Experimental study on the freezing/thawing characteristic curves of sand/clay mixtures

Abstract

The soil freezing characteristic curve (SFCC), relating temperature and unfrozen water content, is essential in modelling hydrothermal processes in permafrost. In this study, the SFCC of sand/clay mixtures, with clay content varying from 0 to 20%, was determined. Compacted soil samples were first subjected to a freezing path (temperature decreasing from 0 °C to -3 °C) followed by a subsequent thawing path (temperature increasing from -3 °C to 0 °C). During this freezing/thawing cycle, volumetric unfrozen water content was measured as a function of soil temperature. The results show a significant hysteresis of the relationship between these two parameters. This finding is important because the hysteresis of SFCC is rarely considered in the modelling of hydro-thermal processes in permafrost. In addition, clear effects of clay content on the thawing curve were identified. At a given temperature, volumetric unfrozen water increases with clay content. Finally, a model predicting the SFCC of sandy soils was introduced, considering the effect of clay content.