Abstract
On the 4th and 5th of March 2005, about 100 rainfall-induced landslides occurred along volcanic slopes of Camaldoli Hill in Naples, Italy. These started as soil slips in the upper substratum of incoherent and welded volcaniclastic deposits, then evolved downslope according to debris avalanche and debris flow mechanisms. This specific case of slope instability on complex volcaniclastic deposits remains poorly characterized and understood, although similar shallow landsliding phenomena have largely been studied in other peri-volcanic areas of the Campania region underlain by carbonate bedrock. Considering the landslide hazard in this urbanized area, this study focused on quantitatively advancing the understanding of the predisposing factors and hydrological conditions contributing to the initial landslide triggering. Borehole drilling, trial pits, dynamic penetrometer tests, topographic surveys, and infiltration tests were conducted on a slope sector of Camaldoli Hill to develop a geological framework model. Undisturbed soil samples were collected for laboratory testing to further characterize hydraulic and geotechnical properties of the soil units identified. In situ soil pressure head monitoring probes were also installed. A numerical model of two-dimensional variably saturated subsurface water flow was parameterized for the monitored hillslope using field and laboratory data. Based on the observed soil pressure head dynamics, the model was calibrated by adjusting the evapotranspiration parameters. This physically based hydrologic model was combined with an infinite-slope stability analysis to reconstruct the critical unsaturated/saturated conditions leading to slope failure. This coupled hydromechanical numerical model was then used to determine intensity–duration (I-D) thresholds for landslide initiation over a range of plausible rainfall intensities and topographic slope angles for the region. The proposed approach can be conceived as a practicable method for defining a warning criterion in urbanized areas threatened by rainfall-induced shallow landslides, given the unavailability of a consistent inventory of past landslide events that prevents a rigorous empirical analysis.
Highlights
The city of Naples, the regional capital and the third most populous city ofItaly with about one million inhabitants, is an emblematic urban setting highly vulnerable to aWater 2019, 11, 1915; doi:10.3390/w11091915 www.mdpi.com/journal/waterThe city of Naples, the regional capital and the third most populous city of Italy with about one million inhabitants, is an emblematic urban setting highly vulnerable to a variety of variety of geohazards, such as eruptions, volcanic eruptions, bradyseism, earthquakes, coastal erosion, sinkholes, geohazards, such as volcanic bradyseism, earthquakes, coastal erosion, sinkholes, floods, floods, and landslides.Due to uncontrolled growth of the city after the Second WorldWar, which and landslides
Given that Naples’ peripheral urban areas are exposed to dangerous effects of shallow flow-like landslides occurring along steep volcanic slopes of the Phlegrean Fields, the principal objectives of this study are to advance the understanding of antecedent and triggering hydrological conditions leading to onset of slope instability and to estimate an Intensity-Duration (I-D) rainfall threshold [17] to be used for establishing an early warning system in areas underlain by volcanic bedrock
The stratigraphic setting of the source area of the landslide studied is formed by a surficial loose sandy gravel with silt (SM), corresponding to the pedogenized present-day soil (A and B soil horizons), overlapping dense silty sand (SM, C soil horizon), formed by fine ash, sometimes with gravel (GP)
Summary
The city of Naples (southern Italy), the regional capital and the third most populous city ofItaly with about one million inhabitants, is an emblematic urban setting highly vulnerable to aWater 2019, 11, 1915; doi:10.3390/w11091915 www.mdpi.com/journal/waterThe city of Naples (southern Italy), the regional capital and the third most populous city of Italy with about one million inhabitants, is an emblematic urban setting highly vulnerable to a variety of variety of geohazards, such as eruptions, volcanic eruptions, bradyseism, earthquakes, coastal erosion, sinkholes, geohazards, such as volcanic bradyseism, earthquakes, coastal erosion, sinkholes, floods, floods, and landslides.Due to uncontrolled growth of the city after the Second WorldWar, which and landslides. The city of Naples (southern Italy), the regional capital and the third most populous city of Italy with about one million inhabitants, is an emblematic urban setting highly vulnerable to a variety of variety of geohazards, such as eruptions, volcanic eruptions, bradyseism, earthquakes, coastal erosion, sinkholes, geohazards, such as volcanic bradyseism, earthquakes, coastal erosion, sinkholes, floods, floods, and landslides. Due to uncontrolled growth of the city after the Second World War, which accelerated accelerated in peripheral the 1970s, peripheral zones to exposed natural hazards, as floods and landslides, in the 1970s, zones exposed naturalto hazards, such as such floods and landslides, were were progressively occupied, inducing a consequent increase of risk [1]. In recent years, progressively occupied, inducing a consequent increase of risk [1]. One of the most important landslide events on the 4thon andthe
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