Assesing the applicability of GPR method for tunnelling inspection: Characterization and volumetric reconstruction

This work presents the analysis and corresponding characterization of two representative tunnelling constructions, showing different constructive conditions. Diverse data acquisition and processing approaches were considered depending on the type of the structure, geometric characteristics and surveying conditions. The first study case includes an underground reinforced concrete tunnel system with symmetric geometry, which is composed by a central corridor and lateral branches. For its documentation and characterization, three-dimensional imaging methodologies were applied to create a volumetric reconstruction of its whole underground network. Problems of moisture were also detected by the attenuation of the radar-wave signal, and finite-difference time-domain modelling was used as a supporting tool for data interpretation. After a deeper analysis of both field and synthetic data, and additional visual inspection, it was concluded that such portions of the structure, presenting this lack of information, are affected by corrosion in reinforcement. On the other hand, a GPR study was conducted through a bench excavation tunnel, in order to monitor quality control during the early stages of construction and to evaluate the tunnel stability. According to this benchmark, results provided noteworthy characteristics, namely: thickness of the shotcrete layer, lining damages and moisture problems.