Study on mechanical properties and microscopic mechanism of MICP-modified expansive soil

Expansive soils, characterised by significant hydrophilicity and water swelling properties, frequently cause foundation expansion, cracking, and reduced bearing capacity and strength. This study used microbially induced calcium carbonate precipitation (MICP) technology to improve expansive soils’ swelling and strength characteristics. The expansive soil was treated by adjusting the cementing solution concentration (0.5–1.5 mol/l). The physical and mechanical indices and fracture development of soil samples before and after improvement were compared with evaluate the improvement effect. Meanwhile, the action mechanism of MICP technology was explored from a microscopic point of view. It was found that 1 mol/l cementing solution concentration had the most significant effect on the swelling inhibition of expansive soil. Under this condition, the soil samples’ unconfined compressive strength, shear strength, and calcium carbonate (CaCO3) generation reached the highest values. Moreover, its fracture development was also significantly improved. Microanalysis showed that calcium carbonate crystals generated by the MICP technique formed attachments on the surface of soil particles, effectively filling the soil pores and cementing the soil particles. The large pores were filled into small pores, improving the expanded soil microstructure. This study provides an effective solution for improving expansive soils with important engineering application value significance.