Annalisa Galeandro

Analysis of rainfall infiltration effects on the stability of pyroclastic soil veneer affected by vertical drying shrinkage fractures

The paper presents a preliminary, simplified evaluation of the effects of rainfall infiltration on the stability of slopes in layered pyroclastic soils affected by shrinkage vertical fractures. The analysis has been developed with a special reference to a stratigraphic sequence obtained by an in situ survey at Pizzo d’Alvano (Southern Italy). The analysis of rainfall infiltration is performed using an original dual-permeability model. Results show how fractures strongly condition infiltration depending on rainfall intensity. Prolonged low-intensity rainfall may lead to a higher saturation of the surface soil layer than short, intense rainfall when water may flow quickly through fractures into the underlying more permeable soil layers. Calculated distributions of pore pressure are used for the slope stability analysis using the infinite slope approach. Variations of the safety factor as a consequence of infiltration show that prolonged rainfall can induce a more relevant decrease in the safety factor than intense precipitations.

Analysis of the Rainfall Preceding the Activation of the Large Maierato Landslide in 2010

This work focuses on the impact of the antecedent rainfall as triggering factor of the large landslide occurred in Maierato (south Italy) on February 15, 2010. According to previous studies by Guerricchio et al. (Tecniche per la difesa dall’inquinamento – 31° Corso di aggiornamento, pp 661–706, 2010) the predisposing factor of the landslide is an ancient deep-seated gravitational slope deformation that significantly affected landforms, drainage networks and infiltration processes of the whole slope where Maierato is located. Here after a brief introduction of the landslide according to the aforementioned study, a hydrological analysis of the rainfall preceding the landslide is presented. The analysis aims at evaluating the exceptionality and some peculiar characters of rainfall, which may be considered among the triggering factors of the landslide.

A Simple Model for Passive Failure Compression Structure at the Toe of Landslide

The toe of landslides is subject to compression stresses induced by the upward sliding masses and often characterized by a co mpression 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 spreadsheet 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.

Success of Reclamation Works and Effects of Climatic Changes in Taranto Area: South Italy

The 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.

Evolutionary Data-Driven Modelling of Salento Shallow Aquifer Response to Rainfall

Data-driven techniques are among the most powerful approaches to model environmental phenomena. Evolutionary modelling constitutes and interesting approach able to combine the regressive feature of data-driven modelling with the power of evolutionary optimization. Here an evolutionary data-driven paradigm is used in order to model aquifer response to rainfall. The aquifer is shallow and located in south-east Apulia, south Italy, for which a long and reliable time series of monthly water table levels, measured in monitoring wells, are available. The identified models are consistent with past studies and with the hydrogeological characteristics of the aquifer, allowing for explicating the main rainfall components influencing the water table and the lag between rainfall and water table oscillations.

A data-driven model of the dynamic response to rainfall of a shallow porous aquifer of south Basilicata - Italy

The analysis of the dynamic response of a shallow aquifer to rainfall is a hot topic for groundwater resources management. A data-driven methodology namely Evolutionary Polynomial Regression is here undertaken to perform this kind of analysis. The introduced methodology is an evolutionary modeling approach, based on the multiobjective evolution of a population of explicit models. The methodology is here applied to a particular case study involving a shallow porous aquifer located in south Italy, showing some peculiar characters. The outcome of this approach is here discussed focusing on the hydrogeology of the aquifer. Then some hydrological considerations on the results are presented. Finally, the obtained model is consistent with past studies on the same aquifer by other authors and based on different methodologies.

Statistical analyses of inherent variability of soil strength and effects on engineering geology design

Clayey soil strata, as all natural deposits, generally show variability in the values of their geotechnical properties. This is due mainly to geological and environmental processes such as deposition and diagenesis, which introduce heterogeneity, anisotropy and variability to soil properties. Other causes of variability, and thus uncertainty, are the representativeness of samples and errors related to testing procedure, measurement and data processing procedures. To improve our knowledge about the inherent variability in the 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 was based on pocket penetrometer strength measurement, performed both punctually and across the whole deposit. The adopted testing procedure, which is fast and reliable, provides a really wide dataset of the investigated soil property, with more than 800 data points. These allow for detailed variability analysis, and a reliable estimation of the coefficient of variation as well as research into the best fitting probability density functions, which are key factors for robust design. The presented case study allows discussion of the inherent variability of soil properties, and its influence on the characteristic values of soil strength in geotechnical design.

The Generation of Runoff Through Ephemeral Streams

Ephemeral streams are elements of the surface drainage network that are normally dry and that occasionally, due to extreme rainfall events, may drain relevant discharges. They are largely diffused in karst areas, characterized by the absence of active stream networks and due to their extremely rare drainage. Their hydrograph in particular may be quite singular and different from the classic IUH. The work compare the hydrographs returned by the classic IUH approach with those obtained by an integrated hydrological-hydraulic approach for ephemeral streams characterized by quite small catchments, called “lame” and located in lower Murgia area (south east Italy). In particular, the peak discharges and the delays of the discharge generation through the ephemeral streams will be carefully analyzed. The differences are relevant especially for rainfall characterized by medium return periods, showing how the classic IUH approach could be completely unreliable.

Tectonic Stress as Possible Co-predisposing Factor for Landslides Along the Central Adriatic Coast of Italy

The central and southern Italian coast on Adriatic Sea is affected by several historically active large and deep-seated landslides. These during the latest decades involved important infrastructures, like the railway and the motorway along the coastline. These landslides were activated in overconsolidated silty clayey deposits of the foredeep domain. Here the position of the main landslides in relation to the position of the buried front of the Apennines is presented. This general early-stage analysis shows that there is an interesting correspondence between the main landslides and the advanced buried thrust of Apennine deposits. The work proposes some thoughts about this correspondence and the possible influence of tectonic tangential stresses as one of the predisposing factor in the activation of these landslides.

Effects of Preferential Flow Pathways on Groundwater Resources Rainfall Supply

Groundwater resources in unconfined coarse grained aquifers are generally supplied by rainfall infiltration. The presence of surficial fine textured soils prevents and delays infiltration of water flow toward deep groundwater. This is due to the lower permeability of fine textured soil but also to the capillary barrier effects and water retention at the bound between layers, until reaching critical conditions which trigger flow downward. These surface soils are commonly characterized by shrinking cracks which seriously affect rainfall infiltration, since they constitute preferential flow paths facilitating deep infiltration. A capillary barrier effect can happens also in fractures, which behave like capillary pipes. In order to show how these mechanisms affect deep groundwater supply and aquifer recharge, the present work applies a dual-permeability model simulating infiltration into fractured and stratified soils to a test soil. Results shows how intense rainfall may flow through fractures reaching groundwater resources, while weak rains may be entrapped in surficial strata without supplying deep groundwater resources, despite of their duration of several days.