3D Electrical Resistivity Tomography: a diagnostic tool for the inspection of submerged foundations of civil infrastructures

In this work we present a study aimed at evaluating the effectiveness and the reliability of a fully noninvasive methodology for the inspection of underwater and inaccessible foundations of civil infrastructures. Three-dimensional Electrical Resistivity Tomography (3D ERT) method was tested to investigate the submerged structures of a railway bridge. To evaluate the effectiveness of the method and the reliability of the measurements, the field procedures were validated by a sensitivity and a resolution analysis. ERT data were filtered and processed through a 3D inversion algorithm. Several synthetic resistivity models were built to improve the interpretation of the results obtained by the inversion process of the experimental data. The complementary approach based on the integration of geophysical surveys and numerical physical modeling is here analyzed and critically discussed. The results of the geophysical survey highlight that this methodology represents an effective tool for the diagnosis of the geometrical features of inaccessible parts of submerged engineering structures, and suggest future developments and applications also for non-destructive analyses of historical bridges