Generalized Equation for Soil Shrinkage Curve

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. (C) 2018 American Society of Civil Engineers.