Optimization of one-phase-low-pH enzyme-induced carbonate precipitation method for soil improvement

There are two major challenges for the use of enzyme-induced carbonate precipitation (EICP)-based soil improvement method: cost and treatment effect. Optimizing the parameters of the treatment solution is one way to enhance the treatment effect and/or reduce the treatment cost. In this study, three key factors: the initial pH (i.e. pH 0 ) of the enzyme solution used to prepare the treatment solution (i.e. the mixture of enzyme solution, CaCl 2 and urea), the urease activity of the treatment solution and the concentration of cementation solution (i.e. CaCl 2 and urea) are investigated. Crude soybean enzyme solution and the one-phase-low-pH injection method are adopted for the treatment of sand. The results show that the pH 0 of the enzyme solution affects the urease activity of enzyme and thus the urease activity of the prepared treatment solution. It is discovered in this paper that there is a threshold pH value for the treatment solution. Only when the pH of the treatment solution is higher than the threshold pH value, calcium ions convert completely into calcium carbonate. There is also a threshold urease activity which is affected by the concentration of cementation solution, CCS . The optimal CCS is 1.0 M. When the CCS is higher than 1.75 M, the urease activity of soybean enzyme solution would be completely lost. These findings are important in guiding the application of EICP treatment using the crude soybean enzyme in real soil improvement projects.