37 research outputs found
Lateral strength and critical depth in infinite slope stability analysis
No full textInfinite slope method is the simplest limit equilibrium method for slope stability analysis. It gives reliable results for slides where the longitudinal dimension prevails on the depth of the landslide. Usually results are conservative since not accounting for the effects of the strength along lateral bounds. Starting from an infinite slope analysis accounting the effects of the shear strength along lateral bounds a simplified rectangular cross section, hHere a new expressions of the factor of safety areis introduced, evaluated in a similar way but by an infinite slope analysis accounting for the effects of the shear strength along lateral bounds assuming using an elliptical and a parabolic cross section of the landslide body. The safety factor evaluated in this way can be quite different from those returned by the classic infinite slope model formula, in particular when the width of the landslide is narrow with respect to its depth and the ratio between the width and the depth of the landslide is lower than 5. An interesting implication of the proposed model is that if cohesion is different from zero, there is a “critical depth”, where the safety factor has a minimum value
Statistical analyses of inherent variability of soil strength and effects on engineering geology design
No full textClayey soil strata, as all natural deposits, generally show variability of the values of their geotechnical properties. This is mainly due to geological and environmental processes, such as deposition and diagenesis, which introduce heterogeneity, anisotropy and variability in soil properties. Other causes of variability and then uncertainty are the representativeness of samples and errors related to testing procedure, measurement and data processing procedures.
To improve the knowledge about the inherent variability of geomechanical properties of clays, this work presents a case study related to the analysis of the strength variability along a log of marine stiff clay deposits, which are apparently quite homogeneous. The analysis is based on pocket penetrometer strength measure and it is performed both punctually and across the whole deposit. The adopted fast and reliable testing procedure provides a really wide dataset of the investigated soil property, more than 800 strength data. These allow for a detailed variability analysis and a reliable estimation of coefficient of variations as well as for the research of the best fitting probability density functions, which are key factors for robust design. The presented case study allows to discuss on inherent variability of soil properties and its influence on the characteristic values of soil strength for geotechnical design
Success of Reclamation Works and Effects of Climatic Changes in Taranto Area: South Italy
No full textThe paper presents some considerations on the potential influence of climatic changes on the effectiveness and the success of reclamation works made between the 19th and the 20th century in some areas of the west bound of Taranto (South Italy), characterized by large swamps for centuries. Historical documents underline the difficulty to make effective and successful reclamation works in the area of Taranto, as in other areas of the Mediterranean basin because swamps were continuously supplied by upward groundwater flow from the powerful deep karst aquifer. Success were obtained during Thirties thanks to improvement in technical knowledge and design technics, but these successes were obtained in a period characterized by rainfall decreasing. This paper aims at emphasizing that successes in reclamation works were obtained during a period of rainfall decreasing that affected Taranto area and all southern Italy between the 19th and the 20th century. Rainfall decreasing induced a lowering of groundwater table and a reduction of swamp supply, favoring the success of reclamation works
Data driven analysis of the discharge variations at Mercure spring South Italy
No full textMercure Spring collects groundwater from a large catchment on the north-western side of Mount Pollino massif. This spring area is characterized by several small springs in a zone where fluvial and lacustrine deposits overlay the limestone of Pollino Unit. Fluvial-lacustrine deposits of Mercure river are generally impermeable due to the silty clayey fraction and hinder the flow through the limestone with a permeability threshold that force groundwater to come out as spring. Groundwater hydrology of mount Pollino Massif is strictly conditioned by the relative permeability of the geological units and by tectonic structure and karst phenomena and groundwater circulation are quite complex, so there are flow paths of quite different length supplying the spring. The average discharge of the spring is about 1.8 m3/s with a minimum value of 1.10 m3/s and a maximum one of more than 2.50 m3/s. A detailed analysis of hydrograph allows to observe interesting short term variations up to 15-20% of the discharge values, occurring during the year. These variations are related to specific rainfall events or periods, in fact these local peaks are normally during January and February when severe rainfall periods are more common. The available discharge data are not long enough to use a data-driven approach to relate discharge to rainfall for all the annual hydrograph. Anyway available data permit an analysis of short-term variations of discharge in relation to the rainfall. For this purpose it was used a symbolic regression technique namely EPR: Evolutionary Polynomial Regression based on a Genetic Algorithm implemented in the tool EPRMOGA-XL. As input data rainfall measured at Rotonda rain gauge station were used and, as output, data of the spring discharge time-series. Daily data on a period of about 4 years (2007-2010) were used. Data-driven analysis allows to recognize a quite quick flow path of 5-7 days and a longer one of about 15-20 days that determine the short-term discharge variability. In addition, it is possible to try to relate this variation to the geological structure. Anyway, there are long term variations like those occurring during the entire year that cannot be caught by the model, due to the limited set of available data
Analysis of infiltration processes into fractured and swelling soils as triggering factors of landslides
No full textRainfall infiltration can cause a dramatic decrease of suction in unsaturated soils and, consequently, of shear strength, triggering various instability phenomena, such as the slip of steep surface soil layers. Swelling of cracked soils and capillary barrier effects, induced by fine-grained soils overlying a more permeable material, can also affect water flow through this type of soil systems. In the past, few studies on infiltration and rainfall-induced landslides considered the simultaneous effects of surface cracks, swelling materials, and/or the capillary barrier phenomenon. To this purpose, this paper presents the results obtained by a dual-permeability model, which simulates water flow through a fractured swelling soil overlying a more permeable soil and focusing on the influence of these phenomena on triggering of landslides. Numerical results show that for high-intensity precipitations, flow through fractures quickly reaches significant depths and the capillary barrier is broken, while soil swelling leads to a uniform narrowing of cracks. On the other hand, for low-intensity precipitations, fracture flow and swelling are limited only to the first 30-50 cm of the topsoil, while cracks almost completely closed. Evaluations of the slope stability show that prolonged low-intensity rainfalls might be more dangerous than short high-intensity rains in triggering surface landslides. © 2013 Springer-Verlag Berlin Heidelberg
Assessing ionospheric activity by long time series of GNSS signals: the search of possible connection with seismicity
No full textThe modifications of some atmospheric physical properties prior to a high magnitude earthquake were recently
debated in the frame of the Lithosphere-Atmosphere-Ionosphere (LAI) Coupling model. Among this variety of
phenomena, the ionization of air at the ionospheric levels due to leaking of gases from earth crust through the
analysis of long time series of GNSS (Global Navigation Satellite System) signals was investigated in this work.
Several authors used the dispersive properties of the ionospheric strata towards the GNSS signals to detect possible
ionospheric anomalies over areas affected by earthquakes and some evidences were encountered. However, the
spatial scale and temporal domains over which such disturbances come into evidence is still a controversial item.
Furthermore, the correspondence by chance between ionospheric disturbances and relevant seismic activity is
even more difficult to model whenever the reference time period and spatial extent of investigation are confined.
Problems could also arise from phenomena due to solar activity (now at culmination within the 11 years-long solar
cycle) because such global effects could reduce the ability to detect disturbances at regional or local spatial scale.
In this work, two case studies were investigated. The first one focuses on the M = 6.3 earthquake occurred on April
6, 2009, close to the city of L’Aquila (Abruzzo, Italy). The second concerns the M = 5.9 earthquake occurred on
May 20, 2012, between the cities of Ferrara and Modena (Emilia Romagna, Italy). To investigate possible connections
between the ionospheric activity and seismicity for such events, a five-year (2008-2012) long series of high
resolution ionospheric maps was used. These maps were produced by authors from GNSS data collected by permanent
stations uniformly distributed around the epicenters and allowed to assess the ionospheric activity through
the analysis of the TEC (Total Electron Content). To avoid the influence of solar activity, only nighttime hours
were considered. Moreover, to de?ne the temporal domain of potential ionospheric disturbances and separate local
from global effects, results from local observations were compared with regional TEC series. The whole analysis
shows episodes where anomalies in the ionospheric activity were detected in the vicinity of the mentioned shocks.
However, their statistical significance and the temporal correlation with seismic activity are still controversial
Condizionamenti indotti da tettonica e grandi frane sulla suscettività ai fenomeni alluvionali e da frana nelle aree al fronte della catena
No full textNelle zone orogenetiche le spinte tettoniche del fronte più avanzato della catena creano sollevamenti e deformazioni significative del lato più interno dei depositi di avanfossa. Nel presente lavoro, prendendo spunto da un caso relativo all’Appennino meridionale viene illustrato come al fronte della catena, a seguito di dette spinte si verificano frane ciclopiche da esse indotte, che condizionano sia il reticolo idrografico principale che la pericolosità idraulica e da frana di una vasta area a valle del fronte della catena stessa.
Viene inoltre sottolineata l’importanza di riconoscere questo tipo di fenomeni al fine di poter correttamente interpretare le dinamiche fluviali e la suscettibilità da frana delle aree da questi coinvolte.
In particolare, è illustrato il caso del versante destro della bassa valle del fiume Biferno, dove è stata riconosciuta e ricostruita una gigantesca frana profonda, coinvolgente un’area di circa 40 km2, che controlla profondamente il percorso del Biferno oltre che quello del suo affluente in sponda destra, il torrente Cigno. In particolare la presenza della grande frana condiziona la pericolosità idraulica di tutta la piana di Termoli (CB), ma anche la suscettività al rischio da frana del fianco sinistro della vallata del Biferno a valle dell’abitato di Guglionesi (CB)
A simple model for passive failure compression structure at the toe of landslide
No full textThe toe of landslides is subject to compression stresses induced by the upward sliding masses and often characterized by a compression structure. These structures can evolve in passive toe thrust, which bias the geomorphologic evolution of the toe zone, particularly for prevailing longitudinal dimension landslide. This work presents a simple analytic model of the passive thrust at the toe of landslide based on the infinite slope approach to stability analysis. It is based on the analysis of the state of stresses according to Mohr circle representation and can be implemented also into a spread-sheet and making it possible to evaluate the form of failure surface at the toe of the landslide and the shear strength contribution to the factor of safety of a landslide
