Study on radargram characteristics of the backfill grouting quality evaluation of a shield tunnel using GPR

The distribution of a backfill grouting layer behind concrete lining of a large diameter shield tunnel under construction is important for evaluation of its stability. In the paper, the numerical simulation is developed considering the three layered media of segment, backfill grouting and surrounding soil. In the simulation, the influences on the radargram from the steel bars in the segment are analyzed. To eliminate the multiple wave from the steel bars, coincidence information removing method (CIRM) is used and Karhunen-Loève (K-L) filtering is discussed. To calculate the thickness of the grouting layer more precisely, the field tests on segment, grouting layer and surrounding soil are carried out to acquire their dielectric permittivity. The detection of Guang-Shen-Gang large diameter shield tunnel shows, the measured thickness of backfill grouting layer using GPR is very close to the designed.