1,721,018 research outputs found
Mechanics of Catastrophic Landslides : The role of frictional heating and thermal pressurisation in promoting sudden collapse
No full text
Numerical modelling to assess the energy efficiency of shallow geothermal installations
No full textIn recent years, so-called energy geostructures have gained increasing popularity among both academics and professionals in Europe. They typically consist of closed-loop heat exchanger systems embedded in geotechnical structures, which serve the double purpose of supporting soil and/or the overlying structure and providing sustainable energy for heating and cooling of buildings. Such installations allow significant cost savings compared to traditional borehole heat exchangers, as they do not require ad-hoc excavations. However, their non-standard geometry and peculiar boundary conditions means that established calculation tools (e.g. simplified analytical models) are not suitable to predict their energy performance. In this work, a numerical finite element model able to carry out both thermal and thermo-mechanical analyses of energy geostructures is described, and validated against field data. The model is then used to carry out parametric studies to assess the energy efficiency of three different types of geothermal installations, namely: rotary bored energy piles, continuous flight auger energy piles and energy walls. It emerges that different thermal design criteria should be used for different energy geostructures, in order to maximise the geothermal exchanged power. Guidelines are also provided aimed at improving the energy efficiency of such installations by acting on parameters that are relatively easy to engineer, without altering the structural and geotechnical design arrangements
Analisi numerica delle prestazioni di pali energetici di piccolo diametro
No full textLe fondazioni energetiche, in grado di svolgere sia la funzione strutturale che quella di scambia-
tori di calore, sono state ampiamente studiate negli ultimi anni, sia dal punto di vista termo-meccanico che da
quello delle prestazioni energetiche. Ad oggi, la maggior parte della ricerca si riferisce a pali trivellati di me-
dio/grande diametro (pali energetici, PE), installati in edifici di nuova costruzione. Una minore attenzione è
stata invece dedicata ai pali di piccolo diametro (micro-pali energetici, MPE), che possono trovare applicazioni
interessanti nel consolidamento strutturale e miglioramento energetico di edifici esistenti. Gli studi condotti in
precedenza mostrano che i MPE possono operare meccanicamente e termicamente in modo diverso rispetto ai
PE, per le diverse caratteristiche geometriche del palo stesso e del circuito idraulico collocato all’interno, tutta-
via, in termini di flusso di calore specifico le prestazioni sono confrontabili. In questo lavoro è stato impiegato
un modello 3D a Elementi Finiti per svolgere uno studio parametrico completo sulle variabili più importanti
che influenzano le prestazioni energetiche dei MPE. Il campo di variabilità dei parametri è stato esplorato at-
traverso la tecnica statistica di tipo Taguchi. I risultati mostrano che la progettazione geotermica dei MPE non
dovrebbe seguire gli stessi criteri adottati per i PE. È opportuno riservare particolare attenzione al diametro dei
tubi scambiatori di calore, in quanto questo esercita una forte influenza sulla prestazione dei MPE
Il ruolo della Temperatura nell’evoluzione tenso-deformativa di un versante roccioso alpino
Full text linkIn contesto alpino le frane in roccia e le deformazioni profonde di versante rappresentano fenomeni
di grande impatto ambientale e sociale. In questo studio i ricercatori del Dipartimento di Scienze
della Terra dell’Università Statale di Milano hanno valutato attraverso un’analisi numerica termo-
meccanica, gli effetti delle variazioni di temperatura atmosferica sullo stato tensionale e sulla
risposta deformativa dei versanti rocciosi
Dynamical effects during compaction band formation affecting their spatial periodicity
Full text linkCompaction bands (CBs) are responsible for significant anisotropy alterations of permeability in geological materials; hence, understanding their formation conditions appears of key importance to all applications involving fluid extraction/injection from/into the ground. While most of the available models to understand CB formation are focused on interpreting the onset of a single CB, little effort has been so far dedicated to understand the documented periodicity of CBs. In this paper, the role of dynamical effects in inducing the post onset evolution of CBs is analyzed by means of a dedicated model for porous media with compressible constituents, with reference to a horizontal layer of sandy, water-saturated material. Elastic waves are generated as a first CB occurs due to sudden, localized volumetric collapse. If the waves are reflected at the interface with a softer material or with a previously formed CB, they produce significant local effective stress concentrations, which can promote the formation of further CBs in a cascade fashion, according to a regular geometric pattern. The spatial distribution of dynamically generated CBs, as well as the extent of the phenomenon, depends on the geometry of the domain and on the material's permeability. Sensitivity analysis is also performed to assess the key properties that promote dynamical CB in situ formation, identifying as the most influential conditions large stratum stiffness (increasing with depth) and the presence of softer layers. In contrast, the presence of less permeable and/or stiffer layers is not believed to play a major role in the proposed mechanism
Studio sperimentale sull'applicazione del metodo Particle Image Velocimetry (PIV) per la misura delle deformazioni nelle prove triassiali
No full textLa ricerca riguarda l’applicazione alle prove triassiali di un metodo sperimentale basato sulla fotografia digitale, detto Particle Image Velocimetry (PIV), per la misura di spostamenti e
deformazioni. Il metodo PIV, ideato qualche decennio fa per applicazioni di fluidodinamica (Keane e
Adrian, 1990), è stato recentemente adattato alla geotecnica (White et al., 2003), ed applicato per rilevare campi di spostamento in casi di deformazione piana (come tests in centrifuga e prove biassiali). L'obiettivo è lo sviluppo di una strategia sperimentale che, attraverso una serie di modifiche agli
algoritmi PIV esistenti, permetta di misurare accuratamente deformazioni e spostamenti nel caso non planare
della prova triassiale su terreni granulari, con una precisione che sia almeno dello stesso ordine di grandezza di quella fornita dai sensori esterni tradizionali
Numerical modelling of liquefied sand-pipeline interaction
No full textSand liquefaction is known to cause significant damage to buildings and infrastructure, and has been documented in several civil and energy engineering applications. In particular, offshore buried pipelines are bound to be exposed to liquefaction problems, and may consequently undergo flotation or sinking. Soil liquefaction, which can be triggered by different types of dynamic loading, implies the development of excess pore pressure up to causing the effective stress to vanish. This changes significantly the soil’s mechanical behaviour, which cannot be captured with standard geotechnical analyses. However the behaviour of liquefied sand may be related, with a simplified one-phase approach, to that of a non-newtonian viscous fluid. In this work, a numerical framework is presented that combines, in a partially coupled fashion, the Particle Finite Element Method (e.g. see Cremonesi et al., 2010, 2017, Della Vecchia et al., 2019) with post-liquefaction re-consolidation Finite Difference calculations. The model is then validated against physical model experimental data of liquefied sand-pipeline interaction, both for the case of pipe sinking and flotation. Results show that, despite the inherent simplifications, this approach is able to capture both qualitatively and quantitatively the fundamental features of pipeline motion in fluidised soil
Influence of thermomechanics in the catastrophic collapse of planar landslides
Full text linkFrictional heating has long been considered a mechanism responsible for the high velocities and long run-out of some large-scale landslides. In this work a landslide model is presented, applicable to large-scale planar landslides occurring in a coherent fashion. The model accounts for temperature rise in the slip zone due to the heat produced by friction, leading to water expansion, thermoplastic collapse of the soil skeleton, and subsequently to an increase of pore-water pressure. The landslide model, comprising equations that describe heat and pore pressure diffusion and the dynamics of the moving mass, is used to analyse the evolution of the Jiufengershan planar landslide as an example. Further, its parameter space is systematically and efficiently explored using a Taguchi parametric analysis in an attempt to quantify dominant parameters. It is shown that the process of sliding is dominated by the softening properties of the material, as expected, but also by the permeability of the slip zone and the thickness of the sliding mass. It is worth noting that the latter two parameters do not enter traditional stability analyses of uniform slope
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