Oda (1972) and Arthur & Menzies (1972) were among the first to demonstrate the influence of the initial fabric orientation on the strength of sands. Been & Jefferies, 1985 Ibrahim & Kagawa, 1991). The sensitivity of the mechanical response of sands to fabric can also be observed when the mechanical responses of reconstituted samples formed using different preparation procedures are compared (e.g. The intact material also had a markedly higher stiffness than the reconstituted sand. These experimental studies have demonstrated significant differences in the peak strength and dilation for both materials. Cresswell & Powrie, 2004 Ventouras & Coop, 2009). Directional fabric can be measured using particle long-axis orientations or contact normal orientations, and the statistical approaches to analyse datasets of orientation vectors are relatively well established ( Satake, 1982 Oda et al., 1985 Thornton, 2000).Įxperimental evidence of the effect of fabric on the mechanical behaviour of sands has been shown by comparing the behaviour of intact and reconstituted samples (e.g. Examples of scalar measures of fabric include the coordination number, the void ratio distribution within the sample, and the contact index. Fabric can be quantified using either scalar parameters or directional parameters. Most prior measurements of real soil fabric and the preferential orientation of elements of the soil fabric have been via observation of two-dimensional images using either optical microscopy or scanning electron microscopy (e.g. Ibraim et al., 2010), as well as using numerical discrete-element modelling (DEM) (e.g. Oda et al., 1985) or Schneebeli rods (e.g. Quantitative observations of fabric have been made with physical models using photoelastic discs (e.g. Chan & Kenney, 1973), or comparison of the mechanical response of specimens prepared using different approaches (e.g. Kuwano & Jardine, 2002), anisotropy of permeability (e.g. In geomechanics research, fabric has been qualitatively described, and the fabric changes have frequently been inferred from macro-scale observations of soil response: for example, anisotropy of small-strain stiffness (e.g. The response of soils and other granular materials is known to be sensitive to the material fabric, that is, the topology of the internal structure of the material.
Different patterns were observed within the shear band, as both the particles and the contact normal vectors appeared to rotate along the shear plane. 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.
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. This paper investigates methods of quantifying the directional fabric of a real sand and its evolution under loading. 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. Up until now there have been relatively few attempts to describe this fabric quantitatively. 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.