The influence of particle characteristics on the behaviour of coarse grained soils

Abstract

This paper describes an experimental study examining the influence of the mechanical and geometrical properties of the constituent grains on the overall material response of cohesionless granular materials. Glass ballotini were used as an analogue soil; their relatively simple geometry allowed the influence of particle shape and inter-particle friction to be examined independently. Techniques were developed to control the surface roughness of the ballotini to facilitate a parametric study. The particle shape was also varied by crushing the ballotini. At the micro-scale, the particle characterisation included accurate measurements of inter-particle friction, contact stiffness, particle surface roughness and particle shape. At the macro-scale the sensitivity of overall material response to changes in surface roughness and geometry was characterised using triaxial tests and oedometer tests on smooth spherical ballotini, roughened ballotini and crushed angular ballotini. Compression tests indicated that the initial load deformation response at particle–particle contact points is significantly softer than previously believed. Optical interferometry of particles after single particle–particle shearing tests confirmed that plastic strains occurred at the contact point, which were related to plastic yield. A Hertzian response was only seen at higher contact loads. A clear relationship between the inter-particle friction and the particle surface roughness was found. However, the macro-scale experiments indicated that while the material response may be slightly dependent on the surface roughness and friction, the influence of particle shape is very much more significant.

Effect of Particle Shape on the Mechanical Behavior of Natural Sands

“…The aspect ratio (AR) is the ratio between Feret minimum and Feret maximum diameters, while sphericity (S) is calculated as the ratio of the perimeter of the equivalent circle with the same area as the particle, to the actual perimeter. This definition is effectively equal to the square root of circularity as defined by the International Standard ISO/DIS (2006) (Cavarretta et al, 2010). Although it is not the same value or definition it correlates well with the sphericity values in the Krumbein & Sloss (1963) visual identification chart as well as those in the chart proposed by Powers (1953) (Altuhafi et al, 2013).…”

“…Additionally, some non-soil materials are included such as intact and crushed glass beads (ballotini); in the literature these materials have often been employed as an analog soil (e.g. Cavarretta et al, 2010;Cho et al, 2006;Kuwano, 1999;Lesniewska & Muir Wood, 2011). The sands that have undergone significant diagenesis are indicated, and a few weak sandstones are included which have been tested in a reconstituted i.e.…”

“…It is interesting that there is no clear effect of roughness on ϕ'cs, apart from that arising from shape. While inter-particle friction may be related to particle roughness (Cavarretta et al, 2010), as Mitchell & Soga (2005) highlight, the role of inter-particle friction in determining ϕ'cs is strictly secondary, as its main function is in maintaining stability of the strong force chains.…”

“…: Santamarina & Cascante, 1998;Cho et al, 2006;Cavarretta et al, 2010;Georgiannou, 2011, Otsubo et al, 2015.…”

Single-Grain Virtualization for Contact Behavior Analysis on Sand

“…Oda & Iwashita, 1999;Lu & McDowell, 2007;Vlahinić et al, 2014;Nguyen, et al, 2015). There are, however, very few studies on the effect of single grain morphology and contact topology on contact interaction (Cavarretta et al, 2010;Wang & Coop, 2016). Previous studies on single grain response have, for the most part, focused on the tensile strength and breakage potential of a single grain at high stress level (McDowell & Bolton, 1998;Nakata et al, 2001;Zhao et al, 2015).…”