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Pyroclastic soils cover significant parts of the world's surface, including areas occupied by urban settlements, vital structures and infrastructures. Despite these materials present significant physical and mechanical differences from site to site, posing sometimes severe geotechnical problems, a comprehensive and worldwide accepted geotechnical c...
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... The state properties, the stiffness and the strength characteristics of the granular pyroclastic soils constituting the soft rock's cover were obtained by a joint interpretation of penetrometer and geophysical tests using the empirical correlations available in the literature for cohesionless soils [43,44] and the available data on pyroclastic soils of air-fall deposition widely diffused in the area [45][46][47]. Regarding the tuff formations, due to the lack of direct measurements, typical values reported in the literature for pyroclastic weak rocks [48][49][50] were adopted. At the present stage of the study, it was not possible to individuate the eventual presence of joints or discontinuities; therefore, the tuff rock formation was assumed to be continuous. ...
In northern Campania (Southern Italy), the historic center of many towns is characterized by the widespread presence of cavities in the subsoil, excavated over the centuries for quarrying tuff blocks for buildings, along with cathedrals, churches and chapels. A singular feature of these places of worship is, in fact, the presence of a wide and frequently connected network of underground cavities and tunnels, which were used for hydraulic, religious or connecting purposes. The cavity network is often unknown, abandoned or even buried, thus representing a risk for their susceptibility to sinkholes. Such elements are important as cultural heritage of inestimable value and as attractors for tourism; for this reason, the multidisciplinary study conducted on a place of worship in the Caserta area is illustrated herein: the Cloister of Sant’Agostino, in Caserta (XVI century CE). A geological and geotechnical characterization of the subsoil was performed at first. A laser scanner survey of the accessible cavities and the external churchyard was carried out. The resulting 3D model of the underground sector allowed for a clear understanding of the room size, their location, the levels and the path of the corridors. To understand the extension and layout of the crypts, Electrical Resistivity Tomography (ERT) surveys were undertaken in the surrounding areas. The analysis of the ERT measurements revealed some anomalies that could be ascribed to unknown structures (crypts). Finally, numerical methods were applied to estimate the stress state of the soft rocks and the potential areas of crisis, with preliminary assessments of the influence of the presence of cavities on the stability of the subsoil. The results allowed us to improve the knowledge of the study site and provide useful data for the planning of future targeted investigations, underlining how integrated research between applied disciplines can provide indispensable support both in the management and mitigation of geological risks in urban areas and in the sustainable reuse of hypogea.
... Surge deposits often contain small, rounded structures, called pisolites, comprising ash particles. The substantial difference between flow and surge deposits is the different percentage of the aeriform component, which is greater in surge deposits [13]. ...
... Surge deposits often contain small, rounded structures, called pisolites, comprising ash particles. The substantial difference between flow and surge deposits is the different percentage of the aeriform component, which is greater in surge deposits [13]. In recent years, the scientific community has shown considerable interest in the landslide events of Campania along the slope covered by airfall pyroclastic deposits that evolved into flowslides. ...
Broad mountainous areas in the western Campania (southern Italy), where young pyroclastic deposits extensively outcrop, frequently experience rainfall-induced slope movements of different degrees of mobility, causing heavy damage and fatalities. Such landslides cannot be easily mitigated, and the implementation of physically based early warning systems is still not able to predict the post-failure evolution of slope movements and the exposed areas at risk. This paper is devoted to overcoming this limit. To this end, the mechanical characterization of pyroclastic soil, carried out through an extensive laboratory testing program, is presented and compared with those of two other ashy soils of different depositional mechanisms. The results show that the depositional mode influences soil properties; to begin with, it affects the unsaturated shear strength, whose intercept of cohesion is up to 5 kPa higher in ashes of flow deposition than in airfall ash deposits. The saturated undrained soil response allowed for the identification of different levels of susceptibility to the liquefaction of pyroclastic deposits, which is one of the main factors governing the post-failure evolution of landslides. Gathering all the acquired information, including saturated and unsaturated soil shear strength, permeability function, and water retention curves, into a soil database, it was possible to present all data under a unitary framework. Finally, the implementation of the proposed flowchart for a simplified assessment of post-failure evolution to be employed in regional early warning systems can enhance our knowledge of the areas at risk.
... The Neapolitan metropolitan area is mainly covered by the products of two main volcanic edifices: Campi Flegrei and Somma Vesuvio. The volcanic products of Campi Flegrei cover the urban area of Napoli and its neighbors, where the typical stratigraphic sequence includes the Neapolitan yellow tuff covered by the same formation in its unlithified condition, which in turn underlies the pyroclastic products of the volcanic activity of Campi Flegrei younger than 15 ky (IPD-intra caldera deposits of Campi Flegrei (Picarelli et al., 2006). ...
... In this case, they are generally in partially saturated condition and very often, during extreme meteoric events, they have been involved in catastrophic slope instability phenomena. For this reason, research on these pyroclastic soils has been mainly devoted to the assessment of the hydrogeological hazard of the Neapolitan area (Evangelista et al., 2002;Picarelli et al., 2006). These studies highlighted the significant role of grain size, void ratio, degree of saturation and structure on the mechanical behaviour of pyroclastic covers and their relationship with mechanisms of generation and formation of the deposits. ...
... Figure 2 reports data about the main physical properties measured on more than 600 samples retrieved in different sites around Naples (Evangelista et al., 2002) showing that these deposits are characterised by quite a low particle weight ranging between 2.44 and 2.51 (in terms of specific gravity, Gs) and a porosity varying between 50% and 60% with a resulting low unit weight not exceeding 18.5 kN/m 3 . The same soils are also characterised by narrow values of shear strength, with a friction angle ranging between 32 and 35 degrees (Figure 2b) but highly sensitive to the change in the degree of saturation (Picarelli et al., 2006). Nevertheless, the city of Naples is also featured by a relevant seismic hazard, as highlighted by the map reported in Figure 3 where the probabilistic hazard distribution of peak ground accelerations with a 10% of exceedance in 50 years is shown. ...
... 16 MPa and 28 MPa (Ducci and Napolitano, 1994), decreasing with the water content (Evangelista and Pellegrino, 1990). For this reason, a value of 7.5 MPa is assigned to σ c parameter (Table 3), while the tensile strength is about 1/4 of the compressive strength (Evangelista and Pellegrino, 1990;Picarelli et al., 2006;Ito et al., 2008;Heap et al., 2018). ...
Procida Island, located in the Gulf of Naples (southern Italy), is characterized by steep cliffed coasts, articulated in a succession of headlands and small embayments with narrow pocket beaches, such as Ciraccio and Chiaia, often characterized by instability.
In this study, a methodology for coastal cliff susceptibility assessment has been conceived based on hydraulic and geomorphological characteristics, which supported the construction of a Cliff Stability Index (CSI). The geomorphological characteristics are related to the whole cliff face, the cliff material resistance, and the cliff failure mechanisms. The hydraulic actions on the cliff are related to the wave impact which is exerted by the breaking waves once the wave run-up distance exceeds the beach width. The index takes into account the slope of the cliff, the rock strength, the wave energy at the cliff base produced by the broken wave and the presence of defence structures at the cliff base. The resulting index classification, obtained by addition of the partial sub-indices, has been compared with the observed coastal cliff evolution from 1954 to 2021.
... The literature proposes several models to explain observed relationships between soil physical properties. Relationships between ′ and d (Picarelli et al. 2006;Bardet et al. 2011) and between K s and n p (Franzmeier, 1991;Fallico et al. 2010) have been reported. Further correlations between the variables discussed in this paper can also be found for certain locations or soil types. ...
Numerous early warning systems based on rainfall measurements have been designed to forecast the onset of rainfall-induced shallow landslides. However, their use over large areas poses challenges due to uncertainties related to the interaction among various controlling factors. We propose a hybrid stochastic-mechanical approach to quantify the role of the hydro-mechanical factors influencing slope stability and rank their importance. The proposed methodology relies on a physically based model of landslide triggering and a stochastic approach treating selected model parameters as correlated aleatory variables. The features of the methodology are illustrated by referencing data for Campania, an Italian region characterized by landslide-prone volcanic deposits. Synthetic regional intensity-duration (ID) thresholds are computed through Monte Carlo simulations. Several key variables are treated as aleatoric, constraining their statistical properties through available measurements. The variabilities of topographic features (e.g., slope angle), physical and hydrological properties (e.g., porosity, dry unit weight γd, and saturated hydraulic conductivity, Ks), and pre-rainstorm suction are evaluated to inspect its role on the resulting scatter of ID thresholds. We find that: (1) Ks is most significant for high-intensity storms; (2) in steep slopes, changes in pressure head greatly reduce the timescale of landslide triggering, making the system heavily reliant on initial conditions; (3) for events occurring at long failure times (gentle slopes and/or low-intensity storms), the significance of the evolving stress level (through γd) is highest. The proposed approach can be translated to other regions, expanded to encompass new aleatory variables, and combined with other hydro-mechanical triggering models.
... On average, the soil, originating from the deposition of pyroclastic material resulting from 79 AD eruptions of Mount Vesuvius, is characterized by a very high porosity (approximately 0.70) and low dry soil unit weight (approximately 8.2 kN m -3 ). The porosity and dry unit weight of Mount Faito soil are similar to those reported for other pyroclastic soils in the Campania region [47]. The soil was partially saturated at the site throughout the year [17], and the volumetric water content measured for the specimens sampled at the site during the dry period (July 2016) varied between 0.10 and 0.15. ...
In many geotechnical applications, especially in the study of weather-induced landslides, a reliable soil hydraulic characterization in unsaturated conditions is required. Currently, the experimental techniques that neglect the hydraulic hysteresis represent the greatest limitation to landslide forecasting. In this paper, a procedure to obtain an unsaturated soil hydraulic characterization on natural pyroclastic samples is proposed and verified. The approach enables the evaluation of the soil hydraulic properties along the main drying path and wetting/drying cycles to fully quantify the effects of the hydraulic hysteresis. Pyroclastic soil samples collected at a test site at Mount Faito in the Campania region (southern Italy) were tested. The experimental investigation consisted of a sequence of testing phases: a constant-head hydraulic conductivity test, a forced evaporation test followed by several wetting–drying cycles, and a drying test in a pressure plate apparatus. The hysteretic model proposed by Parker and Lenhard (1987) was adopted to fit the data, while inverse modelling of the forced evaporation tests allowed to derive the model parameters. Therefore, the main drying and wetting branches and the soil response to drying and wetting cycles from any reversal point were reproduced with the model, which suitably described the hysteretic behaviour of the pyroclastic soil under all conditions and along all paths.
... One of the main concerns which will be addressed in this paper is the geotechnical characteristics of volcanic soils (including pumiceous sands) and their susceptibility to liquefaction. Volcanic soils are present in some parts of Japan (Hyodo et al., 1998;Miura et al., 2003;Sahaphol and Miura, 2005;Suzuki and Yamamoto, 2004), Italy (de Cristofaro et al., 2022;Papa et al., 2008;Picarelli et al., 2007), South/Central America (Crenairz, 2010;Sandoval and Pando, 2012) and New Zealand (Beanland et al., 1989;Orense et al., 2012). The Taupo Volcanic Zone (TVZ), in the central region of the North Island, New Zealand, has extensive deposits of volcanic ash and pumiceous sands. ...
Natural pumiceous (NP) sands containing pumice particles, a type of volcanic soil, are commonly found in the central part of the North Island in New Zealand. The pumice particles are highly crushable, compressible, lightweight and angular, making engineering assessment of their properties problematic. In this paper, several series of bender element and undrained cyclic triaxial tests were performed on reconstituted and undisturbed NP sands to determine their small-strain shear modulus (Gmax) and cyclic resistance ratio (CRR). Furthermore, similar tests were also conducted on normal hard-grained sands (e.g., Toyoura sand) for the purpose of comparison. The results showed that the NP sands have considerably lower Gmax compared to normal sands, resulting in their higher deformability during the initial stages of the cyclic loading test. The high angularity of NP sands play an important role toward the end of the cyclic loading and contributed to their higher CRR. Next, the ratio of CRR/Gmax for each sample was correlated to a level of strain denoted as cyclic yield strain (εay), which was found to be significantly dependent on the percentages of pumice particles present in the natural soils. On the other hand, the εay was found to be less sensitive to the consolidation stress (σ′c) and the relative density (Dr) of the materials. For example, over different values of σ′c and Dr, NP sands have substantially higher values of cyclic yield strain due to their lower Gmax and higher CRR when compared with those of ordinary sands.
... The literature proposes several models to explain observed relationships between soil physical properties. Relationships between ′ and (Picarelli et al., 2006;Bardet et al., 2011) and between and (Franzmeier, 1991;Fallico et al., 2010) have been reported. Further correlations between the variables discussed in this paper can also be found for certain locations or soil types. ...
Numerous early warning systems based on rainfall measurements have been designed over the last decades to forecast the onset of rainfall-induced shallow landslides. However, their use over large areas poses challenges due to uncertainties related with the interaction among various controlling factors. We propose a hybrid stochastic-mechanical approach to quantify the role of the hydro-mechanical factors influencing slope stability and rank their importance. The proposed methodology relies on a physically-based model of landslide triggering, and a stochastic approach treating selected model parameters as correlated aleatory variables. The features of the methodology are illustrated by referencing data for Campania, an Italian region characterized by landslide-prone volcanic deposits. Synthetic intensity-duration (ID) thresholds are computed through Monte Carlo simulations. Several key variables are treated as aleatoric, constraining their statistical properties through available measurements. The variabilities of topographic features (e.g., slope angle), physical and hydrological properties (e.g., porosity, dry unit weight ${\gamma}_d$, and saturated hydraulic conductivity, $K_s$), and pre-rainstorm suction is evaluated to inspect its role on the resulting scatter of ID thresholds. We find that: i) $K_s$ is most significant for high-intensity storms; ii) in steep slopes, changes in pressure head greatly reduce the timescale of landslide triggering, making the system heavily reliant on initial conditions; iii) for events occurring at long failure times (gentle slopes and/or low intensity storms), the significance of the evolving stress level (through ${\gamma}_d$) is highest. The proposed approach can be translated to other regions, expanded to encompass new aleatory variables, and combined with other hydro-mechanical triggering models.
... The soil layering sketched in Fig. 2 consists of a series of deposits of volcanic origin with geological and geotechnical features typical of the urban area of Napoli as discussed by a number of authors (e.g., Pellegrino 1967;Evangelista et al. 2002;Picarelli et al. 2007). A soft rock known as Neapolitan yellow tuff (NYT) is found at the base of the stratigraphical model; the depth of the NYT top boundary, located at a depth between 37 and 46 m, was carefully investigated to fix the minimum depth of the diaphragm walls in order to obtain a sufficient embedment. ...
The movements around a deep excavation in urban environment is one of the main design issue to be addressed. Various tools are available and they are categorized in different approaches. The first one, the semi-empirical approach, is based on empirical relations between displacements and simple geometrical parameters such as the depth of the excavation He, or the depth of the bedrock Hb. Generally these methods allow for separate predictions of transversal and longitudinal settlement trough. A second one, the numerical approach, is based on the prediction of the green field subsidence trough by means of FEM or DFM. In this case a 2D simulation of the shaft excavation under plane strain assumption is a typical and nearly routinely design step. The large computational resources available have recently pushed forward the frontier of the simulation capabilities allowing a relatively easy access to large 3D numerical models. In the paper FEM analyses of a deep excavation in an urban environment are presented. The subsoil layering is typical of the Napoli area (Italy) and computed 3D settlement troughs are exposed. The influence of typical buildings in the subsidence area is evaluated and discussed on the basis of the computed results and of fitting functions combining longitudinal and transversal settlement trough.
... Figure 4 reports mean monthly values of rainfall height, mean daily temperature and evapotranspiration. Geological surveys and geotechnical investigations reveal that the basal Mesozoic-Cenozoic fractured limestones are 75 overlain by air-fall sandy soils resulting from the explosive volcanic activity of Somma-Vesuvius and Phleagraean Fields (Fiorillo et al., 2001;Picarelli et al., 2006;Damiano et al., 2012). In particular, the pyroclastic deposits consist of alternating layers of ashes and pumices, more or less parallel to the bedrock surface, with a thickness strongly dependent on the slope angle, ranging from some decimetres in the steepest upslope zones (about 50°) to more than 10 m at the foot of the hill (Guadagno et al., 2011). ...
The paper reports field data provided by the automatic monitoring of the annual hydrological response of a shallow deposit of loose pyroclastic soils located in a mountainous area of Campania, Southern Italy. The monitoring station is installed along the northern slope of mount Cornito, about 2 km east of the town of Cervinara, which in December 1999 had been involved in a rainfall-induced flowslide. The collected data concern rainfall height, soil moisture content and suction. In particular, the installation at the same depths of suction and moisture sensors allows to estimate the soil water retention features that seem to indicate some hysteretic nature of the wetting/drying processes induced by weather conditions and their influence on the local stability conditions. The data reported in the paper are freely available at https://doi.org/10.5281/zenodo.4281166 (Comegna et al., 2020).
