Mechanical behaviour of MICP-treated silty sand

Most chemical substances utilized in traditional soil improvement methods are environmentally detrimental. As a more ecologically friendly ground improvement method, the microbially induced calcium carbonate precipitation (MICP) technique offers an alternative to most traditional soil improvement methods. The role of bacteria is to produce the urease enzyme to catalyze the hydrolysis of urea. In the presence of calcium ions, the produced carbonate ions in the hydrolysis of urea react with the calcium ions, and calcium carbonate sediment is formed. This paper investigates the effects of this treatment procedure on mechanical behavior change and the microstructure of loose sand and silty sand. To evaluate the influence of treatment, a series of laboratory experiments were conducted, including shear wave velocity, unconfined compressive strength, calcium carbonate content, triaxial shear test, and scanning electron microscopy. The study revealed that this bio-mediated technique causes the improvement of soil strength due to the cementation of sand particles. This method has the potential of making a stable bio-stabilized column of sand and silty sand. Besides, the two-way introduction method is also able to produce a homogeneous bio-cemented soil sample. Results also showed that the increase of cohesion is not significant in the lightly bio-cemented soil samples, but the friction angle increase is notable, especially in biotreated sand. Plus, there is no significant difference between the amounts of calcium carbonate precipitation between sand and silty sand.