The design of an open-pit quarry must continuously adapt to the real conditions of the excavation faces, to meet safety requirements and maximize the effectiveness of the operational process. The case study of an ornamental stone quarry characterized by great value and challenging excavation geometry is analyzed in this study. The exploited rock mass is characterized by a non-ubiquitous discontinuity distribution due to the presence of highly fractured bands, mainly parallel to the excavation faces. The discontinuity network needs to be analyzed to forecast the rock mass mechanical behavior during excavation. In this regard, the integration of geotechnical and geophysical surveys allows the rock mass to be studied from the surface to a considerable depth. Trace mapping on scaled digital images was combined with traditional geomechanical methods and GPR surveys, executed on the excavation faces, to assess the variability of discontinuity spacing and to characterize the fractured bands.
The stability of a potentially unstable rock mass is highly sensitive to the continuity of the fractures cutting it. Evaluation of the spacing and persistence of these fractures is generally based on surface geological observations and geomechanical analyses. This approach, however, suffers from the lack of information about the rock mass structure beneath the surface and a precise definition of the fractures properties. With respect to these issues, geophysical surveys could be helpful in obtaining information inside the rock volume and comparing them with the ones coming from the superficial geomechanical observations. This data integration is crucial to get a more comprehensive characterization of the state of fracturing of the rock mass. In consistent rock masses with high electrical resistive properties (i.e., massive rock formations usually present at excavation sites), Ground Penetrating Radar (GPR) is the most suitable technique to provide precise information about the near-surface structures and fracture setting. This is due to the potentially obtainable vertical and horizontal resolution, which depend on the rock characteristics and the frequency of the chosen antenna, the satisfactory penetration depth in resistive materials, to detect deeper fractures, and the low weight and versatility of the GPR equipment. Several literature examples on the application of GPR for fault and fracture mapping are available in the literature (e.g., Grodner, 2001; Lualdi and Zanzi, 2004; Porsani et al., 2006; Deparis et al., 2007; Poisson et al., 2009; Anterrieu et al., 2010).
