Compressibility behaviour of remoulded, fine- grained soils and correlation with index properties A. Sridharan and H.B. Nagaraj Abstract: Correlating engineering properties with index properties has assumed greater significance in the recent past in the field of geotechnical engineering. Although attempts have been made in the past to correlate compressibility with various index properties individually, all the properties affecting compressibility behaviour have not been consid- ered together in any single study to examine which index property of the soil correlates best with compressibility behaviour, especially within a set of test results. In the present study, 10 soils covering a sufficiently wide range of liquid limit, plastic limit, and shrinkage limit were selected and conventional consolidation tests were carried out starting with their initial water contents almost equal to their respective liquid limits. The compressibility behaviour is vastly different for pairs of soils having nearly the same liquid limit, but different plasticity characteristics. The relationship between void ratio and consolidation pressure is more closely related to the shrinkage index (shrinkage index = liquid limit – shrinkage limit) than to the plasticity index. Wide variations are seen with the liquid limit. For the soils investigated, the compression index relates better with the shrinkage index than with the plasticity index or liquid limit. Key words: Atterberg limits, classification, clays, compressibility, laboratory tests. Résumé : La corrélation des propriétés pour fin de conception avec les propriétés d’indices a pris une signification accrue récemment dans le domaine de la géotechnique. Alors que des tentatives ont été faites dans le passé pour corréler la compressibilité avec différents indices pris individuellement, on n’a jamais considéré globalement toutes les propriétés dans une étude donnée pour examiner quelle propriété d’indice présente la meilleure corrélation avec le comportement en compressibilité particulièrement à l’intérieur d’un ensemble de résultats d’essais. Dans la présente étude, dix sols couvrant une plage suffisamment large de limites de liquidité, de plasticité et de gonflement ont été sélectionnés, et des essais de consolidation conventionnels ont été réalisés en partant de leurs teneurs en eau initiales quasiment égales à leurs limites de liquidité respectives. On trouve que le comportement en compressibilité est extrêmement différent pour des paires de sols ayant quasiment la même limite de liquidité, mais différentes caractéristiques de plasticité. On trouve que les courbes d’indice de vide-pression suivent mieux l’indice de gonflement (indice de gonflement = limite de liquidité – limite de gonflement) que l’indice de plasticité. De grandes variations ont été observées avec la limite de liquidité. On voit que pour les sols étudiés, l’indice de compression offre une meilleure corrélation avec l’indice de gonflement qu’avec l’indice de plasticité ou la limite de liquidité. Mots clés : limites d’Atterberg, classification, argiles, compressibilité, essais de laboratoire. [Traduit par la Rédaction] Notes 722 Introduction Compressibility of soils is an important engineering con- sideration. The oedometer test is used to determine the com- pressibility characteristics of soils which are typically described using the compression index, C c , and the coeffi- cient of consolidation, c v . The compression index is used to predict how much settlement will take place, and the coeffi- cient of consolidation is a rate parameter used to predict how long it will take for a given amount of compression to take place. However, oedometer testing requires undisturbed sam- ples and is quite time-consuming and expensive. For this reason, researchers in the past have correlated compressibil- ity characteristics with index properties. The first well-known correlation was presented by Skempton (1944), who gave the following correlation for the compressibility of remoulded soils with liquid limit, w L : [1] C c = 0.007(w L – 10) Other subsequent correlations are presented in Table 1, which shows that different researchers have used various parameters, including liquid limit (w L ), natural moisture content (w n ), initial in situ void ratio (e o ), dry unit weight (γ d ), plasticity index (I P ), and void ratio at liquid limit (e L ). The availability of so many equations suggests that none are completely satisfactory to generalize and correlate com- pressibility with the index or other properties. Nagaraj and Srinivasa Murthy (1983) extended Skempton’s compressibility equation (eq. [1]) using the void ratio at liq- uid limit (e L ) to give a generalized equation for compressibility Can. Geotech. J. 37: 712–722 (2000) © 2000 NRC Canada 712 Received May 3, 1999. Accepted October 7, 1999. A. Sridharan. Department of Civil Engineering, Indian Institute of Science, Bangalore 560 012, India. H.B. Nagaraj. Department of Civil Engineering, BMS College of Engineering, Bangalore 560 019, India.