Multiple-phase enzyme-induced carbonate precipitation (EICP) method for soil improvement

Enzyme-induced carbonate precipitation (EICP) is a potential method to improve the mechanical properties of granular soil. The one-phase premixed percolation method using purified urease enzyme is widely adopted for in-situ EICP treatment currently, but it is expensive and uses a relatively large amount of urease. This paper proposes a multiple-phase method consisting of a percolation of premixed soybean crude urease and cementation solution followed by several percolations of cementation solution in one cycle of biocementation. The utilizing rate of urease was increased by at least four times for the production of precipitated carbonate compared with the one-phase method. The proposed method also weakened the clogging of carbonate precipitation, thus bringing out a relatively uniform EICP treatment. After four cycles of biocementation (each cycle included five applications of cementation solution), the unconfined compressive strength of EICP-treated ASTM C778-graded sand exceeded 10 MPa with a CaCO3 content of ~20%.