Soil Freezing Process Research Articles

Impact of frozen soil changes on vegetation phenology in the source region of the Yellow River from 2003 to 2015

Changes in frozen soil caused by global warming are widely expected to have significant effects on ecosystems in cold regions, and the response of the start of the vegetation growing season (SOS) to climate change on the Qinghai-Tibetan Plateau (QTP) has drawn great attention. In this study, we investigated the changes in the freezing/thawing processes and their relationship with the SOS from 2003 to 2015 in the source region of the Yellow River (SRYR) on the northeastern QTP. The results indicate that the soil thaw onset (STO) at a depth of 5 cm advanced significantly in most regions at a rate ranging from 0.09 to 1.47 day · year−1, and the maximum frozen depth decreased in most regions at a rate of 0.007 to 0.031 m · year−1, despite a nonsignificant increase in the spring air temperature. The SOS derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) data advanced in the regions covered by alpine meadow. The logistic method was shown to be better than the polynomial method in retrieving the SOS using remote sensing indexes. The gray relational analysis suggested that the advance in the STO was the major factor leading to the advance in the SOS of alpine meadow regions. Changes in the LAI during the initial period of the growing season were likely to be primarily influenced by the maximum frozen depth and soil temperature. Furthermore, the substantial effect of frozen soil changes on the SOS in the SRYR necessitates the importance of analyzing frozen soil processes to predict the response of spring vegetation phenology to climate change on the QTP.

Evaluation of upward flow of groundwater to freezing soils and rational per-freezing water table depth in agricultural areas

In arid agricultural areas with shallow water table depth, water exchange between vadose zone and groundwater is intensive during the freezing-thawing period, and thus has a significant impact on crop growth. This study is aimed to develop a one-dimensional model that couples heat and variably saturated water in seasonally freezing-thawing agricultural areas. To alleviate numerical oscillations occurring during the phase change at zero temperature, a three-level iteration scheme was developed for solving the water and heat coupling model, which improves numerical stability for variably saturated water and heat modeling. The model accuracy was evaluated by comparing the simulation results with those from SHAW under various soil texture and bottom conditions. The square of correlation coefficient (R2) of freezing and thawing depth and soil temperature profiles are above 0.95 and the values of root mean square error (RMSE) of total soil water content are lower than 0.05 cm3/cm3, which suggest the model accuracy. The model was further applied to simulate the hydrothermal conditions in the Yonglian irrigation field of Hetao Irrigation District in Inner Mongolia, China. Model calibration and validation were conducted, and the validated model was used to predict hydrothermal changes under scenarios with different soil surface temperatures and pre-freezing water table depths. The results show that the soil freezing process has great impact on the fluctuation of water table depth when the pre-freezing water table depth is shallower than 180 cm. The maximum freezing depth has a negative relation with the pre-freezing water table depth when it is shallower than 180 cm. An empirical formula was established to estimate the upward flow of groundwater to freezing soils. The soil moisture and thermal conditions were analyzed in the germination and seedling stages after the freezing-thawing period, and the analysis leads to a recommended pre-freezing water table depth of 100 cm, which provides suitable soil moisture and thermal conditions for the crop growth.

Experimental investigation of physical and mechanical properties of processes accompanied with phase transition in water-saturated soil

Nowadays, in view of increasing occurrence depth and complication of hydrogeological conditions in mineral deposits, the construction of vertical shafts is conducted using the artificial freezing technology. Therefore, mechanical processes mechanical behavior of water-saturated rock layers during freezing and thawing processes require a deep analysis.The paper considers the possibility of using a fiber-optic system for recording a temperature decrease during a soil freezing process and deformations arising in water-saturated soil due to frost heave. The features of the freezing front propagation and moisture redistribution are discussed. Two types of experiment were carried out all-round freezing and one-side freezing. It is important that the experiments simulate different direction of freezing front propagation. To analyze the experimental data a thermo-hydro-mechanical model is proposed. The model takes into account non-instantons kinetics of water crystallization, residual moisture content contained in the soil under temperature below the freezing temperature, moisture migration to the freezing front and an evolution of a stress-strain state of the soil caused by thermal strain and volumetric expansion due to the phase change of water into ice and the moisture flow. Results of the performed study have been shown that the numerical prediction of temperature change are in good agreement to the measurements, but there is qualitative difference between the frost heave deformation given by the model and registered by the sensors.

天山北坡积雪消融对不同冻融阶段土壤温湿度的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 天山北坡积雪消融对不同冻融阶段土壤温湿度的影响 DOI: 10.5846/stxb201901040044 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 自治区重点实验室课题（2018D04024）；国家自然科学基金项目（U1603342，41961002） The influence of snowmelt on soil temperature and moisture in different freezing-thawing stages on the north slope of Tianshan mountain Author: Affiliation: Fund Project: The National Natural Science Foundation of China (General Program, Key Program, Major Research Plan) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:积雪作为一种特殊的覆被，直接影响着土壤温度、土壤水分分布及其冻结深度、冻结速率等，影响当地的生态水文过程。利用2017年11月1日至2018年3月31日天山北坡伊犁阿热都拜流域的土壤含水率资料，划分土壤不同冻融阶段，结合积雪不同阶段，进而分析积雪消融对季节性冻土温湿度的影响。结果表明：在整个土壤冻融期间，土壤温湿度的变化取决于积雪深度、大气温度和雪面温度的高低，且与其稳定性有关。土壤冻结阶段，土壤温湿度持续下降，表层土壤温湿度受气温影响较大，且波动明显，而深层土壤的温湿度变化平缓；土壤完全冻结时，有稳定积雪覆盖，由于积雪的高反射性、低导热性，影响着地气之间的热量传递，因此土壤的温湿度变化较为平稳，积雪有一定的保温作用；冻土消融阶段，气温回升，积雪消融，地表出露，各层土壤温度随气温变化而变化，且越靠近地表，土壤温度越高，变幅越大，与冻结期完全相反。由于融雪水的下渗，土壤湿度快速增加。进一步分析积雪与土壤温湿度的相关性得出，积雪对土壤温湿度的影响分不同时期，对土壤温度的影响主要在积雪覆盖时，对土壤湿度的影响主要是在积雪消融时期，这对于研究该地生态水文循环及后续融雪性洪水的模拟与预报具有一定的参考价值。 Abstract:As a special cover, snow cover directly affects soil temperature, soil moisture distribution, freezing depth and freezing rate, and affects the local eco-hydrological processes. The existence of snow can affect the frozen soil, the interaction of surface-atmosphere, and change the energy exchange and temperature transfer between the soil and the atmosphere. The freezing-thawing process of soil has an important impact on soil water content. It is of great significance for the effective utilization of frozen soil resources, the guidance of irrigation water, the study of soil evaporation, groundwater recharge and local eco-hydrological cycle. In this paper, meteorological data, soil temperature and moisture data and snow cover data were used to analyze the characteristics of seasonal frozen soil temperature and moisture changes in the study area. Based on the data of soil water content from November 1, 2017 to March 31, 2018 in the Alatobe Basin, Ili, on the northern slope of Tianshan Mountains, the different freezing-thawing stages of soil were divided, and the effects of snow melting on the temperature and moisture of seasonal frozen soil were analyzed. The results show that snow melting has a great influence on the temperature and moisture of seasonal frozen soil. The soil was frozen beginning in November in Alatobe Basin, and the soil freezing time lagged with the increase of soil depth. The soil freezing process is one-way, starting from the surface, while the melting process is two-way, starting from both the surface and the bottom. During the whole freezing-thawing period, the change of soil temperature and moisture depends on the depth of snow cover, atmospheric temperature and snow surface temperature. And it mainly affects the surface soil temperature. The deeper the soil depth is, the more slightly the change of soil temperature and moisture is. During the soil freezing stage, the soil temperature and moisture continued to decline, the surface soil temperature and moisture were greatly affected by temperature, and the fluctuation was obvious, while the deep soil temperature and moisture changed slightly. When the soil was completely frozen, there was stable snow cover. Because the high reflectivity and low thermal conductivity of snow affected the heat transfer of surface-atmosphere, the change of soil temperature and moisture was relatively stable, and the snow cover had a certain degree. During the thawing stage, the temperature rises, the snow melts and the surface exposes. The soil temperature varies with the change of temperature. The closer to the surface, the higher the soil temperature, the larger the change range, which is completely contrary to the freezing period. Soil moisture increases rapidly due to the infiltration of snowmelt water. Further analysis of the correlation between snow cover and soil temperature and moisture shows that the influence of snow cover on soil temperature and moisture can be divided into different periods. The influence on soil temperature is mainly in snow cover, and the influence on soil moisture is mainly in snow melting period, which has a certain reference value for the study of the eco-hydrology cycle and the simulation and prediction of subsequent snowmelt flood in this area. 参考文献 相似文献 引证文献

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

AbstractThe frozen soil processes and their interaction with the environment in the vadose zone of cold regions is vital in both agricultural and engineering practice applications. In a frozen soil, unfrozen water and pore ice coexist. The relationship between the unfrozen water content and subzero temperature is widely known as the soil‐freezing characteristic curve (SFCC). The SFCC is a valuable tool for predicting the hydromechanical properties and for modeling the coupled thermal–hydraulic–mechanical–chemical process in frozen soils. In spite of its importance, the effect of freeze–thaw (F–T) cycling on SFCC has not been well investigated or understood. In this technical note, the effect of F–T cycles on the SFCC of five soils from cold regions of Canada were investigated. The SFCC (including both freezing and thawing branches) of the five soils for different F–T cycles were measured using frequency domain reflectometry (FDR) technique. The experimental results suggest that the effect of F–T cycles on the SFCC of the five soils is not significant. Such a behavior may be attributed to the destruction of soil structure during the saturation process. However, all the five soils’ SFCC exhibited hysteresis behavior for all the F–T cycles. The results of the study are valuable and contribute towards better understanding of the fundamental behavior of SFCC of various cold region soils.

Image processing method for observing ice lenses produced by the frost heave process

During the freezing process of soil, the pore water is segregated into ice lenses with the help of continuous water migration to the freezing front. The in situ and migrated water cause significant frost heave and stress in all directions, which can threaten surrounding structures. Pore ice and segregated ice lenses directly cause changes in the frozen soil properties, such as enhanced strength and water tightness. Although some researchers have developed proper procedures to observe and quantify the formation of ice lenses in soils, the authors are going to indicate a quantitative relationship between the forming of ice lenses with the absorbed water. Therefore, a direct observation method is proposed in this study which can measure ice lenses quantitatively and in real-time, to establish a relationship between ice lenses and absorbed water. Image processing software was applied to analyze pictures of ice lenses that were taken during a frost heave test. Based on the ice lens distribution, the forming pattern of ice lens was confirmed at the macro level. A relationship between the area of ice lenses and the absorbed water was identified, which is expected to be applied for the nondestructive detection of the water content and distribution in freezing soil for real engineering.

INFLUENCE OF THE ROAD BASEMENT WATER AND THERMAL REGIME ON THE PAVEMENT CONDITION

A article is devoted to study of the roads pavement condition influence with improved surface on the road traffic safety. The topicality of the issue is confirmed traffic police statistics and a significant list of scientific papers dealing with issues of water and heat balance of soil mass. The article deals with the road, located in the city and suburban areas. The work shows the temperature and humidity influence on the process of soil freezing and on the road surface integrity directly. Mathematical models of temperature distribution processes and filtration fluid movement in the ground are presented. In article offered option to improve the technical and operational characteristics of roads. It will have a positive impact on the traffic safety and smoothness.

Effects of preferential flow on snowmelt partitioning and groundwater recharge in frozen soils

Abstract. Snowmelt is a major source of groundwater recharge in cold regions. Throughout many landscapes snowmelt occurs when the ground is still frozen; thus frozen soil processes play an important role in snowmelt routing, and, by extension, the timing and magnitude of recharge. This study investigated the vadose zone dynamics governing snowmelt infiltration and groundwater recharge at three grassland sites in the Canadian Prairies over the winter and spring of 2017. The region is characterized by numerous topographic depressions where the ponding of snowmelt runoff results in focused infiltration and recharge. Water balance estimates showed infiltration was the dominant sink (35 %–85 %) of snowmelt under uplands (i.e. areas outside of depressions), even when the ground was frozen, with soil moisture responses indicating flow through the frozen layer. The refreezing of infiltrated meltwater during winter melt events enhanced runoff generation in subsequent melt events. At one site, time lags of up to 3 d between snow cover depletion on uplands and ponding in depressions demonstrated the role of a shallow subsurface transmission pathway or interflow through frozen soil in routing snowmelt from uplands to depressions. At all sites, depression-focused infiltration and recharge began before complete ground thaw and a significant portion (45 %–100 %) occurred while the ground was partially frozen. Relatively rapid infiltration rates and non-sequential soil moisture and groundwater responses, observed prior to ground thaw, indicated preferential flow through frozen soils. The preferential flow dynamics are attributed to macropore networks within the grassland soils, which allow infiltrated meltwater to bypass portions of the frozen soil matrix and facilitate both the lateral transport of meltwater between topographic positions and groundwater recharge through frozen ground. Both of these flow paths may facilitate preferential mass transport to groundwater.

Improving estimation of evapotranspiration during soil freeze-thaw cycles by incorporating a freezing stress index and a coupled heat and water transfer model into the FAO Penman-Monteith model

Evapotranspiration (ET) plays an important role in water and energy balance at the surface-atmosphere interface. It is widely reported that near-surface soil water content (SWC) or soil water potential (SWP) significantly affects ET and this parameter has been incorporated into the FAO Penman-Monteith (FAO-PM) model for prediction of ET during crop growth seasons. However, there is little information on the effect of SWC or SWP on prediction of ET during soil freeze-thaw cycles in winter. We present an experiment conducted at a demonstration farm with a crop of winter wheat, over two winters near Beijing, China. A lysimeter system equipped with a weather station was used to measure the ET flux and meteorological data. Unfrozen soil water content (USWC) and soil temperature (Tsoil) were measured using dielectric tube sensors (DTS) and digital temperature sensors, respectively. SWP was determined by measured USWC and a soil moisture characteristic (SMC) curve derived from the soil freezing characteristic (SFC) curve and the Clapeyron equation in frozen soil. Detailed measurements in year 1 showed that the FAO-PM model exhibited a complex error pattern, underestimating ET from unfrozen soil but overestimating ET from stable frozen soil. To address these errors, we define a freezing stress index (Ksf) as a function of SWP. Incorporation of Ksf as a modifier of the standard crop coefficient in the FAO-PM model improved prediction of ET (RMSE declined from 0.424 to 0.187 mm day−1, in year 1). These data revealed a correlation between SWP near the soil surface (<10 cm) and measured ET over freezing and thawing cycles. We incorporated a coupled heat and water transfer (CHWT) model into the improved FAO-PM model to predict USWC, SWP and ET throughout the winter of year 2 from current meteorological data as upper boundary conditions, initial measurements of ET, USWC and Tsoil as initial conditions, and Ksf and soil hydraulic properties optimized in year 1. The results showed that ET estimation was significantly improved, with RMSE reduced from 0.323 to 0.281 mm day−1 using the combined (FAOPM-Ksf-CHWT) model. Model error primarily derived from an underestimation of simulated SWP during soil freezing process. The combined model extends the utility of the FAO-PM model to non-cropping seasons including winter in temperate climates and reduces the data requirements for accurate prediction of ET from intermittently frozen soil.

Remote Sensing Monitoring and Numerical Simulation Coupling Studies on Frozen Soil in Cold Regions

As an important data source of frozen soil, remote sensing monitoring information has not been fully utilized in the numerical model of frozen soil processes. Few researches exist involving the integration of the two monitoring methods. Following this study, a distributed numerical model for frozen soil processes based on coupled water-heat transferring theory in association with the previously obtained remotely sensed frozen soil datasets will be developed. Parameters characterized the frozen soil status, such as distributions of frozen soils in different types, soil ice content in different times and so on, could be simulated with the developed model. The numerical model systematically integrates the information of surface soil F/T states and considers its impact on the processes of evapotranspiration, infiltration and runoff generation. Several hydrological processes were integrated in the model. Finally, the remote sensing monitoring and numerical simulation coupling method was validated by the in-situ observations over a remote area near the town of Naqu on the East-Central Tibetan Plateau. The results shown that the overall accuracy of the discrimination algorithm based on passive microwave remote sensing was more than 95%. Under the correction of remote sensing monitoring information of frozen soil in the process of numerical simulation, the efficiency of the model and the accuracy of simulation results have been significantly improved.

Effects of NaCl concentration on electrical resistivity of clay with cooling

The influence of salt concentration and gravimetric water content on the freezing process of clay soil is studied by using electrical resistivity as a measurement. Along with the ultrasonic pulse method, the P-wave velocity of samples is obtained to estimate the unfrozen water content of frozen soil, and the development of cracks due to frost heave at different temperatures is also analyzed. The results indicate that the freezing temperatures of samples with a sodium chloride (NaCl) concentration of 0, 2% and 5% are −4 °C, −6 °C and −5 °C respectively. Cracks due to frost heave propagate rapidly at temperatures below the crack coalescence temperature, which results in a steep increase in electrical resistivity. There is a sigmoid function for the relationship between electrical resistivity and temperature. A good power function is found for the relationship between electrical resistivity and the NaCl concentration of clay soil. There is a power function for the relationship between the electrical resistivity of pore water and salinity. The electrical resistivity decreases linearly with water content at temperatures above freezing but increases logarithmically at temperatures below freezing. The generalized relationships between electrical resistivity and water content, NaCl concentration and temperature are effective for predicting the electrical resistivity of frozen saline soil in practice.

Effects of different freezing rates on purification efficiency of sandy soil contaminated by heavy metal copper

Over the last several decades, a variety of methods have been developed for treating contaminated sites. Which technique is applied depends on the type of contaminant, the extent of dispersion, and the likelihood of additional contamination during the cleanup. Among the selection of potential techniques is the artificial freezing method, in which soil is frozen to significantly lower the permeability and prevent further diffusion of pollutants. While this method appears to have merit in theory, few studies have investigated the migration of pollutants during the soil freezing process. In this paper, a series of artificial freezing purification tests were performed and the influences of different freezing rates on purification efficiency were investigated. The experimental results show that the freezing rate is an important factor affecting the freezing purification efficiency for heavy metal copper and the purification rate decreases rapidly with increasing freezing rate. A soil freezing rate of 0.3 °C/h results in a heavy metal copper purification rate of only 27%; far less than that of the freezing rate of 0.05 °C/h, where the purification rate is 85%. This study demonstrates that a strong correlation exists between the purification rate of heavy metal copper and the soil freezing rates. We also demonstrate that the purification rate can be expressed as a cubic of the soil freezing rate. Therefore, the optimal purification of contaminated sites can be obtained by determining the proper freezing rate.

A PZT-Based Electromechanical Impedance Method for Monitoring the Soil Freeze⁻Thaw Process.

It is important to conduct research on the soil freeze–thaw process because concurrent adverse effects always occur during this process and can cause serious damage to engineering structures. In this paper, the variation of the impedance signature and the stress wave signal at different temperatures was monitored by using Lead Zirconate Titanate (PZT) transducers through the electromechanical impedance (EMI) method and the active sensing method. Three piezoceramic-based smart aggregates were used in this research. Among them, two smart aggregates were used for the active sensing method, through which one works as an actuator to emit the stress wave signal and the other one works as a sensor to receive the signal. In addition, another smart aggregate was employed for the EMI testing, in which it serves as both an actuator and a receiver to monitor the impedance signature. The trend of the impedance signature with variation of the temperature during the soil freeze–thaw process was obtained. Moreover, the relationship between the energy index of the stress wave signal and the soil temperature was established based on wavelet packet energy analysis. The results demonstrate that the piezoceramic-based electromechanical impedance method is reliable for monitoring the soil freezing and thawing process.

Study on the Formation Law of the Freezing Temperature Field of Freezing Shaft Sinking under the Action of Large-Flow-Rate Groundwater

Taking into account moisture migration and heat change during the soil freezing process, as well as the influence of absolute porosity reduction on seepage during the freezing process, we construct a numerical model of hydrothermal coupling using laws of conservation of energy and mass. The model is verified by the results of large-scale laboratory tests. By applying the numerical calculation model to the formation of artificial shaft freezing temperature fields under the action of large-flow groundwater, we conclude that groundwater with flow rates of less than 5 m/d will not have a significant impact on the artificial freezing temperature field. The maximum flow rates that can be handled by single-row freezing pipes and double-row freezing pipes are 10 m/d and 20 m/d, respectively, during the process of freezing shaft sinking. By analyzing the variation of groundwater flow rate during freezing process, we find that the groundwater flow velocity can reach 5–7 times the initial flow velocity near the closure moment of the frozen wall. Finally, in light of the action characteristics of groundwater on the freezing temperature field, we make suggestions for optimal pipe and row spacing in freezing pipe arrangement.

Plant community regulates decomposer response to freezing more strongly than the rate or extent of the freezing regime

AbstractArctic tundra ecosystems are warming disproportionately in the winter, including a delayed autumn soil freeze‐up. Because microbial processes are extremely sensitive to change in temperature below freezing, overwinter warming strongly stimulates decomposition and nutrient mineralization and ultimately promotes the conversion of sedge‐dominated tussock tundra into shrub tundra. We characterized the responses of decomposition in shrub tundra and tussock tundra soils to changes in the rate and extent of freezing using laboratory simulations to study a range of active layer freeze‐up scenarios that included variation in time held above 0°C (an acclimation period) and final temperature (−2°C to −20°C). We hypothesized that shrub soil decomposers would be more sensitive to the rate of the freezing process than tussock soil decomposers, but less sensitive to the extent of freezing. Although freezing strongly influenced microbial processes, the effects of freezing tended to not significantly vary across the range freezing regimes tested. Unexpectedly, the tussock‐derived soil decomposer community was more sensitive than shrub‐derived soil to the freezing treatments. Freezing conditions stimulated tussock soil to release more water‐extractable organic carbon (WEOC) that was composed of a greater proportion of microbially derived materials than shrub soil under the same conditions. Freezing‐driven changes in the tussock WEOC pool coincided with reduced microbial decomposer biomass, while the shrub decomposer biomass was relatively insensitive to the freezing treatments. These findings suggest that the microbial community of shrub‐dominated soils is more resistant to the soil freezing process than the tussock‐dominated decomposer community and increases available soil N while reducing labile C release as the soils freeze. Because autumn nutrient dynamics set the stage for overwinter tundra biogeochemical conditions, increasing shrub dominance in tussock tundra may therefore promote both plant N availability and decomposer C limitation during thaw.

Characteristics of water–heat variation and the transfer relationship in sandy loam under different conditions

The soil freezing process affects the distribution of soil water and heat, influencing decisions on the planting of spring crops. To reveal the redistribution characteristics of soil moisture and temperature and their response factors in the unidirectional freezing process, an indoor unidirectional freezing test was carried out. Three levels of initial moisture content (18.84%, 23.43%, 28.78%), three freezing temperatures (−5 °C, −10 °C, −15 °C), and three dry densities (1.33 g·cm−3, 1.45 g·cm−3, 1.58 g·cm−3) were set up. Firstly, the distribution of soil cold structure and the variation in the freezing depth curve during the freezing process were observed under different initial conditions. Additionally, the variation characteristics of soil temperature over time and space scales were analyzed, and the freezing process was divided into the rapid freezing stage and the steady freezing stage according to the rate of soil temperature change. Furthermore, the redistribution effect of soil water under the action of potential energy gradient and the characteristics of water migration in different periods were explored. On this basis, the transfer functions of soil temperature at time and space scales were constructed in accordance with regression theory. On the premise of significance test, the effects of soil moisture content and dry density on soil temperature over time and space scales were explored via function derivation and parameter analysis. With the increase of moisture content, the density of soil temperature contours decreased. However, as the dry density increased and the freezing temperature decreased, the density of soil temperature contours increased. As the soil freezing temperature decreased, the degree of soil freezing increased, the pore structure was blocked by frozen ice, and the amount of soil water migration decreased. At the same time, due to increasing soil dry density, the amount of soil water migration and migration rate also decreased. The parameter analysis showed that on the time scale, the change rate of soil temperature decreased as the moisture content increased, whereas it increased as the soil dry density increased; similarly, on the spatial scale, the soil moisture content was negatively correlated and the dry density of soil positively correlated with the soil temperature change rate. The results of this study are of great relevance for understanding the intrinsic relationships between soil moisture content, temperature and dry density in frozen soil and scientifically guiding the development of water and soil resources in cold regions.

Simulation of Soil Freezing and Thawing for Different Groundwater Table Depths

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.

Soil freezing process and different expressions for the soil-freezing characteristic curve

The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions ( i.e. , power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils ( i.e. , sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.

A resistivity model for testing unfrozen water content of frozen soil

Testing the unfrozen water content (θu) based on frozen soil resistivity (ρ) is considered to be a common and convenient method. However, the reliability of the theoretical model for testing unfrozen water content requires further study; hence this paper proposes a new resistivity model for testing the unfrozen water content. By considering the variable characteristics of unfrozen water in the soil freezing process and based on the three-element electrical conduction model, four types of micro unit representing different unfrozen water contents were proposed, and the resistivity model was established on the basis of microscopic analysis. The resistivity model showed that a power function can be used to describe the relationship between the soil resistivity and unfrozen water content of frozen soil. Silty clay was used as a research object. The temperature, unfrozen water content and resistivity of soil samples with different initial water content and same soil density were tested by Nuclear Magnetic Resonance (NMR) technology and resistivity testing equipment. The results of the experiments performed on frozen silty clay verified the reasonableness of the proposed model for the resistivity of frozen soils. The conductive mechanism of frozen soil was discussed, as well as the resistivity model and its in-situ application for unfrozen water testing.

Three phase heat and mass transfer model for unsaturated soil freezing process: Part 1 - model development

Abstract A three-phase model capable of predicting the heat transfer and moisture migration for soil freezing process was developed based on the Shen-Chen model and the mechanisms of heat and mass transfer in unsaturated soil freezing. The pre-melted film was taken into consideration, and the relationship between film thickness and soil temperature was used to calculate the liquid water fraction in both frozen zone and freezing fringe. The force that causes the moisture migration was calculated by the sum of several interactive forces and the suction in the pre-melted film was regarded as an interactive force between ice and water. Two kinds of resistance were regarded as a kind of body force related to the water films between the ice grains and soil grains, and a block force instead of gravity was introduced to keep balance with gravity before soil freezing. Lattice Boltzmann method was used in the simulation, and the input variables for the simulation included the size of computational domain, obstacle fraction, liquid water fraction, air fraction and soil porosity. The model is capable of predicting the water content distribution along soil depth and variations in water content and temperature during soil freezing process.