Geological hazard zonation in a marble exploitation area (Apuan Alps, Italy)
Abstract
The present paper describes the hazard mapping of an exploitation area sited in the Apuan Alps marble district (Italy) carried out by the integration of various survey and analysis methodologies. The research, supported by the Massa and Carrara Local Sanitary Agency responsible for workplace health and safety activities, aimed to reduce the high degree hazard of rock fall caused by the presence of potentially unstable blocks located on slopes overhanging the marble quarries. The study of rocky fronts bases on the knowledge of both the structural setting and the physical-mechanical properties of intact material and its discontinuities. In this work the main difficulty in obtaining this information was the inaccessibility of the slope overhanging the area (up to 500 meters high). For this reason, the structural and geological-engineering surveys were integrated by outcomes from digital photogrammetry carried out through terrestrial stereoscopic photos acquired from an aerostatic balloon and a helicopter. In this way, it was possible to derive the geometrical characteristics of joints (such as discontinuities dip, dip direction, spacing and persistence), blocks volumes and slopes morphology also in inaccessible areas. This information, combined with data coming from the geological-engineering survey, was used to perform the stability analysis of the slope. Subsequently, using the topographic map at the scale of 1:2,000, the Digital Terrain Model (DTM) of the slopes and several topographic profiles along it were produced. Assuming that there is a good correspondence between travelling paths and maximum down slope angle, probable trajectories of rock fall along the slope were calculated on the DTM by means of a GIS procedure which utilizes the ArcHydro module of EsriTM ArcMap software. When performing such a 2D numerical modelling of rock falls, lateral dispersion of trajectories has often been hampered by the "a priori" choice of the travelling path. Such a choice can be assessed largely subjective and it leads to possible errors. Thus, rock fall hazard zonation needs spatially distributed analyses including a reliable modelling of lateral dispersion. In this research Conefall software, a freeware QuanterraTM code that estimates the potential run out areas by means of a "so-called" cone method, was used to compute the spatial distribution of rock falls frequency, velocities and kinetic energies. In this way, a modelling approach based on local morphologies was employed to assess the accuracy of the 2D analysis by profiles created "a priori" along the maximum down slope angle. Final results about slope stability and run out analysis allowed to create rock fall hazard map and to advise the most suitable protection works to mitigate the hazard in the most risky sites.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMNH13E1423F
- Keywords:
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- 4326 NATURAL HAZARDS / Exposure;
- 4333 NATURAL HAZARDS / Disaster risk analysis and assessment