GIS application in the extractive activities' planning in the Verbano Cusio Ossola Province (Piedmont, NW Italy): a model for preliminary rock slope stability assessment

摘要

The Verbano Cusio Ossola Province' Geological Service, operating in the sector of natural hazard management since carrying out Piedmont regional law n. 44/2000, has promoted a geomechanical and geomorphological analysis of rock masses in 68 dimensional stone quarries (gneiss, marble and granites) located in the provincial territory, with the attempt to form a geological technical database about main structural and mechanical parameters, so as to provide a support tool for environmental and territorial planning of mining activities and related rock mechanics application. The activity is formed by a geostructural survey and by a rock sampling, also in proximity of the main joints, finalized to the acquisition of mechanical parameters by means of some field and laboratory tests and through critical application, regarding the geological context, of geomechanical classifications and failure criteria. A comparative analysis with the approach adopted in describing structural model of rock masses for drawing up previous quarry-projects, sometimes pointed out qualitative differences about data and processing procedures. Row and processed data have been catalogued and organized using GIS technologies to prepare thematic maps, to determine spatial relations among multiple datasets and to make information easy available, both for planners involved in the local government processes and for extractive enterprises as reference for their excavation projects, in order to make possible the sharing and the integration of the information at provincial level. The analysis of spatial relationships and the statistical elaboration of the main geomechanical information and structural parameters of discontinuities has allowed to define 5 homogenous areas on the territory at regional scale. As an application of the geological technical database, has been developed a cartographic tool involving the assessment of spatial variability of SMR index both for planar/wedge and toppling kinematics, through the overlay of informative map levels in a GIS-system, to the forecast of natural and excavated rock slope stability problems in quarrying areas, selected in different structural condition inside some “extractive pole” designed by the Regional Programmatic Document of Extractive Activities. Topographic data were obtained from a digital elevation model with 2 m spatial resolution and the basic-RMR thematic map was derived checking and integrating field mechanical data with morphology and local tectonic style of rock walls. Model validation was done by means of the ending overlay of the SMR stability classes map with the morpho-structural numeric cartography and comparing information collected in some control field stations with the results generated by the model, in which these stations was not included. This application has allowed look for the best suitable areas to continue extractive activity about the strategic provincial quarries' planning.