Experimental Study On Reinforcement Of Silty Soil By Microbial-Magnesium Oxide Interaction

Under the background of energy saving and environmental protection,microbial induced calcium carbonate precipitation technology has attracted wide attention at home and abroad as a new green and sustainable soil improvement technology,and has a very broad application and development prospect.Up to now,domestic and foreign scholars have carried out a lot of indoor and outdoor research on MICP soil reinforcement technology,but there is still a lack of research on solidified silt.At this stage,there is still a lack of an efficient and high-strength silt reinforcement method in MICP technology.In this paper,marine dredger fill silt is taken as the test object,and grouting method is taken as the main reinforcement method.In the microbial-magnesium oxide synergistic reinforcement test,the reinforcement method of mixing first and then grouting is adopted.On the basis of studying the feasibility of industrial-grade cementing fluid on MICP reinforcing silt,the influence of cementing fluid parameters on the reinforcement effect is explored.On the basis of this study,combined with active magnesium oxide and MICP technology,the feasibility of microbial-magnesium oxide synergistic reinforcement of silt and the study of magnesium oxide parameters as the main influencing factors were explored in solution environment and soil environment.The main contents and conclusions of this paper are as follows :(1)The influence of industrial cementing fluid parameters on the effect of MICP technology on silt reinforcement was studied.The test of microbial grouting reinforcement of silt was carried out with the concentration of cementing liquid,the number of cementing liquid rounds and the interval time as variables.The results show that the MICP treatment with industrial-grade cementing liquid can effectively reinforce the silt.The reinforcement effect of silt samples increases first and then decreases with the concentration of cementing fluid,and increases with the increase of the number of cementing fluid rounds.The two intervals of 12 h and 24 h have no significant effect on the reinforcement effect of silt.(2)The effect of active magnesium oxide on urease activity and carbonate formation in solution environment was studied.The solution test was carried out with the activity of magnesium oxide and the content of magnesium oxide as the main variables.The results showed that the two kinds of active magnesium oxide used in this experiment would reduce the urea hydrolysis rate of Bacillus pasteurii,resulting in a decrease in carbonate production.The carbonate formation of the two active microorganisms-magnesium oxide samples increased with the increase of magnesium oxide content.However,under the same dosage conditions,the carbonate formation of high-activity magnesium oxide samples is higher than that of low-activity magnesium oxide samples.(3)The effect of magnesium oxide activity and content on the effect of microbial-magnesium oxide synergistic reinforcement of silt was studied.The microbial grouting reinforcement silt test was carried out with magnesium oxide activity and magnesium oxide content as variables respectively.The results show that the synergistic effect of microorganism-magnesium oxide on silt reinforcement is obvious.Under the same dosage,the reinforcement effect of high active magnesium oxide on silt is better than that of low active magnesium oxide.The strength of the two active magnesium oxide solidified samples increases with the increase of the content.(4)The effects of microbial-magnesium oxide synergistic reinforcement and MICP reinforcement on silt were compared.The test results show that the microbial-magnesium oxide synergistic solidified sample is effectively reinforced when the number of rounds of grouting(1round,2rounds)is low,and the strength of the sample reaches the effect of multi-round treatment and reinforcement of MICP technology.The test method of multi-round treatment can be effectively replaced by adding a certain amount of magnesium oxide to achieve the purpose of saving processing time and processing cost.