Shear Strength Improvement of Silty Soil Via Microbial-Induced Calcite Precipitation for Wind Erosion Mitigation

Abstract

The low shear strength of silty soils in arid and semi-arid regions contributes significantly to their vulnerability to wind erosion. This study evaluates the effect of Microbial-Induced Calcite Precipitation (MICP) using Bacillus thuringiensis on the shear strength parameters of silty soils from Northwestern Nigeria. Laboratory tests, including direct shear testing, were conducted on untreated and MICP-treated soil samples to assess changes in cohesion and internal friction angle. Results show that bio-treatment significantly alters the shear strength behavior of silty sand. Cohesion decreased from 38.21 kN/m² (control) to a minimum of 25.11 kN/m², indicating a transition from clay-like behavior to a more stable granular structure. Conversely, the angle of internal friction increased from 28.2° to a peak of 42.0°, while shear strength improved markedly from 26.3 kN/m² to 82.39 kN/m² at the optimum treatment condition of 1.8 × 10⁹ cells/ml and 0.75 M. The improvements are attributed to calcium carbonate precipitation via microbial-induced calcite precipitation (MICP), which enhances interparticle bonding, increases surface roughness, and reduces pore spaces. Statistical analysis using two-way ANOVA confirmed that both bacterial density and reagent concentration have significant effects (p < 0.05) on all measured parameters.
Microstructural analysis (SEM) revealed a transition from a loose, porous structure to a dense, cemented matrix, while XRD analysis confirmed the presence of calcite as the dominant cementing agent. The findings demonstrate the potential of Bt-based MICP as an effective and sustainable technique for improving the mechanical properties and erosion resistance of silty sand.