The Influence Of Injecting Parameters And Curing Conditions On Microbial Cemented Silt

With the rapid development of China’s economy,the demand for construction land is increasing day by day,and the treatment of soft soil foundation is facing new challenges.The basic principle of reinforcing soil by microbial-induced calcium carbonate precipitation is to use urease produced by urea-producing microorganisms in soil,hydrolyze urea in cementation solution to produce CO₃^2-and react with Ca²⁺to produce calcium carbonate,fill the pore between soil particles and cemented soil particles,so as to make soil produce strength.Because of its advantages of less pollution and lower residual than traditional soil reinforcement methods,it has been widely used in many fields such as soil reinforcement,soil seepage prevention,liquefaction prevention,remediation of contaminated soil and so on.At present,the injecting method and infiltration method are mainly used to reinforce silt by using this technology.The results show that microbial-induced calcium carbonate deposition is effective to reinforce silt.The existing research on the effect of silt reinforcement mainly includes temperature,pH value,cement concentration,injecting pressure and time.However,some parameters are not specific enough,such as the less concentration of cementing fluid,the lack of research on the effect of single-round injecting cementing fluid dosage on the reinforcement effect,the lack of research on the effect of changing urea ratio under different calcium ion concentration on the reinforcement effect,and the lack of research on the effect of curing conditions on the strength development of samples.Therefore,in view of the above points,this paper uses the injecting method to reinforce silt and studies the effecting factors of the reinforcement effect deeply,focusing on the factors related to the cementing liquid in the injecting process and the curing conditions after injecting.（1）The influence of the concentration and volume of cementing fluid on the reinforcement effect is studied.Four kinds of cementing fluids（1-fold pore volume,1.5-fold pore volume and 2-fold pore volume）of 0.25M,0.5M,0.75M and 1.0M were selected to be researched.By comparing the relationship between the amount of calcium carbonate produced and the unconfined compressive strength of the treated specimens,the results show that the percentage and strength of calcium carbonate produced by 0.25M cementing solution are smaller than those treated by 1.0M cementing solution when the amount of cementing solution is the same,and the percentage of calcium carbonate and strength produced by 1.0M cementing solution are larger.The relationship between calcium ion dosage and strength of cementing solution with different concentration was analyzed.It was concluded that 0.25M group had better effect when calcium ion dosage was the same,and 1.0M group had lower utilization rate of calcium ion.Moreover,when the amount of cementing fluid is 1.5times the pore volume,the samples can quickly achieve the desired reinforcement effect,and have a higher utilization rate of calcium ions treated by 0.5M and 0.75M.（2）The influence of different injecting rounds on reinforcement effect is studied.The injecting rounds has a direct impact on the reinforcement effect.The strength and uniformity of the specimens increase with the increase of the number of injecting rounds.In the early stage of injecting,the strength of samples develops slowly.When the injecting rounds exceeds a certain number,the strength of samples develops rapidly.The production of calcium carbonate increases with the increase of injecting rounds,but the conversion efficiency of calcium chloride to calcium carbonate decreases with the increase of injecting rounds.There is a good correlation between strength and the percentage of calcium carbonate formation.（3）The influence of cement mixture ratio on reinforcement effect was studied.Increasing the urea content in the cementing solution can obviously increase the pH value of the effluent.When the number of injecting rounds is small,the strength of the specimen can be increased to a certain extent.When the urea/calcium chloride ratio in the cementing fluid is 1.5,the reinforcement effect is the most obvious.With the increase of the injecting rounds,the effect of improvement decreases gradually.When the number of injecting rounds reaches a certain value,the specimens treated with equal proportion cementing fluid have better reinforcement effect.（4）The effect of curing conditions on the strength development of specimens was studied.The moisture content of the sample will directly affect the strength of the sample.The strength of the sample is the highest when the moisture content is zero,i.e.when the sample is dried.The strength of the sample will be lost to a certain extent after soaking,but the moisture content and soaking have no effect on the calcium carbonate production of the sample.When the moisture content of the sample is the same,the curing temperature have no obvious influence on the strength development of the sample.