Geomechanical characterization of carbonate rock masses by means of laser scanner technique

Knowledge of the geometrical and structural setting of rock masses is crucial to evaluate the stability and to design the most suitable stabilization works. The traditional survey techniques are often expensive, and present great difficulties related to logistics in accessing the sites, the high hazard for the operators, and the height of the rock faces, or simply beacuse of the wide extent of the rock walls to be examined. In this work we use the Terrestrial Laser Scanning (TLS) at the site of the Grave of the Castellana Caves, a famous show cave in southern Italy. The Grave is the natural access to the cave system, produced by the collapse of the vault of the original cave, due to upward progression of instabilities in the carbonate rock masses. It is about 55-m high, bell.shaped, and shows a maximum width of 120 m. Aim of the work is the characterization of carbonate rock masses from both the structural and geo-mechanical standpoints through the use of innovative survey techniques. TLS survey provides a product consisting of milions of geo-referenced points, to be managed in space, to become a suitable database for the morphological and geological-structural analysis. Studying by means of TLS a rock face, partly inaccessible or located in very complex environments, allows to investigate slopes in their overall areal extent, thus offering advantages both as regards safety of the workers and time needed for the survey. In addition to TLS, the traditional approach was also followed by performing scanlines surveys along the rims of the Grave, following the ISRM recommendations for characterization of discontuity in rock masses. A quantitative comparison among the data obtained by TLS technique and those deriving from the classical geo-mechanical survey is eventually presented, to discuss potentiality of drawbacks of the different techniques used for surveying the rock masses.