A comparative study on strength behavior of microbially induced calcite precipitation and fibre reinforced soil

Abstract

Microbially induced calcite precipitation (MICP) is increasingly recognized as a sustainable and bio-based alternative to conventional soil stabilization techniques such as cement or lime treatment. However, the durability of MICP-treated soil under cyclic environmental stresses and the potential of integrating natural fibres for enhanced performance remain underexplored. This thesis addresses these gaps by investigating the combined effect of MICP and natural fibres, specifically bamboo and vetiver, on the strength, permeability, and freeze-thaw (F-T) durability of poorly graded sandy-silt soil. Results demonstrated that bamboo fibre-MICP treatment improved soil shear strength nearly threefold (32 kPa to 99 kPa) and increased the soaked California Bearing Ratio from 5% to 13.5%, meeting requirements for pavement subgrades. Permeability was significantly reduced (6.42 × 10-3 to 4.0 × 10-3 cm/s) as calcite filled pore spaces. A key novelty of this work lies in its F-T testing: after 10 cycles, bamboo fibre-MICP soil retained 80% of its original strength, whereas untreated soil lost 50%, demonstrating enhanced durability in cold climates. Bamboo outperformed vetiver due to its higher tensile strength and calcium content, which facilitated greater calcite bonding. The key contribution of this research lies in establishing a framework for integrating bio-mediated calcification with natural fibre reinforcement, demonstrating not only improved geomechanical behaviour but also enhanced durability under harsh environmental conditions. Moreover, the findings provide new insights into eco-friendly ground improvement, with strong implications for infrastructure development in cold and high-altitude regions. Future work is recommended on fibre uniformity, microbial adaptability, and field-scale validation. newline