基于空气耦合式探地雷达探测的衬砌层位特征识别的正演模拟

Forward Simulation for Identification of Tunnel Lining Layer Characteristics Based on Detecting by Air-Coupled Ground Penetrating Radar

采用探地雷达进行隧道衬砌检测时,需要准确提取衬砌的层位特征(含相应病害信息)。采用空气耦合式探地雷达对隧道衬砌质量进行检测,基于Gpr Max2D和Matlab为平台环境,对衬砌层位特征识别进行研究。主要研究及结论如下:1)对多种实际工况的衬砌形式进行二维正演模拟分析,并对电磁波在多层介质中反射特征进行研究。研究表明,探地雷达反射回波的起始位非零,而电磁波在介质分界层处发生反射的时刻取决于电磁波所传播层面的厚度,当2层介质差别较大或2层介质之间有空气存在时,反射时刻位于波形的最大波峰或波谷所在位置,而与脉冲源的位置和第2层介质的介电常数无关。2)根据隧道衬砌的分层特征,在实际隧道衬砌中,对探地雷达数据和实际干扰因素进行分析处理,对与理论反射时间误差太大的进行修正。研究成果对应隧道衬砌层位及病害性状识别均具有指导和借鉴意义。

The characteristics of the depth and defects of the tunnel lining layers need to be extracted accurately from the data collected in the tunnel lining quality detection by means of Ground Penetrating Radar（ GPR）. In the paper,aircoupled GPR is used for the lining quality detection,and the identification of the characteristics of the lining layer is studied based on Matlab and Gpr Max2 D platforms. Conclusions drawn are as follows： 1） 2D forward simulation of several types of lining and the characteristics of electromagnetic wave reflection within multi-layered mediums are studied under actual working conditions. The analysis shows that the reflection echo of GPR does not start from zero,and the reflection time of the electromagnetic wave on the boundary layer between two mediums depends on the thickness of the electromagnetic wave propagation layer. For two medium layers with big difference or with some air between the two medium layers,the reflection time is located at the maximum peak or the trough of the waveform,which is independent of the position of the impulse source emitted from GPR and the dielectric constant of the second medium layer. 2） The GPR data and actual interference factors of the tunnel lining are analyzed on basis of the characteristics of the tunnel lining layers,and the big errors from the theoretical reflection time is modified. The paper can provide guidance and reference for the identification of the tunnel lining layers and defect properties of similar projects in the future.