3D high resolution GPR applied for evaluating the hypogeum structure conservation state in urban area

Ground-penetrating Radar (GPR) is a non-destructive methodology that have become a very important tool for non-destructive underground exploration. For the localisation of buried structures, it uses short time duration electromagnetic (EM) pulses lasting from about 1 ns to about 30 ns. Therefore, GPR is characterised by a wide frequency band ranging from 10 MHz to some GHz, and is useful in the localisation of EM discontinuities in the subsurface with high resolution. This case study shows a practical example of the usage of the 3D GPR technique to evaluate the state of maintenance of an hypogeum structure located in an urban area. The hypogeum structure is in danger of falling because of the numerous fractures present in the rock that constitutes the roof of the same structure. The study was made to assist the design of the restoration works of the hypogeum. Because of the very narrow thickness of the fractures, special care was needed in the acquisition and processing steps. Although pushed to the limit of the resolution achievable by the available antenna, the study has given quite good results.