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Title: Microfabric changes during the deformation of clays
Author: Wong, Kwong Yan
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1976
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Abstract:
An investigation of the fabric of clays was carried out using both the scanning electron microscope and an x- ray di f fractometer. A great deal of effort was devoted to the development o f new and more reliable methods of specimen preparation. Free z e drying and �critical point drying were found to be the most reliable for scanning electron microscopy. The latter me t hod has been used with great success by the writer using acet one as an intermediate liquid and carbon dioxide as the working fluid. The freeze-drying apparatus designed by Tovey (1 9 70) was modified for more convenient use, and a new liquid, Ar cton , as was used as the coolant and/a substitute for the inflammable Propane during the freezing process. New techniques have been developed for the substitut ion of the pore fluids within soils, and it is now possible to extend the investigation of soil fabric to illite, montmorillonite and other natural clays. These techniques are a pre-requisite in the� preparation of resinified samples f or x-ray diffraction. The writer found Carbowax to be less suitable than Araldite AY18 as a stabilising resin for optical microscopy or x - ray diff raction. A gas adsorption method was used for determining the specific surface area and pore size distribution of soils. The technique was used not only to examine changes during consolidation etc., but also as a means to compare the reliability of the various specimen preparation techniques. A new technique for the preparation of fresh surfaces has been developed. This enables fresh surfaces in any direction to be revealed and produces a smoother surface than the alternative fracturing method. By taking successive peelings, the change of fabric with depth can be observed. The determination of preferred orientation using both the standard x - ray diffractometer and the x-ray texture diffractometer have been investigated. For the first technique, the importance of choosing peak area rather than / . the peak height intensities has been discussed and also the importance of taking into account the diffraction potential of each crystallographic plane. A simpler and more efficient way of obtaining a complete pole figure is introduced by running tests on a single 1 54.7� 1 section. A computer program has been developed to enable the evaluation of a least square ellipsoid from the data. Such analyses as these permit the evaluation of the degree of particle orientation anisotropy at any direction to . the principle stress direction. The change of particle orientation of kaolin subjecte d to various conditions of consolidation has been discussed. It was found that the increase in particle alignment during one-dimensional consolidation was limited until a stress of 100 kPa had been ;1'.'eached. This finding confirms to some extent the findings , of Morgernstern and Tchalenko (1967) who used an optical technique, and Martin and Ladd (1970) who used an x-ray technique. They are, however, at variance with the results of McConnachie � (1971). � In the studies using the scanning electron mic'roscope the writer has developed the photogrammetrio and optical diffraction methods first used by Tovey (1970) . In particular, the optical diffraction method was quantified and the results obtained from consolidated samples confirm the results from the x-ray diffraction methods.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.477819  DOI:
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