Effects of different chloride salts on granite residual soil: properties and water–soil chemical interaction mechanisms

Purpose Soil salinization is a common concern; the physical and mechanical properties of soil play an important role in the process of salinization for the stability of land sites. This study aims to clarify the different chlorine salts on the critical threshold of soil physical and mechanical properties under a flowing state and investigate the mechanism. Method In this study, using the self-developed water–soil chemical circulation system, the granite residual soil was soaked in NaCl and CaCl 2 solutions of different concentrations for 7/14 days, and then the soil’s physical, mechanical and microscopic properties were studied. Results The results reveal that the decrease in liquid limit and plastic limit of soil samples soaked in CaCl 2 solution is greater than that of NaCl solution. When the two chloride solutions were soaked for 7 days, the soil compressibility showed a trend of “first increasing and then decreasing” with the raise of salt concentration, and the shear strength indexes displayed a trend of “first decreasing and then increasing.” After soaking for 14 days, the compressibility of soil samples exhibited a trend of “first decreasing, then increasing, and finally decreasing” with the increase of salt concentration, while the shear strength indexes of soil samples remained basically unchanged, but the internal friction angle of soil samples tended to increase overall with the increase of salt concentration. Finally, the influence mechanism of soil physical and mechanical properties change is explained from the perspective of microstructure, and it is proposed that iron aluminum cement and clay minerals are the key substances that determine the water–soil chemical interaction. Conclusion The findings can provide some guidance for the sustainable development of coastal saline land areas.