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.

Addressing loess salinisation is a crucial element in preserving ecological stability and fostering sustainable development in the northwest Loess Plateau. To investigate the impacts of salt solution on the properties of loess, independently designed salt solution-loess dynamic cyclic erosion equipment was used to soak the loess. Then, numerous tests were performed to analyse the variability of the effects of salt solution concentrations (SSC) and type, as well as the duration of soaking time, on these physico-mechanical properties. The results demonstrated that after being soaked in two different types of salt solutions for 3 days, the shear strength index of loess preliminary decreased and then increased. The compressibility preliminary increased and then declined when the SSC increased. After a 7-day soaking period, the cohesion of the loess did not change considerably, whereas the internal friction angle increased in proportion to the SSC. The compression of loess tended to initially decrease, subsequently increase, and eventually decrease. Loess can be slowed down in its disintegration process by salt solution, and disintegration duration can be effectively shortened with a prolonged soaking time. Finally, it is examined the evolutionary process of the impact of salt solution on loess microstructure. Moreover, the exchange of clay minerals with iron and aluminium ions is proposed to be the key element determining the water-loess chemical interaction. This study may function as an insightful guide for preventing and treating salinised loess on the Loess Plateau of Northwest China, while also serving as a reference for similar areas worldwide.

To investigate the corrosion degradation law and service life of reinforced concrete in various salt solution environments, reinforced concrete specimens were semi-immersed in 3% Na2CO3(N3-0-0), 3% Na2CO3+3% NaCl (N3-Cl3-0) and 3% Na2CO3+3% NaCl+3% Na2SO4(N3-Cl3-S3)salt solutions. The electrochemical workstation was used for regular non-destructive testing, and the polarization curve and related electrochemical parameters were used as the macroscopic durability evaluation indicators, while microscopic analysis of steel bar corrosion products was performed in combination with SEM and EDS. In addition, the corrosion current density degradation model of GM (1,1) was established and compared with the modified GM (1,1)-Markov degradation model. The results showed that the prediction error of the GM (1,1)-Markov model was smaller and more accurate than that of GM (1,1). The reinforced concrete specimens in the N3-0-0, N3-Cl3-0 and N3-Cl3-S3 solutions reached the failure state in 3.08, 1.67, and 2.30 years, respectively, as predicted by the GM (1,1)-Markov model. According to ESM and EDS microscopic analysis of reinforcement, carbonate had no significant effect on reinforcement corrosion, chloride ions played a dominant role in reinforcement corrosion, and sulfate ion improved concrete's resistance to chloride ion corrosion. Based on GM (1,1)-Markov model, the failure and damage of reinforced concrete in saline soil areas can be quantitatively evaluated in the whole life cycle, which provides a theoretical basis for the early maintenance or reinforcing of reinforced concrete.

Different chemical solutions can significantly change the contact angle (CA) of soil, but few studies have studied the change rule and action mechanism of the CA from the mineral composition of soil essence. In unsaturated soil mechanics, the CA is an important parameter to calculate the wet suction between soil particles in unsaturated soil. When the chemical composition of the soil pore liquid changes, the CA will also change, which will affect the wet suction and other parameters, thus changing the macroscopic mechanical properties of the soil. In this study, the CA of air-solution-mineral phases with different solution components (pH, type and concentration of salt solution) of different minerals (quartz, orthoclase and plagioclase) were measured. The results show that the CAs of quartz, orthoclase and plagioclase all rise first and then drop with the rise of pH. The peak CAs are pH = 5, pH = 4 and pH = 3, respectively. Quartz, orthoclase and plagioclase all have valley values in different concentrations of NaCl and KCl solutions. In CaCl2 solution, only quartz has valley value, while orthoclase and plagioclase increase monotonously. Quartz in soil plays a main role in the influence of soil CA, followed by orthoclase and plagioclase. The CA of different minerals in different chemical solutions is mainly controlled by electric double layer interaction and functional groups interaction. In different salt solution environment, in addition to the above two effects, the mineral CA is also affected by the surface tension.

Understanding the shrinkage behavior of bentonite considering physicochemical effects is important to assess the efficiency of buffer barriers in environmental geotechnical engineering. In this paper, shrinkage experiments were conducted on Na-bentonite specimens prepared with salt solutions at various concentrations. NMR and SEM tests were conducted to study the moisture distribution and structural evolution of specimens during the evaporation of water. After sample saturation, the porosity decreases as the pore water salinity increases due to the decreasing swelling deformation with pore water concentration during the saturation process. During drying, the shrinkage deformation of compacted bentonite is anisotropic, with larger axial strains than radial strains. At the fully dried state, the bentonite specimen prepared with distilled water is the densest due to the least crystalline salts in the specimen. At the microscale, as pore water salinity increases, pore water is distributed to smaller pores, and the microstructure is more aggregated. The saline effect on water retention and distribution is weakened as pore water evaporates, originating from physicochemical effects. The structure is also more aggregated after evaporation of pore water. Theoretically, the shrinkage behavior of Na-bentonite considering the influence of water salinity is well described from the perspective of an effective stress-based constitutive relationship.