Influence of Microbe and Enzyme-Induced Treatments on Cemented Sand Shear Response

Microbial-induced calcium carbonate precipitation (MICP) and enzyme-induced calcium carbonate precipitation (EICP) are both soil improvement techniques that improve the shear response of sands. However, the source of urease to hydrolyze the urea is different between the two techniques, and these differences may result in different shear responses. The macro- and microscale behavior of MICP- and EICP-treated sands are evaluated using triaxial tests and scanning electron microscopy (SEM) images. To compare the macroscale behavior, triaxial specimens were treated using MICP and EICP techniques to reach a moderate level of cementation, assessed using shear wave velocity. EICP-treated sand needs less calcium carbonate than MICP-treated sand to reach the same shear wave velocity. The specimens were sheared under drained conditions, and shear responses are compared. The obtained results show that a higher shear strength and larger dilative strain were observed for MICP-treated sand compared to EICP-treated sand when treated to the same shear wave velocity; however, more injections were required for the MICP treatment, which resulted in a higher carbonate content. The SEM images revealed that the shape and structure of precipitated CaCO3 is different in these two treatment techniques, which in turn likely influenced the macroscale response. The advantages of each method are also discussed. (c) 2019 American Society of Civil Engineers.