探地雷达在隧道衬砌空洞检测的正演模拟应用研究

按照时域有限差分解麦克斯韦偏微分方程的思路,通过基于时域有限差分的数值模拟方法,利用Matlab语言,编制了隧道衬砌空洞的二维正演程序,正演探地雷达波形在隧道衬砌空洞中的传播规律,分析了探地雷达在探测隧道衬砌空洞的有效性以及衬砌空洞的雷达波反射特征。正演模拟结果表明:衬砌空洞雷达反射信号强,且呈现多次反射特征,通常呈现双曲线特征,振幅强,频率低,在空洞下部仍有强反射界面信号,上下界面两组信号时程差较大。借助于实例,将模拟结果与实际检测结果进行了对比分析,取得了良好的效果,说明数值模拟是探地雷达波形识别的一种有效手段,因而,可以采用该方法对隧道结构衬砌背后的空洞病害进行有效检测,以指导隧道的安全评估。

Study on application of forward modelling for inspecting void in tunnel lining by ground probing radar

In accordance with the ideas of the finite-difference time-domain method for Maxwell partial differential equations and the numerical simulation model based on the finite-difference time-domain method,this paper programmed two-dimensional forward process of tunnel lining cavity,gave the forward propagation rule of ground-penetrating radar waveform in the tunnel lining cavity,analyzed the effectiveness of ground penetrating radar in detecting the tunnel lining cavity and radar reflectivity characteristics of the tunnel lining cavity by Matlab language.The forward modeling results showed that the radar reflection signal in tunnel lining cavity is strong and shows the feature of multiple reflections which usually presents the hyperbolic characteristics,strong amplitude,and low frequency,there is still strong radar reflection signal in the lower cavity,and the two signal time produced by the upper and lower interface of cavity exist larger difference.Combining with the engineering practice,this paper compared the simulation results with actual test results and the results indicated that numerical modeling method of detecting in tunnel lining cavity by GPR is valid and significant,which is an effective means of ground penetrating radar waveform recognition,can be used to detect diseases behind tunnel lining cavity and guide the tunnel safety assessment.