Experimental study on creep and long-term strength characteristics of expansive soil improved by the MICP method

Microbial-induced carbonate precipitation (MICP) is a promising method for improving the properties of geotechnical engineering materials. However, little research has been conducted on the creep behavior and long-term strength of MICP-treated expansive soil. Therefore, this study performed triaxial consolidated undrained creep tests to investigate the improvement effect of MICP on the creep behavior and long-term strength of expansive soil. The results indicate that with the increase of deviatoric stress, the creep process of MICP-treated expansive soil includes four stages: instantaneous creep, decelerating creep, steady-state creep, and accelerated creep. Based on the creep test results, a calculation method has been proposed to quickly and accurately determine the long-term shear strength of MICP-treated expansive soil. Under different confining pressure conditions, the long-term shear strength of the improved expansive soil has been significantly increased, indicating that the MICP method can effectively enhance the long-term shear strength of expansive soil. Furthermore, both the long-term cohesion and the long-term internal friction angle of the MICP-improved expansive soil have been slightly reduced, with the long-term shear strength being approximately 65 to 70% of the short-term shear strength. This study confirms the positive effects of the MICP method on inhibiting the creep of expansive soil and enhancing its long-term strength.