Studio geostrutturale e geomeccanico della cava Piastrone (Seravezza, Italia)

The study is aimed at the geological and structural characterization of the rock mass mainly consisting of marble outcropping at the site called Piastrone quarry. The quarry, located in the municipality of Seravezza (LU) and owned by the Henraux Spa, is part of the Retro-Altissimo mining basin of the Apuan Alps. Recently, the mining activity has been resumed after about thirty years of inactivity. Cultivation involves the portion below 1250 m a.s.l., while the upper part over this altitude presents a high degree of fracturing, which is not always compatible with the extraction activity. The analysis focuses on the portion located at 1260 m a.s.l. to evaluate the possibility of carrying out a cultivation also in portion telling. To reach this finality, the thesis is divided into three parts; the first is a geological-structural framework of the area, the second focuses on the geomechanical characterization of the rock mass and the third on stability analysis of the different excavation fronts. The first part, preparatory to the subsequent work phases, defines the deformation history to which the rock mass was subjected; the study was carried out both through bibliographical references and through the detection and description of the structures on the meso and microscopic scale. The second part analyzes the data coming from the traditional geomechanical survey, carried out on 7 different fronts placed between 1224 and 1266 m a.s.l.; the cataloged systems are compared with those deriving from bibliographical references and those obtained through non-contact techniques. The focus is on the comparison between the geomechanical survey and these techniques, which are based on the study of mesh and texture models (DSM, Digital Surface Model), generated from images acquired by aerophotogrammetric with drones and terrestrial surveys (Structure from Motion algorithm). CloudCompare software was used for this study. The aerophotogrammetric survey reduces the risks in the work phase of the operators and allows the observation of areas otherwise unreachable, however the results obtained show a lower detail than the traditional geomechanical survey. The data deriving from this analysis are useful for the evaluation and quantification of the stability degree of the rock mass, object of the last part of the elaborate. The first step for the execution of a stability analysis is the Markland Test for identifying the kinematics that can potentially occur along a front. Subsequently, the degree of stability is quantified by estimating the safety factor, for the calculation of which different resistance criteria were used. Here the safety factors with respect to planar and wedge sliding were calculated both through analytical methods and through software. The results obtained with the two methods are close in 90% of cases and, above all confirm the role of primary importance that rock bridges, that is intact portions that increase cohesion along intermittent discontinuities, play in the stability of a front.