风沙土的微生物固化试验研究
Experimental Investigation of Microbial Solidification of Aeolian Sand

风沙土主要分布于干旱少雨的沙漠地区,是一种结构松散、颗粒细小而均匀、自稳能力差、且不易压实的特殊土体,作为建筑物基础时须进行加固处理。因此,风沙土的加固技术是一个重要的研究课题。微生物诱导碳酸钙沉淀(MICP)是一种新型的微生物土壤强化技术,本文采用微生物诱导碳酸钙沉淀技术,利用巴氏芽孢杆菌,对风沙土进行加固试验研究,进而为风沙土的工程应用提供技术支撑。主要研究内容和成果如下:(1)采用巴氏芽孢杆菌(Sporosarcina pasteurii)和胶结液(尿素和氯化钙的混合溶液),利用微生物诱导碳酸钙沉积(MICP)技术,可以在风沙土颗粒之间生成具有胶结作用的碳酸钙晶体,有效地固化风沙土,提高了风沙土的强度,改善了风沙土的工程性能。(2)采用非饱和入渗法固化风沙土时,胶结液的加注速度对固化风沙土的均匀性有显著的影响。当胶结液加注流速为0.278 mol·L-1·h-1时,试样中生成的碳酸钙分布较均匀,无侧限抗压强度在4.585.03MPa之间,固化的风沙土试样质地比较均匀。(3)采用MICP技术在风沙土颗粒表面及孔隙中生成的碳酸钙晶体越多,则固化风沙土的密度越大,渗透系数越小,无侧限抗压强度越大。固化风沙土的渗透系数由原状沙的1.08×10-3 cm/s减小至1.67×10-5cm/s。无侧限抗压强度最大值达到了14.01MPa。无侧限抗压强度随碳酸钙含量的增加而增大,两者呈正相关关系。(4)采用分层固化的方法能够有效增大胶结风沙土的体积,非饱和入渗法受沙柱层高的影响较小,而饱和灌浆法则受层高影响较大。层高越小,无侧限抗压强度越高。层高相同时,非饱和入渗法比饱和灌浆法固化试样平均强度更高。饱和灌浆法固化风沙土的有效深度为0.20.7m,无侧限抗压强度在0.4m左右处达到峰值。(5)细菌在饱和沙柱中的分布是不均匀的,随着深度的增加,细菌浓度逐渐降低。细菌在沙柱中的最佳静置时间为4h,胶结液在沙柱中的最佳静置时间为24h。(6)X射线衍射分析结果表明固化风沙土中碳酸钙晶体类型均为方解石型。经光学显微镜和SEM分析,固化风沙土中有白色的方解石生成,晶体呈斜方六面体型,尺寸约为510μm,不同胶结液加注速度对微生物诱导生成的碳酸钙形态和尺寸无明显影响。

Aeolian sand is mainly distributed in arid and rainless desert areas.It is a kind of special soil with loose structure,fine and uniform particles,poor self-stabilization ability and not easy to compact.It should be reinforced when it is used as building foundation.Therefore,the reinforcement technology of aeolian sand is an important research topic.Microbial induced calcite precipitation(MICP)is a novel microbial soil-strengthening technique.In this paper,microbial-induced calcium carbonate precipitation technology and Bacillus pasteurium are used to reinforce aeolian sand,which can provide technical support for the engineering application of aeolian sand.(1)Using Sporosarcina pasteurii and cementing solution(mixed solution of urea and calcium chloride)by microbial induced calcium carbonate deposition(MICP)technology,calcium carbonate crystals with cementation effect can be formed between aeolian sand particles,effectively solidifying aeolian sand,improving the strength of aeolian sand,and improving the engineering performance of aeolian sand.(2)The injection rate of the cementing solution had a significant effect on the uniformity of the solidified aeolian sand.When the injection rate of the cementing solution was 0.278mol·L-1·h-1,the solidified aeolian sand sample was relatively uniform,and the calcium carbonate generated in the sample was evenly distributed,and the solidified aeolian sands have moderate unconfined compressive strength between 4.585.03MPa.The texture of solidified aeolian sand samples is relatively uniform.(3)The more calcium carbonate crystals are formed on the surface and pore of aeolian sand particles by MICP technology,the greater the density of solidified aeolian sand,the smaller the permeability coefficient and the greater the unconfined compressive strength.The permeability coefficient of the solidified aeolian sand gradually decreased from1.08×10-3cm/s of the original sand to 1.67×10-5 cm/s.The maximum unconfined compressive strength reached 14.01MPa.Unconfined compressive strength increases with the increase of calcium carbonate content,and the two are positively correlated.(4)Layered consolidation can effectively increase the volume of cemented aeolian sand.The unsaturated infiltration method is less affected by the higher sand column layer,while the saturated grouting method is more affected by the higher layer.The smaller the layer height,the higher the unconfined compressive strength.When the layer height is the same,the average strength of unsaturated infiltration method is higher than that of saturated grouting method.The effective depth of solidifying aeolian sand by saturated grouting is0.2-0.7m,and the unconfined compressive strength reaches its peak at about 0.4m.(5)The distribution of bacteria in the saturated sand column is not uniform.With the increase of depth,the concentration of bacteria decreases gradually.The optimum static time of bacteria in sand column is 4 hours,and the optimum static time of cementing fluid in sand column is 24 hours.(6)X-ray diffraction analysis shows that the calcium carbonate crystals generated by MICP in solidified aeolian sand are calcite.The results of optical microscopy and SEM analysis show that white calcite is formed in the solidified aeolian sand,and the crystal is hexahedron with a size of 510μm.The different filling rates of cementing solution have no significant effect on the morphology and size of calcium carbonate induced by microorganisms.

风沙土; 微生物诱导碳酸钙沉淀; 固化; 巴氏芽孢杆菌; 工程力学性能;

aeolian sand; microbially induced calcium precipitation; solidification; sporosarcina pasteurii; engineering mechanical properties;

国家重点研发计划:战略性国际科技创新合作重点专项 “丝绸之路经济带沿线国家流沙固定及植被恢复关键技术与示范 ”基金(编号:2016YF E0203400);

骆亚生;

TU41

221694394K