Experimental Study On Sandy Soil Solidification Based On MICP Technology

Microorganism solidification is a new type of rock and soil material reinforcement technology,which has the advantages of more economical,environmental protection,high curing efficiency and ideal treatment effect than traditional physical methods and chemical methods.The technology to geotechnical material is through the internal Sporosarcina pasteurii injection and cementing solution,after a period of curing can put the geotechnical materials originally loose cementation become has certain mechanical performance,can satisfy the engineering demand.Based on sandy soil as the research object,this paper on the microbial curing processing sample has carried out a series of laboratory tests,including permeability test,porosity test,unconfined compressive strength test and microstructure observation,calcium carbonate content,etc.,the effect and mechanism of microbe solidification sand soil were studied systematically,and the influence of the concentration,curing temperature and sand particle size on the solidification effect of microbe was analyzed,and the optimal value of the related parameters was determined.In addition,this article also innovative fiber reinforcement technology and the combination of sandy soil microbial curing technology modification,discusses the interaction mechanism and advantages of two kinds of technology,master the fiber content on the influence law of microbial solidified soil mechanics performance,for the future of microbial curing technology in engineering application provides a theoretical basis and new ideas.This work was supported by outstanding youth science foundation(41322019),National Natural Science Foundation of China(Grant No.41572246,41772280)by professor Chaosheng Tang.The main research contents and achievements of this paper are as follows:(1)The effect of cementing concentration on the solidification of sand soil was studied.The results showed that:with the increase of the concentration of the cementing solution,the anti-permeability,unconfined compressive strength and the content of calcium carbonate and the decrease of porosity were all increased first and then decreased.The corresponding concentration of the best anti-permeability was 1.3-1.5mol/L,and the optimum strength was 1.1mol/L,and the highest calcium carbonate and porosity was 1.3-1.5mol/L.(2)The effect of curing temperature on the curing effect of sand soil was studied.The results showed that:As the temperature increases,the calcium carbonate crystals gradually decrease.The anti-permeability,unconfined compressive strength,calcium carbonate content and porosity were all increased and then decreased.The best resistance to permeability,pore filling quantity and high calcium carbonate content of the corresponding temperature of 30℃.Due to the temperature effect on calcium carbonate crystal size,best intensity corresponding to the temperature of 20℃ to 30℃.(3)The effect of sand particle size on curing effect was studied.The results showed that:Sand particle size is too big or too small an adverse effect on cementation effect of MICP.The change of calcium carbonate content and the unconfined compressive strength curve of the samples showed a trend of first increase and decrease with the increase of particle size,and the optimal particle size was medium size(D10=0.1、D30=0.34、D60=0.5),The permeability and porosity of samples have been decreasing with the increase of particle size.(4)Through the analysis,it is found that the decrease of the porosity of the sample after curing is mainly determined by the amount of calcium carbonate.The content of calcium carbonate was positively correlated with the anti-permeability and unconfined compressive strength of the samples:the higher the calcium carbonate content,the higher the anti-permeability and unconfined compressive strength of the sample(5)Proposed fiber reinforcement technology and where the method of combining can significantly improve soil unconfined compressive strength and residual strength,especially to improve microbial cementation sand originally brittle faults,increase the toughness of damage,this to improve the security and stability of the engineering structure has positive significance."Bridge" effect of fiber can effectively inhibit soil samples in the crack extension,which is an important factor to improve toughness,also led to the decrease of the peak dynamic stress-strain curve after the important factors.(6)Under the same fiber content,the strength of fiber reinforced calcareous sand is lower than that of fiber reinforced quartz sand,but the comprehensive reinforcement efficiency in calcareous sand is better than that of quartz sand.The unconfined compressive strength of calcareous sand increased with the increase of polypropylene fiber content,and reached a maximum of 0.55MPa when the fiber content was 0.4%,which was 2.8 times of the strength of the soil.The unconfined compressive strength of quartz sand samples reached a maximum of 4.3MPa when the polypropylene fiber content was 0.1%,which was 1.6 times the strength of the soil.In comparison,the reinforcement effect of basalt fiber is slightly inferior to that of polypropylene fiber,and the optimal content of basalt fiber reinforced quartz sand soil is 0.2%,with a strength of 3.8MPa,and about 1.5 times higher than that of plain soil.