1,720,998 research outputs found
Simulations of landslide hazard scenarios by a geophysical safety factor
No full textSoil response to rainfall is a complex phenomenon that requires modeling of many sources of heterogeneity, whose variations can be relevant on various timescales and whose precise description requires a large amount of data inputs. Due to the great complexity of the problem, many simplifying assumptions are usually made in modeling landslides triggered by rainfall. As regards rainfall-induced shallow landslides, conventional approaches base slope stability analyses on the infinite slope model combined with hydrological models, which provide the time evolution of groundwater pressure head and volumetric water content. On the other hand, the response of geophysical quantities to water changes depends also on the variations in mechanical and hydrological properties. For this reason, we attempt a different approach to the problem of slope stability assessment by shifting the focus on the analysis of variations in geophysical properties. In this paper, starting from experimental resistivity data acquired in a test area, we perform a series of numerical simulations to study how changes in soil resistivity spatial distributions may affect the size of unstable areas. We use a simple cellular automaton whose states are defined by the values of a local and time-dependent geophysical factor of safety, which depends on soil electrical resistivity and slope inclination. We studied the probability of occurrence of rainfall-induced shallow landslide events by driving the system to instability through a decrease in electrical resistivity values. Numerical simulations are performed by varying number and intensity of the applied perturbations. Hazard scenarios obtained by in situ distributions of resistivity values are compared with those coming from initial random distributed resistivity values. Our results suggest possible critical rates of resistivity changes for triggering instability in the investigated area and point out the crucial role of resistivity variations in prediction of larger events
A study of stability analysis of pyroclastic covers based on electrical resistivity measurements
No full textUsually, the degree of stability of a slope is quantified by the Factor of Safety whose values depend on physical and mechanical soil properties analyzed on samples of much reduced sizes or referring to very small soil volumes around porous probes. To overcome the limit of point-sampled information, we propose a semi-empirical approach based on the use of geophysical methods and the employment of a geophysical Factor of Safety recently introduced by the authors in terms of local resistivities and slope angles. In this paper, we show an application of our proposal on a test area of about 2000 m2 on Sarno Mountains (Campania Region – Southern Italy), where shallow landslides involving pyroclastic soils periodically occur triggered by critical rainfall events. Starting from two resistivity tomography surveys performed on the test area in autumn and spring, we obtained maps of the geophysical Factor of Safety at different depths for the two seasons. We also estimated the values of the Factor of Safety by using the infinite slope model in the dry and saturated scenario. A comparison between the values of the geophysical and geotechnical Factor of Safety shows advantages and disadvantages of our approach
Source depth estimation of self-potential anomalies by spectral methods
No full textSpectral analysis of the self-potential (SP) field for geometrically simple anomalous bodies is studied. In particular, three spectral techniques, i.e. Periodogram (PM), Multi Taper (MTM) and Maximum Entropy (MEM) methods, are proposed to derive the depth of the anomalous bodies. An extensive numerical analysis at varying the source parameters outlines that MEM is successful in determining the source depth with a percent error less than 5%. The application of the proposed spectral approach to the interpretation of field datasets has provided depth estimations of the SP anomaly sources in very good agreement with those obtained by other numerical methods
Water storage mapping of pyroclastic covers through electrical resistivity measurements
No full textThe knowledge of the geological setting of pyroclastic covers and their water content distribution represents crucial information for stability analyses of slopes potentially subject to debris-flow phenomena. The study we here present would provide a contribution to this issue by means of an approach based on electrical resistivitymeasurements. Specifically, we describe the results of high-resolution 2D resistivity surveys carried out in a test area on SarnoMountains (Campania Region – Southern Italy), where shallowlandslides involving pyroclastic soils periodically occur triggered by critical rainfall events. We discuss the results in relation to the geology of the area in order to locate characteristic horizons of pyroclastic soils below the ground surface. Then, on the basis of a laboratory characterization of pyroclastic samples collected from the same test area at representative depths, we provide an estimation of the soil water content distribution in the field. Finally, we analyze temporal variations of the soil water content distribution by comparing the data of two surveys carried out in the autumnal and spring seasons, respectively
Estimating soil suction from electrical resistivity
Full text linkSoil suction and resistivity strongly depend on the degree of soil saturation and, therefore, both are used for estimating water content variations. The main difference between them is that soil suction is measured using tensiometers, which give point information, while resistivity is obtained by tomography surveys, which provide distributions of resistivity values in large volumes, although with less accuracy. In this paper, we have related soil suction to electrical resistivity with the aim of obtaining information about soil suction changes in large volumes, and not only for small areas around soil suction probes. We derived analytical relationships between soil matric suction and electrical resistivity by combining the empirical laws of van Genuchten and Archie. The obtained relationships were used to evaluate maps of soil suction values in different ashy layers originating in the explosive activity of the Mt Somma-Vesuvius volcano (southern Italy). Our findings provided a further example of the high potential of geophysical methods in contributing to more effective monitoring of soil stress conditions; this is of primary importance in areas where rainfall-induced landslides occur periodically
Heat wave vulnerability maps of Naples (Italy) from Landsat images and machine learning
No full textMaps of land surface temperature of the area of Naples (Southern Italy) show large spatial variation of temperature anomalies. In particular, the metropolitan area of Naples is generally characterized by higher temperatures than the rest of the area considered.
Since heat waves have become more frequent in the last decade, the creation of heat maps helps to understand the location where a town’s population may be more affected by them. Ideally, this kind of maps would provide residents with accurate information about the health problems they may face.
Large temperature anomalies variations are caused by multiple or competing factors, leaving uncertainty in identifying vulnerable areas at this time.
To overcome this limitation and identify areas more vulnerable to the effects of heat waves, not only in the city of Naples but also in its suburbs, we combine the use of Landsat data with unsupervised machine learning algorithms to provide detailed heat wave vulnerability maps. In particular, we develop a procedure based on a combined use of hierarchical and partitional cluster analyses that allows us to better identify areas characterized by temperature anomalies that are more similar to each other than to any other all over the year. This has important implications allowing discrimination between locations that potentially would be impacted higher or lower energy consumption
A combined use of Archie and van Genuchten models for predicting hydraulic conductivity of unsaturated pyroclastic soils
No full textHydrogeophysics has been developing in recent years to improve characterization and monitoring of saturated/unsaturated aquifers, through the combination of geophysical and hydrogeological methods. To exploit the potential benefits of this integration, definition of petrophysical relationships that allowthe translation of geophysical data into hydrogeological parameters (and vice versa) is essential. In this paper, Archie's and van Genuchten's models, which relate electrical resistivity and hydraulic conductivity to the degree of saturation, are combined to obtain a closed-form link between hydraulic conductivity and electrical resistivity. Such an expression is used to characterize pyroclastic deposits covering Sarno Mountains (southern Italy), which are often affected by landslide phenomena. As expected, an inverse relationship is found between hydraulic conductivity and electrical resistivity due to predominance of the electrolytic component over the interfacial component of the electrical conductivity. The variability of the hydraulic conductivity marks out the texture of the investigated pyroclastic horizons. Finally, a hydraulic conductivity–matric suction relationship is retrieved by using an empirical correlation between electrical resistivity and matric suction
A quantitative analysis of IRT data for the evaluation of plaster degradation at the Dome of Magdeburg (Germany)
No full textInfrared Thermography (IRT) is a helpful method for the nondestructive evaluation of artworks and buildings of historical interest since it is able to provide indications about most of degradation sources, such as alteration of material consistency, formation of microcracks, debondings, etc. The most used procedures for physical and geometrical characterization of the thermal anomaly sources are based on numerical models that solve the forward thermal problem, i.e. they find the solution of the Fourier differential equation, which describes the heat transfer
in a medium. In this framework, we present a Finite Difference method to evaluate the conservation state of the Dome of Magdeburg (Germany). Numerical simulations have shown a very good match between the experimental and theoretical curves for all the considered anomalous areas, for both 1D and 2D formulations, providing an average percentage error of the order of 0.1%. In particular, the study allowed to define thickness, depth and nature (density, thermal conductivity and specific heat) of the thermal anomaly sources, attributable to the degradation of
the lime mortar layer at different depths. The application of the codes provided helpful indications for restoration work planning
A study of the correlation between electrical resistivity and matric suction for unsaturated ash-fall pyroclastic soils in the Campania Region (southern Italy)
No full textIn the territory of the Campania region (southern Italy), critical rainfall events periodically trigger dangerous fast slope movements involving ashy and pyroclastic soils originated by the explosive phases of the Mt. Somma-Vesuvius volcano and deposited along the surrounding mountain ranges. In this paper, an integration of engineering-geological and geophysical measurements is presented to characterize unsaturated pyroclastic samples collected in a test area on the Sarno Mountains (Salerno and Avellino provinces, Campania region). The laboratory analyses were aimed at defining both soil water retention and electrical resistivity curves versus water content. From the matching of the experimental data, a direct relationship
between electrical resistivity and matric suction is retrieved
for the investigated soil horizons typical of an ash-fall pyroclastic succession. The obtained relation turns out to be helpful in characterizing soils up to close saturation, which is a critical condition for the trigger of slope failure. In such a regime, the water content and the matric suction have small variations, while electrical resistivity variations can be appreciated in a larger range of values. For this reason, besides suction measurements on very small soil volumes through classical tensiometers, our analyses suggest the direct monitoring of in situ electrical resistivity values as an effective tool to recognise the hydrological
state of larger and more representative soil volumes and to
improve early warning of dangerous slope movements
Electric effects induced by artificial seismic sources at Somma-Vesuvius volcano
No full textIn this paper, we present a series of self-potential measurements at Somma-Vesuvius volcanic area acquired in conjunction with an active seismic tomography survey. The aim of our study is both to provide further confirmation to the occurrence of seismo-electric coupling and to identify sites suitable for self-potential signal monitoring at Somma-Vesuvius district. The data, which were collected along two perpendicular dipoles, show significant changes on the natural electric field pattern. These variations, attributable to electrokinetic processes triggered by the artificial seismic waves, were observed after explosions occurred at a distance less than 5 km from the SP dipole arrays. In particular, we found that the NW-SE component of the natural electric field was more sensible to the shots than the NE-SW one, and the major effects did not correspond to the nearest shots. Such evidences were interpreted considering the underground electrical properties as deduced by previous detailed resistivity and self-potential surveys performed in the study area
- …
