Calcium carbonate precipitation catalyzed by soybean urease as an improvement method for fine-grained soil

Although great advances have recently been made in biological soil-improvement methods, the treatments of fine-grained soil using these methods are still challenging. In this study, we tested a new method for the improvement of silty soil. This method adopts the calcium carbonate precipitation process catalyzed by soybean urease. Crude urease is derived simply by collecting the liquid formed by soaking soybean powder in water. The activity of crude urease is linearly related to the amount of soybean powder added to the water, and is high enough to be used for soil treatment. Under batch conditions, the reactions catalyzed by crude urease can be completed, although the reaction rates are slower than those using live bacteria with the same initial activity. In triaxial consolidated undrained tests, the treated silty soil shows more dilative responses in the stress-strain curves and larger peak deviatoric stresses as compared with the untreated soil, indicating significant improvements in the mechanical behaviour. In the results of CaCO3 measurements, it is seen that there are continuous increases in the CaCO3 content of the samples during the treatment process, which implies that the silty soil samples are not clogged when treated by crude urease. Such results indicate that calcium carbonate precipitation catalyzed by soybean urease can be used for the improvement of fine-grained soil. (C) 2019 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.