Effect of biochar on water permeability and cracking behaviour of granite residual soil

The long-term stability of compacted soil liners in landfill barriers depends on maintaining extremely low water permeability and resisting cracking induced by wet–dry cycles. This study investigated the potential of biochar as an amendment to improve the characteristics of granite residual soil, a commonly used material in barrier construction. Laboratory experiments were conducted on soil-biochar blends at different compaction levels (60% and 80%) and biochar concentrations (0%, 5%, 10%, and 20% by mass). The results showed that biochar addition gradually reduced saturated soil water permeability by up to one order of magnitude. Alterations in pore size distributions indicated a shift towards smaller diameters, suggesting the role of biochar in blocking macropores. The crack experiments demonstrated that biochar lowered surface crack ratios by 75% compared with untreated soil. Moreover, biochar affected the drying behaviour of residual granite soils, prolonging the evaporation period from 10 to 12 days and increasing the residual moisture content from 5% to 8%. In conclusion, biochar exhibited the potential to diminish soil permeability coefficients and alleviate soil cracking, providing valuable insights for enhancing the long-term performance of landfill containment barriers.