Soil bio-cementation using an improved 2-step injection method

To improve the uniformity of calcium carbonate distribution in soil treated by microbially induced carbonate precipitation (MICP), an improved biological injection method, namely “2-step method”, was proposed. This method was achieved by first injecting a certain volume of pure bacterial suspension into soil, followed by injecting the remaining pore volume with the mixed bacterial suspension, which was prepared by mixing pure bacterial suspension and fixation solution containing CaCl2. The method was validated through various physical and mechanical properties of the bio-cemented sand, including the bacterial adsorption efficiency, calcium carbonate content and distribution, and unconfined compressive strength. The results showed that the proposed 2-step method could effectively improve the bacterial adsorption, calcium carbonate content, and strength of bio-cemented sand. The prepared bio-cemented sand had relatively uniform distribution of calcium carbonate and higher strength. The optimal volume ratio between the mixed bacterial suspension and pure bacterial suspension for the 2-step method was 0.6:0.4.