http://ihome.ust.hk/~jzhao/home/PDFs/SignatureAnisotropy.pdf

The signature of shear-induced anisotropy in granular media

An Anisotropic Critical State Theory (ACST) for granular media is presented, which accounts for the role of anisotropic fabric at critical state. It enhances the requirements of critical values for the stress and void ratio of the classical Critical State Theory (CST) by an additional requirement of critical value for an appropriate measure of fabric-anisotropy. A fabric tensor and its evolution toward a critical value, norm-wise and direction-wise, is introduced motivated by micromechanical and experimental studies. On the basis of a scalar-valued fabric-anisotropy variable relating the evolving fabric tensor to the loading direction, a dilatancy state line is defined in the void ratio—pressure plane which determines a dilatancy state parameter ζ that characterizes the contracting or dilating trends of the current state. When the fabric-anisotropy variable reaches its critical state value, the dilatancy state line becomes identical to the critical state line and the ζ identical to the well-known state pa...

Anisotropic Critical State Theory: Role of Fabric

This paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behavior of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behavior of fresh and fouled ballast were simulated and compared with the experimental results. Clump logic in particle flow code in three dimensions (PFC3D) incorporated in a subroutine was used to simulate irregular-shaped particles in which groups of 10–20 spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with a various void contaminant index (VCI) ranging from 20 to 70% VCI was modeled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behavior of fresh and fouled ballast as observed in the laboratory, showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing VCI. Furthermore, th...

/pdf/behavior-of-fresh-and-fouled-railway-ballast-subjected-to-2uusyy6iy3.pdf

Behavior of fresh and fouled railway ballast subjected to direct shear testing: discrete element simulation

This paper presents a systematic experimental investigation into the impact of specimen preparation on the cyclic loading behavior of saturated sand, including the deformation pattern, pore-water pressure generation, stress-strain relationship, and cyclic shear strength. Moist tamping and dry deposition were used in the laboratory to prepare sand specimens with distinct fabrics for cyclic triaxial tests under a range of conditions. It is found that the soil fabric formed by dry deposition can lead to unique failure modes different from those of moist-tamped sam- ples in certain situations. These failure modes are hybrid in nature, characterized by a contractive response in the form of limited flow followed by cyclic strain hardening in the form of either cyclic mobility or plastic-strain accumulation. The hybrid nature of the failure patterns makes defining failure for liquefaction-resistance evaluation crucial; the conventional failure criteria based on a certain level of strain or pore-water pressure do not appear to properly represent the failure mechanism involved and may lead to a substantial overestimation of liquefaction re- sistance. The experiments reveal that the method used to reconstitute specimens or the soil fabric they form plays a role that is far more com- plicated than previously thought. Depending on the combination of relative density, confining stress, and degree of stress reversal in cyclic loading, a change of reconstitution method can have a marked or little effect on the nature of the response in terms of deformation pattern and failure mechanism; nevertheless, the two reconstitution methods always give significantly different liquefaction-resistance values under otherwise similar testing conditions. DOI: 10.1061/(ASCE)GT.1943-5606.0000971. © 2014 American Society of Civil Engineers.

Failure Modes of Sand in Undrained Cyclic Loading: Impact of Sample Preparation

https://hal.archives-ouvertes.fr/hal-01393138/document

Conjugate gradient type algorithms for frictional multi-contact problems: applications to granular materials

This textbook compiles reports written by about 35 internationally recognized authorities, and covers a range of interests for geotechnical engineers. Topics include: fundamentals for mechanics of granular materials; continuum theory of granular materials; and discrete element approaches.

匡寛小田

Papers

Mechanics of granular materials : an introduction

The effect of crack geometry on hydrodynamic dispersion in cracked media

匡寛 小田

Papers

Mechanics of granular materials : an introduction

The effect of crack geometry on hydrodynamic dispersion in cracked media

匡寛小田