Impact of biochar produced from hardwood of mesquite on the hydraulic and physical properties of compacted soils for potential application in engineered structures

Biochar is a carbon-rich porous material obtained after pyrolysis of labile biomass in oxygen deficit condition. The production of biochar from invasive weed mesquite biomass could be beneficial of managing waste and preventing the emission of CO2 gas by open combustion, and amending them in soil could sequester carbon in soil and improve soil properties. The effect of biochar on soil hydraulic properties was studied for loose soils suitable for agriculture. However, soils in engineered/bioengineered structures often compacted for achieving structural stability. Moreover, biochar of different feedstock poses variable effect on soil hydro-physical properties and a combined study of hydro-physical properties of soil amended with mesquite biochar lacks in the existing literature. In the present study, the effect of mesquite biochar on the hydro-physical properties, such as Atterberg limits, compaction characteristics, infiltration rate (I) and saturated hydraulic conductivity (Ksat) of compacted silty sand and pure sand is investigated for potential application in bioengineered structures. The results show that the amendment of 5%, 10% and 15% biochar increased the atterberg limits and water absorption capacity while decreased the plasticity index, specific gravity, dry density and I of the soils. Moreover, the Ksat is found to be increased in silty sand whereas decreased in pure sand due to biochar amended. These changes in soil properties are attributed to the altered physical properties, mainly porosity (inter-pores) of the soil by the biochar amendment and the presence of chemical compound in biochar surface. The reduced I and Ksat in the present study suggest application of biochar amended soil in bioengineered structures; however, further field-scale studies are needed before implication.