Comparison of soil improvement methods using crude soybean enzyme, bacterial enzyme or bacteria-induced carbonate precipitation

Either microbial or enzyme-induced carbonate precipitation (MICP or EICP) has emerged to provide an alternative to cement-based ground improvement methods. For EICP, either plant urease or bacterial enzyme can be used. The effect of treatments can differ when different methods are adopted. In this study, the soil improvement effects for three methods were compared. The newly developed one-phase-low-pH method was adopted for both the MICP and EICP processes in this study. The crude urease enzyme was extracted from soybean and urease-producing bacteria. The results show that the amount of calcium carbonate induced by the crude soybean urease enzyme is comparable to that produced by bacteria or bacterial urease under the same urease activity. However, the treatment using the crude soybean urease enzyme has the advantage of being more effective in enhancing the strength and reducing the permeability of soil than the other two treatments, especially for soil with small grain sizes. This can be explained by the difference in the precipitation pattern of calcium carbonate using various urea hydrolysis media.