Microbial induced calcite precipitation (MICP) is one of the potential methods for improvement of engineering properties of soil. A laboratory study was conducted to investigate the influence of various factors on engineering properties of MICP-treated soil catalyzed by bacteria and ureases. Some of these factors include bacteria concentration, urease concentration, cementation media concentration, reaction time, type of sand, and curing conditions. The experiments of MICP catalyzed by Sporosarcina pasteurii and urease were conducted in similar conditions. The soil samples were prepared with full contact flexible molds (FCFMs). The results of unconfined compression test show that the experimental factors (bacteria/urease concentration, cementation media concentration, reaction time, and type of sand) have a significant impact on the MICP process and engineering properties of sand treated by both bacteria and urease, whereas the curing conditions has a small effect. The unconfined compression strength (approximately 1.76–2.04 MPa) of bacteria treated samples is almost $5\times$ (approximately 0.33–0.43 MPa) that of urease treated samples under similar urease activity. The MICP process catalyzed by bacteria is much more effective than the process catalyzed by urease in terms of engineering soil properties improvement.

Microbial-induced calcite precipitation (MICP) is one of the environmentally friendly ways to improve engineering properties of sandy soil. A laboratory study was conducted to investigate the effect of randomly distributed discrete fiber on the mechanical properties of MICP-treated soil and to discover the corresponding mechanisms. Specimens were prepared at four different fiber ratios (0.1, 0.2, 0.3, and 0.4% by weight of sand). MICP were catalyzed by Sporosarcina pasteurii at the concentration of 4.3×107 cells/mL. MICP-treated sand samples were prepared using full-contact flexible molds. The results showed that remarkable improvements in shear strength, ductility, and failure strain were achieved with fiber addition in the MICP-treated sand. The unconfined compression strength (UCS) and shear strength increased gradually with an increase in fiber content up to a fiber content of 0.3%. The optimum fiber content in the MICP-treated sand was found to be 0.2–0.3%. The UCS of MICP-treated sand at th...

Microbially induced calcite precipitation (MICP) is a sustainable biological ground improvement technology that is capable of improving the engineering properties of soil. A laboratory study was conducted to investigate the influence of some key environmental parameters on the long-term engineering performance of MICP-treated sandy soil, including wet-dry cycles, freeze-thaw cycles, and acid rain conditions, and to study the effect of enhancement through fiber reinforcement and multiple MICP treatments. Experimental results indicated that durability of MICP-treated soil was weak in wet-dry cycles, freeze-thaw cycles, and acid rain conditions. The unconfined compression strength (UCS) of MICP-treated soil had nearly 80% reduction after one wet-dry cycle, 58% reduction after 15 freeze-thaw cycles, and 83% reduction after 15 days immersed in acid rain solution with the pH of 3.5. Fiber reinforcement mainly enhanced the ductility of MICP-treated samples. The failure strain of fiber-reinforced samples reached 1.6% compared with unreinforced samples of 0.4% after 5 wet-dry cycles. Multiple treatments enhanced the durability of MICP-treated samples. The UCS of multiple MICP-treated samples had no significant reduction after wet-dry and freeze-thaw cycles. For quadruple MICP-treated samples, a 51.9% UCS still remained after 15 days immersed in acid rain solution with the pH of 3.5.