Generalized Equation for Soil Shrinkage Curve

Abstract

The soil shrinkage curve (SSC) defines a constitutive relationship between soil volume and water content under drying conditions. Nearly all work to date considers a zero volume shrinkage for water content below a certain value such as shrinkage limit, which contradicts some recent experimental evidence of pervasive nonzero shrinkage for clayey soils. This paper uses a soil-water retention (SWR)-based conception to theorize such nonzero shrinkage behavior by considering the mechanical effect of capillary and adsorptive SWR mechanisms. A mathematical equation for SSC in the full water content range is developed, which conceptualizes a linear relation for adsorption shrinkage and a sigmoid relation for capillary shrinkage. The equation is validated with test data for a variety of soils. For given soils, the maximum adsorption water contents inferred independently from the SWR and SSC data are highly correlated, with a factor of 2.47. The analysis shows that the adsorption shrinkage rate is strongly correlated with the SWR characteristics of specific surface area (SSA) and cation exchange capacity (CEC). A universal exponential form between the adsorption shrinkage rate and SSA and between the adsorption shrinkage rate and CEC is discovered for silty and clayey soils.