Stabilization Behavior of Sepaku Clay Shale Using Bacillus Subtilis

Abstract

Clay shale in the Sepaku region exhibits geotechnical vulnerability (slaking, cohesion loss, saturation expansion) that threatens slope stability and road foundations. Conventional stabilization methods (cement/lime) cause high environmental impact; therefore, this study explores a biotechnical approach, microbially induced carbonate precipitation (MICP), to improve the mechanical properties of clay shale with a lower environmental impact. MICP utilizes microbial activity (urease enzyme or alternative pathways) to trigger CaCO₃ precipitation that binds soil particles and fills pores; the mechanism and controlling factors (cell density, [urea], Ca source, pH, permeability) have been documented in recent literature.  This study tested the effectiveness of Bacillus subtilis (reference strain and/or characterized local isolates) as a MICP agent on Sepaku clay shale samples. The experimental design included bench-scale (mixing) and injection column (multi-cycle, low rate) experiments with variations in cell density and reagent concentration; Pre and post treatment evaluations included mechanical tests (UCS, direct shear, slake durability, permeability) and mineralogical/microstructural characterization using XRD (identification & quantification of CaCO₃ phase), XRF (changes in Ca/CaO content) and SEM/EDS (morphology & precipitation distribution). Effluent data (NH⁴⁺, pH, conductivity) were monitored to assess environmental impact. It is expected that the optimized Bacillus subtilis treatment will result in localized CaCO₃ precipitation that correlates positively with increased strength and resistance to slaking in Sepaku clay shale; convergent evidence from XRD–XRF–SEM will reinforce the claim of a biomineralization mechanism. The results of this study are expected to provide an applicable protocol for stabilizing low-permeability clay shale and guidelines for mitigating NH⁴⁺ runoff, contributing significantly to more environmentally friendly soil improvement solutions in the Sepaku District.