The salt concentration of the pore solution can alter the micro-pore and particle structure of soil, thereby affecting its engineering properties. To investigate the compression characteristics of marine soil under different salt concentrations, one-dimensional compression and SEM scanning tests were conducted on marine reconstituted clay from the Yellow Sea with varying NaCl concentrations (0-5%). The effects of NaCl concentration on the compression characteristics and microstructure of marine sedimentary clay were analyzed. The results indicate that: (1) Compressibility increases up to a NaCl concentration of 2.5%, after which it declines. At 2.5% NaCl threshold concentration, the coefficient of compression, compressibility index, and consolidation coefficient reach their peak values, and the response becomes more pronounced with increasing compression pressure. During the secondary compression stage, as pore water is expelled, the impact of NaCl concentration on compressibility diminishes, while the rebound characteristics remain unaffected by NaCl concentration; (2) SEM analysis reveals that at a NaCl threshold concentration of 2.5%, the pore fractal dimension, particle fractal dimension, pore anisotropy, and particle anisotropy reach their maximum values, with the most complex shape and pores and particles aligning in the same direction. When the concentration is less than 2.5%, the soil exhibits narrow pores and rounded particles upon compression. When the concentration exceeds 2.5%, the microstructure changes in the opposite direction, confirming the particle rearrangement mechanism driven by surface contact under moderate salinity. At the threshold concentration of 2.5%, a balance between electrostatic forces and attractive forces enables stable surface-to-surface contacts, maximizing compressibility. The findings of this study provide valuable references for the foundation design of marine geotechnical engineering in specific sea areas, thereby enhancing the safety and reliability of related projects.

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.

Due to climate change, human activities and natural disturbances in high-latitude permafrost and seasonally frozen areas are gradually increasing, attracting more attention from scholars. However, research primarily focuses on soil biology and chemistry in these regions, with limited exploration of their mechanical properties, especially compression properties. This study aims to evaluate the effects of gravel content and freeze-thaw (F-T) cycles on the compression properties of coarse-grained layered forest soil from northeast China's seasonally frozen regions, with the goal of predicting the soil's compressive changes under heavy mechanical loads. Specifically, using uniaxial confined compression tests (UCCT) on 252 disturbed soil samples (including two soil layers: AB and Bhs; hs ; six gravel contents; and seven F-T cycles), three characteristic compression coefficients-precompression stress (6pc), compression index (Cc),and swelling index (Cs)-were s )-were measured. Additionally, scanning electron microscopy (SEM) was used to analyze the mesostructure evolution of coarse-grained gravel-bearing soil. Volume changes of samples were measured after 15F-T cycles with varying gravel contents. Results indicate non-linear effects of gravel content and F-T cycles on 6pc. pc . Gravel content below 50% positively influences 6 pc , while content above 50% increases soil pore content, decreasing 6 pc . Cc c and Cs s exhibit an approximately negative correlation with gravel content and initially increase followed by a decrease with more F-T cycles. Moreover, the 6pcand pc and Ccof c of the AB layer are higher than those in the B hs layer, likely due to differences in clay and organic carbon contents. Notably, the observed trends differ from previous studies on other soil types such as farmland and paddy fields. This study fills a gap in understanding the compression characteristics of layered gravel-bearing forest soil in seasonally frozen regions, providing valuable insights for evaluating soil compression in both seasonally frozen and permafrost regions, and understanding mechanical vehicle- soil interactions. It also lays the theoretical groundwork and provides data support for constructing compression models of layered gravel-bearing forest soil.

A water conveyance open channel project in the northern Xinjiang region crosses a large area of collapsible loess. The mechanical properties of the collapsible loess have undergone severe degradation after years of exposure to rainfall, evaporation, and seasonal temperature fluctuations, making it highly susceptible to engineering phenomena such as channel foundation collapse and slope failure. To delve into the deterioration mechanism, direct shear, compression, and microscopic scanning tests were conducted on the collapsible loess under dry-wet & freeze-thaw cycles. The deterioration patterns of shear strength and compression properties, as well as their damage mechanisms, were analyzed at both macro and microscopic scales. The results of the study indicate (1) Straight shear test: with increasing the number of dry-wet-freeze-thaw cycles, the peak shear strength exhibits a three-stage trend: rapid decrease, decelerated rate of decrease, and eventual stabilization. The cohesion decreased exponentially, with the largest reduction occurring during the first cycle, and stabilizing after 5 cycles, reaching a degradation degree of 44.55%. The change in internal friction angle, which varied within 2.1 degrees, was less affected by the wet-dry-freeze-thaw cycles, with a maximum degradation of 7.04%. (2) Compression test: the compression curve can be divided into two stages of elastic deformation and elastic-plastic deformation according to the consolidation yield stress sigma(k), and sigma(k) shifts forward as the cycle times increase. The compression coefficient and compression index decreased exponentially or in a power function form with increasing cycle times, indicating reduced overall compressibility of the soil body. (3) Microstructure: through scanning electron microscope (SEM) analysis, under cycling, the number of large pores decreased while the number of medium and small pores increased, with the arrangement tending towards disorder. Large particles gradually transformed into medium and small particles, and their morphology tended to become rounded. Correlation analysis indicates that pore size and its angle are the main factors influencing shear strength. Pearson's correlation coefficient reveals that particle morphology and pore size have the greatest influence on compression indices.