Reduction of Brittleness of Fine Sandy Soil Biocemented by Microbial-Induced Calcite Precipitation

Microbial-induced calcite precipitation (MICP) is a sustainable soil improvement technology widely used in the biogeotechnical field. However, the high brittleness of calcium bonding in biomineralization has limited the application of MICP. The objective of this study was to find an efficient microbial treatment that reduces the brittleness of traditional MICP. An experiment was conducted in three stages in 2016 (MICP-B), 2018 (MICP-C), and 2020 (MICP-E). Unconfined compressive strength and triaxial compression tests were performed. Residual strength and failure and residual strain increased, the post-peak stress drop rate decreased, and the failure pattern changed from vertical through crack to oblique crack. Brittleness was substantially reduced. The cement between the sand particles was analyzed by SEM, EDS, and IR spectroscopy. It consisted of calcium carbonate plus glial extracellular polysaccharides and was mainly responsible for reducing MICP brittleness. The final MICP-E test was based on a highly effective microbial strain screened from the soil. This bacterium had good brittleness reduction efficacy and has excellent practical potential for MICP biocementation. The experimental results of the study provide theoretical and empirical foundations for brittleness reduction in MICP-treated soils. Ameliorated biocementation technology could be used for the microbial reinforcement of mechanically unstable soils.