program of the two boundary conditions is developed and the finite element forward modeling of the test is carried out.The main research results of this paper are as follows:(1)Through the combination of physical model test and numerical simulation test to study the lining disease,the numerical simulation results are basically consistent with the measured results of physical model.Aiming at the shortcomings of transmission boundary conditions,a more optimized boundary condition,that is,the second type of global numerical boundary condition,is applied.The superiority of the second kind of global numerical boundary condition is determined by comparing two different boundary conditions.(2)The ground penetrating radar is used to detect the physical model,and RADAN7 software is used to process the original data.The imaging results show that the data processing can effectively remove the interference signals.Then through the interpretation of two-dimensional profile and three-dimensional radar map,the combination of two-dimensional and three-dimensional detection method can be more accurate and comprehensive to determine the disease information.(3)The results of physical model test and numerical simulation test show that when the steel bar spacing is greater than 250 mm,the influence of the steel bar on the detection result is small.However,when the steel bar spacing is less than 110 mm,the steel bar has a huge impact on the detection results.The deeper the disease is buried,the weaker the detected signal is.The more complex the shape of the disease,the less favorable it is for detection.(4)The detection resolution determines the minimum size that the GPR can detect the target body.When the crack width meets the GPR resolution,the crack can be detected and the depth of the crack can be estimated.The crack has a certain effect on the reflected signal wave of the disease below.