Interpretation of soil-water characteristic curves when volume change occurs as soil suction is changed

The soil-water characteristic curve, SWCC, has become a valuable tool for the estimation of unsaturated soil property functions, USPF, in geotechnical engineering practice. At the same time, indiscriminate usage of the estimation techniques for unsaturated soils can lead to erroneous analytical results and poor engineering judgment. Soils that undergo significant volume changes as soil suction is changed constitute one situation where erroneous estimations can occur. In particular, it is the evaluation of the correct air-entry value for the soil that has a significant effect on the estimation of subsequent USPFs. This paper defines the characteristics of a high volume change material and then proceeds to describe how the SWCC laboratory results can be properly interpreted with the assistance of a shrinkage curve. Two laboratory data sets are presented and used to illustrate how the test data should be interpreted in the case of high volume change soils. There have also been developments in the design of SWCC laboratory equipment with the result that both overall volume change and water content change can be monitored when measuring SWCCs. As a result, all volume-mass properties can be calculated. One such apparatus is described along with a description of its benefits and limitations.