Harnessing Native Ureolytic Bacteria from the Hilly Region for Soil Strength Improvement: Investigating the Effect of Urea-Cacl2 Concentration

Mitigating geo-hazards such as soil erosion and landslides is a great challenge in hilly regions worldwide.The biocementation of soil using native ureolytic bacteria is an environmentally friendly approach to improve the strength of hilly region soil.This study presents the biological investigations and soil improvement potential of the urease-producing bacteria isolated from the slope failure region of Uttarakhand, India.To this end, the bio-mineralization test and quantitative urease assay were used to screen potential ureolytic bacteria among the six bacterial strains isolated from the soil sample.Out of them, three bacterial strains showed high pH values (8.45 -8.78) and CaCO3 precipitation (160.96-175.30mg/10ml) in the biomineralization test and high urease activity values (1912.7 -3494.8µM/ml).The 16S rRNA gene sequencing analysis of the outperforming bacterial strain revealed that the strain belongs to Cytobacillus sp.Later, the effect of different urea-CaCl2 concentrations on the soil improvement potential was evaluated through unconfined compressive strength tests, calcium carbonate precipitation in soil, pH of outflow, and dry density values of the MICP-treated soil using outperforming bacterial strain.A maximum unconfined compressive strength of 1 MPa was achieved using 500 mM urea-CaCl2 concentration, and the trend of test results matched with pH and dry density values.The FESEM images of soil samples confirmed that the high unconfined compressive strength is due to a high amount of rhombohedral-shaped calcium carbonate crystals at the particle contact and soil surface.