In a large open-pit quarry of basalt north of Firenze (Italy), cultivation was executed by drill & blast. Close to the quarry site there is a large rock-ridge overhanging, with steep slopes, a national road and a small village. The aim of our work was to verify if the quarry-blasting could induce rock-fall and subsequently become a hazard for road and village safety. In order to evaluate the rock-mass behaviour we carried out a detailed geostructural-geomechanical survey and seismic monitoring. Seismic monitoring data were used to define the seismic attenuation/amplification all along the slope in order to evaluate what kind of seismic input to use in the stability analysis. Geostructural and geomechanical data were analysed, in the frame of a GIS procedure, according to SMR and KARS methods, for each TIN-grid of the slope in order to produce probabilistic maps of the different types of rock-fall (plane-slide, toppling, wedge, …) which potentially could occur on the slopes overhanging the road and the village. Trajectories, distances and probability of rock-falls were calculated and mapped for each slope-site which displayed a high-rate in generating rock-falls. The results allowed for a correct evaluation of the potential hazard to the road and the village and a verification that no real risk could be related to the quarrying activity. This method allows a classical slope-stability analysis to be developed for each TIN-grid, thus overcoming the limitations of analysing only a single average slop orientation. This method also allows seismic monitoring data to be incorporated in the stability analysis. This method's results can be easily developed and applied to any slope stability-analysis in order to obtain a better evaluation of the potential hazards related to rock-fall.
North of Florence (Italy), in a huge ophiolitic body it was opened a large open-pit quarry of basalt in order to obtain aggregate for concrete. Close to the quarry site there is a large rockridge overhanging, with steep slopes, a national road and a small village (Figure 1). The aim of this work is to verify if the quarry-blasting can induce rock-fall and subsequently become a hazard for road and village safety. Stability analysis were performed in the frame of a GIS procedure, according to MARKLAND (1972)  and ROMANA (1985)  methods, for each TINgrid of the slope in order to produce probabilistic maps of the different types of rock-fall (planeslide, toppling, wedge, …) which potentially could occur on the slopes overhanging the road and the village.
In the area where the quarry is opened there are large outcrops of clayey tectonic melange of the alloctonous Ligurian Units of oceanic realm origin [3, 4, 5]. Clay-stone and shale display widespread gliding occurrences ; the quarry is opened in N-S elongated ridge, which represents a large olistolite, constituted by an ophiolite body of massive basalt, pillow basalt and basalt breccias topped by its sedimentary cover: Calpionella Limestones, Cherts and Palombini Shales.