Abstract
ABSTRACT The compression index obtained from an oedometer test is often used to estimate the settlements of clayey subsoil, but compressibility parameters are rarely available during the preliminary geotechnical design phase. Various empirical correlations linking compressibility to other properties such as water content have been proposed. However, as Scandinavian clays are soft and exhibit greater compressibility, the existing transformation models for compressibility can be biased when applied to Finnish clays. This paper compiles a partial multivariate database of Finnish clayey soils and demonstrates that the existing transformation models tend to underestimate the compressibility of Finnish clays. The new transformation models are constructed by means of a 2-degree polynomial regression applied to the natural logarithms of the soil properties. Finally, the transformation uncertainties are quantified via the standard deviation of errors and the coefficient of variation. The best predictors for the compressibility of Finnish clayey soils were found to be the void ratio and water content. When the void ratio was combined with a secondary predictor, such as the ratio between undrained shear strength and preconsolidation pressure or plastic limit, the transformation uncertainty decreased notably.
Highlights
The compression index obtained from an oedometer test is often used to estimate the settlements of clayey subsoil, but compressibility parameters are rarely available during the preliminary geotechnical design phase
When the void ratio was combined with a secondary predictor, such as the ratio between undrained shear strength and preconsolidation pressure or plastic limit, the transformation uncertainty decreased notably
The compression index Cc, which is defined as the decrease in void ratio per tenfold increase in vertical stress, is often used to estimate the compression of clayey subsoil
Summary
The compression index Cc, which is defined as the decrease in void ratio per tenfold increase in vertical stress, is often used to estimate the compression of clayey subsoil. Most Finnish geotechnical handbooks present only two models: Helenelund’s (1951) non-linear empirical correlation for compressibility index using wn and Janbu’s (1988) model, which links the modulus number to wn. Neither of these transformation models were derived for Finnish clays, and they lack the statistical measures required for use in reliability analyses. Because these transformation models for compressibility are characterised by a rather large transformation uncertainty, it is essential that they can be defined in probabilistic terms Saarelainen (1978, 1981) created linear regression models for municipal data (Helsinki capital area) and Di Buò et al (2019) studied the empirical correlations for the compressibility of soft sensitive clays from four sites in Finland
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