47,125 research outputs found
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
Time evolution of the height of dredged mud in a containment facility: a comparison between monitoring data and numerical predictions
No full textAn efficient and sustainable way to handle dredged sediments is to re-use them to fill coastal containment facilities and then reclaim their areas. When large volumes of fine-grained soils are involved, the dredging is usually carried out hydraulically. Adopting this technology, the soil is transported as a slurry and deposited in containment facilities, where it initially sediments at high void ratios before experiencing great deformations during consolidation. The paper presents a numerical model able to simulate the distinctive features of this class of boundary value problems. The soil behaviour was modelled adopting the Modified Cam-clay model, in conjunction with a strongly non-linear void ratio:permeability law. The gradual filling of the containment facility was modelled by generating the whole soil column and then progressively applying gravity to each element. The model was tested simulating a challenging and well-documented case study. The comparison between numerical results and monitoring data confirms the effectiveness of the developed model and remarks its usefulness both at the design stage and during works
Unsaturated structured soils: constitutive modelling and stability analyses
No full textThe paper presents a new single-surface elasto-plastic model for unsaturated cemented soils, formulated within the critical state soil mechanics framework, which should be considered as an extension to unsaturated conditions of a recently proposed constitutive law for saturated structured soils. The model has been developed with the main purpose of inspecting the mechanical instabilities induced in natural soils by bond degradation resulting from the accumulation of plastic strains and/or the changes in pore saturation. At this scope, the constitutive equations are used to simulate typical geotechnical testing conditions, whose results are then analysed in light of the controllability theory. The results of triaxial tests on an ideal fully saturated cemented soil and on the corresponding unsaturated uncemented one are first discussed, aiming at detecting the evidence of potentially unstable conditions throughout the numerical simulations. This is followed by similar analyses considering the combined effects of both the above features. For each analysed case, a simple analytical stability criterion is proposed and validated against the numerical results, generalizing the results, and highlighting the crucial role of state variables and model parameters on the possible occurrence of failure conditions
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
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
Studio del comportamento di rilevati stradali durante processi di imbibizione
No full textI rilevati stradali e ferroviari sono opere realizzate compattando terreni in condizioni di parziale saturazione, che possono subire, a causa di eventi piovosi o di oscillazioni dei livelli piezometrici nei terreni di imposta, variazioni significative del grado di saturazione. Se soggetti a processi di imbibizione, i terreni parzialmente saturi possono collassare causando elevati spostamenti in testa al rilevato o subire significative riduzioni di resistenza al taglio, innescando fenomeni di rottura in prossimità delle scarpate. Lo studio numerico presentato in questa nota è finalizzato alla valutazione degli effetti indotti dall'innalzamento della superficie libera in un rilevato stradale, in termini di campi di spostamento e meccanismi deformativi. Le simulazioni sono eseguite con il codice agli elementi finiti Abaqus/Standard in condizioni di deformazione piana, valutando, in particolare, l'influenza delle condizioni di post-compattazione, della perturbazione esterna e delle caratteristiche del materiale sulla risposta dell'opera
Numerical study of the mechanical behavior of fine- grained dredged sediments
No full textIn the last few decades dredging activities have experienced a significant growth. An efficient way to manage the dredged material is to reuse it to reclaim coastal confined containment facilities. When fine-grained sediments are involved, hydraulic dredging is a common, highly appreciated choice. This technology causes the dredged mud to sediment at very high water-to-solid volumetric ratios and then undergo dramatic deformations during consolidation. The paper presents the results of a numerical study conducted simulating the whole filling-consolidation process. The soil behaviour was modelled adopting the well-known Modified Cam-clay model, in conjunction with a strongly non-linear void ratio:permeability law. A series of parametric analyses was performed to investigate the influence of the hydro-mechanical properties on the dredged mud behaviour during the hydraulic filling and the subsequent consolidation process. The numerical results emphasize that the design of the filling works can significantly benefit from a deeper knowledge of these processes
Numerical investigation of the behaviour of hydraulically dredged fine-grained soils during and after filling of the containment facility of the port of Gaeta
No full textFine-grained dredged sediments can be efficiently and sustainably handled by hydraulically filling containment facilities, which can then be reclaimed. This study presents two numerical modelling strategies, characterized by markedly different levels of complexity, that simulate the gradual filling and subsequent consolidation process. Both numerical models employ hydro-mechanical constitutive relations apt to cover wide state ranges, starting from very low effective stresses. Class A predictions of a well-documented case study, where an articulated construction sequence was implemented, are reported and the effectiveness of the two proposed strategies is compared. After updating the numerical predictions according to the recorded construction timeline, the numerical results are validated against field data, specifically versus the monitored height of dredged mud. Finally, the monitoring data are back-analysed, emphasizing the influence of the hydro-mechanical behaviour at high void ratios. The results show that both modelling strategies are sufficiently accurate and can provide substantial benefits to the design of the filling works and to the evaluation of the actual storage capacity of the impoundments, especially if the available volume is limited or if complex construction procedures are implemented
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
Simulation of mechanical behaviour of Toyoura sand using Severn Trent constitutive model
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