Mahdi Maleki Kakelar - Department of Chemical Engineering, University of Zanjan, Zanjan, Iran.
Mohsen Yavari - Department of Chemical Engineering, University of Zanjan, Zanjan, Iran.
Mohammad Reza Yousefi - Department of Chemical Engineering, University of Zanjan, Zanjan, Iran.
Amir Nimtaj - Department of Civil Engineering, Sahand University of Technology, Tabriz, Iran.

Background: Microbial induced carbonate precipitation (MICP) is a promising biological soil improvement method in geotechnical and geo-environmental engineering, which requires the recognition of the effects of various treatment methods on its applications. Methods: To improve the efficiency of MICP by urea hydrolysis bacteria, bio-grouting experiments were conducted at low urease activity using laboratory sand columns, and injection scenarios with different procedure steps were performed. The scenarios varied in the incubation time, fixation fluid, and number of the injection steps, and their efficiency was assessed using the unconfined compressive strength test. Results: The sand column experiments with multistep injection of bacteria and cementation solution showed that when the precipitated calcium carbonate content increased from ۷.۷% to ۱۸.۹%, the strength of the samples enhanced from ۰.۲۵ to ۱.۵۵ MPa, respectively. The precipitation conditions were influenced by the sand grain properties. The samples with diversified particle sizes had greater strength than those with uniform particle sizes. The multistep cementation solution injection at various concentrations had a significant clogging effect, thereby decreasing the sand column permeability. Conclusion: According to the laboratory results, this innovative technique could be potentially practical for engineering applications, such as liquefaction prevention, clogging, and sand in oil reservoir consolidation.

Soil consolidation, Microbial induced carbonate precipitation, Urease, Injection procedure, Clogging