Freeze-thaw cycles significantly affect soil behavior, leading to pavement failures and infrastructure damage, especially in seasonally freezing regions. The application of road salt for deicing operations introduces high salt concentrations into soils, which can alter their physical properties. Salt in soils affects their freezing point, moisture migration, and overall freeze-thaw behavior. This study investigates the effects of varying sodium chloride (NaCl) concentrations on sandy soil using both the ASTM and low-temperature-gradient methods to simulate different freezing protocols. The methodology involved subjecting soil specimens with 0%, 0.2%, 1%, and 5% salt concentrations to freeze-thaw cycles and measuring parameters such as heave rate, maximum heave, water intake, moisture content, and salt migration. The results revealed that increasing salt concentration leads to a reduction in the freezing point, with the 5% NaCl concentration showing the most significant depression at 2.96 degrees C. The heave rate and maximum heave decreased with higher salt concentrations: the 5% NaCl concentration reduced the heave rate to 11.3 mm/day (ASTM method) and 1.5 mm/day (low-temperature-gradient method) from 22.5 mm/day (ASTM method) and 17.2 mm/day (low-temperature-gradient method) in control. Salt migration analysis indicated more variability in salt distribution within the soil profile under the low-temperature-gradient method, especially at higher salt concentrations. This variability is linked to osmotic suction effects, which retain more water within the soil matrix during freeze-thaw cycles. The study highlights the importance of considering both salinity and freezing protocols in understanding soil behavior under freeze-thaw conditions.

Horizontal frost damage is a significant hazard threatening the safety of structures in cold regions. The frozen fringe represents the transitional zone between unfrozen and frozen soil. Its formation and migration not only directly influence the distribution of water during freezing but also play a significant role in the frost heave behavior. This study employed self-developed horizontal frost heave equipment to conduct seven experiments, exploring the effects of initial water content and dry density on the development of the frozen fringe in kaolin clay. As the initial water content increases, the water migration speed accelerates, and frost heave increases. The experimental results show that for every 5% increase in initial water content, the frost heave increases by an average of 3.43 mm. With increasing initial dry density, frost heave decreases, and the water migration speed decreases. For every 0.1 g/cm3 increase in initial dry density, the frost heave increases by an average of 3.26 mm. The study also found that the frozen fringe does not strictly advance in the vertical direction, which may have a potential impact on the structural integrity. Based on these experimental results, this study proposes an improved method for predicting the frozen fringe using the freezing point, building upon the Mizoguchi model, and validates its accuracy with field data. The research provides a theoretical basis for the design of slopes, retaining walls, and foundation pits, as well as for the implementation of frost heave prevention measures in cold regions.

The loess in northern Shaanxi is situated in the seasonal frozen region, where the soil water phase transition is predominantly caused by freeze-thaw cycles. Engineering practices have evidenced that the transformation of water from soil causes considerable damage to structures, roadways, slopes, canals, and other infrastructure. The temperature-time characteristics of loess, particularly freezing point, serve as a crucial indicator for assessing the freeze-thaw state of soil. To investigate the influence of water content w and the number of freeze-thaw cycles N on temperature-time behaviours, the temperature-time curves of loess with diverse water content were depicted through freeze-thaw cycle tests. The alterations in freeze-thaw characteristics such as freezing point, freezing time, supercooling phenomenon, thawing time, and thawing point were analysed. The findings indicated that: 1) The phenomenon of supercooling was significantly affected by w and N. When w = 9 % and 13 %, the supercooling phenomenon gradually became significant as N increment. Conversely, when w = 17 %, the supercooling phenomenon became less significant as N increment. The decline curves of various w were essentially identical in the supercooling stage, and the cooling rate decreased as w increased during continual freezing stage. 2) The freezing point of loess gradually decreased as N increment. Freezing time did not exhibit significant variations in relation to N, however, a higher water content led to a longer freezing duration. All soil samples attained a stable freezing temperature within 12 hours. 3) The thawing point of soil samples remained constant at 0 degrees C under varying N, however, the stability levels of all curves at zero degrees varied. Except for N = 3, all other cases exhibited a gradual increment after 12 hours, which might be attributed to the instability of the thawing temperature during the experiment. 4) During the rapid ascent stage of the thawing curve, the ascending rate slightly increased with the increase of N. In the slow rise stage, the rising rate was relatively rapid during N <= 3, the rate of increase experienced a sudden drop at N = 10, and then proceeded at a relatively slower. The change pattern of the thawing curve remained consistent across various w, with only a certain extent of influence on the rate of change. The results might provide theoretical support for the engineering design, construction, and maintenance of the seasonal frozen soil area in northern Shaanxi Province and other regions with comparable weather conditions.

We present a method to characterize soil moisture freeze-thaw events and freezing/melting point depression using permittivity and temperature measurements, readily available from in situ sources. In cold regions soil freeze-thaw processes play a critical role in the surface energy and water balance, with implications ranging from agricultural yields to natural disasters. Although monitoring of the soil moisture phase state is of critical importance, there is an inability to interpret soil moisture instrumentation in frozen conditions. To address this gap, we investigated the freeze-thaw response of a widely used soil moisture probe, the HydraProbe, in the laboratory. Soil freezing curves (SFCs) and soil thawing curves (STCs) were identified using the relationship between soil permittivity and temperature. The permittivity SFC/STC was fit using a logistic growth model to estimate the freezing/melting point depression (T-f/m) and its spread (s). Laboratory results showed that the fitting routine requires permittivity changes greater than 3.8 to provide robust estimates and suggested that a temperature bias is inherent in horizontally placed HydraProbes. We tested the method using field measurements collected over the last 7 years from the Environment and Climate Change Canada and the University of Guelph's Kenaston Soil Moisture Network in Saskatchewan, Canada. By dividing the time series into freeze-thaw events and then into individual transitions, the permittivity SFC/STC was identified. The freezing and melting point depression for the network was estimated as T-f/m = - 0.35 +/- 0.2,with T-f = - 0.41 +/- 0.22 degrees C and T-m = - 0.29 +/- 0.16 degrees C, respectively.