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利用时间域有限差分(FDTD)软件GprMax,根据初衬中钢拱架和钢筋的电磁参数,建立不同模型,模拟地质雷达对隧道衬砌的检测过程。由于隧道衬砌、围岩、钢筋等各种工程介质的介电常数存在不同的差异,使得不同目标在雷达图像上显示出不同特性的波形特征。结果表明:钢拱架雷达图像明显,反射回波显著,波形特征为分散的月牙形强反射信号,无明显多次反射波;钢筋的波形为向上凸起的弧形,且交织在一起。将这一结果与实例探测结果进行对比。对比实际探测结果表明:二衬内有钢筋分布的情况下,不可能在二衬之后准确检测出初衬内的钢拱架的数量及分布情况,所以初衬检测与二衬检测应分开进行;利用软件GprMax模拟地质雷达在初衬中的检测是准确可行的,能够清晰地反映隧道衬砌中钢拱架和钢筋的成像特征,效果较好,可为工程实践判别提供依据。
Based on the electromagnetic parameters of the steel arch and steel bars in the initial lining, different models were set up to simulate the detection process of the tunnel lining by the GPR, using the FDTD software GprMax. Due to the different dielectric constants of tunnel lining, surrounding rock, steel and other engineering media, different targets show different characteristics of waveform characteristics on radar images. The results show that the steel arch radar image is obvious and the reflected echo is significant. The waveform features are scattered crescent shaped strong reflected signals with no obvious multiple reflections. The shape of the steel bars is upward convex arc and intertwined. This result is compared with the results of the example detection. Contrasting with the actual detection results, it is shown that it is impossible to accurately detect the number and distribution of the steel arches in the first lining after the second lining, so the initial lining inspection and the second lining inspection should be carried out separately. The software GprMax simulated geologic radar is accurate and feasible in the initial lining, which can clearly reflect the imaging features of the steel arch and the steel bar in the tunnel lining, and has a good effect. It can provide basis for engineering practice.