Quantifying the evolution of soil fabric during shearing using directional parameters

Abstract

Over the past 50 years, experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric, that is, the arrangement of the grains. Up until now there have been relatively few attempts to describe this fabric quantitatively. Much of our understanding of the link between the particle movements and interactions and the macro-scale response of granular materials, including sand, comes from discrete-element modelling and experiments on 'analogue' sands with simple, idealised shapes. This paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading. Statistical analyses of the distribution of fabric directional data in terms of particle, contact normal, branch vector and void orientations were carried out at different stages of shearing deformation. The data show that the initial particle orientation fabric that develops during the deposition of the material tends to persist during shearing, while in the post-peak regime the contact normals seem to be reoriented along the direction of the major principal stress. Different patterns were observed within the shear band, as both the particles and the contact normal vectors appeared to rotate along the shear plane.

Linking Carbonate Sand Fabric and Mechanical Anisotropy from Hollow Cylinder Tests: Motivation and Application

“…To obtain quantitative information about specimen fabric at any test stage, an epoxy impregnation technique is used. This was achieved by modifying existing methodologies for preservation of triaxial specimens (Fonseca et al 2013;Jang et al 1999). Figure 3a shows one step of the new epoxy-impregnation method used.…”

“…Soil fabric quantification may be carried out using various approaches. Detailed descriptions of the approaches available for soil fabric quantification are presented elsewhere (Fonseca et al 2013;Oda 1972;O'Sullivan 2011). Soil fabric may be assessed in a relatively simple way through quantification of the preferred orientation of major particle axis (Oda 1972).…”

“…Fundamental research into the role of soil fabric has been carried out using both imaging of preserved soil fabric from element tests (Fonseca et al 2013;Frost and Jang 2000;Oda 1972) and discrete element method (DEM) simulations (Ai et al 2014;Tong et al 2014). However, major gaps still exist on the quantification of soil fabric from element tests for certain soils.…”

“…DEM may be a crucial tool to better understand and model particulate soil behavior, but models must always be validated by relevant, quality experimental data, which is sparse for generalized loading scenarios. Even though approaches are available to preserve and quantify soil fabric in triaxial tests (Fonseca et al 2013;Jang et al 1999), further attempts have not been made to include other element tests that are capable of applying more general boundary conditions. The acquisition of soil fabric data and its evolution from element tests whose boundary conditions are more complex than axisymmetric ones is important because most real world applications result in non-proportional loading conditions, leading to changes in both orientation and magnitude of principal stresses.…”

Investigation of the change in soil fabric during cone penetration in silt using 2D measurements

“…A number of experimental and numerical studies have repeatedly demonstrated that the mechanical behavior is sensitive to the soil fabric, defined here as the arrangement of the grains and pore spaces in the soil according to Mitchell and Soga [17]. Fonseca et al [8,9] have shown that the differences in response between intact and reconstituted specimens of a silica sand could be explained based on differences in the initial fabric and the way this fabric evolves under loading. The authors have quantified the orientation of the grains, the orientation of the contact normal and orientation of the voids and observed their changes under shearing.…”