Pantaleone De Vita

A new approach for landslide-induced damage assessment

ABSTRACT The accurate evaluation of landslide-induced damage is a necessity for planning of proper and effective mitigation measures. It requires the implementation of field investigations to identify structural failures to more effectively trace landslide boundaries. Many methods have been proposed to classify landslide-induced damage of buildings. The existing methods demonstrate several advantages and drawbacks depending on the parameters considered, as lack of some important features and difficulties in applicability. A new classification approach of landslide-induced damage of facilities is proposed, which specifically focuses on assessing of damage degree and its relationship to the ground motion intensity and impact severity. The new approach is designed in two steps: a chart utilized during surveys to quantify cracks on structures and ground surface; an a posteriori ranking of structures performed using a cell-grid matrix. Furthermore, a damage recording scheme useful for field surveying is proposed. This approach considers several parameters derived from different existing methodologies by smoothing out drawbacks and homogenizing the considered features. The resulting approach provides a new procedure of landslide-induced damage assessment adoptable in case of private dwellings, as it does not require internal accessibility, and it is exploitable for different landslide events and for different kinds of structures and facilities.

Regional Distribution of Ash-Fall Pyroclastic Soils for Landslide Susceptibility Assessment

Debris flows involving ash-fall pyroclastic soils, which mantle slopes in the mountain ranges around the Somma-Vesuvius, represent a relevant societal risk. In the last years, many methods were applied to evaluate susceptibility and mobility of these landslides, considering at least two fundamental parameters: the slope angle and the thickness of the pyroclastic mantle. Despite this understanding, the assessment of soil thickness along slopes is still a challenging issue due to its high spatial variability and the steep morphological conditions that limit the use of traditional exploration methods. To overcome this problem, heuristic geomorphological methods were mostly applied up to now. In this paper, a regional-scale model of the ash-fall pyroclastic soils distribution along slopes is proposed, considering the isopach maps of each principal eruption. By means of field surveys, the model was validated and an inverse relationship between thickness and slope angle was found.

Spatial modeling of ash-fall pyroclastic deposits for the assessment of rainfall thresholds triggering debris flows in the Sarno and Lattari mountains (Campania, southern Italy)

Among the mountain ranges that surround the Somma-Vesuvius volcano (southern Italy), the Sarno and Lattari mounts are the closest and those where the highest thicknesses of ash-fall pyroclastic soils were deposited. Therefore, pyroclastic soil mantled slopes along these physiographic units are the most affected by rainfall-induced debris flows that, in these areas, represent one of the major geohazards of Italy. According to their strong societal impact, many studies were focused on the assessment of early warning systems based on the analysis of hydrological forcing that trigger debris flows. In this research, an attempt to consider the effect of spatial variability of ash-fall pyroclastic soil deposits and the related stratigraphic settings was carried out to assess rainfall conditions leading to initial slope instabilities that trigger debris flows. A key point was to model the spatial distribution of ash-fall pyroclastic deposits by considering the orientation of the dispersion axes of the main Plinian eruptions, the distance from the eruptive centre and the slope angle. The resulted conceptual geomorphological models, reconstructed for both the considered mountain ranges, were used to simulate hydrological processes that determine initial slope instabilities and to assess the related rainfall thresholds, taking also into account antecedent conditions.

Hydrological behavior of ash-fall pyroclastic soil mantled slopes of the Sarno Mountains (Campania - southern Italy)

The instability of ash-fall pyroclastic deposits that mantle mountain ranges around the Mount Somma-Vesuvius (Campania, southern Italy) are well known to represent a main geological hazard due to their frequent involvement in shallow flow-like landslides, triggered by high-intensity and prolonged rainfall. In such a geomorphological framework, which is similar to other mountain areas that surround volcanic centers of the world, the comprehension of hydrological dynamics occurring into pyroclastic deposits is a key factor for assessing and modelling the landslide hazard. Despite the general relevance of hydrological analysis in studying shallow landslides, this type of approach is particularly significant for pyroclastic soils due to their special hydrological properties and complex stratigraphic settings. Along with this goal, in a test area of the Sarno Mountains, upslope of a debris flow source area, a monitoring station was installed to assess hydrological processes that predispose and lead to landslide triggering. Monitoring data, covering about three hydrological years (Dec. 2010 - Dec. 2013), showed a regime of pore pressures always ranging in unsaturated conditions. Marked seasonal and interannual variations of pore pressure were observed at different depths with respectively delayed and damped dynamics. These observations were correlated to rainfall patterns and the evapotranspiration regime, which is concentrated during the activity period of the existing deciduous forest. Results of this approach allow understanding hydrological processes at slope scale, to set and calibrate numerical models for estimating rainfall thresholds by a deterministic approach as well as to assess landslide hazard.

Approaches for mapping susceptibility to rockfalls initiation in carbonate rock-masses: a case study from the Sorrento coast (southern Italy)

Most of the shoreline of the Campania region, Southern Italy, is characterized by steep and high rocky slopes, then several localities, densely populated and highly touristic attractive for the worldwide famous landscapes are exposed to an high rockfall risk. Particularly, the touristic localities on the Sorrentine Peninsula, such as Sorrento, Vico Equense and Amalfi, can be considered among the most representative case-studies prone to the recurrent instability of rockblocks. Due to the frequent location of settlements and roads underneath and at very limited or null distances from the carbonate steep slopes, a diffuse condition of high rockfall risk exists. Consequently, the assessment of priorities in directing active remedial works to be carried out on the unstable rock slopes is still a challenging issue.In order to find an effective method for assessing the susceptibility to rockfall initiation with approaches suitable for detailed mapping, a combined application of standard methods was tested.The Romanas Slope Mass Rating (SMR) and the Mathesons graphical tests, for assessing the number of fundamental instability mechanisms, were applied in a test site of the Sorrento coast. Results of the two methods were separately evaluated and then combined in a new rating approach by indexing the respective susceptibility classes. In addition, the number of joint sets and the macro-structural features of the rock-mass (faults and master joints) were considered. By means of statistical analyses of rockfalls occurred in the test area, the results obtained with the new combined approach were found more accurate in assessing and mapping the most susceptible areas.

Assessment of landslide-induced damage to structures: the Agnone landslide case study (southern Italy)

Landslides are among the most important and frequent natural calamities that cause severe socio-economic and human losses. After earthquakes, landslides are responsible for the greatest number of casualties and the largest amount of damage to man-made structures. On average, southern Italy is affected by a high spatial density of landslides due to its complex geological setting, which often predisposes it to slope instability phenomena under both natural and anthropogenic influences. Structurally complex formations are widespread in the southern Apennines and are characterized by high heterogeneity and very poor mechanical properties. Thus, these formations represent one of the main factors contributing to the predisposition of slopes to landsliding. In this paper, landslide-induced damage was investigated and analyzed in an area within the municipality of Agnone (Molise region), which is affected by a complex landslide that involves a structurally complex formation. The approaches used were based on six different methods that have previously been described in the literature, and a comparison of the results was made. Data regarding the damage, which consists largely of cracks observed in buildings and at the ground, were compiled through field surveys. The results were critically analyzed to note the advantages and constraints of each classification scheme. The aim of the work was to apply and compare different approaches in order to test the best and most accurate procedures for assessing damage due to landslides at the scale of individual buildings as well as to provide an objective assessment of the degree of landslide damage to structures and facilities.

Hydrological Monitoring of Ash-Fall Pyroclastic Soil Mantled Slopes in Campania (Southern Italy)

Open image in new window Ash-fall pyroclastic deposits that mantle mountain slopes around the Mount Somma-Vesuvius (Campania, southern Italy) are frequently involved in debris flows under high-intensity and prolonged rainfall, thus representing a principal geohazard for settlements located alongside the footslope areas. In such a geomorphological framework, to understand temporal and spatial hydrological dynamics occurring into ash-fall pyroclastic soil coverings is a key factor for assessing and modelling landslide hazard as well as for setting reliable early warning system. Along with this research focus, since 2011 field monitoring activities were carried out in a test area of the Sarno Mountains to assess hillslope hydrological processes that predispose and lead to slope instability. The analysis of pressure head time series, recorded along four hydrological years (Jan 2011–Dec 2014) in the whole thickness of the ash-fall pyroclastic soil cover, showed a composite temporal variability, from the daily to the seasonal time scales, related to rainfall patterns and evapotranspiration regime as well as to unsaturated flow dynamics. Unsaturated conditions were always observed with pressure head values ranging at the annual scale from about −0.6 m to, and beyond, −20 m. Such a marked hydrological dynamics of the ash-fall pyroclastic soil covers demonstrates the relevant role of antecedent hydrological conditions in predisposing landslide triggering under a single rainfall event. Therefore, results obtained by the proposed approach can be conceived as a fundamental basis to understand hydrological processes at slope scale. Moreover they can be used to set and calibrate hydrological numerical and slope stability models for estimating rainfall thresholds triggering slope instabilities as well as to assess inherent landslide hazard.

Long-Term Hydrological Modelling of Pyroclastic Soil Mantled Slopes for Assessing Rainfall Thresholds Triggering Debris Flows: The Case of the Sarno Mountains (Campania—Southern Italy)

Air-fall pyroclastic deposits covering Campanian mountain slopes (southern Italy) are very prone to instability under heavy and prolonged rainfall. In such a geo-hazard framework, to understand hydrological dynamics of pyroclastic mantle is a step further toward the deterministic assessment of rainfall thresholds and landslide hazard. In this research, the hydrological modelling of a pyroclastic soil mantled slope of the Sarno Mountains is proposed to assess the role of antecedent hydrological conditions on rainfall triggering debris flows. The approach is based on the finite difference modelling, from seasonal to inter-annual timescales, of unsaturated/saturated flows occurring into the pyroclastic mantle upslope of a source area of a debris flow. Modelling results were calibrated by means of field measurements achieved by a tensiometer monitoring station. Among the main results, the pressure head distribution into the pyroclastic deposits showed a dominant unsaturated condition and a relevant seasonal variation extending below the root zone and down to the bedrock interface, about 4 m deep. This hydrological regime is attributable both to the distinctive water retention properties of pyroclastic soils and to the existence of a deciduous forest, which concentrates water losses due to evapotranspiration during the dry season. This behavior highlights the remarkable role of antecedent hydrological conditions as a not negligible predisposing factor to instability during short and heavy rainstorms.

Physically-Based Models for Estimating Rainfall Triggering Debris Flows in Campania (Southern Italy)

The societal risk related to rainfall-triggered rapid debris flows is commonly managed in urbanized areas by means of early warning systems based on monitoring of hydrological parameters (such as rainfall or soil moisture) and analysis of thresholds values. This paper deals with physically-based modelling of ash-fall pyroclastic soil coverings involved in debris flows along mountain slopes nearby the Somma-Vesuvius volcano (Campania, southern Italy), which represent one of the major geohazards of Italy. The methods adopted combine deterministic approaches at the site-specific and distributed scales to estimate Intensity-Duration rainfall thresholds triggering debris flows. The first approach is based on the reconstruction of detailed physical models of ash-fall pyroclastic soil coverings in representative source areas of debris flows and on the related hydrological and slope stability modelling. The second is focused on a regional distribution model of ash-fall pyroclastic soils over mountain slopes surrounding the Somma-Vesuvius volcano, which takes into account total thicknesses of pyroclastic coverings and variable stratigraphic settings. For both, effects of different initial antecedent hydrological conditions, associated with summer and winter, are considered.

Rising groundwater levels and impacts in urban and semirural areas around Naples (southern Italy)

The rising of groundwater levels in urban and rural areas is a relevant topic of the Urban Hydrogeology because it affects different areas of the world requiring specific analyses and mitigation measures by the institutions involved in the protection and security of the territory.In the last century, in many developed countries processes of deindustrialization and urban transformation have caused the rising of groundwater levels and severe economic and social impacts.The aim of this paper is to analyse the rising of groundwater levels in a multi-layered pyroclastic-alluvial aquifer, located in the coastal plain eastward of Naples (southern Italy) and its interactions with buildings and agricultural lands.The research has been carried out by means of: i) analysis of stratigraphic settings by 86 boreholes and reconstruction of hydraulic conductivity logs; ii) reconstruction of a 2D hydrostratigraphic model of the multi-layered pyroclastic-alluvial aquifer; iii) slug test and multi-temporal hydrogeological monitoring of 83 wells, 9 piezometers and 12 river water levels; iv) analysis of daily rainfall time series; v) hydrogeological monitoring of impacted buildings and agricultural lands.For the monitored period (November 2013-March 2015), the groundwater table showed a generalized rise, although with a spatial variability. The rise of groundwater levels ranged from a minimum of 0.10 meters, in the central and eastern sector of the study area, to a maximum of 2.05 meters, in the south-western sector, with an average growth rate of about 0.16 m.The distribution of the impacted areas is not spatially homogeneous, and it was observed to vary over time. The hydrogeological interactions between groundwater and urban and rural areas are affected by: i) foundation types of buildings and the depth of the underground structures; ii) presence of shallow aquicludes (marshy clay-sands, clay-silts and peat levels) that determine local conditions of confinement for groundwater; iii) hydraulic efficiency and maintenance state of the dense network of drainage channels and micro-channels, which were historically built to drain surface water and groundwater in rural areas.The obtained results provide the basic data to set up a numerical groundwater flow model, which is an indispensable tool to simulate and predict the hydrogeological effects of possible safeguard actions on urban and agricultural areas.