Abstract: To improve the liquefaction resistance of calcareous sand foundations, microbially induced calcium carbonate precipitation (MICP) technology and fiber reinforcement technology was combined to treat the calcareous sand sampled from the South China Sea. Based on dynamic triaxial tests, the dynamic behaviors of MICP-treated and fiber-reinforced calcareous sand, including dynamic strain, dynamic pore pressure, stress−strain hysteresis loop and dynamic modulus of elasticity, were analyzed. Then, the strengthening mechanism of MICP and fiber on the mechanical properties of the treated calcareous sand was explored from the microscopic point of view, based on the scanning electron microscope (SEM) test results. The results show that: (1) MICP could improve the deformation and liquefaction resistance of calcareous sand. Compared with the untreated specimen, the dynamic strain and dynamic pore pressure of calcareous sand treated by MICP decreased by 95.74% and 92.46%, respectively. (2) The addition of fibers further improved the reinforcement effect of MICP. Compared to the MICP-treated samples, the dynamic strain and dynamic pore pressure of MICP-treated and fiber-reinforced specimens decreased by 74.32% and 74.18%, respectively. (3) Combined MICP treatment and fiber reinforcement technology improved the deformation and liquefaction resistance of calcareous sand subjected to cyclic loading by reducing the intensity of cyclic activity and energy dissipation, increasing the dynamic modulus of elasticity and reducing its attenuation rate. (4) The results of the SEM test showed that MICP treatment and fiber reinforcement had a synergistic effect on the improvement of the dynamic behaviors of calcareous sand. The addition of fibers provided more spots for bacterial adhesion and promoted the formation of calcium carbonate crystals, which not only increased the bonding strength between sand particles, but also enhanced the constraint of fiber network by fixing fibers and sand particles together.

Key words: calcareous sand, microbially induced calcium carbonate precipitation (MICP), fiber reinforcement, dynamic triaxial test, sand foundation liquefaction, scanning electron microscope (SEM)