Micro mechanics of drained and undrained shearing of compacted and overconsolidated crushable sand

J P De Bono,G R Mcdowell

doi:10.1680/jgeot.16.p.318

Abstract

A numerical crushable soil sample has been created using the previously published McDowell and de Bono (2013) model and subjected to a range of stress paths. Compacted sand simulations are performed using conventional triaxial stress paths, constant mean stress and constant volume conditions and a critical state line established. Overconsolidated samples have been created by crushing the soil down the isotropic normal compression line, unloading, and shearing at constant radial stress, constant mean stress or constant volume and a critical state line is again established. The critical state line is unique at high stresses for the simulated compacted and overconsolidated sands and is parallel to the isotropic normal compression line, in agreement with available data and a previously published theory. The critical state line at low stress levels is non-unique and a function of the particle size distribution, in agreement with available data. Constant volume tests exhibit the well-known phenomena of phase transformation points and peak strengths are observed for ‘drained’ soils on the dense side of critical. The numerical soil produces a state boundary surface that compares well to available data.

Highlights

It is well known that particle crushing has a major influence on the physical behaviour of granular soil
A cylindrical sample of spheres was isotropically compressed to high stresses using a new model, which features a flexible membrane allowing triaxial tests to be performed
normally consolidated (NC) triaxial tests from p' = 15 MPa

Summary

INTRODUCTION

It is well known that particle crushing has a major influence on the physical behaviour of granular soil. There have been several efforts to use the discrete-element method (DEM) to model and investigate the general shearing behaviour of soil using crushable particles Discrete-element modelling of triaxial tests using such agglomerates (Cheng et al, 2004; Bolton et al, 2008) provides useful quantitative insight on aspects such as yielding and plastic deformation, as well the general effects of particle crushing during shearing. This paper follows on from that work by aiming to establish a full CSL over a wide range of stresses for a simulated silica sand and provide an in-depth fundamental analysis of the micro-scale behaviour of a crushable soil during and after being sheared to a critical state, from initial states looser and denser than critical, involving a range of different stress paths, including constant-volume conditions

BACKGROUND

Findings

CONCLUSIONS