Freezing point and unfrozen water contents of permafrost soils: Estimation by the water potential method

Abstract

The freezing point and unfrozen pore water content are important parameters of frozen soils monitored for various geotechnical and permafrost engineering purposes. The current paper summarizes experimental data using a novel water potential method for determining a freezing point and unfrozen water content. To examine this method, the results of freezing point determination were compared with direct freezing point measurements and data on unfrozen water content — with the contact method and NMR results. Studies were conducted on natural soils of various particle size distribution, mineral composition, salinity, and total organic carbon (TOC) content. The obtained freezing point and unfrozen water content estimates showed good agreement with the results of direct measurements. For example, the freezing point data indicates a difference of about ±0.05 °C. The average data misfit of water potential with NMR and contact methods is about 0.3 °C in temperature and not more than 0.5 wt% in unfrozen water content. Additionally, the article discusses the advantages and limitations and the practical application of the water potential method. In summary, based on the study results, the water potential method can be recommended to determine the freezing point and unfrozen water content for different types of soils.