Multi-scale analysis of the mechanism of microbially induced calcium carbonate precipitation consolidation loess.

Abstract

Microbial-induced calcium carbonate precipitation (MICP) treatment of consolidated loess has the advantages of high efficiency and environmental protection. In this study, changes in the microscopic pore structure of loess before and after MICP treatment were compared and quantified, combined with test results at different scales, to better understand the mechanisms of MICP-consolidated loess. The unconfined compressive strength (UCS) of MICP-consolidated loess is significantly increased, and the stress-strain curve indicates improved strength and stability of the loess. X-ray diffraction (XRD) test results show that the signal strength of calcium carbonate crystals is significantly enhanced after loess consolidation. The microstructure of the loess was determined by scanning electron microscopy (SEM). The loess SEM microstructure images are quantitatively analyzed using comprehensive image processing methods (including gamma adjustment, grayscale threshold selection, median processing). The changes in microscopic pore area and average pore sizes (Feret diameter) of the loess before and after consolidation are described. More than 95% of the pores consist of pores with a pore area of less than 100 μm2 and an average pore size of less than 20μm. The total percentage of pore numbers with pore areas of 100-200 and 200-1000 μm2 decreased by 1.15% after MICP consolidation, while those with 0-1 and 1-100 μm2 increased. The percentage of pore numbers with an average pore size greater than 20μm decreased by 0.93%, while the 0-1, 1-10, and 10-20μm increased. Particle size distributions revealed a significant increase in particle size after MICP consolidation, with an increase of 89μm in D50.