基于原生微生物MICP的土体加固试验研究

Experimental Study on Soil Reinforcement by Native Microbial Induced Calcite Precipitation

为研究原生微生物加固砂土的影响因素,进行了室内胶结试验。采用不同灌注方式和不同配比的溶液,对试样中原生脲酶微生物进行激活,待微生物分解尿素能力达到阈值后,鉴定试样中微生物种属并对其进行系统发育分析,然后开展微生物诱导碳酸钙沉淀(MICP)胶结试验。通过微生物浓度、尿素浓度来监测试样的生物化学变化,根据无侧限抗压强度(UCS)和扫描电子显微镜成像(SEM)来评估试样加固效果。试验结果表明:加固效果与胶结液的灌注方式、有机质浓度、尿素浓度关系密切,双向交替灌注有利于改善试样胶结的均匀程度,较高浓度的有机质(酵母提取物)对土体中微生物多样性产生不利影响,激活和胶结效果较差;使用0.35 mol/L尿素的试样残余尿素浓度较高,而使用0.20 mol/L尿素的试样中,尿素残余较少;此次研究中,采用双向交替灌注、1.0 g/L酵母提取物、0.20 mol/L尿素处理的试样,生成的碳酸钙晶体连接紧密,胶结程度较好,其UCS值达1.55 MPa。研究成果表明,使用一定配比的溶液,可激活土体中的原生微生物,达到加固土体的目的。

Laboratory consolidation test was carried out to study the influence factors of sand reinforcement by native microorganism.The native urease organisms in the soil were activated by using different injection methods with different concentrations of organic matters.After the urea hydrolysis ability reached the threshold value by the urease bacteria proliferated in the soil samples,the microbial species in the samples were identified and phylogenetic analysis was carried out,and then MICP cementaion treatment was performed.Biochemical changes in soil samples were monitored by cells density of urease bacteria and urea concentration.The reinforcement effects of soil samples were evaluated via unconfined compressive strength(UCS)and scanning electron microscope imaging(SEM).Results demonstrate that the reinforcement effect is strongly related to the way of injection and the concentrations of organic matter and urea.Bidirectional alternative grouting is beneficial to enhancing the uniformity of cementation.Biochemical analysis indicates that high concentration of organic matter(yeast extract)has adverse impact on the microbial diversity in soil,the activation of native urease bacteria in soil and the cementation effect.The residual concentration of urea in the sample with 0.35 mol/L urea was higher than that in the samples with 0.20 mol/L urea.In the present study,the soil column treated by 1.0 g/L yeast extract,0.20 mol/L urea/calcium chloride solution and bidirectional injection achieved sound uniformity of cementation,with its carbonate crystals tightly connected and the UCS value reaching 1.55 MPa.The results conclude that the native microorganism in the soil can be activated effectively by a proper proportion of solution,hence strengthening the soil.