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The soil freezing characteristic curve (SFCC) plays a crucial role in investigating the soil freezing‐thawing process. Due to the challenges associated with measuring the SFCC, there is a shortage of high‐quality or rigorous test results with sufficient metadata to be effectively used for applications. Current researchers typically conduct freezing tests to measure the SFCC and assume a singular SFCC when studying the freezing‐thawing process of soils, although limited studies indicated that there is a hysteresis during the freezing and thawing process. In this paper, a series of freezing‐thawing tests were performed to assess the SFCC, utilizing a precise nuclear magnetic resonance apparatus. The test results reveal a hysteresis between the SFCC obtained from the freezing process and that from the thawing process. Through analyzing the test results, the hysteresis mechanism of the SFCC is attributed to supercooling. Supercooling inhibits initial pore ice formation during freezing, causing a drastic liquid water‐ice phase change once supercooling ends. Despite being considered closely related, the hysteresis of the SFCC differs from the soil water characteristic curve (SWCC), and the models used to simulate the hysteresis of SWCC cannot directly be used. To address the impact of supercooling on soil freezing‐thawing hysteresis, a novel theoretical model is proposed. Comparisons between the measured and predicted results affirm the validity of the proposed model. Plain Language Summary Understanding the freezing and thawing behavior of soils is critical for construction in cold regions. The soil freezing characteristic curve (SFCC), which describes the relationship between temperature and unfrozen water content, is essential for characterizing soil behavior during freeze‐thaw cycles. However, measuring SFCCs for both freezing and thawing presents significant challenges, often resulting in simplifications and incomplete data in many studies. In this research, we conducted freezing‐thawing tests using precise technology called nuclear magnetic resonance to examine the SFCC. We found a hysteresis between the SFCC during freezing and thawing, primarily attributed to supercooling, where the soil remains liquid below the freezing temperature. Supercooling delays initial ice formation, causing a rapid transition from liquid water to ice once it ceases. Importantly, the SFCC hysteresis differs significantly from the drying‐wetting hysteresis in the soil water characteristic curve. To address this, we propose a novel model considering the impact of supercooling on soil freezing‐thawing hysteresis. The proposed model fits well with the measured data and outperforms existing models. This study introduces a new understanding and a reliable model for soil freezing‐thawing process, contributing to better comprehension of frozen soil phase changes. Key Points Supercooling is the primary cause of freezing‐thawing hysteresis The hysteresis of the soil freezing characteristic curve differs substantively from that of the soil water characteristic curve The proposed model can address the impact of supercooling on soil freezing‐thawing hysteresis

The quantitative determination of liquid water content and salinity in soils is crucial for the preservation of hydrological environments and engineering infrastructures, especially in frozen regions. Electrical conductivity, as a fundamental physical parameter in electrical and electromagnetic non‐destructive techniques, varies significantly with the physical and chemical properties, such as pore water conductivity, salinity, water saturation, and temperature. In this study, accounting for pore size and tortuous length following fractal distributions, we develop a new capillary bundle model for variation of electrical conductivity as a function of temperature in broad water saturation and salinity ranges. In this new model, we consider the contributions of bulk and surface conductivities to the total electrical conductivity. To test this model, a series of laboratory experiments were carried out for different initial water saturations and salinities using an electrical resistance apparatus and a nuclear magnetic resonance method. The experimental results show that unfrozen water saturation and ionic concentration affect the electrical conductivity of unsaturated frozen soils. Furthermore, the proposed model is capable of fitting the main trends of the experimental data from the literature and acquired in this study in unfrozen‐frozen conditions for different water contents. Relying on the proposed model, we also determine the expression of the apparent formation factor, which is significantly sensitive to porosity, water saturation, and temperature. The predicted values of the apparent formation factor also agree very well with the experimental data. This new capillary bundle model provides a new perspective in interpreting electrical monitoring to easily deduce changes in key variables in the cryosphere such as liquid water content and moisture gradients. Key Points We propose a new capillary bundle model that accounts for fractal pore size and tortuosity distributions in the electrical conductivity of frozen porous media Electrical conductivity changes with decreasing temperature in two stages: a gradual decrease followed by a sharp drop below the freezing temperature This new model correctly reproduces experimental data in a wide temperature, water saturation, and salinity ranges

Frost heave susceptibility is a key index for designing the subgrade fillings of high-speed railways in cold regions. The existing methods for assessing frost heave susceptibility are mainly empirical or semi-empirical, and most of them are defined based on the fine content of soils. This study attempts to propose a new criterion based on the analytical solution of frost heave in the soil. A number of experiments are used to validate the proposed analytical model, which shows that the computed value of frost heave matches well with the measured data. The proposed model indicates that frost heave is a proportional function of the square root of time. Thus, the slope R named frost heave classification index of the proportional function is defined as a new index for frost heave susceptibility classification. A value of R less than 0.21 corresponds to a non-frost heave susceptibility condition, a value greater than 1.18 corresponds to a high frost heave susceptibility condition, and a value in the range of 0.21 and 1.18 means a frost heave susceptibility condition. R is directly related to the boundary temperatures and soil–water and soil-freezing characteristics. The parameter study shows that reducing the values of SWCC fitting parameter α and cold end temperature T c or increasing the values of permeability of frozen soil k f , the saturated volumetric water content θ s , the unfrozen water content at the frost front θ u and the residual volumetric water content θ r increases the possibility of frost heave. Compared with the existing method, the new index has a clear theoretical basis, and the parameters are easily obtained. It may be a rational method for assessing frost heave susceptibility.

The freezing-thawing characteristics of frozen soil are crucial for safe and reliable construction projects in cold regions. In this study, nuclear magnetic resonance (NMR) technology is employed to carry out freezing-thawing tests, aiming to explore the hysteresis behavior of soil during freezing and thawing. Three representative soil types (poorly graded sand, silt, and fat clay) are tested under different temperature modes to analyze their hysteretic characteristics of the soil freezing characteristic curve (SFCC). The results show that the hysteresis primarily occurs in the supercooling and rapid-decline stages, and the hysteresis loops of fat clay and silt are more distinct. The SFCC tests under different temperature modes reveal differences between the hysteresis of SFCC and that of the soil water characteristic curve (SWCC). Importantly, the supercooling phenomenon is identified as the main cause of this hysteresis. Based on this, we propose a theoretical model that incorporates the supercooling phenomenon into predictions of freezing-thawing hysteresis. By comparing with the measured data, this model can effectively capture all three stages of soil freezing-thawing hysteresis and particularly excel in predicting the supercooling and rapid freezing stages, with higher correlation coefficients and broader applicability. This study clarifies the critical role of supercooling in soil freezing-thawing hysteresis and builds a robust model for applications in cold-region engineering.

The landslide signs were discovered in a high filling embankment slope, which was located on an express highway construction site in Guizhou, China. According to the in-situ monitoring results, the landslide mechanism and the stabilization effect of the portal anti-slide pile were preliminarily analyzed. The sliding shear zone of the landslide was obtained by the in-situ monitoring. Tw o numerical models with imposed sliding shear zone were established to analyze the evolution of the landslide instability and the stabilizing effect of the portal anti-slide pile. The comparative analysis of in-situ monitoring data and numerical simulation result shows that the two numerical model are reliable. Furthermore, the numerical model of embankment slope that reinforced by portal anti-slide pile was implemented to analyze the structural behavior of pile under the different pile parameters, and the pile-soil interaction was considered in the numerical model. The influence of the pile parameters (pile spacing, pile row spacing, and linked beam size) on the stabilization effect, structural deformation, and economic benefit were studied. The numerical results provide a guide for determining the optimum parameters of the portal anti-slide pile.

The lateral force on stabilizing piles due to the movement of the landslide has been studied by many researchers. One of the most widely used methods was proposed by Ito and Matsui in 1975 based on the plastic deformation theory. This paper aims to extend the approach of Ito and Matsui by considering the soil arching effects along the height of the sliding layer between two neighboring piles. The analysis is carried out in two stages. First stage involves the plastic deformation of soil adjacent to piles. In this stage, considering the arching effects along the height of the sliding layer, a typical cross section of the soil is employed to analyze the soil stress in the rear of piles. In the second stage, the plastic deformation theory proposed by Ito and Matsui is adopted to analyze the squeezing effects between two neighboring piles. Moreover, the parametric analysis is performed to investigate the susceptibility of the governing factors, which include the geometric and mechanical parameters. The results show that both the geometric and mechanical parameters impart the significant influence on the lateral force. Finally, both the numerical simulation results and the field experiment data from the literatures are introduced to validate the proposed approach. The comparison charts illustrate that the predictions by the proposed approach are consistent with the experimental results.

A series of unconfined compressive strength tests and flexural strength tests are carried out to evaluate the improved effect of polypropylene fiber on the defects of cement mortar soil. The following factors, including the fiber content, cement content, sand content and curing age, are studied to investigate the influences on the mechanical properties and microstructure of the samples. The results show that the unconfined compressive strength (UCS), residual strength and flexural strength of the fiber reinforced cement mortar soil (FRCMS) substantially increase with increasing fiber content. The peak strain and ratio of the flexural-compression strength ( R fcs ) of the FRCMS first increase and then decrease with an increase in fiber content, and the optimal fiber content is 3.5%. The brittleness index of the FRCMS is found to be inversely proportional to fiber content. The results suggest that the addition of an appropriate amount of fibers can substantially improve the plasticity and lateral stress capacity of the FRCMS. The strength of the FRCMS improves with the increase in cement content, sand content and curing age within a certain range. The microstructure of the FRCMS are analyzed by scanning electron microscopy (SEM) tests.

In order to study the characteristics of P-wave velocity and resistivity of loess with different moisture contents, low-field nuclear magnetic resonance, resistivity, and P-wave velocity tests were carried out on loess samples with 11 different moisture contents. The test results show that under the condition of the same dry density, the water in loess exists in two forms: bound water and free water. With the increase in moisture content, the water porosity of loess increases, the proportion of free water increases, and the resistivity gradually decreases and then tends to be stable, showing a power function relationship with moisture content. When the moisture content is less than 20%, the P-wave velocity decreases with the increase in the moisture content. In comparison, when the moisture content is greater than 20%, the wave velocity increases with the increase in the moisture content. A modified relation between wave velocity and moisture content and saturation is put forward, and the relationship expression between wave velocity and resistivity of loess is established. Finally, the reliability is verified by experimental data. The research results have a certain guiding significance for real-time monitoring of loess moisture content and engineering stability analysis in the loess area.

A series of triaxial compression tests were conducted to investigate the influence of the fiber content and confining pressure on the shearing characteristics of cement-stabilized clay reinforced with glass fibers. The glass fiber contents were 0, 1‰, 2‰, 3‰, and 4‰ by weight of the dry soil. The stress strain and volume change behavior, shear strength, and energy absorption of the test specimen were obtained. The results indicate that the inclusion of glass fibers can increase the shear strength, inhibit the volumetric dilation of the test specimen, and improve its brittle behavior. The cohesion of the cement-stabilized clay reinforced with 4‰ glass fiber content is 2.8 times greater than that of the cement-stabilized clay. The effect of the fiber content on the friction angle is not obvious. It is found that the glass fiber reinforcement is more substantial under a low confining pressure. The scanning electron microscopy test results show that the surface of the glass fiber is wrapped with cement hydrate crystals, which increases the bite force and friction between the fiber and the soil particles. A single fiber is similar to an anchor in the soil, which enhances the mechanical properties of the cement-stabilized clay reinforced with fibers.

Surface evaporation is one of the main processes in the soil–atmosphere interaction. Since it is highly related to meteorological factors and soil properties, determination of evaporation rate from soil surface remains a challenge. To investigate the evaporation from unsaturated soil, a climate control apparatus has been newly developed, which has a feature of completely controlling air temperature, relative humidity and wind speed. Twelve climatic conditions are applied to three kinds of soil specimens to carry out the evaporation tests. The results show that only water content cannot allow an accurate estimation, additional variables accounting for soil texture and wind speed must be included as well. Moreover, a simple approach to parameterize evaporation is presented by the soil moisture θ of top 1-cm layer with considering the effect of soil texture and wind speed. It is found that the new approach is able to accurately estimate the evaporation from unsaturated soil.