Abstract:

To address the limitations of traditional microbially induced calcium carbonate precipitation (MICP) technology, including reliance on exogenous bacterial strains, high costs, and poor applicability to fine-grained loess, this study introduces environmentally friendly calcium lignosulfonate into the cement solution instead of the traditional calcium source, and optimizes concentrations of nutrient yeast extract (YE), NH₄Cl, urea-calcium source through single-factor and response surface Box-Behnken design experiments. By targeting the activation of indigenous urease-producing microorganisms for loess solidification, we systematically investigate the solidification mechanisms using bioactivity monitoring, unconfined compressive strength tests, calcium carbonate quantification, scanning electron microscope (SEM), X-ray diffraction (XRD) and high-throughput sequencing. The results show that: the optimized nutrient concentrations are 1.2 g/L for YE, 125 mmol/L for NH₄Cl and 0.8 mol/L for urea-calcium source; the urease activity, pH value, and viable bacterial count in the optimized group peak at 120 hours of reaction, significantly promoting calcium carbonate deposition; compared to the control group (untreated loess), the optimized group exhibits 131.42%, 194.32%, and 734.65% improvements in unconfined compressive strength, secant modulus, and calcium carbonate content, respectively; needle/rod-shaped calcium carbonate crystals formed during the reaction significantly enhance soil strength and compactness through filling-bridging-cementation effects; the relative abundance of Bacillales in the optimized group reaches 93%, with notable changes in microbial community diversity and composition. These findings provide a reference for the engineering application of targeted activation technology in loess regions.

Key words: microbially induced calcium carbonate precipitation, loess, calcium lignosulfonate, response surface methodology, microscopic mechanism