MICP固化粉土细菌的分布和固定规律研究

Distribution and fixation characteristics of microorganism in MICP treated silt column

采用一维注浆方式对50 cm长柱状粉土试样进行微生物固化试验,通过测定孔隙液中细菌数量、NH+4浓度和pH、及固化土体中的胶结CaCO_3生成量等参量,分析注浆菌液配比和胶结液浓度对细菌与反应产物沿程分布特性的影响。结果表明,当注入浓度为1.223×108 CFU/mL的原菌液时,固定菌与游离菌沿柱状试样渗流方向沿程衰减显著,细菌主要分布于注浆端25 cm以内,提高胶结液浓度对试样碳酸钙生成量的影响主要集中在注浆端5 cm以内区域。当注入用营养液稀释的菌液(浓度8.20×106 CFU/mL)或用营养液稀释的上清液(浓度1.80×106 CFU/mL)时,孔隙液中细菌能快速繁殖增长且分布较为均匀,吸附菌和被拦截的游离菌共同组成固定菌,对土中碳酸钙的生成量产生影响,胶结液浓度的变化对碳酸钙生成量的影响较小。研究结果表明,微生物注浆加固粉土的均匀性主要受固定菌分布的均匀性控制,将菌液或上清液稀释后注入粉土能够使固定菌沿程分布均匀,可较好地改善固化土体均匀性。

Cementing silt by microbial induced calcite precipitation (MICP) is a new environmentally-friendly techno- logy .The distribution of microorganisms is an important factor that affects the uniformity of silt cemented by grouting.By measuring the amount of bacteria,the concentration of NH + 4 and the pH in the pore fluid,as well as the content of CaCO3 in the cemented silt,the impact that the concentrations of bacteria and cement solution exerted on the distribution of bacteria and reaction products in the process of grouting columnar silt sample were investigated in this study.The results showed that the amount of microbial biomass in columnar silt sample decayed significantly along the direction of seepage when the original bacterium suspension of 1.223×10^8 CFU/mL was injected.In addition,the bacteria were mainly distributed within 25 cm of the grouting end.The increasing concentration of cement solution mainly influenced the amount of calcium carbonate within 5 cm of the grouting end.There was a good agreement between the CaCO3 content in cemented silt columns and the amount of free bacteria in pore fluid along the direction of seepage.For comparison,the supernatant was diluted to 8.20×10^6 CFU/mL and bacterium suspension was diluted to 1.80×10^6 CFU/mL with nutrient solution,respectively,which were used instead of the original bacterium.When the diluted supernatant or diluted bacterium suspension was injected into the silt column,the amount of bacteria in the pore fluid was much larger than that in the original suspension after 2 h of static adsorption because of the rapid reproduction of bacteria,and the distribution of microorganism was relatively uniform.The diluted supernatant or diluted bacterium suspension demonstrated an excellent infiltration capacity.The cemented silt columns presented more uniform than the columns injected original bacterium suspension.The decrease in CaCO3 content was less than microbial biomass in columnar silt sample along the direction of seepage.Fixed bacteria were composed of adsorbed bacteria and detained free bacteria which both affected the content of calcium carbonate produced in the process of grouting columnar silt samples.When a supernatant or bacterium suspension diluted by a nutrient solution was injected,the change in cement solution concentration had little effect on the content of calcium carbonate produced.The results of this study revealed that the heterogeneity of silt reinforced by microbial grouting is mainly determined by the heterogeneity of fixed bacteria.Injecting diluted bacterium supernatant or suspension can improve the uniformity of biocemented silty soil.