Modeling and testing of high frequency GPR data for evaluation of structural deformation

The paper describes the application, on a hollow pier, of a high frequency multi-component 2 GHz GPR antenna for the evaluation of deformation induced by mechanical stress. The study, performed in the laboratory, was made on a reinforced concrete hollow pier built to scale 1:5. The GPR survey data were obtained before and after the mechanical stress application, in reflection and transillumination modes. The data interpretation was supported by a GPR theoretical model of a pier. The interpretation of the GPR reflection data was very challenging as the iron rods used to reinforce the pier led to wave diffraction and the air inter-space inside the pier itself produced multiple reflections. No continuous fractures were revealed, probably because the stress caused only micro-fractures. This assumption was supported by analyses of the time slices from reflection data and the first direct wave arrival times from transillumination data. In the second survey we observed increased reflectivity in the time slices and decreased first arrival times of the direct wave, with respect to the first survey. The theoretical GPR data carried out on the physical model, which reproduced the actual pier, were found to be very useful tools for interpreting the actual data as they allow signal to noise separation.