Modified one-phase-low-pH method for bacteria or enzyme-induced carbonate precipitation for soil improvement

One of the latest developments in biocementation is the use of one-phase-low-pH MICP or EICP method as a more effective and efficient alternative to the traditional two-phase method for the treatment of sandy soil. However, the one-phase-low-pH method has its own limitation. The pH of the solution has to be adjusted before every treatment. In this study, a modified one-phase-low-pH MICP or EICP method is proposed in order to simplify the treatment procedure to improve the efficiency of biotreatment in real constructions. In this method, the low-pH bacteria or urease solution is only used together with the cementation solution (i.e., CaCl₂ and urea) for the first treatment and for the subsequent treatment, only cementation solution is used. The test results show that using the modified one-phase-low-pH MICP method with a bacterial solution of a volume ratio of 0.75 is comparable to that using the original one-phase-low-pH method, and 80% of the calcium conversion efficiency can be maintained for up to 5 treatments. However, the modified one-phase-low-pH EICP method may only be used for the first 2 or 3 treatments due to the relatively poor durability of urease enzyme in inducing calcium carbonate during the subsequent injections of cementation solution.