Core Ideas: The SHAW model was used to simulate the freeze–thaw process during freeze–thaw periods. It revealed the effects of soil texture and groundwater table depth on soil freezing and thawing. The frost depth and accumulated negative soil surface temperature relationship was determined. During freeze–thaw periods, the transformation between phreatic water and soil water will change the soil hydrothermal properties and affect the soil freezing and thawing in shallow groundwater areas. The purpose of this study was to determine the effect of four different groundwater table depths (GTDs) and two soil textures on the process of soil freezing and thawing during two successive freeze–thaw periods using the Simultaneous Heat and Water (SHAW) model. The results show that the frost depth was the maximum when the GTD was 1.0 m, and the maximum frost depths of sandy loam and fine sand were 97.6 and 98.9 cm, respectively. When the GTD was larger than 1.5 m, the maximum frost depth decreased with an increase in GTD, and the maximum frost depth of the soil profile was more sensitive to changes in the air temperature. The frost depth of the soil profile was linear with the square root of the accumulated negative soil surface temperature (ANST) under different GTDs. The ANST was influenced by the phreatic evaporation, and the soil freezing rate increased with an increase in GTD under the same ANST. This research is significant for the rational development of soil water and heat resources and the study of soil water–heat transfer in shallow groundwater areas.

The exchange between shallow groundwater and soil water is unusually strong during freeze-thaw periods. The purpose of this study is to determine the effect of four different groundwater table depths (GTDs) and two soil textures on soil water moisture migration and phreatic evaporation during a freeze-thaw period using lysimeters. The results show that a high-moisture zone (HMZ) formed at a depth of 25–35 cm for sandy loam with a soil moisture content of 52%, while no obvious HMZ formed for fine sand when the GTD was 0.5 m. When the GTD was 2.0 m, a HMZ formed at a depth of 50–70 cm for sandy loam at the highest soil moisture content of 22%, while a HMZ formed at a depth of 60–80 cm for fine sand with a soil moisture content of 10%. The cumulative phreatic evaporation increased by a power function on freezing days during the freezing period. The total phreatic evaporation for sandy loam declined linearly with the increasing of GTD, and with the largest evaporation value of 73.6 mm for fine sand when the GTD was 1.0 m during the freeze-thaw period. The research would be significant for water resource assessment, the conversion of farmland water, and the prevention of saline land.

Underground mining severely lowers the water table and worsens the ecological environment. To determine the mechanism influencing drawdown in unconsolidated aquifers induced by deep mining combined with overburden movement, with a view to environmental protection, physical simulations for three different depths were designed to investigate and contrast deformation and fracture distribution characteristics at diverse depths after mining. The impacts on overlying unconsolidated aquifers were then analyzed by monitoring overburden movement and ground water level data, and the deformation limit was estimated. Modeling results indicated that coal mining had different impacts on the overlying unconsolidated aquifer via various mechanisms of groundwater level reduction. The aquifer outside the fractured water-conducting zone could be affected by coal mining, and the water tables dropped rapidly. The failure and the deformation features of the aquitard floor were the key to revealing the mechanism of groundwater depletion in deep mining. The effects on aquitard decreased as the distance from the working face increased. A relationship between the strata deformation and the drawdown rate was established; that is, the rate of decline of the groundwater level did not accelerate until the maximum subsidence of the aquitard floor exceeded approximately 0.9 m, or the subsidence-bending area of the aquitard floor exceeded approximately 156 m².

Reducing soil evaporation is important to alleviate water shortages in arid and semi-arid regions. The objective of this work was to reveal the effect of straw mulch on soil evaporation based on field experiments during a freeze–thaw period in Northern China. Four soil surface mulch treatment modes were investigated: Bare soil (BS), 1 cm thick straw mulch with 100% coverage rate (J1), 2 cm thick straw mulch with 100% coverage rate (J2), and 2 cm thick straw mulch with 50% coverage rate (J3). Principal component analysis was used to analyze the major factors influencing soil evaporation in three freeze–thaw stages. The results show that cumulative soil evaporation decreased with increased straw mulch thickness and coverage rate. The effect of straw mulching on soil evaporation was obvious during the stable freezing period, and soil evaporation with straw mulch treatments was reduced by 49.0% to 58.8% compared to BS treatment, while there was little difference for straw mulch treatments in the thawing stage. The relationship between cumulative soil evaporation under different straw mulch modes and time was well fitted by the power function. In the unstable freezing stage, the major factors for all treatments influencing soil evaporation were surface soil temperature and water surface evaporation; in the stable stage, they were solar radiation and relative humidity, and in the thawing stage, they were solar radiation and air temperature. The research results can provide a basis for addressing soil water storage and moisture conservation and restraining ineffective soil evaporation in arid and semi-arid areas.

During freeze–thaw periods, the exchange between shallow groundwater and soil water is unusually strong and bidirectional, which causes soil salinization and affects the accuracy of water resources assessment. The objectives of this study were to explore the laws of transformation between phreatic water and soil water through nine different groundwater table depths (GTDs) and three kinds of lithologies during three successive freeze–thaw periods using field lysimeters. The results showed that phreatic evaporation increased with smaller average soil particle sizes. The differences between phreatic evaporation and recharge to groundwater (DPR) and GTDs were well fitted by the semi-logarithmic model, and the regression coefficients A and B of the model were well fitted by the linear relationship with the average soil particle size. With the increase of soil particle size, the change of DPR decreased with the change rate of soil particle size. The extent of transformation between phreatic water and soil water decreased with the increase of soil particle size. During the whole freeze–thaw period, the negative value of DPR increased with an decrease in GTD. The groundwater depths of zero DPR (D-zero) of sandy loam, fine sand and sandy soil during the freeze–thaw periods were 2.79 m, 2.21 m and 2.12 m, respectively. This research is significant for the prevention of soil salinization disasters and the accurate assessment of water resources.