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Granular Soils (granular + soil)
Selected AbstractsFabric evolution of granular assembly under K0 loading/unloadingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 13 2003Jyh-Chau Liou Abstract This study attempted to investigate the fabric evolution in K0 loading/unloading. The work made use of a field simulator to control K0 loading/unloading in large specimens prepared by air-pluviation. In each loading stage, wave velocities along various propagation directions were measured. On the basis of the theories of micro-mechanics and wave propagation, the microscopic parameters of the granular assembly were back calculated to investigate the fabric evolution of granular soil during K0 loading/unloading. In this study, the Geometric fabric was modelled by fabric tensors of ranks 2 and 4. The comparison of calibrated results using ranks 2 and 4 revealed the advantage of the usage of rank-4 fabric tensor in modelling fabric evolution in spite of its complexity. By comparing relative magnitudes of vertical and horizontal components of geometric fabric, it was demonstrated that relative constraint in lateral directions increased during K0 -unloading in order to maintain a K0 condition. It revealed that fabric evolution was responsible for a higher K0 in unloading than K0 in loading. Copyright © 2003 John Wiley & Sons, Ltd. [source] Influence of inherent anisotropy on mechanical behavior of granular materials based on DEM simulationsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2010Zafar Mahmood Abstract We study the influence of inherent anisotropy, i.e. bedding angle on stress,strain behavior and shear band formation in quasi-static granular media. Plane strain biaxial tests are carried out using two-dimensional distinct element method (DEM). Oval/elliptical-shaped particles are generated by overlapping the discrete circular elements. Particle assemblies with four different bedding angles are tested. Evolution of the microstructure inside and outside the shear band and effect of bedding angle on the microstructure are investigated. Influence of bedding angle on fabric and force anisotropy is studied. It is found that by using non-circular particles, generation of large voids and excess particle rotations inside the shear band are reproduced in a quite similar manner to those of the natural granular soils, which are difficult to produce with standard DEM simulations using circular particles. Copyright © 2009 John Wiley & Sons, Ltd. [source] Micromechanical aspects of the shear strength of wet granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2008U. El Shamy Abstract This paper presents a micromechanical model for the analysis of wet granular soils at low saturation (below 30%). The discrete element method is employed to model the solid particles. The capillary water is assumed to be in a pendular state and thus exists in the form of liquid bridges at the particle-to-particle contacts. The resulting inter-particle adhesion is accounted for using the toroidal approximation of the bridge. Hydraulic hysteresis is accounted for based on the possible mechanism of the formation and breakage of the liquid bridges during wetting and drying phases. Shear test computational simulations were conducted at different water contents under relatively low net normal stresses. The results of these simulations suggest that capillary-induced attractive forces and hydraulic hysteresis play an important role in affecting the shear strength of the soil. These attractive forces produce a tensile stress that contributes to the apparent cohesion of the soil and increases its stiffness. During a drying phase, capillary-induced tensile stresses, and hence shear strength, tend to be larger than those during a wetting phase. The proposed model appears to capture the macroscopic response of wet granular materials and revealed a number of salient micromechanical mechanisms and response patterns consistent with theoretical considerations. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical modelling of dynamic consolidation on granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2008S. López-Querol Abstract The application of Pastor,Zienkiewicz constitutive model for sands to dynamic consolidation problems is presented in this paper. This model is implemented in a coupled code formulated in terms of displacements for both solid and fluid phases (u,w formulation), which is firstly compared with u,pw formulation for some simple examples. Its range of validity, previously established for elastic problems and harmonic loading, is explored. Once the suitability of the u,w formulation has been ascertained for this kind of dynamic problems in soils, one- and two-dimensional (plane strain) dynamic consolidation numerical examples are provided, aiming to give some light into the physics of this ground improvement technique. A ,wave of dryness', observed at the soil surface during the impact in field cases, is numerically reproduced and justified. Some hints on the influence of the loading zone size are also given. Copyright © 2007 John Wiley & Sons, Ltd. [source] Load-displacement and bearing capacity of foundations on granular soils using a multi-surface kinematic constitutive soil modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2006M. Banimahd Abstract A finite element approach based on an advanced multi-surface kinematic constitutive model is used to evaluate the bearing capacity of footings resting on granular soils. Unlike simple elastic-perfectly plastic models, often applied to granular foundation problems, the present model realistically accounts for stress dependency of the friction angle, strain softening,hardening and non-associativity. After the model and its implementation into a finite element code are briefly discussed, the numerical difficulty due to the singularity at the footing edge is addressed. The bearing capacity factor N, is then calculated for different granular materials. The effect of footing size, shape, relative density and roughness on the ultimate bearing capacity are studied and the computed results compare very favourably with the general experimental trends. In addition, it is shown that the finite element solution can clearly represent counteracting mechanisms of progressive failure which have an important effect on the bearing capacity of granular foundations. Copyright © 2006 John Wiley & Sons, Ltd. [source] Discrete element modelling of deep penetration in granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2006M. J. Jiang Abstract This paper presents a numerical study on deep penetration mechanisms in granular materials with the focus on the effect of soil,penetrometer interface friction. A two-dimensional discrete element method has been used to carry out simulation of deep penetration tests on a granular ground that is under an amplified gravity with a K0 lateral stress boundary. The numerical results show that the deep penetration makes the soil near the penetrometer move in a complex displacement path, undergo an evident loading and unloading process, and a rotation of principal stresses as large as 180°. In addition, the penetration leads to significant changes in displacement and velocity fields as well as the magnitude and direction of stresses. In general, during the whole penetration process, the granular ground undergoes several kinds of failure mechanisms in sequence, and the soil of large deformation may reach a stress state slightly over the strength envelope obtained from conventional compression tests. Soil,penetrometer interface friction has clear effects on the actual penetration mechanisms. Copyright © 2005 John Wiley & Sons, Ltd. [source] Microstructural deformation mechanisms of unsaturated granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2002J. A. Gili Abstract A discrete model for unsaturated granular soils has been developed. Three discrete entities have been defined: particles, water menisci and pores. Local interaction forces and water transfer mechanisms have been integrated into a model through the appropriate equilibrium and balance equations. The results of several numerical tests using this model have been described and discussed. Simulations include wetting and drying under load tests, the application of suction cycles and the effect of a deviatoric stress ratio on wetting-induced collapse. The model reacts just as true granular soil samples behave in laboratory tests. The model provides a new insight into the internal mechanisms leading to large-scale features of behaviour such as wetting-induced collapse or the increase in soil strength provided by suction. The paper also stresses that matric suction changes acting on a granular structure are capable of explaining most of the macroscopic features of stress,strain behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] A visco-plastic constitutive model for granular soils modified according to non-local and gradient approachesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2002C. di Prisco Abstract An already available non-associated elastic,viscoplastic constitutive model with anisotropic strain hardening is modified in order to describe both the constitutive parameter dependency on relative density and the spatio-temporal evolution of strain localization. To achieve this latter goal, two distinct but similar approaches are introduced: one inspired by the gradient theory and one by the non-local theory. A one-dimensional case concerning a simple shear test for a non-homogeneous infinitely long dense sand specimen is numerically discussed and a finite difference scheme is employed for this purpose. The results obtained by following the two different approaches are critically analysed and compared. Copyright © 2001 John Wiley & Sons, Ltd. [source] Theoretical investigation of the cavity expansion problem based on a hypoplasticity modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2001V. A. Osinov Abstract The problem of the symmetric quasi-static large-strain expansion of a cavity in an infinite granular body is studied. The body is assumed to be dry or fully drained so that the presence of the pore water can be disregarded. Both spherical and cylindrical cavities are considered. Numerical solutions to the boundary value problem are obtained with the use of the hypoplastic constitutive relation calibrated for a series of granular soils. As the radius of the cavity increases, the stresses and the density on the cavity surface asymptotically approach limit values corresponding to a so-called critical state. For a given soil, the limit values depend on the initial stresses and the initial density. A comparison is made between the solutions for different initial states and different soils. Applications to geotechnical problems such as cone penetration test and pressuremeter test are discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] A bounding surface plasticity model for cyclic loading of granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2005N. Khalili Abstract A constitutive model for describing the stress,strain behaviour of granular soils subjected to cyclic loading is presented. The model is formulated using bounding surface theory within a critical state framework. A single set of material parameters is introduced for the complete characterization of the constitutive model. The shape of the bounding surface is based on experimental observations of undrained stress paths for loose samples. A mapping rule which passes through stress reversal points is introduced to depict the stress,strain behaviour during unloading and reloading. The effect of particle crushing is considered through a modified critical state line. Essential features of the model are validated using several experimental data from the literature. Both drained and undrained loading conditions are considered. The characteristic features of behaviour in granular soils subjected to cyclic loading are captured. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerische Modellierungen mit einem zyklisch-viskoplastischen Stoffansatz für granulare BödenBAUTECHNIK, Issue 1 2005vormals Universität Kassel Tim Stöcker Dr.-Ing. In der Geotechnik, insbesondere aber im Verkehrswegebau, gewinnt die Frage der Boden-Bauwerk-Interaktion bei nichtruhenden Lasteinwirkungen zunehmend an Bedeutung. Dabei stehen neben sicherheitsrelevanten Aspekten besonders Fragen zur Gebrauchstauglichkeit sowie wirtschaftliche Aspekte im Vordergrund. Ziel einer anwendungsorientierten Forschung muß daher die Entwicklung eines praxisorientierten Verfahrens zur ingenieurmäßigen Modellierung der Langzeitverformungen bzw. des Langzeitverhaltens des Baugrundes unter nichtruhender Belastung sein. Die dargestellten Arbeiten beschäftigen sich daher mit der Implementierung, Validierung und Anwendung eines neuen, im folgenden als "zyklisch-viskoplastisch" bezeichneten Stoffansatzes für granulare Böden unter nichtruhender Lasteinwirkung. Die wesentlichen Grundlagen dieses Ansatzes sind dabei im Heft 4, 2004, dieser Zeitschrift beschrieben, [1]. Das erreichte Ziel war, den Stoffansatz für numerische Berechnungsmodelle ingenieurmäßig aufzubereiten, zu implementieren, sowie das Berechnungsmodell zu verifizieren und auf reale Problemstellungen anzuwenden. Numerical modelling with a cyclic viscoplastic constitutive approach for granular soils. In modern Geotechnics, especially in track engineering, research for soil-structure interaction under cyclic loading has been gaining importance over the past decades. Next to states of system/structure failure, the long-term (deformation) behaviour is of major interest, as it has a major impact on e.g. maintenance costs in track engineering. Hence, the objective of this work is to be seen in the necessity of investigations on the long-term deformation behaviour of granular soils and ballast under cyclic loading. In the present paper the validation and implementation of a cyclic viscoplastic constitutive approach for granular under cyclic dynamic loading, [1], into a numerical model is carried out. The investigation and set up of a theoretical and physical complete model has not been intended. The objective rather is the development of an engineering type model, appropriate for practical tasks. Some modelling examples are given to illustrate modelling capacities. [source] | ||||||||||