In a considerable part of Campania, landslides that originate in pyroclastic soil covers are rather common phenomena after intense and/or prolonged rainstorms. The fact that such landslides predominantly originate as debris slides draws attention towards the possibility of investigating the spatial component of the related hazard, based on the spatial distribution of past landslides. The latter is related to the spatial characters of the soils and their bedrock, as well as to the spatial distribution of critical rainfall sequences. The attempts that have been made in the last two decades to relate landslides that occurred over limited areas to rainfall data that were, on the other hand, significant in terms of averages over larger areas, achieved only partial success. This is due to the fact that the rainfall data were collected too coarsely for landslide analyses and, in addition, at elevations that were generally much lower than those of the initial debris slides. The spatial distribution of most of these landslides for a given sequence indeed demonstrates the fact that landslide-triggering rainfall sequences in Campania can be highly variable over space, even within short distances. It appears reasonable, however, to approach the volcanic debris slides spatial distribution problem independent of the spatial distribution of the triggering rainfall events. This allows to concentrate on the possible assessment of where landslides of this type can originate in case of critical rainfall. The application of the distributed modeling approach, either based on assumptions of steady-state or transient rainfall rates and flow, has shown however only partial effectiveness in identifying the loci of initial sliding for such landslides. This is due to the fact that (i) a significant percentage of such slides originate on steep slopes, where little or no relationship with drainage patterns can be recognized, and (ii) the majority of them occurs just above or below discontinuities of the soil cover, generally represented by rock cliffs or artificial cuts, where these methods are not applicable due to the assumption of infinite slope. For slides within soils on carbonate reliefs, several Authors report that the crowns of the studied landslides occurred within 10 m of a soil discontinuity (above or below it) for percentages averaging about 60% of the total studied landslides. The concentration of initial slides close to discontinuities in the soil cover is understandable because, for a spatially homogeneous precipitation pattern over a given soil cover of homogeneous properties, the slope gradient at which limit equilibrium conditions are reached can reasonably be considered higher where the cover is continuous than where the same cover shows unsupported and/or free drainage surfaces, as it does above or below discontinuities. A consequence of these findings is that it would be desirable to separate the crown and sliding zone slopes statistics for landslides that originate within continuous volcanic soil covers from those that originate within discontinuous ones. In this framework, a method is proposed for the assessment of the susceptibility to sliding of volcanic soils in Campania, based (i) on a good resolution assessment of slope gradients, (ii) on the detection of discontinuities in the volcanic soil cover, and (iii) on slope variation patterns. The aim of the research in which the method has been developed is to investigate the spatial component of the widely perceived “unpredictability” of this type of landslides, by means of searching the slope areas which can be more susceptible to sliding of the volcanic soil cover. Starting from these, guidelines for further investigation of landslide hazard and risk mitigation strategies can be developed, based not only on the presumable avalanche-flow paths and on vulnerability considerations downwards, but also on local, targeted stabilization of the volcanic soil cover itself.

A method for the assessment of the sliding susceptibility of volcanic soils in Campania

PERRIELLO ZAMPELLI, SEBASTIANO
2007

Abstract

In a considerable part of Campania, landslides that originate in pyroclastic soil covers are rather common phenomena after intense and/or prolonged rainstorms. The fact that such landslides predominantly originate as debris slides draws attention towards the possibility of investigating the spatial component of the related hazard, based on the spatial distribution of past landslides. The latter is related to the spatial characters of the soils and their bedrock, as well as to the spatial distribution of critical rainfall sequences. The attempts that have been made in the last two decades to relate landslides that occurred over limited areas to rainfall data that were, on the other hand, significant in terms of averages over larger areas, achieved only partial success. This is due to the fact that the rainfall data were collected too coarsely for landslide analyses and, in addition, at elevations that were generally much lower than those of the initial debris slides. The spatial distribution of most of these landslides for a given sequence indeed demonstrates the fact that landslide-triggering rainfall sequences in Campania can be highly variable over space, even within short distances. It appears reasonable, however, to approach the volcanic debris slides spatial distribution problem independent of the spatial distribution of the triggering rainfall events. This allows to concentrate on the possible assessment of where landslides of this type can originate in case of critical rainfall. The application of the distributed modeling approach, either based on assumptions of steady-state or transient rainfall rates and flow, has shown however only partial effectiveness in identifying the loci of initial sliding for such landslides. This is due to the fact that (i) a significant percentage of such slides originate on steep slopes, where little or no relationship with drainage patterns can be recognized, and (ii) the majority of them occurs just above or below discontinuities of the soil cover, generally represented by rock cliffs or artificial cuts, where these methods are not applicable due to the assumption of infinite slope. For slides within soils on carbonate reliefs, several Authors report that the crowns of the studied landslides occurred within 10 m of a soil discontinuity (above or below it) for percentages averaging about 60% of the total studied landslides. The concentration of initial slides close to discontinuities in the soil cover is understandable because, for a spatially homogeneous precipitation pattern over a given soil cover of homogeneous properties, the slope gradient at which limit equilibrium conditions are reached can reasonably be considered higher where the cover is continuous than where the same cover shows unsupported and/or free drainage surfaces, as it does above or below discontinuities. A consequence of these findings is that it would be desirable to separate the crown and sliding zone slopes statistics for landslides that originate within continuous volcanic soil covers from those that originate within discontinuous ones. In this framework, a method is proposed for the assessment of the susceptibility to sliding of volcanic soils in Campania, based (i) on a good resolution assessment of slope gradients, (ii) on the detection of discontinuities in the volcanic soil cover, and (iii) on slope variation patterns. The aim of the research in which the method has been developed is to investigate the spatial component of the widely perceived “unpredictability” of this type of landslides, by means of searching the slope areas which can be more susceptible to sliding of the volcanic soil cover. Starting from these, guidelines for further investigation of landslide hazard and risk mitigation strategies can be developed, based not only on the presumable avalanche-flow paths and on vulnerability considerations downwards, but also on local, targeted stabilization of the volcanic soil cover itself.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/374945
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