Compression index of clays and silts

Robinson, RG and Allam, MM (2003) Compression index of clays and silts. In: Journal of Testing and Evaluation, 31 (1). pp. 22-27.

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Abstract

The consolidation settlement of a structure founded on a normally consolidated soil can be calculated from the knowledge of the compression index C-c. The value of C-c is usually obtained from the laboratory oedometer test on the assumption that the void ratio (e)-logarithm of pressure (log sigma'(nu)) plot is linear. While the literature reveals that in the case of highly plastic clays the plots are concave upwards with their C-c (computed between successive load increments) decreasing with an increase in sigma'(nu), little is known regarding soils that are less plastic, in particular, silty soils. This paper reports the e-log sigma'(nu) plots of clays and silts. It was found that the e-log sigma'(nu) curves of the silts are not linear but are convex upwards. This results in an increase in C-c with an increase in sigma'(nu). Convex curves are to be regarded as a normal feature in such soils and can be explained from consideration of the mechanical and physicochemical factors that govern the compressibility of clays. These factors establish that C-c increases with sigma'(nu) for those soils whose compressibility behavior is governed by mechanical factors, in contrast to soils like very plastic clays whose compressibility behavior is governed by physicochemical factors. In the latter, C-c decreases with an increase in the consolidation pressure.

Item Type:	Journal Article
Publication:	Journal of Testing and Evaluation
Publisher:	ASTM International
Additional Information:	Copyright of this article belongs ASTM International
Keywords:	consolidation;clays;silts;compression index;physicochemical factors.
Department/Centre:	Division of Mechanical Sciences > Civil Engineering
Date Deposited:	28 May 2009 11:14
Last Modified:	19 Sep 2010 04:54
URI:	http://eprints.iisc.ac.in/id/eprint/16978

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