3D geomechanical characterization for a safe design of an open pit exploitation

The aggregate quarries represent over 64% of the total amount authorized in Italy. In this scenario, the demand for an extension of a limestone quarry arises. This thesis analyses the slope stability of the exploitation expansion of the Faraona quarry; the quarry is located in the municipality of Travedona Monate, Varese Province, and it is managed by Holcim Italia SpA. The quarry plan estimates the potential extraction of 6,780,000 m3 of limestone for the next two decades. The mining area is located between Comabbio and Monate lakes. The exploitation involves an outcrop of the Ternate geological formation. Starting from the legislative background that prescribes some technical constrains, this work describes, in particular, the design process of the Faraona quarry. A planning of the exploitation cannot always be kept during the extraction, as changes which require an adaptation plan can occur. During the exploitation of the quarry, some phenomena of instability occurred. As a first solution, a more conservative layout has been suggested, but other tension cracks and planar sliding occurred. An important and flexible tool for slope stability assessment is the numerical modelling, which, through the reconstruction of the three-dimensional model with specific software, allows to simulate the behaviour of the rock mass to evaluate the pit stability. The existing 2D model provided a good assessment of the scenarios; nevertheless, this work is based on a more accurate and complex series of 3D-FEM and 3D-DEM analyses to better describe the overall and local stability of the new slopes characterising the expansion of the quarry. The correct setting of the rock mass parameters represents an important criticality in the numerical modelling, both in a continuum and discontinuum model: with a sensitivity analysis, the modelling guaranties a suitable evaluation of the influence of the rock mass parameters in the slope stability assessment. The results based on the design parameters showed that the instability is just localized in a few sliding blocks, as observed on site; on the contrary, the results of the sensitivity analysis showed that more severe landslides can occur only if the parameters of the joints are heavily weathered by some external events.