Use of innovative technologies for the analysis of brittle failure mechanisms applied to underground and open pit marble mines

The exploitation of rock material usually results in a change of the in-situ force field surrounding the rock mass. Mine design is one of the major challenges when planning and operating a mine in a complex environmental context such as the Apuan Alps marble district (Italy). There could be significant risks related to the safety of both personnel and equipment. This research focuses on data collection, geo-structural interpretation and rock mechanics analysis by means of advanced remote sensing techniques (e.g. Structure for Motion methods, Terrestrial Laser Scanning, change detection analysis, etc.), numerical modelling for the stability analysis of both surface and underground structures, and modelling of brittle failure. In particular, this research investigates the application of Remotely Piloted Aircraft Systems (RPASs) and of Structure from Motion (SfM) methods for geo-hazard identification, awareness and risk reduction. Limit equilibrium and numerical analyses were carried out to study the stability of two large marble blocks in an open pit marble mine area. These analyses were focused on the important role that rock bridges have on slope stability, and to investigate the active-passive wedge mechanism that may develop due to rock mass strength degradation and brittle failure mechanisms. Additionally, the spalling failure of an underground marble pillar was investigated to include a multifaceted/multitemporal stability analysis with the objective of studying mining engineering issues related with the extraction of valuable rock resources. Morphological variations were identified using a change detection approach and analysed using both Finite Element (FEM) and hybrid Finite-Discrete Element (FDEM) methods. In this context, understanding the mechanical behaviour of a rock mass has always been a major concern for increasing the safety and minimizing economic loss. A mine design concerns the stability of the excavations, including the potential collapse of slopes and quarry faces, spalling of the sidewalls, and the structurally controlled failure of the underground openings. The cornerstone of an engineering understanding of a rock mass structure is represented by data collection and interpretation. The starting point is represented by the knowledge of the lithologies and the major structural features present in the rock mass. Such information provides essential background to rock mechanics studies, but may be available in limited form using classical mapping techniques due to the limited accessibility of rock outcrops. Indeed, measurements can be made on natural slopes or on faces exposed by surface excavations, but the data collected may not be representative of the whole site. In this context, it is now possible to drastically increase the quantity of mapping information by using advanced and modern geomatics techniques. In order to analyse rock outcrops, the use of RPAS allows to overcome data acquisition issues related to high steep quarry walls, while at the same time it provides high resolution images and 3D models. This is particularly important because fractures characteristics may be spatially variable due to stress relaxation induced by excavation activity. Terrestrial Laser Scanning allows to rapidly acquire information as point clouds with a millimetre level of detail from the surrounding surfaces. Both aerial and terrestrial measurement techniques can be useful to perform detailed and accurate structural analysis and periodical estimates of surface changes by means of the so-called change detection analysis, in order to identify modified surfaces in the mining area. In this context, geomatics techniques and conventional geological/engineering-geological surveys techniques should be used simultaneously because when used together they allow to reduce data uncertainty and to provide a better characterisation of data variability. Indeed, the reliability of the analysis depends on the quality, quantity and interpretation of available field information. Many design structures in mine engineering practice involve complex problems and it is often necessary to carry out detailed rock mechanics analysis using powerful numerical tools. Indeed, stress and stability analysis can be carried out using continuous and/or discontinuous numerical approaches. These techniques are currently used in the civil and mining engineering sectors due to the possibility to take account of complex rock mass deformation and failure. Numerical methods allow to consider the whole rock mass mechanical behaviour on the contrary of classical approaches that, for example, consider a block as an isolated object. In this context, numerical methods are able to investigate and illustrate the involved rock failure mechanisms during mining activities and particularly the initiation, propagation, and coalescence of cracks, and the propagation of discrete fractures