Experimental study and model prediction of the influence of different factors on the mechanical properties of saline clay
Authors: Cheng Hui , Zhang Lingkai , Shi Chong , Fan Pei Pei 
Published: December 2024

Water conveyance open channels in cold and arid regions pass through several saline-alkali soil areas. Canal water leakage exacerbates the salt expansion traits of such soil, damaging canal slope lining structures. To investigate saline clay's mechanical property variations, this study conducts indoor tests, including direct shear, compression, permeation, and scanning electron microscopy analysis on soil samples from typical sites. The study aims to elucidate the impact of various factors on saline clay's mechanical properties from a macro-micro perspective and unveil its physical mechanisms. A prediction model is formulated and validated. Findings indicate: (1) Cohesion in direct shear tests exhibits a linear negative correlation with water content, a positive correlation with dry density, and initially decreases with salt content until 2%, after which it increases. The internal friction angle initially rises and then falls with increasing water content, reaching a peak at optimal water content, and gradually increases with dry density while exhibiting an initial decrease followed by an increase in salt content, stabilizing thereafter. Water content, dry density, or salt content chiefly affect cohesion by influencing electrostatic attraction, van der Waals force, particle cementation, and valence bonds at particle contact points. (2) Compression tests reveal a linear positive correlation between compression coefficient and water content, a negative correlation with dry density, and a stage-wise linear correlation with salt content, peaking at 2%. The compression index declines with increasing water content and dry density, following a trend similar to that of compression coefficient with salt content increase. The rebound index shows a linear negative correlation with water content and dry density, transitioning from a negative to a positive correlation at 2% salt content. Scanning electron microscopy analysis indicates particle flattening and increased aggregation with rising consolidation pressure, reducing compressibility. Large pores and three-dimensional porosity have the greatest influence on soil compressibility. (3) Permeability tests reveal an exponential negative correlation between permeability coefficient and dry density. As dry density rises, particle arrangement becomes denser, decreasing pore quantity, with small pores disproportionately impacting the permeability coefficient. Salinity increase initially boosts the permeability coefficient before a decline. The boundary point of 2% salt content divides salt ions' effect from promoting free water flow to blocking seepage channels, with micropores' pro-portion being the primary influencing factor. (4) Employing statistical theory and machine learning algorithms, dry density, water content, and salinity are used to predict mechanical index values. The improved PSO-SVR model exhibits high accuracy and general applicability. These findings offer insights for the construction and upkeep of open channel projects in arid regions.