Forward Simulation And Experimental Signal Analysis Of Irregular Cavities In Tunnel Lining Structure

Due to the influence of geological conditions,site construction environment,construction technology and other obj ective factors,it is easy to lead to the quality problems of tunnel lining structure.The irregular shape of cavity defect in tunnel lining structure leads to the complex stress of the lining structure.In the research on the quality and safety of the lining structure,there are few related researches on the irregular shape of cavity.Therefore,how to effectively detect and accurately identify irregular shaped cavities in tunnel lining structure is a topic worthy of study.Based on the non-destructive testing technology of GPR(Ground Penetrating Rader),Gprmax 2D software based on FDTD(Finite Difference Time Domain Method)and wavelet packet analysis as signal processing tool are used in this paper to study the detection and recognition of irregular shaped cavities inside tunnel lining structure.The main contents are as follows:(1)Based on Gprmax numerical simulation software,geometric detection models of tunnel lining containing various irregular shapes,different burial depths and cavities with different filling media were constructed,and forward simulation and imaging results of the models were analyzed.With the transition of the upper boundary of the cavity model from straight line to arc or sharp angle,the number of multiple waves generated by the cavity reflection decreases,and the corresponding amplitude of single channel signal decreases gradually.With the increase of the depth of the cavity model and the decrease of the relative permittivity difference between the filling medium and the background medium,the number of reflected wave clusters decreases and the reflected signal weakens.(2)The typical single channel signals reflecting the characteristic information of GPR images with irregular shape GPR model are extracted.Based on the theory of wavelet packet analysis,the influence of different shape of GPR on the echo energy characteristics is analyzed.With the increase of the order of wavelet packet nodes,the amplitude of sub-signals generated by wavelet packet decomposition gradually decreases,and the signal energy is mainly distributed in the low frequency band.The GPR model with straight upper boundary has the highest total energy of GPR signal,followed by the circular cavity model,and the sharp angle cavity model has the lowest energy.(3)The physical model tests of radar detection of various irregular shapes and different depths of cavities were carried out in the laboratory.Reflexw software was used to preprocess the original image of cavity model detection,and the processed radar image was analyzed by wavelet packet decomposition and energy characteristics.Compared with forward modeling signals,it can be seen that the change regularity of total energy of detection signals with different shapes and different buried depths is consistent,which verifies the effectiveness and accuracy of forward modeling by Gprmax software.The research content of this paper can provide a basis for the accurate identification of irregular cavities in the lining structure and has certain reference value for judging different types of cavities and treating the quality defects of tunnel lining structure.