Void Detection Behind Shield Tunnel Segments Using Ground Penetrating Radar: A Laboratory Experiment

As a recognized non-destructive testing (NDT) method, ground penetrating radar (GPR) has been applied for void detection in shield tunnel. However, due to the complex structures of shield segment with double-layer rebar meshes inside, the GPR responses of voids behind shield segment are still not clear. This paper presents a series of laboratory experiments to analyze and characterize the radar responses of voids based on a platform which is composed of two 1:1 scale shield segment. Results preliminarily show that the low-frequency radar signals from the near-segment voids are less obvious than the high-frequency signals. For the voids which are far away from the segment, the radar reflections appear as multi hyperbolas.