Unfrozen Water Content Research Articles

Experimental investigation of thawing behavior of saline soils using resistivity method

Abstract Electrical resistivity method has been widely used to study permafrost and to monitor the process of freezing-thawing. However, a thorough understanding of the mechanism of electrical response during thawing is missing. In this study, we investigated the thawing behavior of saline soils in the temperature range from roughly −10 to 15°C considering the effects of soil type and salinity. A total of nine experiments were performed with three soil types (silica sand, sandy soil, and silt) and three salinities (0.01, 0.1, and 1 S m−1). The results show that resistivity variations with temperature can be divided into three stages. In Stage I, tortuosity and unfrozen water content play major roles in the decrease of resistivity. In Stage Ⅱ, which is an isothermal or near isothermal process, resistivity still decreases slightly due to the thawing of residual ice and pore water movement. In Stage III, ionic mobility plays an important impact on decreasing resistivity. In addition, the isothermal process is found to only occur in silica sand that can be explained by latent heat effect. Exponential and linear models linking temperature with resistivity are used to fit the experimental data in Stages I and III. The fitting parameter in different models shows great correlation with soil type and salinity. Furthermore, unfrozen water content below 0°C is also estimated and uncertainty of estimation is analyzed.

Modeling hydraulic conductivity function of frozen soil

Hydraulic conductivity function for frozen soils (HCFF) is crucial for accurately simulating the water transfer process in cold regions, impacting hydrological states and frost heave diseases. However, the HCFF model capturing the relation between hydraulic conductivity and unfrozen water content (θ) or temperature (T) remains an open question. This study delves into HCFF encompassing both empirical and prediction models. This study begins with introducing θ-form and innovative T-form empirical HCFF models, showcasing their solid performance in fitting measured hydraulic conductivity data. Furthermore, the extension of the T-form empirical model to incorporate vapor flow and bimodal soils, through the introduction of maximum vapor conductivity and weighting factors, demonstrates a closer alignment with physical mechanisms and observed trends. In terms of predicting HCFF, the study provides a theoretical foundation through statistical hydraulic conductivity models and thermodynamic equilibrium in frozen soils. Additionally, it clarifies three routes for HCFF prediction—single Soil Freeze Characteristic Curve (SFCC), single Soil Water Characteristic Curve (SWCC), and a combination of the two—and validates their effectiveness through test results and comparison of HCFF prediction outcomes using SWCC and SFCC data from specific soil samples. In practice, the empirical and prediction models are recommended for available hydraulic conductivity data and available SFCC or SWCC data, respectively. Overall, this study not only lays the theoretical groundwork for most prediction models but also presents a valid empirical equation for modeling hydraulic conductivity function tailored specifically for frozen soils.

The Possibility of Estimating the Permafrost’s Porosity In Situ in the Hydrocarbon Industry and Environment

Global warming firstly influences the permafrost regions where numerous and rich world hydrocarbon deposits are located. Permafrost thawing has caused severe problems in exploring known hydrocarbon deposits and searching for new targets. This process is also dangerous for any industrial and living regions in cold regions. Knowledge of permafrost’s ice and unfrozen water content is critical for predicting permafrost behavior during the water–ice transition. This is especially relevant when ice and permafrost are melting in many regions under the influence of global warming. It is well known that only part of the formation’s pore water turns into ice at 0 °C. After further lowering the temperature, the water phase transition continues, but at gradually decreasing rates. Thus, the porous space is filled with ice and unfrozen water. Laboratory data show that frozen formations’ mechanical, thermal, and rheological properties strongly depend on the moisture content. Hence, porosity and temperature are essential parameters of permafrost. In this paper, it is shown that by combining research in three fields, (1) geophysical exploration, (2) numerical modeling, and (3) temperature logging, it is possible to estimate the porosity of permafrost in situ. Five examples of numerical modeling (where all input parameters are specified) are given to demonstrate the procedure. This investigation is the first attempt to quantitatively analyze permafrost’s porosity in situ.

A Novel Generalized Clapeyron Equation-Based Model for Capturing the Soil Freezing Characteristics Curve of Saline Soil: Validation by Small Sample Lab and Field Experiments

The soil freezing characteristic curve (SFCC) describes the relationship between the freezing point and unfrozen water content, which are two critical parameters in depicting the heat, solute, and water transport in frozen soil. In this paper, we propose a novel Generalized Clapeyron Equation (GCE)-based model, the GCE-Salt Model, to better capture the SFCC in frozen soil in the presence of solute. It keeps the matric potential Ψf in the GCE as its original meaning and incorporates the effect of solute potential in the equilibrium freezing temperature. The performance of our GCE-Salt Model was validated by both lab and field experimental data and compared with related models (Combined Model and GCE-Tan Model). The GCE-Salt Model performed exceptionally well in extremely saline soil and it performed well in both non-saline and saline soil. (1) Our GCE-Salt Model could capture the SFCC of non-saline soil equally as well as the Combined Model (NSE = 0.866); (2) our GCE-Salt Model performed similarly well as the Combined Model and a little better than the GCE-Tan Model for the slightly to highly saline soil (NSE ≥ 0.80 for three models); and (3) our GCE-Salt Model (NSE = 0.919) beat the Combined Model (NSE = 0.863) and the GCE-Tan Model (NSE = 0.62) in capturing the SFCC of extremely saline soil, mainly because the inherent expression of our GCE-Salt Model can more accurately capture the freezing point. Our findings highlight the effect of solute potential on the ice–water change and could improve the understanding of the effect of freezing and thawing on the thermal–hydrological processes, structure of saline soil, and landscape evolution in cold regions.

Study on electrical properties of saline frozen soil and influence mechanism of unfrozen water content

Temperature and unfrozen water content are important affecting parameters in soil freezing process. This study aims to explore correlation between electrical conductivity, unfrozen water content, and temperature for silty clay under various salt content conditions and propose new theoretical relationships to predict the changes of related parameters in the freezing process. Frequency domain reflection(FDR)sensors were employed to conduct electrical performance tests on frozen soil, elucidating the response of frozen soil's electrical conductivity to unfrozen water content and temperature. The conduction mechanism of frozen soil was analyzed using Stern-Gouy electrical double-layer theory. The analysis showed a negative correlation between soil salt content and freezing temperature. Before freezing, salt content significantly affected the crystallization pattern of salt and volumetric water content. There exists a threshold value below which no salt crystallization occurs in soil, and volumetric water content remains relatively constant, while electrical conductivity slightly decreases with decreasing temperature. When salt content exceeds the threshold value, the starting temperature of salt crystallization was influenced by the salt content, and both volumetric water content and electrical conductivity changes significantly after salt phase transition point. After freezing, both unfrozen water content and electrical conductivity significantly decrease. The remaining moisture content in soil slightly decreases with an increase in salt content. Different relevant parameter models have been proposed to describe variations in unfrozen water content and electrical conductivity with temperature after soil phase transition point. The effectiveness of different parameter-related models was validated by comparing experimental data with calculated and fitted results under various conditions. The electrical conductivity of soils with varying salt contents depends on both salt concentration of pore solution and migration pathways of ions. The primary conduction pathways include pore conduction and surface conduction, with latter gradually becoming predominant below its freezing temperature. This study provides a scientific basis for revealing the mechanism and prevention measures of freeze-thaw damage in the construction of subway tunnels using the artificial ground freezing (AGF) technique.

Shear strength model of unsaturated frozen soil based on soil freezing characteristic and soil water characteristic

The strength characteristics of unsaturated soil after freezing significantly influence the safety of engineering construction in frozen soil regions. In this study, the soil freezing characteristic curve (SFCC) and soil water characteristic curve (SWCC) of unsaturated lean clay were tested. Based on the similarity between SFCC and SWCC, the unfrozen water content of SFCC was used to replace the water content of the SWCC to obtain the expression for soil suction under different negative temperatures. A shear strength model of unsaturated frozen soil was established. According to unsaturated triaxial tests under different conditions, the effectiveness of the established unsaturated soil shear strength model was verified. The test results show that in the rapid freezing stage of the SFCC, the volumetric unfrozen water content with an initial matrix suction of 57 kPa exhibited the largest rate of change. The stress-strain curve of soil at positive temperature is strain hardening type, and that at negative temperature presents different types under the influence of temperature, initial matrix suction and confining pressure. The effective cohesion and internal friction angle of soil varied significantly under the influence of temperature and initial matrix suction. When the initial matrix suction was constant, the unsaturated shear strength of the soil increased nonlinearly with a decrease in temperature. When the temperature was ≥−5 °C, the shear strength increased with an increase in initial matrix suction, but decreased when the temperature was ≤−5 °C. The model fitting results were consistent with the measured results of the unsaturated triaxial test, which verifies the validity of the model. This research can provide a reference for studying the mechanical characteristics of unsaturated frozen soil under negative temperature.

Coupled thermo–geophysical inversion for permafrost monitoring

Abstract. This study explores an alternative way of deriving soil thermal properties from surface geophysical measurements. We combined ground surface temperature time series with time lapse geoelectrical acquisitions measured from the ground surface in a fully coupled inversion scheme to calibrate a heat conduction model. The quantitative link between the thermal and geoelectrical parts of the modeling framework is the temperature-dependent unfrozen water content, which is also the main factor influencing electrical response of the ground. The apparent resistivity data were incorporated into the coupled framework without being inverted separately, thus reducing the uncertainty inevitably associated with inverted resistivity models. We show that geoelectrical time lapse data are useful as alternative calibration data and can provide as good results as borehole temperature measurements. The fully coupled modeling framework using field data achieved performance comparable to calibration on borehole temperature records in terms of model fit within 0.6 ∘C, inversion convergence metrics, as well as the predictive performance of the calibrated model.

Hydrothermal characteristics of a cold regional tunnel under different climatic scenarios

Cold regional tunnels have been encountering numerous frost damages as a result of dynamic changes in hydrothermal conditions of tunnel structural layers. The climate change is recognized as a major contributor for the problems. In this study, the hydrothermal conditions of a high speed railway tunnel are evaluated under different climate scenarios based on in-situ data and numerical analysis. Subsequently, the effect of different thicknesses of insulation board on hydrothermal conditions inside the tunnel is compared and the reasonable thickness is obtained. The main findings are: The temperature and unfrozen water content gradually decreased and the ice content gradually increased with the service time of the tunnel in the early 15 years; the maximum frozen depth occurs at the tunnel sidewall and it with a depth of 1.64 m within 30 years after the construction. The hydrothermal conditions inside the tunnel are significantly affected by annu?al mean air temperature (AMAT) and annual range of air temperature (ARAT); the maximum frozen depth decreases with AMAT, but increases with ARAT. After the XPS board with a thickness of 5 cm is laid in tunnel structural layers, the temperature at the most unfavorable position is 0.55?C in the cold season, which suggests that frost damages disappeared and this method can be used to protect the tunnel against the frost damages. This paper can provide a basis for heat insulation design of the cold regional tunnels.

Experimental Investigation on the Effect of Salt Solution on the Soil Freezing Characteristic Curve for Expansive Soils

With the development of the Belt and Road Initiative in China, high-speed railways are booming and inevitably pass through seasonal frost regions. In Nanyang basin, due to seasonal changes, railway subgrades will undergo frost heaving and thawing subsidence. The freezing characteristics of the soil are characterized by the freezing characteristic curve, and the important factors affecting the freezing characteristic curve are the content of expansive clay minerals in the soil and the salt solution. Therefore, three soil samples with different montmorillonite contents were saturated with salt solutions of different concentrations, and the freezing temperature of the soil samples was controlled by a cold bath. After the temperature equilibrium, the frozen stable soil samples were put into a nuclear magnetic resonance instrument to test the unfrozen water content, and the relationship between the freezing temperature and the unfrozen water content of expansive soil under different salt solution concentrations was obtained. Additionally, a unified model was used to simulate the test results. The results show that SFCC shifts to the left, that is, the sodium chloride salt solution reduces the freezing point of the soil sample so that it has more unfrozen water at the same temperature. At the same time, the soil’s freezing characteristic curves are closely related to content of expansive clay minerals in the soil. The more expansive clay mineral content, the greater the corresponding unfrozen water content. These results provide some basic insights for improving the frost heave and thaw subsidence problems of railway subgrades in seasonal permafrost regions, which will have a positive impact on promoting the management and rational application of land resources and the promotion of sustainable development.

Estimation of unfrozen water content in frozen soils based on data interpolation and constrained monotonic neural network

Accurately predicting the unfrozen water content (UWC) in frozen soils is crucial for modeling various soil processes in cold regions. However, existing empirical and theoretical models suffer limitations due to oversimplified assumptions or limited applicable conditions. Meanwhile, data-driven approaches are typically challenged by insufficient high-quality data and poor alignment with the underlying mechanisms in question. In the present study, a monotonic neural network (MNN) model for generalized UWC prediction was developed by leveraging data interpolation and monotonicity constraints. Experimental UWC data of various soils were collected from the literature and a raw dataset was formed. By first best-fitting each UWC curve in the raw dataset and then data interpolation, a new large dataset was generated and used for model development. A constrained MNN architecture for estimating UWC was constructed by constraining the weights of the neural network. The performance of the MNN was then compared with a standard deep neural network (DNN). The results demonstrated that the statistical characteristics of the generated dataset were comparable to that of the raw dataset. Both the MNN and DNN achieved good performance on the generated dataset. However, compared to DNN, the MNN yielded much more accurate prediction when tested on three new soils. In addition, the MNN was able to consistently give monotonic prediction on the UWC-Temperature relationship, even though both the monotonic and non-monotonic data were used for training. Overall, the monotonicity-constrained MNN can provide a robust and physical mechanisms aligned solution for estimating UWC in frozen soils.

Assessment of Unfrozen Water Content in Copper Bentonites Using the 1H NMR Technique: Optimization, the Method's Limitation, and Comparative Analysis with DSC.

Studies on changes in unfrozen water content in copper bentonite from Slovakia were conducted using both differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) methods. The aims of this study were to 1. optimize the method for determining changes in unfrozen water content using the 1H NMR technique in model bentonites based on the DSC results; 2. analyze the relationship between unfrozen water content, as determined via DSC and the optimized NMR technique, and the physicochemical parameters of bentonites; and 3. identify the limitations in determining changes in unfrozen water content using the 1H NMR technique in relation to copper-contaminated bentonites. The results obtained using the optimized NMR method applied to the model bentonites correlated well with the DSC results. The unfrozen water content in the Cu-contaminated bentonites was 2-18% lower after NMR compared to the DSC results, likely due to the mobility of copper ions and their paramagnetic properties. Statistically significant differences in unfrozen water content between the DSC and NMR methods were observed, depending on molar concentration, copper ion concentration, and temperature, confirmed via Analysis of Variance (ANOVA). Calorimetric studies are recommended for investigating unfrozen water content changes in contaminated clays. Further NMR research could identify metals influencing free induction decay signals under varying physicochemical conditions.

Disconnected active layers and unfrozen permafrost: A discussion of permafrost-related terms and definitions

Permafrost is ground that remains at or below 0 °C for two or more consecutive years. It is overlain by an active layer which thaws and freezes annually. The difference between these definitions – the active layer based on pore water phase and permafrost based on soil temperature – leads to challenges when monitoring and modelling permafrost environments. Contrary to its definition, the key properties of permafrost including hardness, bearing capacity, permeability, unfrozen water content, and energy content, depend primarily on the ice content of permafrost and not its temperature. Temperature-based measurements in permafrost systems often overlook key features, e.g. taliks and cryopegs, and comparisons between measured and modelled systems can differ energetically by up to 90 % while reporting the same temperature. Due to the shortcomings of the temperature-based definition, it is recommended that an estimate of ice content be reported alongside temperature in permafrost systems for both in-situ measurements and modelling applications. Plain language summaryPermafrost is ground that remains at or below 0 °C for two or more consecutive years. Above it sits an active layer which thaws and freezes annually (meaning that the water in the ground changes to ice each winter). The difference between these definitions – the active layer based on the state or water in the ground and permafrost based on ground temperature – leads to challenges when measuring (in the field) and modelling (using computers) permafrost environments. In addition to these challenges, the key properties of permafrost including its ability to support infrastructure, convey water, and absorb energy depend more on its ice content than its temperature. Due to the shortcomings of the temperature-based definition, it is recommended that an estimate of ice content be reported alongside temperature in permafrost systems for both field measurements and modelling applications.

Modelling polarization effect in electrical conductivity of frozen soil

Unfrozen water content is a critical index for understanding the hydromechanical behavior of frozen soil in cold regions. The electrical conductivity of frozen soil has been commonly used to determine the unfrozen water content in soil in both laboratory and field tests. However, the polarization effect caused by the frequency of the alternating current significantly influences measurements of the electrical conductivity of frozen soil. The mechanism of the polarization effect has yet to be thoroughly investigated and understood, and a precise theoretical model is lacking. This study first develops a polarization model for soil at positive and negative temperatures based on the multi-peak Cole-Cole model, which can theoretically give a better frequency range for electrical conductivity. Furthermore, the relationship between the test frequency range and temperature is established based on Arrhenius' law. A series of electrical conductivity tests are performed on multiple soil samples at positive and negative temperatures to validate the proposed model. It found that the polarization area of silt and sand increased rapidly with increasing frequency and gradually expanded to low frequencies with decreasing temperature. This study finally recommends an accurate reference range of test frequency for measuring the electrical conductivity of frozen soils.

A dynamic soil freezing characteristic curve model for frozen soil

The soil freezing characteristic curve (SFCC) plays a fundamental role in comprehending thermo-hydraulic behavior and numerical simulation of frozen soil. This study proposes a dynamic model to uniformly express SFCCs amidst varying total water contents throughout the freezing-thawing process. Firstly, a general model is proposed, wherein the unfrozen water content at arbitrary temperature is determined as the lesser of the current total water content and the reference value derived from saturated SFCC. The dynamic performance of this model is verified through test data. Subsequently, in accordance with electric double layer (EDL) theory, the theoretical residual and minimum temperatures in SFCC are calculated to be −14.5 °C to −20 °C for clay particles and −260 °C, respectively. To ensure that the SFCC curve ends at minimum temperature, a correction function is introduced into the general model. Furthermore, a simplified dynamic model is proposed and investigated, necessitating only three parameters inherited from the general model. Additionally, both general and simplified models are evaluated based on a test database and proven to fit the test data exactly across the entire temperature range. Typical recommended parameter values for various types of soils are summarized. Overall, this study provides not only a theoretical basis for most empirical equations but also proposes a new and more general equation to describe the SFCC.

Investigations on the freezing characteristic and flexural mechanical properties of frozen loess

The exploitation of deep resources increases with the implementation of the western development strategy. The artificial freezing technique is used for shaft construction when facing complex geological conditions. Due to the large deformation of frozen soil wall, disasters often occur during shaft excavation, such as freezing pipe deflection, and rupture. The flexural mechanical property of frozen loess is important for the design of shaft construction in the western region. In this study, the nuclear magnetic resonance (NMR) tests of frozen loess were carried out under different freezing temperatures, and the evolution law of unfrozen water content in frozen loess was investigated. The results show that the pore ice content increases rapidly when the temperature decreases from −1 °C to −7 °C; then the phase transition of residual unfrozen water becomes difficult as the further decrease in temperature. The flexural tests of frozen loess with different water content (10%, 15%, 20%, 25%) were carried out at different freezing temperatures (−5 °C, −10 °C, −15 °C, −20 °C). The flexural strength of frozen loess increases with the decrease of unfrozen water content, and it increases first and then decreases as the initial water content increase. The flexural toughness gradually increases at −5 °C and − 10 °C with the increase of water content, while increasing first and then decreasing at −15 °C and − 20 °C. The roughness of the fracture surface increases with the decrease in temperature.

Study on spatiotemporal changes and influencing factors of frozen soil moisture during freeze-thaw period under different ecological construction measures in the loess plateau of China

The climatic conditions and soil characteristics of the Loess Plateau in China make it have a unique freeze–thaw process and the distribution of soil unfrozen water. In order to elucidate the spatio-temporal variation of soil unfrozen water during freeze–thaw period and its influencing factors under different ecological construction measures, The spatial and temporal variation of soil unfrozen moisture and its main influencing factors in five different ecological plots in the Loess Plateau during freeze–thaw period were studied by combining field monitoring and indoor calculation. The results showed that: (1) the spatiotemporal changes of unfrozen water content in soil were different under different vegetation restoration methods. The variation of unfrozen water content in fallow land was the largest at 20cm depth, while the variation in surface 10cm was the largest in the other four plots. (2) The average unfrozen water content of soil in the representative soil layer can be estimated more accurately, and the best representative soil layer in the five sample plots is concentrated in 20–30 cm. (3) During seasonal freeze–thaw period, the main controlling environmental factors of unfrozen water content are air temperature and surface temperature. The results can provide reference for soil protection and water resources management in northwest China, especially in the Loess Plateau.

A coupled cryogenic thermo-hydro-mechanical model for frozen medium: Theory and implementation in FDEM

This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical (THM) processes associated with a freezing medium, which is then implemented in the combined finite-discrete element method code (FDEM) for multi-physics simulation. The governing equations are deduced based on energy and mass conservation, and static equilibrium equations, considering water/ice phase change, where the strong couplings between multi-fields are supplemented by critical coupling parameters (e.g. unfrozen water content, permeability, and thermal conductivity). The proposed model is validated against laboratory and field experiments. Results show that the cryogenic THM model can well predict the evolution of strongly coupled processes observed in frozen media (e.g. heat transfer, water migration, and frost heave deformation), while also capturing, as emergent properties of the model, important phenomena (e.g. latent heat, cryogenic suction, ice expansion and distinct three-zone distribution) caused by water/ice phase change at laboratory and field scales, which are difficult to be all revealed by existing THM models. The novel modeling framework presents a gateway to further understanding and predicting the multi-physical coupling behavior of frozen media in cold regions.

Characterization and prediction of compressive strength in ultralow-temperature frozen soil using nuclear magnetic resonance and WOA-ENN Model

Artificial ground freezing（AGF）has been utilized in a range of engineerings, including tunneling, shaft sinking, deep excavations, and the construction of underground structures. Currently, the strength and efficacy of artificial ground freezing technology have become a prominent subject of research. To reveal the trend of changes in the uniaxial compressive strength of ultralow-temperature frozen soil, uniaxial compression tests were carried out on soil samples with varying water contents (17 %, 20 %, and 23 %) and temperatures (-10 °C to −180 °C). To analyze the relationship between the unfrozen water content and compressive strength, the unfrozen water content in the frozen soil was quantitatively measured by nuclear magnetic resonance (NMR). Additionally, a prediction model for the compressive strength of ultralow-temperature frozen soil was built with an Elman neural network based on the whale optimization algorithm (WOA-ENN). The results indicate that the frozen soil exhibits elastic–plastic failure at temperatures above −80 °C and brittle failure at temperatures below −80 °C. In the temperature range from −10 °C to −80 °C, the compressive strength of the frozen soil increases linearly with decreasing temperature, and stabilizes at temperatures ranging from −80 °C to −180 °C. The turning point in compressive strength at −80 °C arises because the content of unfrozen water remains relatively constant below this temperature. Furthermore, the relationship between the unfrozen water content and compressive strength follows a power function. To predict the compressive strength of frozen soil at ultralow-temperatures, a WOA-ENN prediction model is proposed as it has a significantly lower average absolute percentage error (4.00 %) compared to the ENN prediction (24.49 %). Overall, the proposed prediction model effectively addresses the complex nonlinear relationship between the compressive strength of ultralow-temperature frozen soil and its influencing factors, thus providing valuable insights into the mechanical response of frozen soil under ultralow-temperature conditions.

Research on Glazed Hollow Bead Insulation concrete freezing process with different saturation based on nuclear magnetic resonance

This paper uses experimental analysis to understand the freezing law of water to determine the freezing damage mechanism of Glazed Hollow Bead Insulation Concrete (GIC). The critical saturations of GIC with different Glazed Hollow Beads (GHBs) contents were obtained by the relative moving modulus after testing seven saturations of the concrete (70% to 100%, 5% interval). The critical saturation of GIC-0 (i.e., 0% GHBs content) occurred at ∼ 76–78%. GIC-50 occurred at about 86–88%. GIC-100 occurred at about 89–91%. GIC-0, GIC-50, and GIC-100 were then saturated to S60, Scr, and S100 based on their respective critical saturation. Low-field nuclear magnetic resonance (NMR) was used to study the freezing process of different water types in GIC. The results showed that: 1) The water inside GIC was composed of adsorb water, pore water, and free water; 2) The whole freezing process could be roughly divided into four stages: subcooling stage, rapid freezing stage, stable freezing stage, and the end of the freezing phase; 3) During the freezing and thawing process, the change in unfrozen water content of GIC specimens had a hysteresis curve, while the specimens less than the critical saturation had almost no hysteresis curve. Moreover, the saturation significantly influenced the freezing process of different water types, which determined the proportion of them. This study also determined the evolution of the pore size of GIC, which provides a new idea for analyzing the freezing damage mechanism of porous GIC.

Influence of brine leakage on frozen wall development in offshore sand layer when active freezing: A numerical study

Brine leakage after freezing pipe fracture when active freezing will cause local structural defects or even failure of frozen wall. A water-heat-solute coupled model that includes a modified Michalowski model considering both temperature and salt concentration was proposed to simulate the freezing construction in offshore sand layer. It was verified by the artificial freezing model tests of saturated saline sand under seepage. The structural defects of frozen wall were observed at the boundary between straight and arch walls on the upstream. The range of the structural defect and the closing time of frozen wall both rise with larger pressure head. The brine leakage was then simulated to evaluate the effects of both pressure head and fracture range of freezing pipe on the structural defect of frozen wall. As indicated by the normalized unfrozen water content contour, there are obvious flaws in determining whether the frozen wall is closed only by the average temperature when brine leakage. A characteristic index, the area ratio of structural defect of frozen wall, was derived from the normalized unfrozen water content contour. The structural defect results from brine leakage when the pressure head is below 2.0 m, otherwise from both brine leakage and groundwater seepage. It is recommended that in addition to monitoring temperature during active freezing, additional moisture monitoring devices should be installed to prevent brine leakage hazards.