Sudden temperature drops cause soils in natural environments to freeze unidirectionally, resulting in soil expansion and deformation that can lead to damage to engineering structures. The impact of temperature-induced freezing on deformation and solute migration in saline soils, especially under extended freezing, is not well understood due to the lack of knowledge regarding the microscopic mechanisms involved. This study investigated the expansion, deformation, and water-salt migration in chlorinated saline soils, materials commonly used for canal foundations in cold and arid regions, under different roof temperatures and soil compaction levels through unidirectional freezing experiments. The microscopic structures of saline soils were observed using scanning electron microscopy (SEM) and optical microscopy. A quantitative analysis of the microstructural data was conducted before and after freezing to elucidate the microscopic mechanisms of water-salt migration and deformation. The results indicate that soil swelling is enhanced by elevated roof temperatures approaching the soil's freezing point and soil compaction, which prolongs the duration and accelerates the rate of water-salt migration. The unidirectional freezing altered the microstructure of saline soils due to the continuous temperature gradients, leading to four distinct zones: natural frozen zone, peak frozen zone, gradual frozen zone, and unfrozen zone, each exhibiting significant changes in pore types and fractal dimensions. Vacuum suction at the colder end of the soil structure facilitates the upward migration of salt and water, which subsequently undergoes crystallization. This process expands the internal pore structure and causes swelling. The findings provide a theoretical basis for understanding the evolution of soil microstructure in cold and arid regions and for the management of saline soil engineering. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published 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/).

Influenced by factors such as the freeze-thaw cycle and water-salt migration, road construction in Uzbekistan's highway project areas is prone to dissolution and subsidence, salt swelling, corrosion, and other engineering diseases. To investigate how various factors impact saline soils in Uzbekistan's monsoon freezing zone, we conducted analyses of stress-strain curves, failure strength, and shear strength parameters of these soils through freeze-thaw (F-T) cycle tests and unconsolidated and undrained (UU) triaxial shear tests. The findings indicate that with the increase of salt content, the average reduction in the failure strength of saline soil was 15.8%, 6.3%, and 5.7%; with the increase of water content, the average reduction in cohesion was 10.8%, 44.1%, and 32.6%; and the internal friction angle increased with the increase of the number of F-T cycles and decreased with the increase of freezing temperature. Ultimately, we defined the rates of failure strength deterioration and cohesion damage in saline soil due to various factors, analyzing the destructive impacts of these factors. The results demonstrate a strong correlation between the curves of failure strength deterioration and cohesion damage ratios, indicating that the significant degradation of saline soil due to salt is primarily influenced by F-T cycles, with the extent of damage closely linked to water content.

Changes in the pore-water environment have an obvious effect on the physical and mechanical properties of soil. Traditional consolidation theory has not considered the influence of the hydrochemical environment on the mechanical properties of soil. In order to investigate the mechanism of chemical action on geotechnical properties, in this study, one-dimensional compression tests and scanning electron microscope tests are carried out on soils prepared with different concentrations of NaCl solution. The mechanical characteristics reveal that the compression index shows a gradual decrease with an increase in pore-water salinity, and the structural yield stress of the soil increases gradually with the increase in pore-water salinity, reaching a maximum value of 50.34 kPa with a salt content of 5%. Conversely, the change in osmotic suction has minimal impact on the rebound index. Notably, the pore-water salinity primarily affects the intrinsic compression behavior of soft clays, as evidenced by an increase in the slopes of the sedimentary compression curve before yielding higher pore-water salinity. Combined with the analysis of microscopic test results, it is found that as the osmotic suction increases and the interparticle hydration capacity decreases, the soil particles change from a dispersed state to an aggregate state, leading to an increase in mesopores, and this increase indicates that the ability of the soils to resist the external loads also increases, which means an enhancement of the structural characteristic. In addition, the coefficient of permeability of the soil decreases as the consolidation pressure increases. Chemical consolidation produced by the increase in pore salt solution concentration causes a decrease in pore ratio, resulting in a smaller coefficient of permeability, and there exists a critical value for the effect of salt on the coefficient of permeability of the soil, which is related to the structural yield stress of the soil. This research provides a theoretical basis for the settlement prediction and the safety evaluation of soft ground in coastal areas.

In cold regions, saline soils can cause dissolution, settlement, and salt expansion of the roadbed under the influence of freeze-thaw cycles, so they need to be stabilized during road construction. In this study, lime, fly ash (FA), and polyacrylamide (PAM) were used to stabilize sulfate saline soils, and the stabilized saline soils were subjected to the unconfined compressive strength test (UCS), splitting test, and freeze-thaw cycle tests (FTs). The stabilization mechanism of the three materials on saline soils was also studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS). The test results showed that the addition of lime, FA, and PAM to saline soils can improve the mechanical properties and frost resistance of saline soils. After 28 d of curing, the UCS of FA-, PAM-, and lime-stabilized saline soils increased by at least 55%, 23%, and 1068%, respectively, and the splitting strength increased by at least 161%, 75%, and 2720%, respectively. After five freeze-thaw cycles, the residual strength ratios (BDRs) of the UCS of L2 (lime 8%), F2 (FA 11%), and P2 (PAM 1%) stabilized soils and saline soils were 71.78%, 56.42%, 39.05%, and 17.95%, respectively, and the decreasing trend tended to be stable. The saline soils stabilized by lime and FA were chemically stabilized, and their mechanical properties and frost resistance were better than the physical stabilization of PAM.

Infrastructures built on sulfate saline soil foundations in seasonal frozen regions are highly susceptible to saltfrost heave damage and salt corrosion. To address this issue, a method has been proposed utilizing a ternary blend of industrial solid waste materials - fly ash (FA), silica fume (SF), and brick powder (BP) - in conjunction with Portland cement (PC) for the solidification of sulfate saline soil. The feasibility of this solidification technique has been validated through a series of tests, including unconfined compressive strength tests, freeze-thaw cycle tests, salt leaching tests, and microstructural analysis. The results showed that: The unconfined compressive strength of the solidified saline soil at 56 days increased by up to 61.27 times compared to untreated saline soil. During the freeze-thaw cycles, the volume of salt-frost heave in the solidified saline soil was only 10.75% of that in untreated soil, with a reduction in salt-frost heave force by up to 90.94%. Furthermore, during the salt leaching process, the rate of salt migration in the solidified saline soil could be slowed by up to 4.15 times, while the total amount of salt leached was only 31.34% of that in untreated saline soil. Additionally, through the combined use of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS), it was discovered that the interactive synergistic effect of the solidifying agents in a SO42- rich environment facilitated the dissolution of Si-O and Al-O micro-lattices on the surface of the solidifying agent particles. This led to the extensive formation of C-(A)-S-H gels and AFt products, resulting in the transformation of the soil structure from dispersed to flocculated. The comprehensive test results indicate that the mechanical properties, frost resistance, and salt corrosion resistance of the solidified saline soil have significantly improved, with an optimal solidifying agent mixture ratio of 3% PC, 5% FA, 5% SF, and 6% BP. These findings can provide a reference for the solidification treatment of sulfate saline soil foundations in seasonal frozen regions.

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.

This study was conducted to determine whether Arbuscular Mycorrhizal Fungi (AMF) tolerance. The effects of mycorrhiza inoculation and salt on root and stem development, mineral nutrition, enzyme activity and lipid peroxidation levels in pepper (Capsicum annuum L.) plant was investigated. These effects were explored in pepper plants grown under greenhouse conditions in a randomized block design. Four different doses of salt (0, 50, 100 and 150 mM NaCl) were applied to the soil-filled pots, in addition to two different doses of mycorrhiza (0 and 100 spore mycorrhiza plant(-1)). It was found that the root and stem dry weights of pepper plants were greatly reduced in the non-mycorrhiza treatments, whereas the presence of mycorrhiza ameliorated these negative effects. N, P, K, Ca, Mg, S, Fe, Mn, Zn and Cu contents of AMF treated pepper were higher than nonmycorrhizal plants. Owing to the presence of AMF colonization, nutrient uptake was increased and, consequently, the nutrient contents of stem and root tissues of mycorrhizal inoculated plants were enhanced as well. On the other hand, the root and stem enzyme activity of plants increased with salinity. AMF inoculation decreased SOD, CAT, POD and AxPOD enzymes of plant and the MDA and H2O2 contents, indicating lower oxidative damage in the inoculated plants. Our results showed that AMF can contribute to protect plants against salinity by alleviating the salt induced oxidative stress and arranging the ion balance in plant via increasing nutrient uptake in saline soils.