Stress Effects on Soil Freezing Characteristic Curve: Equipment Development and Experimental Results

Abstract

Core Ideas A triaxial apparatus is developed to measure stress‐dependent SFCC. Unfrozen water content of clay and sand increases with increasing confining stress. Stress effects on the SFCC of clay are more significant than sand. The soil freezing characteristic curve (SFCC) defines the relationship between soil temperature and unfrozen water content. This curve is important for predicting water flow and heat conduction in frozen soils, as well as freezing heave and thawing settlement. So far, SFCCs reported in the literature were usually determined at zero stress. To investigate stress effects on SFCC, a stress‐ and temperature‐controlled triaxial apparatus was developed in this study. The unfrozen volumetric water content was measured using a newly developed noninvasive time domain reflectometry (TDR) probe. The new apparatus was used to measure SFCCs of two typical soils (i.e., clay and sand) at different stress conditions (i.e., 30, 100, and 200 kPa). Each specimen was subjected to compression, and then a cycle of freezing and thawing. As expected, for both soils, the saturated water content prior to freezing was smaller at higher stresses because of compression. During the subsequent freezing and thawing, the soil specimen at a higher stress was able to retain more liquid water than that at a lower stress. The higher unfrozen water retention capacity at higher stresses is mainly because the pore size of a soil specimen becomes smaller during compression. Hence, more water can retain a liquid state due to the enhanced capillarity. On the other hand, stress effects on the SFCC were found to be more significant for clay than for sand. This is likely because the stress‐induced change in pore size distribution is larger in clay due to its higher compressibility.

An algorithmic framework for computational estimation of soil freezing characteristic curves

“…This function combines freezing and nonfreezing water content functions into one smoothed function to prevent non-smoothed estimation of SFCC, which may incur convergence issues in numerical modeling. The proposed F I G U R E 1 Unfrozen water content versus temperature for two different consolidation confining pressures for a clay sample-experimental data reported from Mu et al51 SFCC is verified with two different unsaturated freezing soil tests from the literature, and it shows good agreement with the experimental evidence. We consider different soil particle distribution, void ratio, and temperature to compare unfrozen water contents between the developed model and the experiment.…”

“…Another set of numerical analysis has been performed to observe the capability of capturing the unfrozen water content in different porosity. We used the experimental data by Mu et al 51 They have conducted a series of temperature-controlled triaxial tests, which can be used to verify the proposed SFCC in the THM framework. In the experiment, the unfrozen water contents were measured with TDR, which is a noninvasive method for measuring freezing process.…”

“…Unfrozen water content versus temperature for two different consolidation confining pressures for a clay sample—experimental data reported from Mu et al 51 …”

Effect of freeze–thaw cycling on the soil‐freezing characteristic curve of five Canadian soils

“…In other words, the effect of stress on SFCCs is not considered. Mu et al (2019) investigated the effect of confining stress on the SFCC of a lean clay and a silty sand. The cylindrical soil specimens with certain dry densities (void ratios) were prepared by compaction, saturation, and consolidation.…”

“…The subzero temperature is the principal factor controlling the amount of water remaining in an unfrozen state. The relationship between unfrozen water content and subzero temperature in a frozen soil is widely referred to as the soil‐freezing characteristic curve (SFCC) (Azmatch, Sego, Arenson, & Biggar, 2012; Koopmans & Miller, 1966; Mu, Zhou, Ng, & Zhou, 2019; Spaans & Baker, 1996; Watanabe & Wake, 2009). Several soil properties of importance in cold region engineering practice, such as the hydraulic conductivity (Azmatch et al., 2012), segregation potential (Konrad, 2001), resilient modulus (Ren & Vanapalli, 2017), and strength (Agergaard & Ingeman‐Nielsen, 2012; Akagawa & Nishisato, 2009), can be estimated using the SFCC as a tool.…”