微生物矿化加固粉土的试验研究

Experimental study of reinforcing silt based on mineralization of microorganism

目前利用微生物矿化技术胶结加固土体多采用注浆的方法,容易出现生成物分布不均匀及注浆口堵塞的问题.本文以海相粉土为处理对象,选用巴氏芽孢杆菌作为微生物,尿素和氯化钙作为胶结液,采用将菌液与粉土拌合制样,然后从表面多轮入渗胶结液的方法对试样进行整体加固.为确定试验参数,采用血球计数板法确定出菌液在土中的留存时间,通过测定流出液电导率的变化确定出胶结液处理的间隔时间.选取了不同浓度的胶结液分不同入渗轮数进行了试验,结果表明:当胶结液浓度不低于0.50 mol/L时,试样整体的水稳定性较好;试样中生成的CaCO_(3)数量和无侧限抗压强度均随着胶结液浓度增加而提高,但当胶结液浓度为1.50 mol/L时,试样的均匀性和无侧限抗压强度都有明显下降.扫描电子显微镜(SEM)结果显示强度高的试样中,生成的六面形CaCO_(3)晶体更多且尺寸更大.在胶结液浓度处于0.50~1.25 mol/L时,试样的无侧限抗压强度随着CaCO_(3)含量呈指数上升.对胶结液多轮入渗下的表面入渗率进行了测定,结果表明经加固后的试样仍保留了一定的透水性.

At present injection method is usually applied in soil improvement through mineralization of microorganism, which leads to the disadvantages of non-uniform treatment of biocemented soil and pore plugging at the region near injection source. In this study, marine silt was treated with non-injecting MICP method, in which the bacteria was Sporosarcina pasteurii and the cementation solution was urea and calcium chloride. The feasibility experiments indicated that the sample could be reinforced effectively by premixing bacteria with soil followed by cementation solution percolation into soil several times. In order to define parameters of treatment, blood cell counting method was used to determine the retention time of bacteria and conductivity variation was used to determine the interval time of cementation solution treatments. Experiments with different concentration and treatments of cementation solution were conducted. The results indicate that the soil samples have stability in water when concentration of cementation solution was no less than 0.50 mol/L. The amount of precipitated CaCO_(3)and unconfined compression strength increase with cementation solution concentration, however when the concentration equal to 1.50 mol/L, the reinforcement homogeneity and strength decrease. SEM images indicate that precipitated CaCO_(3)crystals are in rhombohedral shape and large size in the samples treated with high strength. When the concentration of cementation solution within 0.50~1.25 mol/L, the unconfined compression strength increases exponentially with the CaCO_(3)content. The surface infiltration velocity of cementation solution treatments was measured and the result shows the samples maintain certain permeability after improvement.