Review of Microbial Grouting Technology: Experimental Studies, Theoretical Models and Engineering Applications

Abstract

Microbial grouting technology based on microbially induced calcite precipitation (MICP) is a new soil improvement method. This technique involves injecting bacteria and a cementation solution into soil pores to generate CaCO3 precipitation, thereby enhancing soil strength. Studies on microbial grouting from the aspects of experimental studies, theoretical models and engineering applications were extensively reviewed. Factors such as grouting methods, grouting rate, cementation solution concentration, and pH significantly influence the size and distribution of CaCO3. The three-phase grouting method enhances bacterial adsorption and soil strength. The higher grouting rate (grouting rate greater than reaction rate) and low pH (pH is not lower than 4) facilitate the uniform distribution of CaCO3. The size of CaCO3 and the soil strength increase with increasing cementation solution concentration. The existing models were established based on equilibrium flow, which overlooks the reduction of solute migration distance caused by the non-uniformity of the medium. Micro-structural analysis shows that CaCO3 precipitation between adjacent soil particles acts as a matrix supporting to increase soil strength. Microbial grouting technology can employ CaCO3 precipitation to seal wellbore cracks for CO2 storage and cement soil particles for slope stability and foundation improvement. Finally, the challenges encountered in microbial grouting technology were discussed.