| As an important project of transportation lines,tunnel engineering directly affects the smoothness and safety of the lines.In the construction and operation process of tunnels,the tunnel lining structure is prone to cracking.If left unchecked,it will induce a series of quality diseases such as carbonization of concrete,peeling of protective layer,water leakage and corrosion of steel bars,thus affecting the normal operation of the tunnel,and even leading to structural instability and damage,resulting in serious economic losses.Therefore,the quality inspection of tunnel lining is particularly important,and the identification of cracks and diseases in lining structures has become an important research topic.As a shallow geophysical exploration technology,ground penetrating radar is widely used in the quality inspection of tunnel lining structures due to its advantages of high precision,high efficiency,and intuitive imaging.Based on the finite difference time domain(FDTD)method,this paper uses Gprmax2.0 software to model and perform forward simulation of lining crack detection to explore the radar imaging law and signal characteristics of cracks in the lining structure.Crack models with different inclination angles and different shapes are made indoors,and the energy characteristics and data processing analysis of the indoor measured crack echo signals are carried out.The main work contents are as follows:(1)Based on the forward simulation software Gprmax2.0,the models of linear cracks with different inclination angles,bending cracks with different curvatures and different bending directions,and special-shaped cracks with different directions are established.The graphs are drawn with the help of Matlab software.The radar imaging of the crack models with different characteristics is summarized.(2)Using Matlab software to perform continuous wavelet transform time-frequency analysis on the crack models with different inclination angles,different bending curvatures,different bending directions and different strikes.Extract the energy(amplitude value)value and variation law of the strongest signal of a single channel.The variation law of amplitude value is consistent with the forward simulation law.At the same time,F-K migration processing is carried out for different crack models to improve the signal resolution,make the waveform converge,and return the image.(3)The indoor physical model test was designed.The RIS-type ground penetrating radar and K2fastwave software were used to complete the test data acquisition.And the Reflexw software was used to remove the background and filter the results.Use Reflexw software to remove background and filter the results,and then perform signal time-frequency analysis and F-K migration processing.At the same time,the measured analysis results of hidden micro-fractures in the model test and the analysis results of crack detection signals in the forward simulation were compared and analyzed,Verifing the accuracy and reliability of wavelet transform time-frequency analysis method and F-K migration method in signal processing and identification of crack detection in different types.In this paper,the cracks of different directions and buried depths inside the lining structure are taken as the research object.The research method of combining and verifying the forward simulation and indoor model test is adopted to explore the imaging laws and signal characteristics of different forms of crack diseases,in order to be used in practical engineering.The detection and identification of cracks and diseases in the tunnel lining structure provide a certain basis for judgment and interpretation. |
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