Optimization Of Microbial-induced Calcium Carbonate Precipitation And Its Application In Silt Solidified

With the construction of large-scale infrastructure,it is particularly important to improve and reinforce the soil on the premise of limited land resources,especially for the reinforcement of weak foundation soil.Traditional grouting materials include cement,epoxy resin,sodium silicate,and polyurethane injected into the pores of the soil to achieve cementation.Chemical slurry used in chemical grouting except sodium silicate is toxic.The microbially induced calcium carbonate deposition technology is a green environmental protection reinforcement technology.This technology is widely used in sand cementation.In order to expand the application scope of this technology,this paper takes Zhengzhou silt as the research object and studies the effect of microbiological reinforcement of silt.By studying the growth factors of Bacillus sakazakii(Ph value,inoculum size,temperature and rotation speed),the optimal basic growth conditions of this species were explored.On this basis,the urease activity of the strains in different culture medium was compared to obtain a higher urease activity.Based on the high urease activity,this paper attempts to study the effect of different grouting conditions(grouting speed and grouting nutrient concentration)on the reinforcement of silt samples at different scales.The main researchs in the paper are the following:(1)By studying urease activity of the strain in the case of temperature(27°C-37°C),pH(6-10),rotation speed(130 r/min-200 r/min)and inoculation amount(1%-5%),it found that the basic conditions for the optimal strains were raising temperature at 32 °C,pH value of culture broth was 8,inoculum was 5%,and culture speed was 180 r/min.(2)Based on the basic growth conditions of the strains,by optimizing the sequence of the A starting medium and the B expanding medium,the best culture order is as the following.the first step is A starting medium streak,followed by the A starting medium picking a single colony culture Live,the last step B expanded the culture live.A medium is peptone,meat extract,urea,(5:3:20);B medium is NH4-YE,yeast powder: ammonium sulfate(2:1).In this method it obtained urease activity up to 45.07 U/ml.(3)Orthogonal test was used to study the effects of urease activity,grouting speed,and nutrient concentration on the small-scale silt in the laboratory.Through the analysis of calcium carbonate content and unconfined uniaxial compressive strength,we obtained the above results.The sequence of the three factors affecting the silt reinforcement effect is urease activity,nutrient concentration,and grouting speed.The degree to which the silt is solidified by the microorganisms is in the range of 41.29%-57.83% of the filling rate,which is a range in which calcium carbonate is generated more and has a more uniform distribution.(4)Microbial reinforcement of silt under different silt particle content distribution and porosity ratio showed that the optimal porosity ratio range was 0.6-0.8,and the calcium carbonate content peaked when the pore ratio was around 1.0.With the increase of clay content(50%-75%),the content of calcium carbonate also increased significantly.The content of calcium carbonate induced by microbes under the 75% clay content was the best,and the clay content was greater than 75%.,calcium carbonate content began to decrease.When the content exceeds a certain amount(porosity ratio of the silt is 0.8-1.0),the unconfined uniaxial compressive strength of the unconfined powder decreases due to the uneven distribution of the calcium carbonate content in the silt soil sample.(5)When the microbe solidifies a large-size silt foundation,the point load strength of the silt foundation processed with MICP can be significantly increased by 44.3-290.89 kPa when microbiological grouting amount is about 1100-3200ml(void ratio e 0.8);For 700 ml microbe grouting volume,the corresponding difference in consolidation radius is the law that the ratio of the public ratio q is equal to 3.Second,the amount of microbial grouting affects the location of the bulge formation in the grouting pipe.