113 research outputs found
Contact anisotropy and coordination number for a granular assembly: a comparison between DEM simulation and theory
No full textWe study an ideal granular aggregate consisting of elastic spherical particles, isotropic in stress and anisotropic in the contact network. Because of the contact anisotropy, a confining pressure applied at zero deviatoric stress, produces shear strain as well as volume strain. Our goal is to predict the coordination number k, the average number of contacts per particle, and the magnitude of the contact anisotropy ɛ, from knowledge of the elastic moduli of the aggregate. We do this through a theoretical model based upon the well known effective medium theory. However, rather than focusing on the moduli, we consider their ratios over the moduli of an equivalent isotropic state. We observe good agreement between numerical simulation and theory
Failure in granular materials based on acoustic tensor: a numerical analysis
No full textWe investigate localization in granular material with the support of numerical simulations based upon DEM (Distinct Element Method). Localization is associated with a discontinuity in a component of the incremental strain over a plane surface through the condition of the determinant of the acoustic tensor to be zero. DEM simulations are carried out on an aggregate of elastic frictional spheres, initially isotropically compressed and then sheared at constant pressure p0. The components of the stiffness tensor are evaluated numerically in stressed states along the triaxial test and employed to evaluate the acoustic tensor in order to predict localization. This occurs in the pre-peak region, where the aggregate hardens under the circumstance to be incrementally frictionless: it is a regime in which the tangential force does not change as the deformation proceedes and, consequently, the deviatoric stress varies only with the normal component of the contact force
A micromechanical numerical analysis for a triaxial compression of granular materials
No full textWe focus on a triaxial compression at constant pressure in which a granular material, after an isotropic preparation, is sheared in a small range of monotone deformation. The aggregate is made by identical, elastic, spheres that interact through a non central contact forces. Because of the loading condition the material is transversely isotropic. Through a numerical analysis we show that aggregates with same pressure and porosity behave differently depending on the initial coordination number (i.e. the average number of contacts per particle). The relation of stress, volume change, elastic moduli and microstructure with the initial contact network is investigated.</p
Innovative solutions for the geo-chemo-mechanical stabilisation of marine sediments
No full textThe work displays the results of an intense experimental research into the geo-chemo-hydromechanical stabilisation of sediments dredged from a fill-in basin in the Port of Taranto (Ionian Sea, Italy). This research was conducted in collaboration with ETH-Zurich and Italcementi HeidelbergGroup and founded by a MIUR- PON RI DRSATE PhD grant.
Taranto, as many port areas worldwide, is facing the problems of disposing two materials currently considered as waste: dredged sediments and mussel shells.
Starting from this premise and on the basis of the extensive literature concerning the stabilisation of marine sediments with the use of hydraulic binders and the related environmental issues, this study proposes the treatment of Taranto sediments through innovative and eco-sustainable solutions. In detail, the stabilisation solutions in which commercial cements were replaced by mussel shell powder (CemShells) were widely illustrated based on the experimental tests conducted on three types of commercial cement: Type III Termocem Green Blast furnace cement, Type I traditional Portland Cement 52.5R and Sulfoaluminate cement.
In order to include the case of the treatment of contaminated sediments in the stabilisation solution, this study also focuses on the artificial contamination of sediments with 5000 ppm Lead to obtain heavy metal contaminated sediment and with 8% kerosene to obtain an organic contaminated sediment.
In the case of kerosene-contaminated sediment, Biochar was also tested as an extra additive of commercial cements used in the case of treatment of uncontaminated sediment. Moreover, in order to stabiles kerosene- polluted sediment, Biochar was also added to CemShells to form another Bio-Binders named CemShellBio.
In order to analyse the efficacy of the stabilisation solutions in terms of effectiveness and environmental sustainability, this study focused on multiscale and multidisciplinary investigations entailing the dredged unpolluted and polluted (artificially) sediments as well as the same materials when treated with the commercial cements and the original binders i.e., the CemShells and the CemShellBios.
The goal of the investigation was to obtain a complete information on the sediment behaviour at both micro- and macro- scale in the natural and treated state. The investigation focused on: i) Chemical, geochemical and thermal, ii) microstructural and iii) geotechnical characteristics of the natural and treated geomaterials.
Microstructural tests were carried out on more than 60 samples. The microstructural testing routine included: pore size distribution with mercury intrusion porosimetry analysis (MIP), microstructure morphology at high magnification imaging with scanning electron microscope (SEM) and mineralogical composition with X-Ray diffraction (XRD).
Chemical, geochemical, and thermal tests were carried out on more than 150 samples. The chemical and geochemical testing programme included measurements of pH, electrical conductivity (EC), cation exchange capacity (CEC), carbon content (TIC/TOC) on matrix solid. Moreover, measurement of Chlorides and Sulphate, pH, conductivity, and salinity were also conducted on curing water (and/or pore water in natural sediments). All geochemical tests aimed at studying the chemical interaction between the clay particles of sediments and the minerals of cements. In addition, they targeted the interaction of sediments and cements with mussel shells and Biochar.
Thermal tests included the thermogravimetry on treated sediment samples to quantify heat and hydration time occurring in the stabilisation process.
Finally, chemical tests were carried out on eluate of both untreated and treated sediments to study the chemical efficiency, in term of leachability, of each treatment.
Geotechnical tests were carried out on more than 80 samples. Standard procedures were properly adapted to consider the influence of salt in the pore fluid and organic compounds of the solid matrix. The geotechnical testing programme included tests the analysis of the physical properties, composition, and state of sediments. Moreover, oedometer tests were carried out to determine the 1D compression and consolidation properties of the soil and CIU triaxial tests were performed to measure isotropic compressibility and effective strength parameters. Furthermore, unconfined strength was also measured by means of unconfined compression test (UCT) and originally used texturometer tests.
The integration of the microstructural, geotechnical, and geochemical/chemical data produced a global picture on the effects of the chemo-mechanical interaction processes on the geotechnical behaviour of both untreated and treated sediments. This study can provide a useful guide towards an original, effective, and more sustainable stabilisation solution for unpolluted and polluted sediments
Constant Pressure Axisymmetric Compression of an Aggregate of Identical, Elastic, Frictional Spheres
No full textWe present a theoretical model to predict the mechanical behavior of an idealized granular material in triaxial
compression. Particle motions involve both the average strain of the aggregate and fluctuations. Force and moment equilibrium
determine fluctuations in translation and rotation. Two regimes of deformations are considered: at the beginning of the
shearing, the aggregate is assumed to behave elastically; then, when sliding between particles first occurs, the incremental
contact forces are assumed to be frictionless. Simulations using the discrete element method are carried out and compared to
the predictions of the theory
From particles in steady state shear bands via micro-macro to macroscopic rheology laws
No full textParticulate systems and granular matter are discrete systems made of many particles; they display interesting dynamic or static, fluid- or solid-like states, respectively, or both together. The challenge of bridging the gap between the particulate, microscopic picture towards their continuum description (via the so-called micro-macro transition) is one of todayâs challenges of modern research. This short paper gives a brief overview of recent progress and some new insights about local granular flow rules for soft particles
L'impero di Alfonso il Magnanimo nella 'Commedia aragonese'
No full textLa cosiddetta Commedia aragonese è un manoscritto illustrato della Commedia di Dante allestito tra Siena e Napoli negli anni Quaranta del Quattrocento. Il codice venne almeno in parte commissionato da Alfonso V il Magnanimo, re di Aragona dal 1416, e anche re di Napoli dal 1442. Le illustrazioni della Commedia aragonese sono opera di due miniatori. Il primo, considerato ancora anonimo dalla maggioranza degli studiosi nonostante diversi tentativi di attribuzione, illustrò Inferno , Purgatorio e la lettera iniziale del Paradiso . La seconda mano è unanimemente riconosciuta in quella di un grande pittore senese del Quattrocento: Giovanni di Paolo. Il saggio si propone di mostrare la funzione celebrativa del manoscritto, vero e proprio monumento a re Alfonso, con particolare attenzione alla politica culturale legata alla Commedia quale supporto letterario del manifesto ideologico proposto dalle illustrazioni
Scrivere al re. La corrispondenza dalla Sardegna al tempo di Alfonso il Magnanimo (1416-1419)
No full textIl nostro contributo si propone di analizzare gli aspetti formali delle missive prodotte nel regno di Sardegna e indirizzate al re d’Aragona dagli ufficiali regi, dai rappresentanti delle élite cittadine, dai nobili e da altri soggetti operanti nell’isola durante i primi anni di regno di Alfonso V il Magnanimo (1416-1458), oggi conservate nella serie Cartas Reales dell’Archivio della Corona d’Aragona di Barcellona. Attraverso l’analisi dei caratteri intrinseci ed estrinseci delle lettere e soffermandoci su alcuni casi specifici, si ricostruisce l’iter di produzione documentaria delle missive, mettendone in luce peculiarità e caratteristiche
Il regno di Napoli: i Durazzo e gli Aragona (1381-1495)
No full textSotto i re aragonesi, che pure dominarono per un periodo tutto sommato breve e non esente da turbolenze, il regno di Napoli visse un periodo veramente felice, per il ruolo che esso ebbe negli equilibri politici europei e per la sua centralità nei contatti tra ambienti culturali e artistici diversi: catalani, spagnoli, fiamminghi, borgognoni, romani, fiorentini e toscani in generale, lombardi, veneti. Meno significativo appare il ruolo della corte napoletana nella storia delle arti sia al tempo degli Angiò-Durazzo (1381-1435) e di Renato d’Angiò (1438-1442), sia nel Cinquecento.
La grandiosità di alcune realizzazioni di Alfonso V il Magnanimo, del figlio naturale Ferdinando o Ferrante I (1458-1494), del nipote Alfonso duca di Calabria (fossero esse “moderne”, cioè tardogotiche, o “all’antica”, cioè esemplate sui nuovi modelli rinascimentali), la varietà e qualità degli artisti assoldati dagli aragonesi giustificano la mitizzazione di quell’epoca, una mitizzazione che si manifestò già durante la vita del Magnanimo, si amplificò dopo la perdita dell’indipendenza, ed è durata, si può dire, fino ad oggi. La corte aragonese di Napoli, affollata di letterati e musici fin dai primi anni della conquista, fu insomma una novità sostanziale nella storia artistica, culturale e politica europea
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