Search

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. [ABSTRACT FROM AUTHOR]

Enzyme induced carbonate precipitation (EICP) is an emerging soil improvement method using free urease enzyme for urea hydrolysis. This method has advantages over the commonly used microbially induced carbonate precipitation (MICP) process as it does not involve issues related to bio-safety. However, in terms of efficiency of calcium carbonate production, EICP is considered lower than that of MICP. In this paper, a high efficiency EICP method is proposed. The key of this new method is to adopt a one-phase injection of low pH solution strategy. In this so-called one-phase-low-pH method, EICP solution consisting of a mixture of urease solution of pH = 6.5, urea and calcium chloride is injected into soil. The test results have shown that the one-phase-low-pH method can improve significantly the calcium conversion efficiency and the uniformity of calcium carbonate distribution in the sand samples as compared with the conventional two-phase EICP method. Furthermore, the unconfined compressive strength of sand treated using the one-phase-low-pH method is much higher than that using the two-phase method and the one-phase-low-pH method is also simpler and more efficient as it involves less number of injections. [ABSTRACT FROM AUTHOR]