The effect of consolidation on undrained behaviour of granular materials: experiment and DEM simulation

Abstract

The characteristic features of undrained responses of granular materials, for example, stress ratio at instability (η IS) and phase transformation (η PT) states and the critical state (CS) behaviour, are often influenced by the consolidation history. However, there are limited studies in the literature, and a consensus has not yet been reached. This study combined the triaxial test of yellow silty sand and the three-dimensional discrete element method (DEM) simulation of ellipsoid particles under a triaxial condition to evaluate the effect of isotropic and K 0 consolidations. Triaxial test data formed non-unique CS lines (CSLs) in the e-log(p¢) space for isotropic and K 0 tests, whereas the CSL was unique for DEM simulations; where e and p¢ are the void ratio and mean effective stress, respectively. The micromechanical quantities, coordination number (C N) and fabric anisotropy (F vM) at the CS, also showed a unique relation with p¢. The characteristic features, η IS and η PT , showed good correlation with the state parameter (x) and the density indices. It was found that the g IS decreased with x, and the correlation was dependent on consolidation type. The micromechanical analysis suggested that F vM is a better parameter than C N to characterise the macromechanical behaviour. This study unambiguously supports the applicability of CS theory and provides insights into micromechanics of granular materials.

Flow liquefaction potential of loose sand: stress path envelope and energy-based evaluation

“…This scenario is related to the interplay between the loading direction and the fabric anisotropy of the sand formed during sample preparation or natural deposition (Sivathayalan and Vaid 2002;Yang et al 2008;. Recent numerical studies by Nguyen et al (2017) and Rahman et al (2018) further indicated that the instability stress ratio of granular materials, which depends on both the state parameter and consolidation stress path, is closely related to the contact orientation of particles. Furthermore, during a cyclic triaxial loading test, such an anisotropic nature of pluviated or deposited sands leads to the following observation: in response to an applied symmetrical cyclic stress, the flow liquefaction of isotropically consolidated samples is typically initiated on the extension side of the stress pace.…”

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

“…Some studies assessed liquefaction potential by considering the dissipated energy approach [1,12,[14][15][16][17][18]. Among the liquefaction assessment methods, the triaxial test is commonly adopted to predict the liquefaction potential under the critical state soil mechanics (CSSM) framework [2,3,5,[19][20][21][22][23][24]. Such a test is performed by controlling the principal stress and strain components in 3 orthogonal directions, where σ 11 and ε 11 are the major principal effective stress and strain, respectively, and σ 33 (equal to σ 22 ) and ε 33 (i.e., equal to ε 22 ) are the minor principal effective stress and strain, respectively.…”