DEM study of the behaviour of granular materials during drained cyclic loading
File(s)
Author(s)
Sassel, Tara
Type
Thesis
Abstract
Geotechnical structures such as offshore wind turbines with monopile foundations or integral bridge abutments are subjected to long term cyclic loading. This can affect the serviceability of those structures because the interaction between the structure and the soil can result in strain ratcheting and densification of the surrounding material. Strain ratcheting is an accumulation of plastic strain which has been well documented in laboratory experiments, leading to soil stiffening. Prior research has indicated that this phenomenon may be closely linked to an evolution in soil fabric. It is difficult to analyse changes in fabric in laboratory experiments and numerous finite element models (FEM) have been developed to reproduce this behaviour by integrating a fabric tensor formulation. However, those formulations are often based on assumptions made from laboratory experiments.
The discrete element method (DEM) is employed in this study to investigate the
effect of drained cyclic loading on granular materials. Drained cyclic triaxial element simulations were performed involving both one-way and two-way stress-controlled cyclic loading as well as strain-controlled cyclic loading. These were carried out on isotropically and anisotropically compressed samples consisting of spheres with a particle size distribution similar to Toyoura sand. The overall or macroscopic behaviour is broadly in agreement with data documented in the literature, the key phenomenon of ratcheting is captured and the changes in earth pressure coefficient align with observations in laboratory experiments. The particle scale energy terms were computed throughout the simulations and these data provide insight into energy dissipation during drained cyclic loading. DEM enables us to establish links between the macro-scale and the micro-scale behaviours. Changes in scalar and directional measures of fabric were studied and associated with changes in the undrained shear strength of the sample. Micro-scale observations include changes in coordination number, degree of anisotropy calculated from the second order fabric tensor and changes in the contact force chains.
The insights provided through this study using DEM, along with the capability of
tracing fabric in DEM, can inform the development of continuum models that aim to predict the overall behavior of granular materials such as sand in various engineering applications. Fundamental understanding of the response of sand to drained cyclic loading and the influence of drained cyclic loading on soil behaviour is advanced in this research.
The discrete element method (DEM) is employed in this study to investigate the
effect of drained cyclic loading on granular materials. Drained cyclic triaxial element simulations were performed involving both one-way and two-way stress-controlled cyclic loading as well as strain-controlled cyclic loading. These were carried out on isotropically and anisotropically compressed samples consisting of spheres with a particle size distribution similar to Toyoura sand. The overall or macroscopic behaviour is broadly in agreement with data documented in the literature, the key phenomenon of ratcheting is captured and the changes in earth pressure coefficient align with observations in laboratory experiments. The particle scale energy terms were computed throughout the simulations and these data provide insight into energy dissipation during drained cyclic loading. DEM enables us to establish links between the macro-scale and the micro-scale behaviours. Changes in scalar and directional measures of fabric were studied and associated with changes in the undrained shear strength of the sample. Micro-scale observations include changes in coordination number, degree of anisotropy calculated from the second order fabric tensor and changes in the contact force chains.
The insights provided through this study using DEM, along with the capability of
tracing fabric in DEM, can inform the development of continuum models that aim to predict the overall behavior of granular materials such as sand in various engineering applications. Fundamental understanding of the response of sand to drained cyclic loading and the influence of drained cyclic loading on soil behaviour is advanced in this research.
Version
Open Access
Date Issued
2023-07
Date Awarded
2024-02
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
O'Sullivan, Catherine
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
EP/L016826/1
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)