Soluble salts significantly influence the freezing characteristic parameters of frozen soil. Previous studies have either insufficiently addressed the effect of sodium sulfate on matric suction or not comprehensively revealed the mechanism by which temperature affects matric suction at freezing temperature. In this study, the moisture and suction sensors were used to quantify the freezing temperature (FT), unfrozen water content (UWC), and matric suction (MS) of Ili loess with varying soluble salt contents. The impact of soluble salt content on three freezing characteristic parameters were investigated with the underlying mechanisms revealed. The results indicated that there was an initial decrease in both freezing and supercooling temperatures as the soluble salt content increased. Beyond a soluble salt content of 14 g/kg, an increase in both the freezing and supercooling temperatures was observed. Specimens with different soluble salt contents exhibited distinct UWC, which could be categorized into three stages based on temperature. A crystal precipitation stage was observed beyond the soluble salt content of 14 g/kg. Moreover, the proposed fitting model for UWC by incorporating the soluble salt content into the Gardner model demonstrated high accuracy. The MS can also be divided into three stages with temperature. Notably, specimens with soluble salt contents of 20 and 26 g/kg exhibited nonlinear increases in MS at temperatures of 5 degrees C and 10 degrees C due to crystal precipitation. Furthermore, theoretical calculations indicated the complete precipitation of sodium sulfate during the positive temperature stage.

Artificial ground freezing technology is commonly used in tunnel construction in coastal soil regions. The static and dynamic strength characteristics, as well as the elastic modulus of freeze-thaw chloride silty clay, are crucial for predicting thaw settlement and designing the stability of artificial ground freezing technology. Hence, consolidated-undrained triaxial compression tests and cyclic triaxial tests were conducted with varying salt content, freeze-thaw cycles, and temperatures to investigate the static and dynamic strength as well as the elastic modulus in more detail. The results indicated that all static triaxial stress-strain curves and dynamic triaxial backbone curves exhibited strain-hardening behavior. The initial linear stage of the curve was more pronounced in specimens without freeze-thaw. The static strength initially decreased and then increased with rising salt content. A critical salt content of 1% corresponded to the minimum static strength. When the salt content was <= 3%, the dynamic strength showed no significant change. However, it increased significantly to 1.8 times that of other salt content specimens when the salt content reached 4% after undergoing freezing-thawing at -10 degrees C. The increase in salt content led to a 1.1-2.0 times increase in the elastic modulus. The elastic modulus can be normalized as E/E-max and described using a hyperbolic model. For specimens with 2% salt content after freeze-thaw cycles, the damage rates of static and dynamic strength were 52%-66% and 69%-78%, respectively. The damage rates of static and dynamic peak elastic modulus were 90% and 81%, respectively. The impact of freezing temperature on static and dynamic strength and elastic modulus was minimal. This research can establish a theoretical foundation for the utilization of artificial ground freezing technology in marine saline formations, as well as for the prediction and control of post-construction thaw settlement to ensure the safe operation of tunnels.

Using geotextiles to improve saline soil roadbeds has become increasingly widespread. However, salt unavoidably enriches at the saline soil-geotextile interface. Under complex external forces, the mechanical properties of the saline soil geotextile interface are not yet clear. Therefore, this study systematically studied the dynamic shear performance of saline soil geotextile interface under dynamic load under different salt content conditions using three shear forms: cyclic direct shear, monotonic direct shear, and post-cycle direct shear. The main research focuses on the influence of salt content, vertical stress and shear displacement amplitude on interface shear strength, stiffness, damping ratio, vertical displacement and other indicators. The results show that after cyclic shear, the strength of the interface of saline soil decreases, and the phenomenon of plastic softening is obvious. The interface shear strength and stiffness exhibit a non-linear relationship with the increase of salt content. When the salt content is 3 %, the interface shear performance reaches its optimum. Excessive salt content can cause crystalline slippage and weaken interface mechanical properties. Increasing vertical stress or reducing shear displacement amplitude is beneficial for improving interface shear strength and stiffness. The amplitude of shear displacement has the greatest impact on the interface damping ratio. The higher the salt content, the more severe the stress damage to the geotextile, and the more significant the accumulation of interface crystallization. The study revealed the mechanical response law of saline soil geotextile interface under dynamic load.

In order to investigate the dynamic characteristics of frozen saline silty clay (studied saline soil) under reciprocating loading, a series of cyclic tri -axial experiments have been conducted for studied saline soil with 0.0, 0.5, 1.5, and 2.5 % of Na 2 SO 4 contents under confining pressures 0 MPa -18 MPa at -6 degrees C, respectively. The test results show that as the increase of number of cycle N , the accumulated axial strain e aN continuously increases, and the relationship between e aN and N can be described by an exponential function: e aN = aN b ; As the number of cycle N increasing, dynamic shear modulus G dN and dynamic bulk modulus K dN increase firstly and then decrease slightly; Salt content and confining pressure have great influences on the e aN , G dN and K dN . Within the same loading cycle, G dN and K dN decrease until reaching their minimums when the salt content is 0.5 %, and then G dN and K dN increase as the increase of salt content. With the change of salt content, e aN presents an opposite change law to G dN and K dN . For the studied saline soil with same salt content, during the same loading cycle, e aN and G dN increase until reaching their minimums, and then decrease as the increase of confining pressure, K dN increases with the increase of confining pressure. This study can be applied to evaluate the elasto-plastic properties of frozen soils and saline soils subjected to cyclic dynamic loading.

For engineering structures with saline soil as a filling material, such as channel slope, road subgrade, etc., the rich soluble salt in the soil is an important potential factor affecting their safety performance. This study examines the Atterberg limits, shear strength, and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China. The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test, a mercury intrusion porosimetry (MIP) test, and a scanning electron microscopic (SEM) test. The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%, the bound water film adsorbed on the surface of clay particles thickened continuously, and correspondingly, the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content. Meanwhile, the bonding force between particles was weakened, the dispersion of large aggregates was enhanced, and the soil structure became looser. Macroscopically, the compressibility increased and the shear strength (mainly cohesion) decreased by 28.64%. However, when the NaHCO3 content exceeded the threshold value of 1.5%, the salt gradually approached solubility and filled the pores between particles in the form of crystals, resulting in a decrease in soil porosity. The cementation effect generated by salt crystals increased the bonding force between soil particles, leading to a decrease in plasticity index and an improvement in soil mechanical properties. Moreover, this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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 SternGouy 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 freezethaw damage in the construction of subway tunnels using the artificial ground freezing (AGF) technique.

Widespread saline soils in Northwest China pose a serious threat to the region's ability to use infrastructure safely because they are prone to soil structure damage when subjected to external environmental fluctuations, which in turn affects the stability of the foundations for buildings. The non-destructive approach of measuring resistivity can be used to swiftly reflect the subsoil body's state and make assumptions about its safety. However, the electrical resistivity of the underground soil body can be used to quickly identify unstable areas because the resistivity is influenced by the water content, salt content, and structural characteristics of the soil body. To do this, it is necessary to understand the coupling relationship between various factors. In this study, we first constructed samples with various water, salt, and soil structure characteristics, and then used indoor tests, such as soil resistivity measurement and thermogravimetric analysis, to analyze the multiple factors affecting the resistivity characteristics of the soil. The relationship between soil resistivity and actual saline soil diseases in Northwest China was then further discussed in conjunction with the results of the indoor tests and analyses. subsequently, the resistivity and soil properties have been measured in the field at specific locations in Northwest China where railway roadbeds are diseased. The study's findings can theoretically support a deeper comprehension of the law and mechanism of soil resistivity change, as well as provide assistance for building infrastructure in Northwest China.