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Title: An investigation of the micromechanical response of soil to one dimensional compression in varied thermal conditions
Author: Ní Bhreasail, Áine
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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This study used synchrotron X-ray micro computed tomography (μCT) to investigate the response of soil to one dimensional compression both at room temperature and below freezing. Synchrotron tomography at the Diamond Light Source in Oxfordshire was used in order to capture high resolution (in the order of μm) images of the soil in situ as it was subject to loading and temperature change. Custom apparatuses were designed and built to control the loading and temperature of the experiment at all times. Two sets of experiments were carried out; one set on dry sands in 'mini-oedometer' tests and another examining the effects of temperatures below zero on sands and silts saturated with water. The particle-scale response of sand in an oedometer test was investigated by examining the evolution of both scalar and directional properties of Leighton Buzzard sand and Reigate sand samples. The scalar properties included void ratio, particle shape, particle size distribution and particle contact area. The variation of void ratio within a sample was examined to determine the boundary effects. The directional properties measured included the particle orientation, contact normals and branch vectors. Tracking of the particle positions for the larger sand during loading was also carried out. This study presents the documentation of many of these properties for a sample under load in situ for the first time. In the second set of experiments the micromechanics of frozen soil, in particular the phenomenon of ice lensing, was investigated. Temperature controlled mini-oedometers developed for this study were used to directly observe the behaviour of saturated soil under temperature conditions below 0°C. Micro-cracks within the ice phase of the frozen soil were observed and it is proposed that under field conditions such micro-cracks are likely to represent the initiation of ice-lenses by providing a conduit for water migration.
Supervisor: O'Sullivan, Catherine; Lee, Peter D.; Fenton, Clark Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available