Maxwell curl equation datuming for GPR based on the Kirchhoff integral solution and application in a tunnel grouting test

摘要

In two-dimensional (2D) ground-penetrating radar (GPR) data, the reflections from detection targets in depth can be severely obscured by strong scattering generated from near-surface non-target structures. By using GPR as a geotechnical non-destructive testing device, it is still a challenge to eliminate the strong scattering caused by near-surface rebars in a tunnel lining and to image and asses the grouting condition behind the tunnel lining. This study proposes a method for the reconstruction of GPR images, termed Maxwell curl equation datuming. To eliminate the deleterious effect caused by near-surface diffractive scattering, we have redefined the reference surface to an actual geologic/engineered interface by using Maxwell curl equation datuming methodology based on the Kirchhoff integral solution. The datuming procedure can redefine the reference surface to a deeper horizon on which GPR transmitters and receivers appear to be located. We conducted a comparison between the datuming and migration to synthetic examples and case studies are presented for a physical model and real GPR data for assessments of shield tunnel grouting in the Shanghai Metro line No.9. The results show that the datuming technique is able to eliminate the strong scattering related to near-surface rebars in a tunnel lining and improves the quality of deeper images beneath the tunnel lining. The datuming images make it easy to identify the distribution of tunnel grouting.