Ornamental stone quarrying in the Carrara basin have determined the formation of several underground voids. A methodology, able to asses the stability conditions of the excavation, has been adopted in order to evaluate the safety conditions of both existing structures and forecasted ones. Rock excavation induced variation of the natural state of stress, consequently the measurement of the acting stress state has been considered has the starting point of this study. The problem connected with the in situ measurements of the stress is strongly influenced by the presence of discontinuities that can influence the stresses in entity and in their orientations. For this reason special regards has been paid to the geometrical reconstruction of the rock mass by means of numerical tools that allow the discrete reconstruction of the rock mass. The methods has, up to now, been applied to one site where hydraulic fracturing measurements have been performed and where the measurements have been considered abd interpreted by means of a 3D reconstruction of the rock. The measured state of stress has been compared with the computed values by Distinct Element Modeling application to the site in all different measurement points.
This work reports on analyses so far conducted for the assessment of conditions of stability in underground excavation for the extraction of ornamental stone. In particular, the study regards the Ordinary and Arabesque B-slabs marble quarry, located within the Apuan Alps, a mountainous zone in Tuscany, Italy. The area of exploitation belongs to the Apuan metamorphic complex and is the result of the tectonic and metamorphic phases that occurred during the alpine orogenesis, some 11 ? 17 million years ago. The Apuan metamorphic complex was brought about following a low grade metamorphic process with a rock load of approximately 3 ? 4 kbar and T = 300°/400°C. In these conditions limestone acquires remarkable plasticity; calcite crystals increase in size, raising the temperature, and flatten out, offering greater resistance to pressure, thus creating a schistose mass.
The quarry is made up of a single tunnel extraction site (Figure 1), inasmuch as the external section has already been subjected to mining activity. The external section is composed of a modest yard at 789 m above sea level, used for storing mining equipment and blocks of marble destined for the market. The single entry provides access to a rectangular tunnel, approximately 15x20 m, which also constitutes the only breast.
