Exploring the use of Eco-Engineered Solution for Minimizing Deformation of Saline Soils: Newly Established SWCCs and SSCCs of Biochar-Amended Cohesive Soils

This study investigates the effects of biochar amendments on the physical and hydromechanical properties of cohesive soils (kaolin-like soil and bentonite) under varying porewater salinities. The research evaluates how biochar content (0%, 5%, and 10%) and NaCl concentrations (0%, 1%, 5%, and 10%) influence soil–water characteristic curves (SWCCs), shrinkage behavior, and Atterberg limits. Results show biochar amendments reduce the liquid limit of kaolin-like soil by 54–95% and bentonite by 2–45% under increasing salinity, while increasing shrinkage limits by up to 31% in bentonite. Biochar significantly mitigates salinity-induced volumetric shrinkage (29.5% reduction in kaolin-like soil) and enhances water retention capacity at high suction (> 65% saturation). These improvements demonstrate direct relevance to geotechnical applications: for landfill liners, biochar minimizes desiccation cracking under saline leachate exposure; and for slope stability, enhanced water retention maintains soil suction during rainfall events, delaying pore pressure buildup. Biochar’s modification of soil fabric supports its potential as an eco-engineered solution in saline environments, though long-term field validation is recommended.