Optimization Research on GPR Detecting of Grouting behind Shield Tunnel S in Water-Soaked Sand and Pebble Stratum

According to the possible question of the defects behind shield tunnel s and its consequences in the water-soaked sand and pebble stratum, Chinese first full-sized test platform of shield tunnel s with Ground Penetrating Radar (GPR) detection were already established. On the basis of the difference of electrical parameters between segments, grouting layer and surrounding rock, the platform has been used to detect the type of defects. In practice there is an interesting phenomenon that the reflection signal of grouting layer always overlaps the one of segments, therefore it is difficult to interpret the overlapping signal. In order to keep the antenna in the optimum scope of radiation field, some measure for optimizing and adjusting the antenna spacing should be taken, which can enhance the grouting layer signal and suppress the segment signal. At last some reference for GPR detecting of grouting behind shield tunnel segments is provided.