Experimental study of solidifying sand using microbial-induced calcium carbonate precipitation

Sand solidification is to increase the strength of sands and decrease infiltration. Culture medium was used to cultivate bacteria, and growth properties were obtained in various conditions. The relationship between pH and Ca²⁺ concentration of effluent was analyzed to reveal the evolution of permeability and unconfined compressive strength. Effect of solidification was investigated through microstructure. The relationship between Ca²⁺ concentration and strength of samples was studied. 2 mL of the bacterial mother liquor was added to 100 mL of the culture medium. The results show that the sporosarcina pasteurii possess optimal growth conditions under a pH of 6 and vibration velocity of 150 rpm with 30℃ incubation. pH decreases during curing, and Ca²⁺ concentration increases. The 0.5 mol/L gel solution shows good curing effect and requires short time of the curing cycle. The gaps between sand particles are filled by calcium carbonate after curing, reducing sample permeability up to 3-4 order of magnitudes. The lower the rate of injection produces longer the curing time and the better the effect of solidification. The failure mode of all specimens is the brittle fracture mode. When the gelling solution is a mixture of urea and calcium acetate, the utilization ratio of Ca²⁺ is dramatically increased.