GPR evaluation of the Damaoshan highway tunnel: A case study

Ground-penetrating radar (GPR) is widely used in the field of civil engineering; it can locate anomalies and record detailed information on the possible presence of damage within a tunnel. However, because of the complexity of tunnel structures and a long data interpretation period, the analysis and interpretation of field data is a relatively difficult and time-consuming task. In this paper, a case study of the Damaoshan Tunnel located in Fujian province, China is executed to perform a condition assessment combining GPR and finite-difference time-domain (FDTD) techniques based on prior information regarding the designed tunnel structure. This combination is used to assist and improve the interpretation of field data. The aims of this survey are to locate the rebar, estimate the thickness of the second lining, and determine the presence and distribution of any damage for an annual inspection. Additionally, a symmetry-based algorithm and a hyperbola match method are combined to achieve these goals and determine the wave velocity inversion. The interpreted results, based on both measured and simulated data, reveal that the combination of FDTD and GPR techniques is a quick and efficient survey methodology for tunnel evaluation. The survey shows that the rebar number is 367 (which is less than the standard 492), the average qualified rate of lining thickness is 79.87% of the design parameters, and there are 81 damages spanning the entire tunnel.