Equivalent state theory for mixtures of sand with non-plastic fines: a DEM investigation

Abstract

The discrete-element method (DEM) was used to simulate constant-volume (undrained) triaxial compression tests for coarse particles (sand) mixed with non-plastic fines. Simulations were performed on granular mixtures with a range of fines contents (fc) – namely, 0, 0·05, 0·10 and 0·20. The critical state and micromechanical responses of these mixtures were evaluated. The influence of fc on sand behaviour was captured when fc < fthre, where fthre represents a threshold fines content, which corresponds to a transition from a fines-in-sand soil matrix to a sand-in-fines soil matrix. The DEM was utilised to assess the micromechanical participation of fines within the sand skeleton (matrix). Such evaluations led to assessing the performance of the equivalent granular void ratio (e*), the equivalent granular state parameter (ψ*) and ultimately their inherent parameter b, which represents the proportion of fines actively participating in the sand skeleton structure. It was observed that through capturing the stress partition of contact types within granular mixtures, a reasonable approximation of the active proportion of contacts within the sand matrix could be obtained. This led to a new DEM interpretation of the b parameter. The study therefore evaluated the concept and applicability of the equivalent state theory for sand–fines mixtures.

An Investigation of Instability on Constant Shear Drained (CSD) Path under the CSSM Framework: A DEM Study

“…Both effective stress paths of ISO4 (e 0 = 0.582 and p 0 = 50 kPa) and ISO9 (e 0 = 0.625 and p 0 = 300 kPa) showed very dilative tendencies and evolved beyond the CSL shown in Figure 3a. This phenomenon was also observed for different granular materials [66]. It can be clearly seen that q values for both simulations were approaching an equilibrium state, i.e., dq ≈ 0 after strain hardening (see Figure 3b).…”

“…The adoption of the elliptical shape gave some angularities for the particles and reduced the rolling tendency of the particles during the simulations. It can be noted that some DEM studies using spherical particles adopted a rolling resistance model to replicate the angularity features of the particle [48,[61][62][63][64][65][66]. As mentioned previously, the behaviour of granular materials under CSD conditions is linked with the observed undrained behaviour [45][46][47].…”

Updated skeleton void ratio for gravelly sand mixtures considering effect of grain-size distribution

“…Thanks to the above-mentioned indices of skeleton void ratios, researchers have provided more consistent characterization of such mixed soils in terms of liquefaction susceptibility, shear strength, stiffness and compressive strength (Hazirbaba and Rathje, 2009;Thevanayagam et al, 2002;Ni et al, 2004;Bobei et al, 2009;Carraro et al, 2009;Sitharam et al, 2013;Rahman et al, 2014;Goudarzy et al, 2016;Barnett et al, 2020). Notwithstanding their merits, application of these indices to describe the anticipated mechanical behavior of gravelly sand has faced two issues: 1) Such skeleton void ratio relies on parameters that are difficult to determine in practice, such as the "B parameter" in Equation (1).…”

Experimental Investigation on Small-Strain Stiffness of Marine Silty Sand

“…It is worth noting that the application of the binary packing model should not be limited to the evaluation of G max . Existing test results show that e* presents a unified correlation with static liquefaction characteristics [39], drained and undrained triaxial compression behaviors [40], critical strength [41], liquefaction strength [42], etc., of silty sand, and the proposed procedure in this paper provides a significant improvement in the evaluation of the above mechanical properties in geotechnical engineering practice. 10); R 2 -coefficient of determination for Equation (10).…”