Study On Filling Effects Of Sediment Induced By Bio-grouting In Silt

Liquefiable silt exists widely in the middle and lower reaches of the Yangtze River region. The treatment of liquefiable silt foundation often needs to spend a lot of money, causing the waste of resources and negative effects on the environment. Using biotechnology to solve the geotechnical engineering problems has broad application prospects and significant engineering technology and economic value. This study uses bio-grouting technology to improve the liquefiable silt on the basis of Europe’s and America’s latest research results.Based on the grouting methods of microbial induced carbonate deposition (MICP) and iron-based, microbial inducer was used to fill the porous in silt. Firstly, the growth characteristics of Sporosarcina and iron bacteria S1968 were researched. The effects of temperature, pH and other factors on the yield of the inducer were studied, and the inducer was identified. Secondly, bio-grouting in silt with different sizes, by metallographic microscope, CT scan, penetration test and energy spectrum analysis (EDX) technology, the inducer filling effect under different grouting methods were analyzed and compared. Finally, through small shaking table test of simple slope, the filling effect of grouting silt was evaluated. This paper gets the following conclusions:(1) After 24h culture, Sporosarcina went into the stable growth time, and the bacterial monomer urease activity decreased after 40h. In the range of 20～40℃, pH=6.0-8.0, the urease of strains could maintain higher activity, and the amount of induced calcium carbonate increased with the increase of temperature. The Sporosarcina solutions, Serum and cells all could generate carbonate in a certain concentration of reaction solution. The main ingredients of carbonate was calcite and vaterite.(2)Iron bacteria S1968 went into logarithmic growth period after 12h culture, the activity of cell increased rapidly in 24h-48h, and the deposition process of iron-based began after 48h and ended after 54h. Under the conditions of 25℃～40℃ and pH=6.0-8.0, the deposition amount of iron-based was ideal, and the deposition amount reached to the maximum value in 30℃ and pH=7.0. Iron-based crystalline form was not obvious, which contained a small amount of basic phosphate iron and other polymorphs, and its location and characteristics of the infrared spectrum peaks were highly consistent with schwertmannite.(3) Metallographic observation and CT scan showed that the connection between the grouting soil particles was relatively compact, soil porosity dropped significantly, the number of large-volume holes reduced significantly, and with the increase in the number of grouting, the filling effect of induced sediment was more obvious.(4) Under the action of gravity grouting, biological inducer only on the surface of the silt had good sedimentary filling effect. The osmotic coefficient of silt with low pressure grouting was two orders of magnitude lower than that of the non-grouting silt. Grouting pressure was conducive to the spread of grouting liquid, and the filling effect of induced sediment was better.(5) The small shaking table tests showed that under the same seismic load, the filling of induced sediment in the grouting silt could effectively suppress the amplification of the seismic wave.