GPR investigations to evaluate the geometry of rock slides and buckling in a limestone formation in northern Italy

Ground Penetrating Radar (GPR) investigations were performed to assess the depth and geometry of rock slides and buckles affecting a dip slope of regularly stratified limestones interbedded with marly-clayey horizons in the south-eastern Alps. This method was chosen because the absence of high cuts in the rock mass and the presence of debris and loosened slabs on the slope did not allow the geometry of the sliding mass to be described solely by means of field mapping. The application of GPR was encouraged by the favourable conditions of the geological "environment". More than 23 medium-frequency GPR lines were performed over compressive and tensile structures as well as over undeformed limestone sequences. Digitally collected data were filtered and processed to enhance deeper reflections, as well as corrected to account for topographic irregularities. GPR was instrumental in assessing the depth of the deformational and failure structures (e.g., buckle folds and tension cracks) induced by the instability phenomena as well as in evaluating deformation continuity along the sliding mass. The GPR surveys confirmed that the layers are continuous over extensive areas (even at the maximum penetration depth of about 6 m) and that deformations involve layer packages which are at least 5 metres thick. The first result indicates the importance of accounting for the mechanical separation of layers when conducting stability analyses while the second points out the inadequacy of common limit-equilibrium/elastic instability analyses. In fact, this type of procedure envisages the instability of much thinner layer packages, thus suggesting that a more complex elasto-plastic deformation analysis of thicker layer packages is more suited to this kind of phenomenon.