Bio-stabilisation of granite residual soil using indigenous microorganisms

Area of Science:

• Geotechnical Engineering
• Environmental Science
• Microbiology

Background:

• Granite residual soil has poor mechanical properties, causing slope instability and settlement.
• Microbial solidification is a sustainable method to improve soil properties.

Purpose of the Study:

• To enhance the strength of granite residual soil using urease-producing Bacillus species.
• To investigate the effect of cementing solution concentration on soil improvement.

Main Methods:

• Extraction of three Bacillus species (B. velezensis, B. subtilis, B. tequilensis) from local soil.
• Conducting solidification experiments with varying cementing solution concentrations.
• Analyzing soil properties using shear strength tests, SEM, and XRD.

Main Results:

• All three bacterial strains significantly improved soil shear strength.
• Optimal improvement occurred at a 2 mol/L cementing solution concentration.
• Bacillus subtilis maximized internal friction angle (+145.32%), while Bacillus tequilensis maximized cohesion (+316.19%).
• B. tequilensis and B. velezensis performed better in higher concentrations.
• SEM and XRD confirmed calcium carbonate precipitation binding soil particles.

Conclusions:

• Microbial solidification effectively enhances granite residual soil's mechanical properties.
• The choice of Bacillus species impacts the specific improvement (friction angle vs. cohesion).
• This method offers an eco-friendly and cost-effective solution for engineering applications.