ORCID Profile
0000-0002-5515-9911
Current Organisation
Zhejiang University
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Publisher: Thomas Telford Ltd.
Date: 08-2015
Abstract: This paper presents a multiscale investigation on the interplay among inherent anisotropy, fabric evolution and strain localisation in granular soils, based on a hierarchical multiscale framework with rigorous coupling of the finite-element method (FEM) and discrete-element method (DEM). DEM assemblies with elongated particles are generated to simulate inherent anisotropy and are embedded to the Gauss points of the FEM mesh to derive the required constitutive relation. Specimens prepared with different bedding plane angles are subjected to biaxial shear under either smooth or rough loading platens. Key factors and physical mechanisms contributing towards the occurrence and development of strain localisation are examined. The competing evolutions of two sources of anisotropy, one related to particle orientations and the other related to contact normals, are found to underpin the development of the shear band. A single band pattern is observed under smooth boundary conditions, and its orientation relative to the bedding plane depends critically on the relative dominance between the two anisotropies. Under rough boundary conditions, the non-coaxial material response and the boundary constraint jointly lead to cross-shaped double shear bands. The multiscale simulations indicate that the DEM assemblies inside the shear band(s) undergo extensive shearing, fabric evolution and particle rotation, and may reach the critical state, while those located outside the shear band(s) experience mild loading followed by unloading. The particle-orientation-based fabric anisotropy needs significantly larger shear and dilation for mobilisation than the contact-normal based one. The asynchrony in evolution of the two fabric anisotropies can cause non-coaxial responses for initially coaxial packings, which directly triggers strain localisation.
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4811909
Publisher: The Japanese Geotechnical Society
Date: 2016
Publisher: Elsevier BV
Date: 11-2019
Publisher: Thomas Telford Ltd.
Date: 06-2013
Abstract: The concept of the critical state in granular soils needs to make proper reference to the fabric structure that develops at critical state. This study identifies a unique property associated with the fabric structure relative to the stresses at critical state. A unique relationship between the mean effective stress and a fabric anisotropy parameter, K, defined by the first joint invariant of the deviatoric stress tensor and the deviatoric fabric tensor, is found at critical state, and is path-independent. Numerical simulations using the discrete-element method under different loading conditions and intermediate principal stress ratios identify a unique power law for this relationship. Based on the findings, a new definition of critical state for granular media is proposed. In addition to the conditions of constant stress and unique void ratio required by the conventional critical state concept, the new definition imposes the additional constraint that K reaches a unique value at critical state. A unique spatial critical state curve in the three-dimensional space K–e–p′ is found for a granular medium, the projection of which onto the e–p′ plane turns out to be the conventional critical state line. The new critical state concept provides an important reference state for a soil to reach, based on which the key concepts in the constitutive modelling of granular media, including the choice of state parameters, dilatancy relation and non-coaxiality, are reassessed, and future exploratory topics are discussed.
Publisher: Thomas Telford Ltd.
Date: 03-2016
Abstract: A novel hierarchical multiscale model has been applied to simulate the thick-walled hollow cylinder tests in dry sand and to investigate the corresponding shear failures. The combined finite-element method and discrete-element method (FEM/DEM) model employs the FEM as a vehicle to advance the solution for a macroscopic non-linear boundary value problem incrementally. It is, meanwhile, free of conventional macroscopic phenomenological constitutive law, which is replaced by discrete-element simulations conducted with representative volume elements (RVEs) associated with the Gauss quadrature points of the FEM mesh. Numerical simulations proposed by the authors indicate that this multiscale approach is capable of replicating the evolution of cavity pressure during cavity expansion – before and after the onset of strain localisation – in qualitative agreement with laboratory tests. In particular, the curvilinear shear bands observed from experiments have been reproduced numerically. The information provided by the mesoscale DEM and the macroscale FEM reveals a close linkage between significant particle rotations taking place inside the dilative shear bands and the highly anisotropic microstructural attributes of the associated RVEs.
Publisher: Elsevier BV
Date: 12-2016
Publisher: Wiley
Date: 14-07-2015
DOI: 10.1002/NAG.2406
Publisher: Springer Science and Business Media LLC
Date: 02-2014
Publisher: AIP
Date: 2013
DOI: 10.1063/1.4812158
Publisher: Springer Netherlands
Date: 2011
Publisher: American Geophysical Union (AGU)
Date: 05-2018
DOI: 10.1029/2017JB015366
Publisher: Elsevier BV
Date: 2013
Publisher: Springer Science and Business Media LLC
Date: 24-05-2017
Publisher: Springer International Publishing
Date: 2017
Publisher: Springer International Publishing
Date: 30-12-2014
Publisher: AIP Publishing
Date: 08-2023
DOI: 10.1063/5.0161344
Abstract: This paper presents a numerical study on suspensions of monodisperse non-Brownian grains in a Couette flow. The fully resolved coupled smoothed particle hydrodynamics and discrete element method is employed to model the motion of arbitrarily shaped grains in a viscous fluid. The numerical method is benchmarked against its capability in accurately handling grain–fluid hydrodynamics and inter-grain collisions. It is then used to simulate suspension flows of varying particle Reynolds and Bagnold numbers subjected to different shear rates, solid concentrations, and solid-to-fluid density ratios. A special focus is placed on the effect of grain shape with different aspect ratios and convexities on the flow behavior. Both the inertia and the grain shape are found to affect the grain–fluid and inter-grain interactions and uniquely contribute to the overall shear stress and the rheology of the suspension. The local profiles of solid concentration suggest the presence of grain layering near the boundary walls, which becomes more pronounced with higher solid concentration and inertia, and increased non-circularity in grain shape. A further examination of the pair distribution function and average particle rotation reveals a strong correlation between suspension viscosity and grain microstructure and kinematics.
Publisher: The Japanese Geotechnical Society
Date: 2016
Publisher: Elsevier BV
Date: 06-2016
Publisher: American Physical Society (APS)
Date: 25-04-2014
Publisher: Wiley
Date: 22-12-2020
DOI: 10.1002/NAG.3175
Publisher: Wiley
Date: 13-06-2014
DOI: 10.1002/NME.4702
Publisher: American Physical Society (APS)
Date: 22-01-2020
No related grants have been discovered for Ning Guo.