An Experimental Investigation of Thermally Induced Hydraulic Hysteresis in Frozen Unsaturated Silts

This study focuses on the investigation of thermally induced hydraulic hysteresis due to freezing and thawing of an unsaturated silty soil layer. Hydraulic hysteresis is relevant with the quantification of volumetric water content in soils that needs to be included in the subsurface modeling in cold regions. Experimental results from existing literature support hydraulic hysteresis for different type of soils; however, results are controversial. To provide a better understanding of the initial and boundary conditions through a well-defined and systematic approach, a series of freeze-thaw experiments are performed at two different laboratory scales and the effects of initial volumetric water content, dry density, sample size, and number of freeze-thaw cycles on hydraulic hysteresis are investigated. During the experiments, temperatures and volumetric water contents are measured using capacitance sensors embedded in silt layers. The results show that the magnitude of hydraulic hysteresis and unfrozen water content in frozen soils increase with increasing initial volumetric water contents for a given dry density. It is observed that the hysteresis depends on sample size and boundary conditions, which is not investigated before. In addition, a critical temperature for the maximum hysteresis for different samples is identified. It is found that the critical temperature is affected by the initial water content. The results from this study will provide accurate constitutive relationships for fully coupled thermo-hydraulic modelling of unsaturated subsurface layers.