31 research outputs found
Effetti dei fenomeni di cavitazione sul comportamento di cassoni a suzione sollecitati da carichi verticali
No full textNella presente nota si descrivono brevemente i risultati di una prova in centrifuga eseguita presso la University of Western Australia. Questa prova si inserisce all'interno di una sperimentazione più ampia finalizzata allo studio della risposta di cassoni a suzione installati in terreni stratificati e sollecitati da carichi verticali. Successivamente si analizzano i risultati delle simulazioni numeriche eseguite con il software FLAC 2D adottando per lo strato di sabbia il legame Severn Trent (Gajo & Wood, 1999a, 1999b) precedentemente implementato nella libreria del codice di calcolo (Rotisciani, 2010). I risultati presentati dimostrano la marcata influenza della rigidezza del cuscinetto d'acqua che separa il coperchio del cassone dal terreno sulla risposta del complesso fondazione-terreno
Numerical analysis of wetting‐induced instabilities in partially saturated soils under plane strain conditions
No full textThis paper concerns the hydromechanical stability of partially saturated soils
during wetting. The response of a loose silty sand is numerically/theoretically
investigated with the main aim of identifying both triggering mechanisms
and predisposing factors to instability. This latter is testified by both a rapid
increase in the pore water pressure and an unexpected loss of numerical
convergence. The study has been conducted at different scales from laboratory
tests to boundary value problems, and in both cases, the controllability theory
has been employed to both interpret and justify the numerical results
Modellazione numerica dei processi di consolidazione dei fanghi di dragaggio nella vasca di colmata di Gaeta
No full textL’immissione in vasca di colmata è una delle principali e più efficienti opzioni di gestione dei materiali di dragaggio. Quando vengono impiegate draghe aspiranti-refluenti, il terreno viene immesso in vasca ad alti rapporti volumetrici acqua:solido e subisce poi significative variazioni di stato, delle proprietà meccaniche e di permeabilità. Nella nota, con riferimento alla vasca di colmata di Gaeta (LT), si illustrano due strategie di modellazione numerica messe a punto impiegando codici di calcolo di diversa complessità per simulare le peculiarità di questa classe di problemi al finito. I risultati ottenuti mostrano che, anche utilizzando un modello semplice, formulare oculatamente le ipotesi necessarie alla modellazione e identificare correttamente le condizioni di carico permette di descrivere i fenomeni in modo ingegneristicamente soddisfacente
Analysis of rainfall-induced slope failures
No full textThe hydro-mechanical behaviour of a pyroclastic soil layer covering a steep slope has been numerically investigated by performing plane strain analyses using a finite element code. The mechanical behaviour of the volcanic soil has been simulated by means of an elastic-plastic constitutive model extended to unsaturated conditions. The influence of the geometry and soil properties on the slope response has been studied by modifying the slope angle, the permeability law and the water retention curve of the pyroclastic cover. A comprehensive analysis of the slope response during the pre-failure phase is presented focusing attention on the evolution of the more significant hydro-mechanical variables and the displacement fields
Simulazione del comportamento meccanico della sabbia di Toyoura con il legame costitutivo Severn Trent
No full textLa risoluzione di problemi al finito in ambiente urbano e in generale in tutti i casi in cui la valutazione del campo di spostamenti e della sua evoluzione risulti progettualmente rilevante, richiede l’impiego di analisi numeriche sofisticate e di legami costitutivi capaci di ben simulare il comportamento deformativo del terreno. Severn Trent è un modello costitutivo avanzato, messo a punto per i terreni a grana grossa, basato sull’elasto-plasticità con incrudimento cinematico e sul concetto di plasticità diffusa, che coniuga l’esigenza di simulare i principali aspetti del comportamento meccanico delle sabbie ad una relativa semplicità matematica. Nella presente nota, dopo una breve descrizione dei tratti salienti del modello, si mostrano le buone capacità previsionali di Severn Trent nel simulare il comportamento della sabbia di Toyoura in prove di compressione triassiale drenate e non drenate. Per ottenere previsioni ufficientemente accurate anche nelle simulazioni di prove di estensione triassiale non drenate e prove triassiali cicliche drenate il modello è stato leggermente modificato introducendoun ulteriore parametro che tiene conto dell’anisotropia strutturale del materiale
Modelling of imbibition process in an embankment scale model
No full textThis paper aims to investigate the hydro-mechanical behaviour of a loosely compacted embankment during an inundation event. This study is based on the results of a centrifuge test carried out on a small-scale embankment model made of an artificially compacted clay-sand mixture. The wetting-induced displacements are analyzed and interpreted by means of a constitutive model adapted to unsaturated conditions. The numerical predictions are presented in terms of time evolutions of settlements, as well as, spatial distributions of vertical displacements. These profiles are compared to those experimentally observed in order to validate the predictive capabilities of the model on a boundary value problem. Moreover, the stress paths followed by elementary soil elements located at different depths are analyzed to emphasize the stress and strain variations due to capillary rise
Numerical modelling of the response of an unsaturated silty soil under wetting and gravitational loading processes
No full textThis paper presents the results of a numerical study aiming at simulating the response of an unsaturated fine-grained soil under wetting and gravitational loading processes. This study is based on the results of some centrifuge tests carried out to assess the influence of partial saturation on the laterally loaded pile response. The hydro-mechanical behaviour of the silty soil is described using a constitutive model adapted to unsaturated conditions. The model predictions are compared with the measurements provided by LVDTs and laser transducers in the first phases of the experimental study. Besides validating the model, the numerical study aimed at investigating the influence of the after-compaction conditions on both the displacement field and the evolution of the more significant state variables during imbibition and gravitational loading processes. Finally, an additional analysis is conducted to determine the effects of the pile installation on the soil response
Wetting-induced instabilities: triggering mechanism and predisposing factors
No full textThis paper addresses the topic of unsaturated soil stability focusing on wetting-induced instability mechanisms occurring before the attainment of the classical shear failure. The study was conducted by simulating a series of imbibition tests on elementary soil volumes by controlling water contentand net stresses. The behaviour of an ideal coarse-grained soil was described by combining the WR2-Unsat model for the solid skeleton and the Van Genuchten relationship for the definition of the water retention curve. The model reproduces the soil response upon wetting, modelling the activation mechanism of the volumetric instability and identifying the factors that most contribute to its triggering
A numerical model to study the response of piles under lateral loading in unsaturated soils
No full textThe interaction between a laterally loaded pile and the surrounding soil is typically limited to the shallower soil layer. Often, this zone is above the water table and therefore the interaction takes place under unsaturated conditions. The available evidence is scarce but suggests that unsaturated conditions play a major role on the pile’s response. The actual mechanisms governing the soil–pile interaction under unsaturated soil conditions are not understood entirely, and this paper provides a useful insight on this topic. The analysis is carried out with a fully coupled three-dimensional numerical model, the soil behaviour is simulated with a Modified Cam Clay Model extended to unsaturated conditions. The model accounts for the increase in stiffness and strength of unsaturated soils as well as the volumetric collapse upon wetting. The constitutive model is calibrated on the laboratory data and validated against centrifuge data with satisfying agreement. The results highlight the substantial differences in the soil reaction against the pile depending on different water saturation profiles. The study also shows that the influence of unsaturated conditions on the pile response increases as the pile’s flexibility increases. Comparing the findings with currently available design methods such as the p-y curves, it is found that these do not adequately describe the unsaturated soil reaction against the pile, which opens the door for new research in the field. The proposed numerical model is a promising tool to further investigate the mechanisms underlying the soil–pile interaction under unsaturated soils
Hydro-mechanical response of collapsible soils under different infiltration events
No full textInternational audienceThe behavior of a partially saturated soil during surface-water infiltration is analyzed by means of an elasto-plastic constitutive model formulated in terms of effective stress and extended to unsaturated conditions. The model is calibrated considering laboratory-scale experimental results under suction-controlled conditions. The wetting process in two collapsing soils, initially loaded at in situ stresses, is simulated by imposing two different boundary conditions: surface ponding and water flow. The stress paths resulting from the imbibition process are analyzed at different points inside the layer
