Influence of depolymerized polyethylene terephthalate (PET) polymer on shrinkage and water retention characteristics of biochar-treated soil

The adoption of sustainable materials, such as biochar and polymers, for soil amendment provides a low-carbon alternative to establishing hydraulic barriers in waste disposal facilities. However, the unsaturated behaviour of the amended liner remains unexplored. The soil water characteristic curve (SWCC) and the soil shrinkage characteristic curve (SSCC) are key to understanding seepage and unsaturated soil resilience, as they provide intrinsic hydraulic and mechanical information required to model and predict the behaviour of unsaturated soils. Therefore, this study provides comprehensive experimental research on the development of SWCC and SSCC for liner soil amended with different dosages of biochar (0%, 5%, 15%, and 25%) and bis(2-hydroxyethyl) terephthalate (BHET) polymer (0%, 2%, and 3%). Various tests, like compressive strength, volumetric shrinkage, water retention, electrical conductivity, and scanning electron microscopy (SEM), were conducted. Results showed that compressive strength, water retention capacity, and electrical conductivity of the samples increased with biochar and polymer content, while higher biochar dosage decreased volumetric shrinkage significantly, indicating improved performance of liner soil. Moreover, SEM analysis showed the formation of polymer connections and films at the interparticle contacts of biochar and soil. The results are promising and provide a framework for using biochar and the BHET polymer as landfill liner materials.