Gas permeability in soil amended with biochar at different compaction states

Biochar amended soil (BAS) is widely studied to apply in green infrastructure, such as landfills and slopes. Presence of biochar improved soil hydraulic properties (e.g. water retention ability) in previous studies, while influence of biochar on gas permeability (k_g) under different compaction states is not clear yet. The main objective of this study is to investigate the k_g of BAS under different soil compaction conditions. The soil selected for investigation was poorly graded sand. BAS was compacted in an in-house built 1-D column set up under three different soil density (65 %, 80 % and 95% degree of compaction) were considered in mixtures with 0% and 10% biochar content. The tests were carried out in a greenhouse at Shantou University. In tests, soil column was designed and subjected to drying-wetting cycles, during which soil suction, moisture content and k_g were measured. Results showed that BAS (i.e. minimum water content 37.2% and 22.1%) had better water retention performance than bare soil (i.e. minimum water content 20.2% and 19.5%) at compaction conditions (65% and 80% degree of compaction). However, when the degree of compaction increased to 95%, bare soil and BAS shows similar water retention characteristic (i.e. minimum water content 15.7% and 15.9% respectively). The addition of biochar could decrease k_g as compared with that of the bare soil, meanwhile, in the lower suction range, k_g decreased with an increase of compaction (i.e. k_g65%>k_g80%>k_g95%).