High-resolution investigation of masonry samples through GPR and electrical resistivity tomography

This paper aims to explore potential and limits of the combined use of ground penetrating radar (GPR) and electrical resistivity tomography (ERT) investigations for the characterization of reinforced masonry samples. To this aim, both techniques were applied on two laboratory small-scale wall samples before and after the application of a shear-compression diagonal load. Laboratory samples (1 × 1 × 0.25 m) are made of bricks and tuff respectively and reinforced with a thin high-strength and high-conductive fibre fabric. In order to improve the sample-antenna coupling in presence of conductive reinforcements, a Plexiglas plate was added underneath the 2 GHz antenna. GPR data were acquired along profiles spaced 0.1 m apart and ERT measurements were executed on a 0.1 m regular spaced grid with a dipole-dipole array operating in a three-dimensional configuration. GPR datasets were also analysed in non-conventional mode, by means of the picking of the reflection time of the EM wave from the rear face of the samples. Results show that GPR and electrical resistivity tomography were both able to detect fractures and weakness zones caused by the load application, even though with a higher resolution for the georadar with respect to the geoelectrical method. The use of a dielectric material between the GPR antenna and the investigated medium improves substantially the signal penetration in the case of shallow high-conductive layers. Finally, three-dimensional synthetic simulations on the same samples validate the experimental evidences. Therefore, we demonstrate that this approach can be a reliable tool to monitor static load tests and it can be extended to the whole load cycle (before, during and after the experiment).