Effect of biochar on permeability of compacted soil and its microscopic mechanism

Biochar has attracted much attention in the field of geo-environmental engineering as a carbon-neutral alternative for soil amendment. In this study, the effects of biochar dosage, type, and particle size on the permeability and physical properties of compacted silty clay were investigated. And the prediction model of permeability coefficient of biochar-amended soil (BAS) was established. Based on the microscopy test results, the influence mechanism of biochar on the permeability of compacted soil was analyzed. Results revealed that adding different biochar types affected the consistency limits, specific gravity, and compaction curves of soil obviously. As the biochar content increased, the permeability coefficient of compacted BAS initially decreased before increasing. The permeability coefficient of compacted BAS with peanut-shell biochar was much higher than with other biochar types. Additionally, reducing the particle size of biochar can effectively decrease the permeability coefficient of BAS due to the pore-filling effect. Microscopy test results show that the permeability coefficient of BAS is affected by both the most probable pore size and the main-peak area of the pore-size distribution curve. Results suggest that controlling the biochar content at 5% and reducing the particle size of biochar are more beneficial to improve the impermeability of compacted BAS.