Experimental Study On Reactive Magnesia-microbial Solidification Of Soft Clay

Guided by the dual goals of " carbon neutralization" and " carbon emissions peak",green,lowcarbon,efficient,economical,and energy-saving soft soil foundation treatment technology is the key to the transformation of modern engineering construction to an ecological and sustainable development model.Soft clay is a common and widely distributed soil in the middle and lower reaches of the Yangtze River,characterized by fine particle size,high water content,poor airtightness,and low bearing capacity.Based on the reactive magnesia(r-Mg O)carbonizing technology and microbial induced carbonate precipitation(MICP)technology,this paper proposes the r-Mg O microbial solidification soft clay technology to improve the mechanical properties of soft clay.The research results provide theoretical support for the r-Mg O-microbial solidification technology of soft clay,and have certain practical significance and application prospects for promoting energy conservation,emission reduction,and green and low-carbon development in the soft clay foundation treatment and engineering construction industries.The research results and conclusions of this paper are presented as follows:(1)The influence of various factors on the strength of reactive magnesia-microbial solidification soft clay was studied.This experiment studied the changes in unconfined compressive strength during the process of reactive magnesia-microbial solidification of soft clay using the dosage of r-Mg O,urea concentration,curing period,and bacterial solution concentration as experimental variables.The experimental results show that the unconfined compressive strength of reactive magnesia-microbial solidification soft clay gradually increases with the increase of r-Mg O content and curing period.As the urea concentration increases,the strength of solidified soft clay shows a characteristic of first increasing and then decreasing.When the urea concentration is 2 mol/L,the strength reaches its maximum,thus obtaining the optimal urea concentration of 2 mol/L.The concentration of bacterial solution also has a significant impact on the strength of reactive magnesiamicrobial solidification soft clay.The strength of microbial solidified samples with low bacterial solution concentration has a significant decrease in the strength of solidified samples with higher bacterial solution concentration(OD600=2).(2)The effects of various factors on the moisture content,pH,and disintegration rate of The concentration of bacterial solution also has a significant impact on the strength of reactive magnesiamicrobial solidification soft clay were studied.The experiment studied the changes in moisture content,pH,and disintegration rate of reactive magnesia-microbial solidification soft clay using the dosage of r-Mg O,urea concentration,curing period,and bacterial solution concentration as experimental variables.The experimental results show that the moisture content,pH,and disintegration rate of reactive magnesia-microbial solidification soft clay gradually decrease with the increase of r-Mg O content and curing age.With the increase of urea concentration,the moisture content,pH,and disintegration rate of solidified soft clay show a characteristic of first decreasing and then increasing.The concentration of bacterial solution also has a significant impact on the moisture content,pH,and disintegration rate of reactive magnesia-microbial solidification soft clay.The moisture content,pH,and disintegration rate of microbial solidified samples with low bacterial solution concentration increased significantly in those with higher bacterial solution concentration.(3)Explored the mechanism of enhancing the strength of reactive magnesia-microbial solidification soft clay.Through XRD and SEM microscopic test and analysis,it is found that the strength of reactive magnesia-microbial solidification soft clay is improved because the r-Mg O mixed in the soil hydrates to produce magnesium hydroxide,and magnesium hydroxide further reacts with the carbonate generated by urease catalyzed urea hydrolysis generated by microbial metabolism to generate basic carbonate products such as boehmite and brucite,fill the pores between soil particles and cement soil particles,Thus,the soil strength is improved.(4)The durability characteristics of r-Mg O-microbe solidification soft clay under dry wet/freeze thaw cycles were clarified.In this experiment,seven dry-wet/freeze-thaw cycles of rMg O-microbial solidification soft clay with two r-Mg O admixtures(15%,20%)and four urea concentrations(1 mol/L,2 mol/L,3 mol/L,4 mol/L)were conducted.The effects of r-Mg O admixtures,urea concentration,and the number of dry-wet/freeze-thaw cycles on the durability of dry-wet/freeze-thaw cycles were studied and analyzed.The test results show that the dry wet/freeze thaw cycle durability of soft clay solidified by r-Mg O-microbe has been significantly improved,and after the dry wet/freeze thaw cycle,it still has high strength,showing good dry wet/freeze thaw cycle durability.With the increase of dry-wet/freeze-thaw cycles,the strength and quality of microbial solidified samples with various r-Mg O content and urea concentration gradually decreased,but the mass loss of freeze-thaw cycles was not significant;With the increase of r-Mg O content,the strength of the sample gradually increased after 7 dry wet/freeze thaw cycles,but compared to the strength of the sample before the dry wet/freeze thaw cycle,the strength decreased;With the increase of urea concentration,the strength of the sample increased first and then decreased after 7 cycles of drywet/freeze-thaw cycles,with a urea concentration of 2 mol/L being the optimal.Through SEM,it was found that the surface of the sample after dry-wet/freeze-thaw dry-wet appeared more holes and became rough compared to that before dry-wet/freeze-thaw.