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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. [ABSTRACT FROM AUTHOR]

As a novel, nature-like biomineralization process, microbially induced carbonate precipitation (MICP) has been successfully applied in soil stabilization. This study investigated the influence of biomass injected on the geotechnical performance of MICP treated sand. Grouting rate and particle sizes were also taken into account. The results showed that the injection of 1.0 or 1.2 PV biological solution achieved the most effective and uniform reinforcement of soil, depending on the grouting rate. Excessive biomass (1.5 PV biological solution) failed to promote the further improvement of the engineering performance of MICP reinforced sand. The relationship between strength and calcium carbonate content and SEM results indicated that for the small CaCO3 content, the improvement of soil strength is mainly controlled by the content of calcium carbonate rather than its distribution. When the amount of carbonate precipitation is sufficient to form bonding between soil particles, the distribution of calcium carbonate has a greater influence on mechanical properties. The strength of biocemented soil measured by layering indicated that the insufficient amount of biological solution (such as 0.5 PV biological solution) greatly weakened the reinforcement effect of soil away from the grouting port, and thus led to larger strength variability. Increasing the grouting rate of biological solution improved the uniformity of reinforcement, especially for medium grain sand. The results of this study provide a guide to facilitate the application of microorganisms in the engineering application practice of MICP. [ABSTRACT FROM AUTHOR]