Experimental Study On Microbial-induced Calcium Carbonate Precipitation And Soil Reaction Rate Control Method

Microbial-induced calcium carbonate precipitation(MICP)can effectively improve the mechanical properties of silt,but in practical applications,there are still many factors that restrict engineering applications.When the microbes reinforce the silty foundation,the uniformity of the grouting method is poor;from sand to silt to clay,the effect of microbial solidification by stirring is not ideal,because the MICP reaction rate is fast,and a lot of damage is caused during the stirring process.Intergranular cement has formed.Slowing down the reaction rate of MICP,and forming inter-granular cement after stirring is completed,can improve the solidification effect of MICP.Therefore,the reaction rate is an important factor restricting MICP in practical engineering applications.Based on the principle of microbial-induced calcium carbonate precipitation,this paper explores the method of slow-release urea and low-soluble calcium salt to control the reaction rate of MICP,and analyzes the effectiveness and internal mechanism of slow-release urea and lowsoluble calcium salt to control the reaction rate of MICP.The feasibility of slow-release urea to control the reaction rate of MICP was verified;the reaction rate of three low-soluble calcium salts in the solution environment was studied;the reaction of low-soluble calcium salt and slow-release urea to control MICP in solidified silt was studied The role of speed.The main conclusions of this article are as follows:(1)Slow releaseof urea controls the reaction rate of MICP.In solution tests,lignin / coppercontaining peeme and lignin / mondeniture slow release urea played a role in controlling the reaction rate of MICP,and had little negative impact on MICP’s reaction efficiency.Among them,lignin / copper-containing soil-containing slow release urea control reaction rate is stronger than lignin / mondeniture slow release urea.(2)When using slow-release urea for MICP reinforcement of sand,the reaction rate of the slow-release urea sample is lower than that of the standard urea sample;within 4 days,the unconfined compressive strength and calcium carbonate formation of the slow-release urea sample The amount is lower than the standard urea sample;at 2d,the MICP reaction of the standard urea sample is basically completed,while the reaction of the slow-release urea sample is still in progress.(3)Low soluble calcium salt has a control effect on the MICP reaction rate.In the lowcalcium-calcium salt solution test,the amount of calcium carbonate produced by the sample in the same time increases as the solubility of calcium salt increases.Considering the reaction rate and reaction efficiency,calcium sulfate is the best performer among the three low-soluble calcium salts.(4)When using the low-solubility calcium salt(calcium sulfate dihydrate)to reinforce the silt,within 4 days,the unconfined compressive strength and calcium carbonate production of the lowsolubility calcium salt sample increase with time,which controls the MICP The reaction rate of solidified silt has a certain effect.(5)When using both slow-release urea and low-soluble calcium salt to reinforce the silt with MICP,within 8 days,at the same time,the slow-release urea sample is better than the low-soluble calcium salt sample using only low-soluble calcium salt It has a lower unconfined compressive strength,and less calcium carbonate is produced in the sample.When slow-release urea and low-soluble calcium salt work together,the effect of controlling the reaction rate of MICP is more obvious.