UBC Theses and Dissertations
Effects of particle size distribution and particle shape on cyclic liquefaction response of granular materials Banerjee, Sounik Kumar
Cyclic liquefaction of granular soils is influenced by particle-level parameters such as particle size distribution and particle shape. These parameters are difficult to isolate in real soils, whereas use of Discrete element method (DEM) can be an important step to resolve this problem. It can also be used to model these individual effects on the undrained cyclic response. Samples with increasing particle size distributions, denoted by an increase in coefficient of uniformity are prepared under isotropic compression at two different relative densities. Constant volume, cyclic simple shear simulations at a low relative density under various loading intensities show that increasing the coefficient of uniformity initially increases, then decreases, the cyclic liquefaction resistance. This observation is largely reversed when the relative density is increased, in which case the liquefaction resistance decreases initially and then increases as the coefficient of uniformity increases. Microscopic examinations of the samples at their initial state are conducted to provide insight into their liquefaction resistance. Microparameters based on inter-particle contacts and normal forces reveal reasonable correlations with the macroscopic response. Furthermore, the initial state-based state parameter is found to significantly correlate with the cyclic resistance ratio irrespective of coefficient of uniformity and relative density. Finally, the determinate structure of particle assemblies (isostaticity) at the advent of cyclic liquefaction is studied in terms of average contacts. A similar approach is used to study the effect of particle shape under constant volume cyclic loading. Samples with a variety of simplified particle shapes denoted by aspect ratio and blockiness are isotropically compressed under two relative densities. Samples with non-spherical particles have lower liquefaction resistance than those with spherical particles at low relative density. In contrast, at a medium relative density, the non-spherical samples show comparatively higher liquefaction resistance. It has been discovered that these macrolevel observations under the influence of particle shape can be adequately explained by microparameters previously used to study the particle size distribution. The determinate structure is also identified here and its variation is studied for the range of particle shape and relative densities.
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