ISSN: 0090-3973
Page Count: 6

Compression Index of Clays and Silts

Robinson, RG
Postdoctorate Fellow,The National University of Singapore,

Allam, MM
Associate professor,Indian Institute of Science,

(Received 26 November 2001; accepted 21 August 2002)

Abstract

The consolidation settlement of a structure founded on a normally consolidated soil can be calcuated 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 σ′^v) 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 σ′^v, little is known regarding soils that are less plastic, in particular, silty soils. This paper reports the e-log σ′^v plots of clays and silits. It was found that the e-log σ′^v curves of the silts are not linear but are convex upwards. This results in an increase in C^c with an increase in σ′^v. 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 σ′^v 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.

Keywords:
consolidation, clays, silts, compression index, physicochemial factors

Paper ID: JTE12353J
DOI: 10.1520/JTE12353J
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