Ground penetrating radar (GPR) has been widely used for detecting cavities and other hidden defects behind reinforced shield tunnel linings. Migration can collapse diffractions and reconstruct the geometries of cavities behind the tunnel, thus aiding accurate interpretation of the GPR data. However, clutters from a segment joint could be misjudged as a cavity in the reconstructed GPR images. In this paper, a band-pass filter is designed to effectively remove interfering joint clutters. Laboratory experiments were carried out in the circumference and longitudinal directions on two full-scale shield tunnel models, in which cavities were buried behind the tunnel lining. Different migration algorithms are tested on the laboratory GPR data, and the results show that the reverse time migration (RTM) algorithm outperforms traditional diffraction stack and Kirchhoff algorithms. RTM can reconstruct both the accurate geometry and location of the cavity behind the lining. The phase of the reflection signal from an air-filled cavity is opposite to that of a water-filled cavity. A portable inspection device is designed to acquire high-quality GPR data in a real shield tunnel. A field measurement in a subway tunnel verifies the effectiveness of the GPR system and the RTM algorithm, and two cavities were found behind the vault and shoulder of the tunnel, respectively. It is concluded that the RTM of GPR data can be used for detecting and characterizing cavities behind shield tunnel segments.

中文翻译：

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加固盾构隧道后面成像腔探地雷达数据的逆时偏移

探地雷达（GPR）已广泛用于检测加固盾构隧道衬砌后面的空洞和其他隐藏缺陷。偏移可以破坏衍射并重建隧道后面空腔的几何形状，从而有助于准确解释探地雷达数据。然而，来自节段接头的杂波可能会被误判为重建探地雷达图像中的空腔。本文设计了带通滤波器来有效去除干扰接头杂波。在两个全尺寸盾构隧道模型上进行了圆周方向和纵向方向的室内试验，其中空腔埋在隧道衬砌后面。在实验室探地雷达数据上测试了不同的偏移算法，结果表明，逆时偏移（RTM）算法优于传统的衍射叠加和基尔霍夫算法。RTM 可以重建衬里后面空腔的精确几何形状和位置。来自充满空气的腔体的反射信号的相位与来自充满水的腔体的反射信号的相位相反。便携式检测设备旨在在真实的盾构隧道中获取高质量的探地雷达数据。通过对地铁隧道的现场测量，验证了探地雷达系统和RTM算法的有效性，在隧道拱顶和路肩后面分别发现了两个空洞。结论是探地雷达数据的 RTM 可用于检测和表征盾构隧道管片后面的空洞。