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Saturated Soils (saturated + soil)
Selected AbstractsCoupled solid-fluid FE-analysis of geotechnical problems involving partially saturated soilsGAMM - MITTEILUNGEN, Issue 1 2010Matthias Hofmann Abstract A numerical model for coupled solid-fluid FE-analyses of geotechnical problems involving partially saturated soils is described. As constitutive model for partially saturated soil serves the Barcelona Basic Model, which is formulated in terms of net stress and capillary pressure. Different stress update algorithms are compared for this model regarding the accuracy and efficiency. The application of the numerical model is demonstrated by numerical simulations of the impoundment of an earth dam and of the injection of compressed air into water saturated soil (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vertical vibration of an elastic strip footing on saturated soilINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2008Y. Q. Cai Abstract Based on Biot's dynamic coupled equations, the vertical vibration of an elastic strip footing on the surface of saturated soil is studied. Utilizing the Fourier transform, the governing dynamic differential equations for saturated poroelastic medium are solved. Considering the mixed boundary value conditions at the bottom of the foundation, a pair of dual integral equations about the vertical vibration of an elastic strip footing is derived, which can be converted to a set of linear equations by means of infinite series of orthogonal functions. The relation between the dynamic compliance coefficients and the dimensionless frequency tends to be gentle with decreasing footing rigidity, while the dimensionless frequency has only small effect on the dynamic compliance coefficients. When the dynamic permeability is large, its effect on the dynamic compliance coefficients should be taken into consideration. Furthermore, the dynamic compliance coefficients are found to be not sensitive to Poisson's ratio of the soil for footing on saturated soil. Copyright © 2007 John Wiley & Sons, Ltd. [source] An operator-split ALE model for large deformation analysis of geomaterialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2007Y. Di Abstract Analysis of large deformation of geomaterials subjected to time-varying load poses a very difficult problem for the geotechnical profession. Conventional finite element schemes using the updated Lagrangian formulation may suffer from serious numerical difficulties when the deformation of geomaterials is significantly large such that the discretized elements are severely distorted. In this paper, an operator-split arbitrary Lagrangian,Eulerian (ALE) finite element model is proposed for large deformation analysis of a soil mass subjected to either static or dynamic loading, where the soil is modelled as a saturated porous material with solid,fluid coupling and strong material non-linearity. Each time step of the operator-split ALE algorithm consists of a Lagrangian step and an Eulerian step. In the Lagrangian step, the equilibrium equation and continuity equation of the saturated soil are solved by the updated Lagrangian method. In the Eulerian step, mesh smoothing is performed for the deformed body and the state variables obtained in the updated Lagrangian step are then transferred to the new mesh system. The accuracy and efficiency of the proposed ALE method are verified by comparison of its results with the results produced by an analytical solution for one-dimensional finite elastic consolidation of a soil column and with the results from the small strain finite element analysis and the updated Lagrangian analysis. Its performance is further illustrated by simulation of a complex problem involving the transient response of an embankment subjected to earthquake loading. Copyright © 2007 John Wiley & Sons, Ltd. [source] Die-off of Cryptosporidium parvum in soil and wastewater effluentsJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2007A.M. Nasser Abstract Aims:, To determine the effect of biotic and abiotic components of soil on the viability and infectivity of Cryptosporidium parvum, and evaluate the suitability of viability tests as a surrogate for oocyst infectivity under various environmental settings. Methods and Results:, The die-off of C. parvum in saturated and dry loamy soil was monitored over time by immunofluorescence assay (IFA) and PCR to estimate oocysts viability and by cell culture to estimate oocysts infectivity. Pseudomonas aeruginosa activity resulted in digestion of the outer layer of the oocysts, as demonstrated by loss of the ability to react in IFA. Whereas, P. aeruginosa activity did not affect the DNA amplification by PCR. A 1-log reduction in the oocysts infectivity was observed at 30 °C in distilled water and in saturated soil while oocysts viability was unchanged. Incubation for 10 days in dry loamy soil at 32 °C resulted in a 3-log10 reduction in their infectivity while no change of oocysts viability was recorded. Conclusions:, Under low temperature, C. parvum oocysts may retain their infectivity for a long time. Soil desiccation and high temperatures enhance the die-off rate of C. parvum. Significance and Impact of the Study:, Previous die-off studies of C. parvum used viability tests that do not necessarily reflect the oocyst infectivity. Under low temperatures, there was an agreement observed between viability and infectivity tests and oocysts retained their infectivity for a long time. Desiccation and high temperatures enhance the loss of infectivity of C. parvum. The presented die-off data have significant implications on the management of wastewater reuse in warm environments. [source] A Simulation Model for Shield Tunnelling and its Interactions with Partially Saturated SoilPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2009Felix Nagel The design of shield supported tunnel construction in urban areas requires the reliable determination of the expected time-variant ground response and the prognosis of possible critical conditions endangering the soil stability. In partially saturated soil the response of the surrounding underground depends strongly on the interactions between the construction process and the surrounding underground and its constituents. The paper gives an overview on a Finite Element model for the simulation of shield supported tunnel advance in partially saturated soil that is capable of accounting for these interactions. Special emphasis is laid on the description of the surrounding underground, modelled as a three phase continuum within the Theory of Porous Media (TPM). Applicability of the simulation model is discussed by results obtained from the simulation of compressed air application for the heading face support. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal developmentEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2009D. N. Warrington Summary Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 × 40 × 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m,3; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures. [source] A Numerical Simulation Model for Shield Tunnelling with Compressed Air SupportGEOMECHANICS AND TUNNELLING, Issue 3 2008Felix Nagel Dipl.-Ing. This paper is concerned with a numerical simulation model (ekate) specifically designed for shield tunnelling in fully and partially saturated soils based upon the Finite Element Method (FEM). The model considers all relevant components , the soil, the lining, the tail void grouting, the hydraulic jacks and different types of face support , involved in shield tunnelling. The surrounding soft soil is formulated as a three-phase material, consisting of the soil skeleton, pore water and air. This model allows for the simulation of consolidation processes in partially saturated soils as well as of flow of compressed air often used as temporary face support during repair interventions at the cutting wheel. Despite the complexity connected with the relatively high degree of realism of the simulation model, only little effort is required from the user to establish a realistic 3D model for shield tunnelling. To this end an automatic model generator has been developed which allows for a user friendly generation of the discretized model including all components involved and to investigate variants with a minimum effort for the user. The model allows for realistic predictions of settlements and also provides information on deformations and stresses in the ground, the lining and the TBM, respectively. In addition to its use as a prognosis tool in the design process, in particular for tunnelling projects in sensitive urban areas, the model also may be used to assist the driving and steering process in mechanized tunnelling. The paper provides an overview over the main components of the model, the automatic model generator and the tri-phasic representation of the soil. A simulation of a compressed air intervention of a shield tunnel in soft soil demonstrates the applicability of the model. Ein numerisches Simulationsmodell für druckluftgestützte Schildvortriebe In diesem Beitrag wird ein Simulationsmodell basierend auf der Methode der Finiten Elemente (FEM) für die Berechnung schildvorgetriebener Tunnel in un-, voll- und teilgesättigten Böden vorgestellt. In diesem numerischen Modell werden alle beim maschinellen Tunnelbau wesentlichen Komponenten , der Boden, der Ausbau, die Schildschwanzverpressung, die Vortriebspressen sowie unterschiedliche Arten der Ortsbruststützung , wirklichkeitsnah berücksichtigt. Der Baugrund wird im Simulationsmodell als dreiphasiges Material modelliert, bestehend aus dem Korngerüst, dem Porenwasser und der Porenluft. Diese Materialformulierung für den Baugrund ermöglicht die Analyse von Konsolidierungsprozessen in teilgesättigten Böden ebenso wie von Strömungsvorgängen im Boden bei Verwendung von Druckluft als temporärer Ortsbruststützung. Druckluft wird häufig beim Wechsel von Schneidwerkzeugen eingesetzt. Ungeachtet der Komplexität des Modells, die mit der relativ wirklichkeitsnahen Abbildung des Vortriebsgeschehens verbunden ist, ist nur ein sehr geringer Aufwand für die Modellgenerierung erforderlich. Um diesen Eingabeaufwand auf ein Minimum zu reduzieren, wurde ein automatischer Modellgenerator entwickelt, der den Ingenieur bei der Eingabe unterstützt und die Untersuchung von Planungsalternativen deutlich vereinfacht. Das Modell ermöglicht wirklichkeitsnahe Prognosen von Bodenbewegungen und Beanspruchungen, wie sie für die Planung von Vortrieben insbesondere unter setzungsempfindlichen, innerstädtischen Gebieten erforderlich sind. Darüber hinaus stellt das Modell ein wertvolles Hilfsmittel bei der vortriebsbegleitenden Steuerung von Vortriebsmaschinen in Lockergestein dar. Neben den wesentlichen Komponenten des numerischen Modells, des Modellgenerators und der Dreiphasen-Formulierung für den Boden enthält der Beitrag als prototypisches Anwendungsbeispiel die Simulation einer Druckluftintervention in Lockergestein. [source] Implicit integration of a chemo-plastic constitutive model for partially saturated soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2008H. W. Zhang Abstract A chemo-plastic constitutive model for partially saturated soils is proposed in this paper based on the existing models developed in Hueckel (Int. J. Numer. Anal. Meth. Geomech. 1997; 21:43,72) and Gallipoli et al. (Geotechnique 2003; 53:123,135). The chemical softening effects due to the increase in contaminant mass concentration are considered based on Hueckel's chemo-plastic model. Gallipoli's model is used to simulate the effects of suction and degree of saturation on mechanical behavior of partially saturated porous materials. In order to implement the proposed model in a finite element code, a fully implicit backward-Euler integration algorithm is put forward. Numerical solutions for the tests at local level and the application of the algorithm to the real boundary value problem demonstrate the accuracy and convergence properties of the proposed integration scheme. Copyright © 2008 John Wiley & Sons, Ltd. [source] Coupled simulation of wave propagation and water flow in soil induced by high-speed trainsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2008P. Kettil Abstract The purpose of this paper is to simulate the coupled dynamic deformation and water flow that occur in saturated soils when subjected to traffic loads, which is a problem with several practical applications. The wave propagation causes vibrations leading to discomfort for passengers and people in the surroundings and increase wear on both the vehicle and road structure. The water flow may cause internal erosion and material transport in the soil. Further, the increased pore water pressure could reduce the bearing capacity of embankments. The saturated soil is modelled as a water-saturated porous medium. The traffic is modelled as a number of moving wheel contact loads. Dynamic effects are accounted for, which lead to a coupled problem with solid displacements, water velocity and pressure as primary unknowns. A finite element program has been developed to perform simulations. The simulations clearly demonstrate the induced wave propagation and water flow in the soil. The simulation technique is applicable to railway as well as road traffic. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effective stress concept in unsaturated soils: Clarification and validation of a unified frameworkINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2008Mathieu Nuth Abstract The effective stress principle, conventionally applied in saturated soils, is reviewed for constitutive modelling purposes. The assumptions for the applicability of Terzaghi's single effective stress are recalled and its advantages are inventoried. The possible stress frameworks applicable to unsaturated soil modelling are reassessed in a comparative manner, specifically the Bishop's single effective stress, the independent stress variables approach and the generalized stress framework. The latter considerations lead to the definition of a unified stress context, suitable for modelling soils under different saturation states. In order to qualify the implications brought by the proposed stress framework, several experimental data sets are re-examined in the light of the generalized effective stress. The critical state lines (CSLs) at different saturation states tend to converge remarkably towards a unique saturated line in the deviatoric stress versus mean effective stress plane. The effective stress interpretation is also applied to isotropic paths and compared with conventional net stress conception. The accent is finally laid on a second key feature for constitutive frameworks based on a unified stress, namely the sufficiency of a unique mechanical yield surface besides the unique CSL. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermal effects in partially saturated soils: a constitutive modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2005Gabriella Bolzon Abstract The present paper is centred on the assessment of an elastic,plastic model for partially saturated soils, earlier proposed by the authors, for its predictive capability with respect to temperature changes, on the light of available experimental results. The model is cast within a constitutive framework that uses Bishop's stress and suction as main variables governing the volumetric response of the material. Some enhancement to the original temperature-independent formulation is proposed. In particular, functions describing the yield surface and the compressibility modulus are modified to account for the shrinking of the elastic domain and for the increase of irreversible volumetric strain with heating. Some examples illustrate the main features of the present proposal. Comparison with some experimental results is also included. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||