隧道衬砌空洞探地雷达三维探测正演研究

从Maxwell旋度方程出发,推导导电介质UPML(单轴各向异性理想匹配层)吸收边界的三维时域有限差分法的计算公式,在不考虑磁导率的情况下,建立模拟区与UPML吸收边界场量间的联系,统一用UPML吸收边界公式进行正演模拟计算,只是系数不同,减少分区及临时存储空间,提高运行速度,并用Matlab编程实现,运用该程序对隧道衬砌内的空洞进行正演模拟,得到其相应的正演合成三维剖视图及切片图,实现雷达三维正演数据的可视化,探讨空洞的三维图谱特性。对隧道衬砌内空洞进行物理模型试验,数值模拟图谱与物理模型试验结果相似,验证了三维数值模拟方法的可行性和有效性。研究结果表明,三维探测能确定空洞大小、形态和位置,更加全面而细致地了解空洞的准确信息,提高雷达探测图谱解释的可靠性和准确性,并可根据缺陷的分布位置及大小评估衬砌内空洞病害的危害程度。为空洞雷达图谱的自动识别技术提供了可靠的理论依据和方法,对隧道质量检测工程及质量司法鉴定具有重要意义。

STUDY OF FORWARD SIMULATION FOR GROUND PENETRATING RADAR THREE-DIMENSIONAL DETECTION OF TUNNEL LINING CAVITY

Based on Maxwell curl equations，the three-dimensional finite difference time domain formula about UPML absorbing boundary of conductive medium is derived；without considering permeability，the link between simulation area and UPML absorbing boundary field is established；UPML absorbing boundary formula is used for forward simulation with different coefficients；but the area and temporary storage space are reduced and the speed is improved. Using Matlab programming to forward simulate the tunnel lining cavity and obtain the corresponding forward synthesis of three-dimensional profiles and slice maps，the three-dimension forward data visualization is achieved；and the three-dimensional map features of cavity are discussed. Through the physical model test of tunnel lining cavity，the results of numerical simulation and physical model test are similar so as to verify that the three-dimensional numerical simulation is feasibility and effectiveness. The results show that three-dimensional detection can not only determine the size，shape and location of cavity，but also understand accurate information of cavity comprehensively；it can improve the reliability and the accuracy of radar map interpretation，and the harmful level of cavity in lining can be assessed according to the distribution of defecting location and size. The study provides a reliable theoretical basis and method for automatic recognition technology of radar cavity map；and it has a great significance in tunnel detection project and tunnel quality of judicial expertise.