A constitutive framework for anisotropic sand including non-proportional loading

Li, X. S.; Dafalias, Yannis F.

doi:10.1680/geot.2004.54.1.41

Cited by 133 publications

(80 citation statements)

References 44 publications

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“…Soil laboratory testing and numerical simulations have mostly been carried out to study proportional loading with a stress history in which the deviatoric stress components are kept in constant ratio to each other, and the soil, if it has an anisotropic fabric, does not rotate with reference to the frame of the principal stresses [1]. The stress path that soils experience in practical engineering however often deviates severely from proportional loading.…”

Section: Introductionmentioning

confidence: 99%

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Macro deformation and micro structure of 3D granular assemblies subjected to rotation of principal stress axes

Yang

2016

Granular Matter

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This paper presents a numerical investigation on the behavior of three dimensional granular materials during continuous rotation of principal stress axes using the discrete element method. A dense specimen has been prepared as a representative element using the deposition method and subjected to stress rotation at different deviatoric stress levels. Significant plastic deformation has been observed despite that the principal stresses are kept constant. This contradicts the classical plasticity theory, but is in agreement with previous laboratory observations on sand and glass beads. Typical deformation characteristics, including volume contraction, deformation non-coaxiality, have been successfully reproduced. After a larger number of rotational cycles, the sample approaches the ultimate state with constant void ratio and follows a periodic strain path. The internal structure anisotropy has been quantified in terms of the contact-based fabric tensor. Rotation of principal stress axes densifies the packing, and leads to the increase in coordination numbers. A cyclic rotation in material anisotropy has been observed. The larger the stress ratio, the structure becomes more anisotropic. A larger fabric trajectory suggests more significant structure re-organization when rotating and explains the occurrence of more significant strain rate. The trajectory of the contactnormal based fabric is not centered in the origin, due to the anisotropy in particle orientation generated during sample generation which is persistent throughout the shearing process. The sample sheared at a lower intermediate principal stress ratio (b = 0.0) has been observed to approach a smaller strain trajectory as compared to the case b = 0.5, consistent with a smaller fabric trajectory and less significant structural re-organisation. It also experiences less volume contraction with the out-of plane strain component being dilative.

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Section: Introductionmentioning

confidence: 99%

“…The introduction of an additional deformation mechanism associated with loading orthogonal to the current stress state is often the practice [1,18,19]. This however implies a large number of model parameters which are often difficult to calibrate.…”

Section: Introductionmentioning

confidence: 99%

Macro deformation and micro structure of 3D granular assemblies subjected to rotation of principal stress axes

Yang

2016

Granular Matter

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“…Based on laboratory observations, a number of advanced constitutive models have been developed, e.g., bounding surface hypoplasticity model (Li and Dafalias 2004;Lashkari and Latifi 2008;Yang and Yu 2012), yield vertex model (Tsutsumi and Hashiguchi 2005), double shearing model (Zhu 2006 a, b), yield vertex and double shearing model (Yu 2008). A state parameter has been introduced in the models to quantify the effect of material anisotropy, and often for simplicity, it is assumed that material anisotropy remains unchanged during the process of loading even though induced anisotropy has been noticed as early as in 1940Õs (Casagrande and Carrillo 1944).…”

Section: ! Introductionmentioning

confidence: 99%

Experimental investigation on the deformation characteristics of granular materials under drained rotational shear

Yang

et al. 2015

Geomechanics and Geoengineering

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Abstract:! This paper presents an experimental investigation revisiting the anisotropic stress-strainstrength behaviour of geomaterials in drained monotonic shear using Hollow Cylinder Apparatus. The test program has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e., non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation is significant. The stress-strain-strength behaviour of the specimen shows strong dependence on the principal stress direction. Pre-loading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in preloaded specimens. The observations on the strength anisotropy and deformation non-coaxiality were successfully explained based on the Stress-

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“…Strength anisotropy is of key engineering importance in estimating the stability of infrastructures and has therefore attracted much research interest. Extensive efforts of experimental testing and constitutive modelling have been made to better estimate the strength and deformation of anisotropic granular soils [2,3,5,6,9,19,22,27,29,32,34,42]. Experiments have been carried out by preparing and testing specimens of different tilting angles or loading a soil specimen along various directions [20,29,30,45].…”

Section: Introductionmentioning

confidence: 99%

“…It has become increasingly popular as particle-scale information has been made more accessible nowadays [10,14,18]. The fabric tensor has been proposed to characterize material structure and incorporated in constitutive model development to better capture the material behaviour [27,33,40,42]. Challenges remain on establishing the correlation between the proposed fabric tensors and the key characteristics of material constitutive behaviours.…”

Section: Introductionmentioning

confidence: 99%

Fabric, force and strength anisotropies in granular materials: a micromechanical insight

2014

Acta Mech

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In micromechanics, the stress-force-fabric (SFF) relationship is referred to as an analytical expression linking the stress state of a granular material with microparameters on contact forces and material fabric. This paper employs the SFF relationship and discrete element modelling to investigate the micromechanics of fabric, force and strength anisotropies in two-dimensional granular materials. The development of the SFF relationship is briefly summarized while more attention is placed on the strength anisotropy and deformation non-coaxiality. Due to the presence of initial anisotropy, a granular material demonstrates a different behaviour when the loading direction relative to the direction of the material fabric varies. Specimens may go through various paths to reach the same critical state at which the fabric and force anisotropies are coaxial with the loading direction. The critical state of anisotropic granular material has been found to be independent of the initial fabric. The fabric anisotropy and the force anisotropy approach their critical magnitudes at the critical state. The particle-scale data obtained from discrete element simulations of anisotropic materials show that in monotonic loading, the principal force direction quickly becomes coaxial with the loading direction (i.e. the strain increment direction as applied). However, material fabric directions differ from the loading direction and they only tend to be coaxial at a very large shear strain. The degree of force anisotropy is in general larger than that of fabric anisotropy. In comparison with the limited variation in the degree of force anisotropy with varying loading directions, the fabric anisotropy adapts in a much slower pace and demonstrates wider disparity in the evolution in the magnitude of fabric anisotropy. The difference in the fabric anisotropy evolution has a more significant contribution to strength anisotropy than that of force anisotropy. There are two key parameters that control the degree of deformation non-coaxiality in granular materials subjected to monotonic shearing: the ratio between the degrees of fabric anisotropy and that of force anisotropy and the angle between the principal fabric direction and the applied loading direction.

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A constitutive framework for anisotropic sand including non-proportional loading

Cited by 133 publications

References 44 publications

Macro deformation and micro structure of 3D granular assemblies subjected to rotation of principal stress axes

Macro deformation and micro structure of 3D granular assemblies subjected to rotation of principal stress axes

Experimental investigation on the deformation characteristics of granular materials under drained rotational shear

Fabric, force and strength anisotropies in granular materials: a micromechanical insight

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