Stabilization of expansive soil using rice husk biochar and stimulation of soil-native bacteria: Mechanical and microstructural analysis

This research explores the stabilization of expansive subgrade soils with microbially induced calcite precipitation (MICP) and rice husk biochar (RHB). The research focuses on addressing the shrink-swell behavior of expansive soils through bio-stimulation with indigenous ureolytic bacteria and the addition of RHB, which enhances biogeochemical reactions due to its pozzolanic properties and high cation exchange capacity. Various concentrations of RHB and MICP treatment durations were tested. Optimal results were achieved with 2% RHB and a four-day MICP mellowing period, significantly improving the soil’s mechanical properties and reducing volume changes. The treatment decreased the free swell index by up to 98 %, linear shrinkage by 85 %, and swelling pressure by 93 %, while increasing unconfined compressive strength and split tensile strength by over 100 %. Enhancements were confirmed through SEM, FTIR analyses, and 16S metagenomic sequencing, demonstrating the efficacy of this dual-modality approach in enhancing stability and strength of expansive subgrade soil.