An Analysis of Freezing Induced Soil Shrinkage.

There is an implicit assumption bulk soil volume will increase during freezing as pore water freezes to ice.  At higher water contents approaching saturation this is true as total soil pore volume cannot accommodate the phase change related volumetric expansion.  However, previous research has shown that at water contents below a threshold value (shown experimentally to be approximately 75-90% saturation) freezing induced bulk soil shrinkage can occur in non-rigid soils.  The concomitant soil structural changes resulting from freezing induced desiccation of intra-aggregate pore space has been linked to structural improvement while negative structural effects have been linked to the effects of freezing induced moisture redistribution upon thawing.  In terms of soil moisture retention, the freezing process has many similarities to the drying process to the extent that the soil freezing characteristic has been compared to the soil moisture characteristic.  The shape of the shrinkage curve of void ratio versus moisture ratio can be used to delineate structural changes in the soil during freezing induced shrinkage.  A constitutive shrinkage equation was developed from basic equilibrium thermodynamics and fitted to freezing induced volume change data using an unbiased least-squares curve fitting procedure.  The resultant equation is differentiable thus allowing precise estimation of the different regions of the unsaturated shrinkage curve.  The range of water contents associated with these different regions may then be related to the observed changes in soil structure resulting from freezing.