Evaluation of karstic cave stability using integrated geophysical methods

This paper describes an integrated data interpretation from seismic refraction tomography (P and S-wave), two-dimensional electrical resistivity tomography (ERT) and ground-penetrating radar (GPR), collected over a cave of great archaeological interest in south Italy. Data results were part of a geophysical campaign performed to locate the real position of a cave at the archaeological site of Parabita (Apulia Region, south Italy). As it is well known rock fractures constitute a serious problems in cave maintenance, in fact the progressive cracking within the base rock is considered to be the main cause of collapse. To assess the stability of the rock that constitutes the roof of the cave, geophysical surveys were preferred to boreholes or geotechnical tests. The interpretation of the integrated data from the seismic refraction tomography, ERT and GPR (200 MHz antenna) allows some of the elastic characteristics (such as the Vp/Vs ratio) to be evaluated and the discontinuities in the rock to be detected. The cracks within the base rock were detected to a depth of about 2 m by using GPR, which allowed the identification of the loosened zone around the cave. The GPR data were visualised in a three-dimensional space by using the iso-amplitude surface of the complex trace amplitude. The immediacy in revealing the spatial position of highly reflecting bodies, such as the anomaly related to the fractures, makes the 3D visualisation technique very attractive in engineering applications of GPR.