Effects of biochar on hydraulic conductivity of compacted kaolin clay

Highlights: • Effects of biochar on permeability of highly compacted soil was first reported. • Biochar application increased saturated permeability of compacted clay. • Adding 20% biochar increased saturated permeability by one order of magnitude. • Biochar application increased the overall pore volume of clay. Compacted clay is widely used as capillary barriers in landfill final cover system. Recently, biochar amended clay (BAC) has been proposed as a sustainable alternative cover material. However, the effects of biochar on saturated hydraulic conductivity (k_sat) of clay with high degree of compaction is not yet understood. The present study aims to investigate the effects of biochar on k_sat of compacted kaolin clay. Soil specimens were prepared by amending kaolin clay with biochar derived from peanut-shell at 0, 5 and 20% (w/w). The k_sat of soil specimens was measured using a flexible water permeameter. The effects of biochar on the microstructure of the compacted clay was also investigated using MIP. Adding 5% and 20% of biochar increased the k_sat of compacted kaolin clay from 1.2 × 10⁻⁹ to 2.1 × 10⁻⁹ and 1.3 × 10⁻⁸ ms^-1, respectively. The increase in k_sat of clay was due to the shift in pore size distribution of compacted biochar-amended clay (BAC). MIP results revealed that adding 20% of biochar shifted the dominant pore diameter of clay from 0.01–0.1 μm (meso– and macropores) to 0.1–4 μm (macropores). Results reported in this communication revealed that biochar application increased the k_sat of compacted clay, and the increment was positively correlated to the biochar percentage.