Abstract: In order to improve the strengthening effect of microbially induced carbonate precipitation (MICP) technology on calcareous sand in the marine environment, on the basis of previous studies, the multi-gradient artificial domestication culture test of Sporosarcina pasteurii in artificial seawater environment was designed and carried out. Combined with the mechanical test and micro-mesostructural analysis of MICP strengthened calcareous sand column, the domestication effect of Sporosarcina pasteurii was comprehensively evaluated. The results showed that: i) The bacterial liquid concentration after five-gradient domestication in seawater environment could reach more than 97% of that in freshwater environment, and the production of carbonate after the interaction with cementing fluid was increased to a certain extent compared with that in freshwater environment. ii) The domesticated Sporosarcina pasteurii had good temperature adaptability, and it had good MICP performance at 10 ℃ to 30 ℃. iii) Both carbonate production and unconfined compressive strength of calcareous sand columns strengthened in seawater environment were higher than those before domestication, especially the bacteria after five-gradient domestication, and the bacteria after domestication became smaller. The carbonate crystals (calcium carbonate and magnesium carbonate) generated in the seawater environment were smaller and denser, which could better fill the pores of calcareous sand particles and cement the adjacent calcareous sand particles, and had better MICP performance. The relevant research ideas and methods can provide reference for the research and application of MICP technology in the reinforcement of calcareous sand foundation in seawater environment.

Key words: seawater environment, gradient domestication, calcareous sand, Sporosarcina pasteurii, microbially induced carbonate precipitation (MICP)