| In the process of tunnel construction,due to unknown geological conditions in front,complex construction environment,construction technology,mechanical equipment and other factors,it may lead to the poor thickness of the lining behind the tunnel,and the quality defects such as cracks or cavities in the lining structure.Moreover,when the tunnel is built and put into operation,the cyclic dynamic load of vehicles and the tectonic in-situ stress field are also easy to produce lining diseases.These diseases will affect the stability and safety of the tunnel.In order to ensure the normal passage of the tunnel,it is necessary to carry out regular inspection and evaluation of the tunnel lining.At present,the preferred method of tunnel quality inspection is ground penetrating radar(GPR)nondestructive detection method.However,due to the concealment and complexity of cavity and other diseases,there are still many difficulties in the actual inspection.Accurate identification of the cavity behind the lining has become an important research topic.Based on the ground penetrating radar method and with the help of the GprMax2.0,this paper studies the radar wave imaging law and accurate identification of the void filled with different water-bearing media by combining forward simulation and model experiment with mutual verification.The main contents are as follows:(1)By referring to a large number of domestic and foreign relevant literatures,the working principle and detection performance of GPR are described,and the development of detection and identification technology of cavity behind tunnel lining structure and the application status of forward simulation and physical model experiment of GPR are analyzed.(2)Aiming at different water features in concrete hollow,the establishment of different moisture content of loess medium filling,different water height medium filling and aqueous composite medium filling empty and void model of different water depth.These models are forward modeling and imaging characteristics of analysis,summarized and empty of GPR reflected wave imaging rule.It provides a certain basis of judgment and interpretation for the different water-bearing cavities behind tunnel lining structures in engineering application.(3)Signal spectrum analysis and wavelet time-frequency analysis were carried out for GPR forward simulation signals of loess medium filling model with different water content,medium filling model with different water content height,medium filling model with different water content combination medium and water content void model with different buried depth,and the change rule of signal frequency was summarized.(4)Design related physical model test,the use of Italian RIS series radar measurement work,and use Reflexw software to remove background and filter processing,the result of the detection of the test result after processing frequency analysis and the time-frequency characteristic analysis,to explore filling medium under the condition of different moisture content,hole detection signal frequency changing characteristics in time and frequency distribution,At the same time,the forward simulation results were compared and verified.The research content of this paper lays a preliminary technical foundation and theoretical basis for the GPR detection and health diagnosis of the quality defects behind the tunnel lining structure,and provides a certain basis for the accurate identification of the cavity defects in different water-bearing states in the lining. |
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