Study on calcareous sand treated by MICP in different NaCl concentrations

Abstract

Calcareous sand foundations may be damaged by waves or earthquakes. Therefore, such foundations should be reinforced. In this study, a series of bacterial solution tests and cyclic triaxial tests were performed to investigate the reinforcing effect of microbially induced carbonate precipitation (MICP) treatment of calcareous sand in different NaCl concentrations. In bacterial solution tests, the microbial activity and microbial mineralization products were examined. At 32 hr, the OD₆₀₀ and urease of MAT₃₅ were lower than MAT₀ by 21.94% and 43.53%. In 0–48 hr, the OD₆₀₀ and activity of MAT₈₀ and MAT₁₀₀ were below 0.15 and 1 mM urea/min. The productivity of calcium carbonate after MICP decreased with an increase in NaCl concentration. The cyclic triaxial tests showed that with an increase in NaCl concentration, the accumulation rate of pore pressure increased, and the number of strain-accumulation cycles decreased. Although the stiffness and cyclic resistance of the samples decreased with an increase in NaCl concentration, both were higher than those of untreated sands. Scanning electron microscopy images showed that as the NaCl concentration increased, the calcium carbonate was precipitated gradually changed from a cluster to individual crystals; this change in form is the main reason for the decrease in liquefaction resistance.

Keywords:

• NaCl
• microbially induced carbonate precipitation (MICP)
• microbial activity
• microbial mineralization products
• cyclic triaxial tests

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research done herein was supported by the National Natural Science Foundation of China (No. 52008121, No. 51908151), and the Chinese Postdoctoral Science Foundation (No. 2020M682652).