On modelling the compressibility of unsaturated fine-grained soils

An empirical expression linking the slope λ of the normal compression line (NCL) for unsaturated soils to the effective degree of saturation Se is studied in this technical note. The parameters in this empirical expression are intrinsic soil parameter α, the slope of the normal compression line (NCL) at full saturation, λ100%, and the slope of the normal compression line at the driest state achievable by a soil, λd (a state at which only adsorbed water remains in the pores). The determination of λ at any other level of saturation usually requires a considerable amount of test data. This technical note explores the relationship between regression parameter α and the particle size, quantified by the D10 of the soil, based on test data for five different soils taken from the literature. A regression equation is developed that relates α to D10. Based on the proposed regression equation, the slope of the normal compression line for unsaturated fine-grained soils at any degree of saturation can be estimated when the test data are limited.