New Correlation Equations for Compression Index of Remolded Clays

Compressibility of a soil mass is among the most important geotechnical properties that is widely used during the design of geotechnical structures. Various regression equations have been proposed by numerous researchers in the past to estimate the compression index of a soil specimen with parameters such as void ratio at liquid limit, initial void ratio, liquid limit, or the combination of the specific gravity, void ratio, and liquid limit. Although all researchers concur that the compression index depends on the mineralogical composition of the soil and initial moisture content, very little research has been performed on the mixtures of minerals composing a wide range of activities under consistent initial moisture contents. This research is conducted on 55 different soil specimens prepared in the laboratory by mixing various proportions of montmorillonite, illite, kaolinite, and quartz at initial moisture contents equal to the liquid limit. The intrinsic compression line (ICL) was unique for most of the mixtures used for this study. Very good regressions were obtained between the compression index and initial void ratio, initial porosity, plasticity index, or liquid limit. Two different equations were proposed to estimate the compression indices of remolded clays with liquid limit—one for soils with activities less than one and the other for soils with activities greater than one. The compression indices of 82 different natural samples, reconstituted at liquid limit, were similar to the values estimated with the proposed equations. Furthermore, the compression indices of the soil samples presented in the literature could also be estimated with reasonable accuracy using the proposed equations.