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 ${\mathrm{CaCO}}_3$ spatial distribution in sand columns with various grouting strategies. ${\mathrm{CaCO}}_3$ 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 ${\mathrm{CaCO}}_3$ vertical uniformity. Moreover, the grouting strategy slightly affected the dispersion degree of radially distributed ${\mathrm{CaCO}}_3$. The variation coefficient basically ranged from 0.1 to 0.3. However, the variation coefficient for radially distributed ${\mathrm{CaCO}}_3$ along the vertical direction was significantly affected by the chemical grouting direction. The biochemical monitoring results indicated that 38% ${\mathrm{Ca}}^{2+}$ was even consumed near the chemical solution outlet in the chemical solution grouting process. The initial ${\mathrm{Ca}}^{2+}$ concentration during the intermittent period gradually decreased along the chemical solution grouting direction. The ${\mathrm{CaCO}}_3$ vertical distribution was controlled by a combination of the total MICP reaction time, biomass, and ${\mathrm{Ca}}^{2+}$ availability in the intermittent phase. Different ${\mathrm{CaCO}}_3$ 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.