Abstract:

To improve the liquefaction resistance of calcareous sand foundations, microbially induced calcium carbonate precipitation (MICP) technology combined with fiber reinforcement technology was proposed to treat the calcareous sand in the South China Sea. Based on dynamic triaxial tests, the dynamic behaviors of MICP and fiber-treated calcareous sand were studied. The dynamic strain, dynamic pore pressure, cyclic stress-strain response and dynamic elastic modulus 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: (i) MICP could improve the deformation resistance and liquefaction resistance of calcareous sands. Compared with the untreated calcareous sand samples, the dynamic strain and dynamic pore pressure of calcareous sand treated by MICP decreased by 95.74% and 92.46%, respectively. (ii) 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 and fiber-treated samples decreased by 74.32% and 74.18%, respectively. (iii) MICP and fiber reinforcement technologies improved the deformation resistance and liquefaction resistance of calcareous sand subjected to cyclic loading by reducing the cyclic activity strength and energy dissipation, increasing the dynamic elastic modulus and reducing the decay rate of the dynamic elastic modulus. (iv) The results of the SEM test showed that MICP and fiber reinforcement had a synergistic effect on the improvement of the mechanical properties of calcareous sands. The incorporation 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 restraint of fiber nets by fixing fibers and sand particles together.

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