Rock slope stability analysis through on-site methods: data from CSIRO Hi Cells tests for calibrating 3D numerical models

Purpose: The main aim of the present study is to evaluate the stability of some marble quarries in the Apuan Alps (Italy) through three-dimensional geometric reconstruction, numerical modelling and calibration of the stress states acting on-site. This research is developed through both in-situ and laboratory investigation techniques, whose results enabled to obtain an in-depth knowledge of the acting stress states (3D stress tensor) and the material elastic properties. The data obtained from these methods allowed us to carry out the stability analysis and therefore to ensure workplaces safety for the personnel involved in mining activities. Methods: The proposed method of investigation is based on: i) the acquisition of the geometric information of the quarry slopes using geo-referenced surveys acquired by terrestrial laser scanner and/or UAV (Unmanned Aerial Vehicle); ii) the acquisition of data about the characteristics of the rock mass through engineering-geological surveys and laboratory tests; iii) the on-site measurement of the acting stress states through CSIRO HI cells tests; iv) the creation of the rock masses 3D numerical models, including their calibration, and the simulation of the various future excavation phases. The data achieved from the various activities flowed into a series of models simulating the geological and stress conditions of the various fronts, whose stability was analyzed by applying both methodologies of distinct elements (DEM), using 3DEC (Itasca®), and finite elements, using RS3 (RocScience®). Results: The strain and stress measurements conducted on site were used to calibrate the models through a reiterated procedure written ad hoc using the MATLAB® language. For each model, the analysis of the stress states, the displacement vectors, the deviatory stress and, consequently, the stability of the slope was carried out in temporal sequence, starting from the initial conditions up to the final state as from the excavation plan. Conclusions: The integrated approach of on-site measurements and geological analyses through 3D numerical modelling, allowed us to define the stress state acting in some quarries of the Apuan Alps’ marble complex. Thanks to the numerical modelling, appropriately calibrated and validated with the on-site stress state measurements, a faithful stability analysis was carried out. This research approach came out suitable for detecting and monitoring, even during the excavation activities, the stress-strain behaviour of the rocky walls and for guaranteeing a safe workplace for the personnel involved.