Research of GPR non-damaged test of grouting behind lining of shield tunnel

As the grouting behind the lining of shield tunnels is an important way to control the different settlement of tunnels induced by construction in soft soil areas, it is a concerned problem how to evaluate the quality of the grouting. This paper applied Ground-Penetrating Radar (GPR) to test the grouting in Shanghai Metro tunnels. Above all, the frame of EKKO 0 radar antennas was successfully improved to fit more in shield tunnels. New designed antenna frame is made up of frame boards, protecting boards, padding boards and truckles. Secondly, the velocity of electromagnetic (EM) wave in the grouting was acquired by the analysis of field common midpoint datum. The grouting EM velocity in the segment of the tunnel is 0.1m/ns. Thirdly, a wave-translated method was put forward to show the GPR images more visually. The processes of the method include time and space filter, defined gain, absolute calculation, and low-pass filter. Furthermore, Using the information acquired by GPR, and combined with the experienced datum, a GPR test standard of the grouting in Shanghai Metro Lines was brought forward. The classified standard is easily taken in practice.