| Expansive soil is widely distributed in China,covering more than 180 cities and counties in more than 20 provinces(regions),with a total area of more than 100,000 square kilometers.With the implementation of the strategic goal of "One Belt And One Road" advocated by the state,many areas inevitably encounter various problems of expansive soil engineering.Expansive soil contains a lot of clay minerals,and it shows the characteristics of swelling and shrinking when water is lost,which makes it impossible to apply expansive soil directly to engineering.At present,the expandable soil is often treated by soil changing method and chemical modification,which has high cost and bad effect on environment.Response to the call of national 12 th five-year plan,the construction of resource saving and environmentally friendly "green project",this article adopts the way of microbial curing of expansive soil improved processing,through the unconfined compressive strength test,direct shear test,expansion shrinkage test,wash test,disintegration test and scanning electron microscopy(SEM),X-ray diffraction(XRD)and a series of indoor test and theoretical analysis,the microbial cultures influence factors,the factors influencing microbial stabilized expansive soil microbial stabilized expansive soil engineering properties and improve the microscopic mechanism of in-depth study,and based on the Box-Behnken-the response surface method,The microbe-cured expansive soil was further improved by using polypropylene fiber and polyacrylamide.The main research contents and results are as follows:(1)Appropriate culture medium,inoculation proportion and culture environment(temperature,p H value)are conducive to the growth and reproduction of microorganisms.The suitable culture temperature of Bacillus pasteurii is 25-30 ?,p H value is 8-10,and inoculation proportion is about5%.The urease activity of the strains cultured under these environmental conditions was relatively high.(2)The main factors affecting the formation of calcium carbonate by microorganisms are the concentration of the cementing liquid and the ratio of the cementing liquid to the bacterial liquid.Under the condition of certain urease activity,the amount of calcium carbonate is proportional to the concentration and ratio of the cementing solution.When the curing temperature is between 25 ?and 30?,the production of calcium carbonate is more,and increases gradually with the increase of curing days,and gradually tends to be stable after 7 days.(3)The microorganism induces the hydrolysis of urea to generate the calcium carbonate with the cementing property,which cements the soil particles and fills the pores,increasing the compactness of the soil and the cohesion and friction between the soil particles,and the curing effect becomes more significant with the increase of curing days.After curing for 30 days,the unconfined compressive strength of microbial solidified soil increased by 52% compared with that of remolded expansive soil.The cohesive strength increased by 24.89%;The internal friction Angle increased by141.8%;The disintegration amount reaches zero disintegration;The amount of brush decreased by92.3%;The free expansion rate decreased by 40.8%;Dilatancy decreased by 38.4%;Linear shrinkage was reduced by 26.64%.(4)The addition of polypropylene fiber and polyacrylamide further improved the microbe solidified expansive soil.Through response surface methodology and verification test,the optimal optimization scheme was obtained as the length of polypropylene fiber was 9mm,the content of polypropylene fiber was 0.5%,and the content of polyacrylamide was 0.12%.Under these conditions,the unconfined compressive strength of the expanded soil cured by microorganism for 7 days can reach 1.24 MPa,and the disintegration amount of the soil cured for 1 day is only 0.34%. |
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