The Spatial Distribution of Microbially Induced Carbonate Precipitation in Sand Column with Different Grouting Strategies

For ground improvement via microbially induced carbonate precipitation (MICP), the spatial distribution of biocementation considerably affects the mechanical performance of soil. This study systematically assessed the CaCO3 spatial distribution in sand columns with various grouting strategies. CaCO3 dispersion along the radial and vertical directions was quantitatively evaluated. Furthermore, a series of biochemical monitoring experiments was conducted to investigate the MICP process in sand. The results indicated that the reversed and downward chemical solution grouting and high rates of microbial grouting all promoted CaCO3 vertical uniformity. Moreover, the grouting strategy slightly affected the dispersion degree of radially distributed CaCO3. The variation coefficient basically ranged from 0.1 to 0.3. However, the variation coefficient for radially distributed CaCO3 along the vertical direction was significantly affected by the chemical grouting direction. The biochemical monitoring results indicated that 38% Ca2+ was even consumed near the chemical solution outlet in the chemical solution grouting process. The initial Ca2+ concentration during the intermittent period gradually decreased along the chemical solution grouting direction. The CaCO3 vertical distribution was controlled by a combination of the total MICP reaction time, biomass, and Ca2+ availability in the intermittent phase. Different CaCO3 distributions resulted in each grouting strategy exhibiting specific applicable engineering requirements. Furthermore, the carbon footprint was preliminarily evaluated. The results in this study provide references for the selection of grouting strategies for the MICP technique in engineering applications.