The Analysis of Volume Change in Unconfined Units of Soil

The assessment of volume change with associated change in water content has been widely used to assess soil structural quality. The possibility of inter‐experiment comparisons has been minimized both by the lack of a theoretically based model for predicting volume change, and the non‐standardization of coordinates to define the data. Three models which have been or could be used to describe soil shrinkage curves—the specific volume versus gravimetric water content relationship—are derived; the three straight lines model, the general soil volume change equation and the logistic model. The important parameters of the models are specified and their interpretation with regard to soil properties given. The three models are compared both theoretically and for worked examples, the latter using published data from Austin Clay (U.S.A.), Hanslope Series (U.K.) and a Typic Pellustert (Australia). The three straight lines model not only performs well for the data presented but also provides model parameters which have direct physical interpretation within soil science.