Holistic Evaluation of MICP–Nano-Silica Stabilization in Expansive Soils: Mechanical, Environmental, and Sensitivity Perspectives

Soil stabilization using Microbial Induced Calcite Precipitation (MICP) offers an eco-friendly alternative to chemical binders, yet optimization and sustainability evaluation remain critical. This study integrates MICP with amorphous nano-silica to improve the mechanical and environmental performance of expansive soils through a Central Composite Design (CCD)–based Response Surface Methodology (RSM) framework, coupled with Life Cycle Assessment (LCA), sensitivity, and cost analyses. Experiments were conducted on sandy clay, silty clay, and clayey sand using Bacillus subtilis (chosen for its strong urease activity and adaptability) at concentrations of 101–107 CFU/mL, cementation solution molarities of 0.25–2.0 M, and nano-silica dosages of 0–2.5%. At the optimized condition (106 CFU/mL, 1.5 M, 2% nano-silica), unconfined compressive strength increased by 56%, CBR by 46%, and maximum dry density by 16%, while optimum moisture content decreased by 30%. LCA results showed 28% lower global warming potential than lime treatment, and the efficiency index improved by 35%, with 22% lower cost. Sensitivity analysis identified bacterial concentration as the most influential variable, followed by nano-silica and cementation molarity. Sandy clay exhibited the best synergy of strength, cost, and sustainability. Although the findings are based on laboratory conditions, this integrated MICP–nano-silica–LCA approach establishes a data-driven foundation for eco-efficient field-scale soil stabilization.