Experimental Study On Microbial Induced Calcium Carbonate Precipitation Technology For Sand Solidification

Microbial induced calcium carbonate precipitation（MICP）is a new soil consolidation technology.Compared with the traditional foundation treatment technology,MICP has the characteristics of simple mechanism,high efficiency,easy to control and high survival rate,and is expected to become an environment-friendly soil reinforcement technology.MICP process includes a series of biochemical reactions,many factors will affect the curing effect,such as the type and quantity of bacteria（or enzymes）,the concentration of reaction solution,reaction time and environmental conditions（pH and temperature）,and even the crystal morphology and grouting method of calcium carbonate precipitation.Therefore,it is of great significance to master the growth law of bacteria,optimize the reaction conditions of MICP process and reduce the impact of environmental factors for the early application and in-depth study of this technology.Starting from the activation culture of Sporosarcina pasteurii,the reaction conditions of CaCO₃ precipitation induced by Sporosarcina pasteurii were optimized,the crystal forms of CaCO₃ under different pH conditions were analyzed,and the sand solidification test was carried out,and the solidification effect was compared and analyzed.The main research contents of this paper are as follows:（1）Through the activation and cultivation of Sporosarcina pasteurii,the preservation and multiplication techniques of Sporosarcina pasteurii were mastered.The concentration,enzyme activity and pH of the bacterial solution were monitored during the bacterial culture.The growth curve of Sporosarcina pasteurii was obtained.The biological characteristics of Sporosarcina pasteurii in each growth period were mastered,and the optimum period of activity was determined to be 28-44 hours.（2）The main influencing factors（bacterial concentration,cementing solution concentration,temperature and pH）in the reaction process were optimized by MICP experiment,and the effects of different reaction conditions were evaluated based on the quality of final calcium carbonate.The reaction conditions of bacterial concentration OD₆₀₀=1.0,cementing solution concentration 1mol/L,30℃and pH=8.0were optimized.（3）Calcium carbonate crystals formed under different pH conditions were analyzed by SEM.When pH=7.0 and 7.5,most of the calcium carbonate crystals were thermodynamically stable calcite;when pH=8.0,unstable aragonite was formed;when pH=8.0,the most unstable spherical columbite was formed;and when pH=9.0,the calcium carbonate crystals showed regular pentahedral shape and were relatively stable.（4）The unconfined compressive strength of sand columns with different content of sodium bentonite was measured after successful consolidation,and the quality of calcium carbonate was weighed.Through comparative analysis of the experimental results,the common sand with different content of sodium bentonite for MICP consolidation was found.The influence rule verifies the feasibility of the technology.