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Optical and Electron Microscopic Investigation of Shear Induced Structures in Lightly Consolidated (Soft) and Heavily Consolidated (Hard) Kaolinite

Published online by Cambridge University Press:  01 July 2024

R. H. Foster  and
P. K. De
R. H. Foster
Affiliation:
The City University, London, England
P. K. De
Affiliation:
The City University, London, England
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Abstract

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A review of fabric studies of clays suggests the need for relating those fabric characteristics which are revealed at the two levels of magnification provided by optical and electron microscopy, and a technique to achieve this has been developed and is described within the context of the initial stages of a long term study of the interrelation between fabric and engineering behaviour. Two kaolinitic clays with contrived fabrics were prepared by controlling particle size, moisture content and pH of suspension, and consolidation load and were subjected to shear loading to failure. Resin impregnation techniques which permit the kaolinite to be cut into thin sections for transmission electron microscopy have been optimized with the object of minimizing fabric strain and damage during ultratomy.

The fabrics of the hard and soft ambient material are qualitatively compared by means of electron micrographs and are explained in terms of the preparatory procedures adopted for fabric control. The fabrics of the two types of shear induced structures are also qualitatively compared and explained in terms of the original fabrics and the subsequent shear loading.

Résumé

Résumé

Une revue des études de structure des argiles suggère la nécessité de rapporter ces caractéristiques qui sont révélées à deux niveaux de grossissement fournis par la microscopie optique et électronique, et une technique, spécialement élaborée pour cette étude, est décrite dans le contexte des premiers stades d’une étude à long terme sur la relation entre la structure et son comportement du point de vue engineering. Deux argiles kaolinitiques, avec structures aménagées, ont été préparées en contrôlant la grosseur des particules, la teneur d’humidité et la pourcentage de la suspension, ainsi que la charge de consolidation, et ces argiles ont été ensuite soumises jusqu’au bout à une force de cisaillement. Les techniques d’imprégnation de résine qui permettent de découper la kaolinite en sections minces, pour la microscopie électronique, ont été optimisées en vue de réduire au minimum la contrainte et l’endommagement de la texture pendant l’ultratomie.

Les structures des matériaux ambiants dures et souples sont comparées qualitativement au moyen de micrographes électroniques et sont expliquées en terme de procédés préparatoires adoptés pour le contrôle de la structure. Les textures des deux types de structure à cisaillement induit sont également comparées, du point de vue qualitatif, et une explication est donnée en terme des textures originelles et de la force de cisaillement ultérieure.

Kurzreferat

Kurzreferat

Eine Übersicht über Untersuchungen der Textur von Tonmineralen lässt es geboten erscheinen diejenigen Texturmerkmale, die auf zwei Vergrösserungsebenen durch optische und durch Elektronenmikroskopie sichtbar gemacht werden, in eine Beziehung zu einander zu bringen, und es ist zu diesem Zwecke eine Methode entwickelt worden, die im Zusammenhang mit den Anfangsphasen einer langzeitigen Untersuchung der Beziehungen zwischen Textur und technischem Verhalten, beschrieben wird. Zwei kaolinitische Tone mit geplanter Textur wurden bereitet durch Kontrolle der Teilchengrösse. des Feuchtigkeitsgehaltes und des pH der Suspension sowie der Verdichtungslast, und wurden einer Scherbeanspruchung bis zum Bruch unterzogen. Verfahren der Kunstharzimprägnierung, die es gestatten den Kaolinit in dünne Schnitte für die Transmissionselektronenmikroskopie zu schneiden, wurden optimisiert um die Beanspruchung der Textur und die Beschädigung während der Ultratomie auf ein Minimum zu beschränken.

Die Texturen des harten und weichen Umgebungsmaterials werden qualitativ mittels Elektronen-mikrographien verglichen und werden mit den für die Kontrolle der Textur angewendeten Verfahren in Beziehung gebracht. Die Texturen der zwei Arten durch Scherung hervorgerufener Gefüge werden ebenfalls qualitativ verglichen und im Zusammenhang mit der ursprünglichen Texturen und der nachfolgenden Scherbelastung erörtert.

Резюме

Резюме

Обзор текстурных исследований глин выявил необходимость сопоставления тех их характеристик, которые получаются на двух уровнях увеличения, т. е. с помощью оптической и электронной микроскопии. Для решения этой задачи разработана методика, которая изложена ранее вместе с результатами длительного предварительного исследования соотношений между структурно-морфологическими и техническими характеристиками глин. Две каолинитовые глины с заданными текстурами приготавливались с контролем размеров частиц, влажности, рН суспензии и степени спрессованности, и подвергались сдвиговым напряжениям с целью образования нарушений. Методика пропитывания пластическими наполнителями, позволяющая получить тонкие срезы каолинита для исследования в электронном микроскопе, была несколько усовершенствована для уменьшения структурных напряжений и повреждений при ультрамикротомировании.

Строение твердых и мягких материалов качественно сравнивалось по электронномикро-скопическим снимкам и трактовалось с учетом методик препарирования, применяемых при структурно-морфологических исследованиях. Особенности сдвиговых структур двух типов также количественно сравнивались и объяснялись на основе данных о строении исходных материалов и степени последующей сдвиговой обработки.

Type
Research Article
Information
Clays and Clay Minerals , Volume 19 , Issue 1 , March 1971 , pp. 31 - 47
Copyright
Copyright © 1971, The Clay Minerals Society

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