Correlation between Soil-Shrinkage Curve and Water-Retention Characteristics

A soil-shrinkage curve (SSC) can be defined as the characteristic volume-water content relation under free external stress conditions. A SSC is traditionally divided into three characteristic states: normal shrinkage when soil is saturated, residual shrinkage when soil is unsaturated and subjected to volume reduction, and zero shrinkage when soil approaches the dry state. Using the measured SSC, soil waterretention (SWR) curve, and suction stress characteristic curve of various silty and clayey soils, the traditional states are found to be not well defined and incorrect, particularly when soil approaches the dry state. A conceptual model for SSC is proposed in which SSC can be divided into four states: capillary, pendular, adsorbed, and tightly adsorbed; each is governed by one or/and two SWR mechanisms: capillary and adsorption. The shrinkage rate, defined here as the change in void ratio due to the change in moisture ratio, is found to be not universally zero in adsorptive states. It is shown that the shrinkage rate in the adsorption SWR regime is highly correlated to SWR characteristics-namely, the specific surface area-or to cation-exchange capacity, or that total amount of adsorption water follows the same exponential form with the shrinkage rate. (C) 2017 American Society of Civil Engineers.