1,721,117 research outputs found
Multiphase soil mechanics for landscape protection: from testing to modelling
No full textThe stability of geotechnical structures is often driven by the superficial layer of soils subject to cycles of drying, wetting, and temperature variation. This shallow layer, interacting with the atmosphere, is often in unsaturated conditions due to the depth of the water table and the change in water content with climate loading. The unsaturated soils comprise at least three phases: the soil particles, the wetting phase, and the non-wetting phase. To tackle this multiphase system, the classical soil mechanics must be generalised, accounting for different phases and the interaction between them. In this study, a review of the principal experimental evidence on unsaturated soils is first presented, followed by a definition of the stress variables used to describe the observed behaviour. Later, a summary of the different classes of constitutive models is depicted. The role of the water retention curve (WRC), linking the amount of water to the suction, is discussed with an emphasis on its dependence on void ratio and microstructure. Further, an extension of the unsaturated soil mechanics to describe the behaviour of frozen soils is treated. Finally, using the framework of unsaturated soil mechanics, a back analysis of different engineering applications spanning from shallow landslides induced by rainfall to frost heave is performed
Effects of partial saturation on the behaviour of a compacted silt
Full text linkThe effects of partial saturation on the behaviour of a compacted silt was investigated.
In the first part of the work the compatibility of the experimental data carried out at Università di Napoli
Federico II to investigate the effects of partial saturation on the volumetric behaviour and on the initial
shear stiffness of a compacted silt with a Bishop Stress Modeln (BSM) were discussed. In the second
part of the work the results of a centrifuge model of a shallow foundation relying of a layer of
unsaturated soil and submitted to axial load for different water level were discussed. The tested
material is an eolian silt from Jossigny, East of Paris. This work was done with the support of MUSE
network. The objective of the work was to represent a foundation of 1.5 m in diameter on a 15 m soil
layer
Deformation induced by wetting: a simple model
Full text linkThis paper presents a simple model for predicting the deformation induced by wetting. The objective is to quantify the deformation induced by saturation of an unsaturated layer of homogeneous soil, causing variation of the initial void ratio and gravimetric water content. The soil is a low-plasticity silty sand. A simple expression for the normal compression line (NCL), which depends on the parameter χ and one more parameter, will be proposed. The model may capture the progressive degradation induced by loading and wetting by linking the dependency of NCL by the parameter χ and water retention curve by porosity
Macchina di prova per caratterizzare un terreno artificialmente congelato
No full textMacchina di prova per caratterizzare un campione di terreno artificialmente
congelato, comprendente una cella triassiale (2) definente un asse longitudinale
(X) ed avente un alloggiamento per alloggiare un campione di terreno (9) lungo
detto asse longitudinale; mezzi di refrigerazione (3) atti a congelare il campione di
terreno (9) alloggiato in detta cella triassiale (2); in cui detti mezzi di refrigerazione
(3) comprendono almeno un membro congelante (4) che attraversa detto
alloggiamento lungo detto asse longitudinale in modo da congelare il campione di
terreno (9) dall’interno verso l’esterno in direzione radial
The construction and the collapse of the Tiber retaining walls in Rome, Italy (1870-1900)
No full textThis paper addresses the construction history of the River Tiber retaining walls (muraglioni) in Rome, Italy, between 1876 and 1900. In particular, the construction and the collapse of the Anguillara and Alberteschi sections are analysed through the analysis of the literature of the time and the archival source of the Genio Civile of Rome, after the river flood of December 1900. The retaining wall collapse and the subsequent studies on stability conditions conducted in 1901 are presented and discussed to improve the knowledge of geotechnical engineering history and its crucial role in the maintenance of existing heritage structures
Coupled processes during rainfall: an experimental investigation on a silty sand
Full text linkhe factors that contributed to the initiation of a triggering mechanism in a shallow landslides induced by rainfall are investigated in this work at laboratory scale. The aim of the work was to characterise the behaviour of the soil in triaxial tests, in the light of the possible failure mechanisms in a slope subjected to rainfall. The material study is a silty sand from a steep slope in Ruedlingen in the North-East of Switzerland, where a landslide triggering experiment was carried out. Conventional drained and undrained triaxial tests for the water phase were conducted to detect critical state conditions as well as peak shear strength as a function of confining pressure for three different water content related to the in situ one. Soil specimens with three different gravimetric water contents were exposed to stress paths simulating the in situ anisotropic compression followed by a decrease of mean effective stress at constant axial load. Possible unstable response along the stress paths analysed was investigated by means of second order work
Influenza della curva di ritenzione del ghiaccio sul criosollevamento
Full text linkI terreni possono essere soggetti a diminuzioni della temperatura che ne determinano il congelamento. Tale
fenomeno può verificarsi sia per effetto della naturale variazione di temperatura dell’ambiente esterno, nelle zone
fredde del pianeta, sia nel caso in cui si utilizzi la tecnica del congelamento artificiale dei terreni (AGF, Artificial
Ground Freezing). L’AGF è una tecnica di impermeabilizzazione del terreno che viene spesso eseguita in ambiente
urbano per la realizzazione di gallerie. In questo contesto risulta estremamente importante effettuare un’attenta
valutazione delle deformazioni volumetriche del terreno indotte dal congelamento. Per poter descrivere,
comprendere e prevedere tale fenomeno risulta opportuno affiancare le evidenze sperimentali e la modellazione
numerica, per effettuare la taratura dei parametri che regolano i processi termici, idraulici e meccanici che si
instaurano con il congelamento. In questo lavoro i risultati sperimentali ottenuti con prove di criosollevamento
sono state interpretate e utilizzate per calibrare la curva di ritenzione del ghiaccio, ossia la legge che lega le
proprietà termodinamiche del terreno e il grado di saturazione dell’acqua liquid
Descrizione della morfologia dei grani tramite l'analisi frattale
Full text linkL’analisi frattale è uno strumento utilizzato per studiare la morfologia di oggetti in diversi settori dell’ingegneria,
che spaziano dall’elettronica fino all’ingegneria medica (e.g. Rangayyan & Nguyen, 2007). Tra i primi autori ad
aver applicato il metodo alla descrizione della morfologia di grani di terreno si citano Orford & Whalley (1983)
e Vallejo (1995). L’analisi frattale consiste nel misurare il perimetro del contorno utilizzando una serie di
bacchette di lunghezza via via decrescente e studiare l’andamento di questo in funzione della lunghezza della
bacchetta adottata. L’obiettivo del lavoro riportato in questa nota è quello di presentare un metodo per
interpretare i risultati dell’analisi frattale, eseguita su oggetti di forma semplice e su immagini di grani naturali,
con l’obiettivo di lungo termine di stabilire un collegamento tra le caratteristiche morfologiche dei grani terreni e
il comportamento meccanico dei terreni
Duality for a boundary driven asymmetric model of energy transport
Full text linkWe study the asymmetric brownian energy, a model of heat conduction defined on the one-dimensional finite lattice with open boundaries. The system is shown to be dual to the symmetric inclusion process with absorbing boundaries. The proof relies on a non-local map transformation procedure relating the model to its symmetric version. As an application, we show how the duality relation can be used to analytically compute suitable exponential moments with respect to the stationary measure
Distribution of Nymphaea alba L. (Nymphaeaceae) in Tuscany [Distribuzione di Nymphaea alba L. (Nymphaeaceae) in Toscana]
No full textThe authors report the distribution of Nymphaea alba L. in Tuscany by the analysis of herbarium specimens, bibliographic references and records on field. The study shows two different situations: the species is distributed almost exclusively along the wetland's net on the northwestern floodplains in the district of Florence, Pistoia, Lucca, Pisa and Massa. Except for few and isolated sites, in the districts of Arezzo, Siena and Grosseto, the species seems not to occur in the rest of Tuscan wetlands. © 2018 Società Botanica Italiana onlus
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