基于微生物体系加固砂土地基力学特性及机理研究

发布时间：2019-02-09 16:02

【摘要】：机械压实和化学灌浆是现今土体加固处理应用最为广泛的两种方式,但其高成本、高能耗以及对环境污染和破坏的缺点促使了对新型土体加固技术的探索。新世纪以来,基于理、化、生交叉学科衍生出的一种微生物诱导碳酸钙沉淀(MICP)技术得到了广泛重视与研究,研究表明,该项技术可以显著改善土体强度、刚度、渗透性及抗液化性能,并且相比于传统土体改良工艺,其绿色环保、环境友好型特点更加符合可持续发展理念。本文主要开展了巴氏芽孢杆菌(Sporosarcina pasteurii)诱导碳酸钙沉淀影响因素及灌浆胶结砂土强度试验研究,并对微生物固化砂柱内部微观结构进行了观测研究以探明胶结机理,主要研究内容和结论如下:(1)首先对巴氏芽孢杆菌诱导碳酸钙沉积影响因素进行了研究,采用对比试验对钙源的选择进行了优化;胶结液浓度小于1.0mol/L时,随着浓度的提升碳酸钙产量得以增加,但胶结液浓度过高钙离子对脲酶活性产生较大的抑制,碳酸钙产量减少;p H值在6~9之间对诱导碳酸钙的影响较小,但碳酸钙产量随着温度的上升而增加。(2)开展了巴氏芽孢杆菌菌液灌注加固砂土试验研究,采用混合注入法和分步灌浆法胶结砂柱发现,分步灌注更有利于砂土的整体固化效果;对比分析单一浓度和高、低浓度胶结液结合灌注对砂柱胶结效果的影响,基于微生物固化砂柱进行无侧限抗压试验,并分析了不同灌注方式对砂柱的破坏模式、碳酸钙含量和强度的影响,高、低浓度结合灌注能在较少的灌注次数下获得比较高的强度,最高强度达到10MPa左右,不同灌注方式对砂柱的破坏模式和碳酸钙含量上没有太大的影响,不同试样的强度区别主要是微生物诱导的碳酸钙在砂柱中分布均匀性不同导致。(3)利用扫描电子显微镜(SEM)对微生物固化砂柱进行微观测试,探明砂颗粒间的胶结方式,并通过化学法诱导碳酸钙加固砂土开展对比试验。试验发现微生物诱导球形状和球形聚集体碳酸钙晶体将砂颗粒包裹,并且尺寸较小晶体间相互交错嵌合将砂颗粒胶结成整体,砂颗粒间依旧保存着一定孔隙,而化学法沉积碳酸钙晶体呈斜六面体尺寸较大并未将砂颗粒粘结成整体。
[Abstract]:Mechanical compaction and chemical grouting are the two most widely used methods of soil reinforcement, but their high cost, high energy consumption and the shortcomings of environmental pollution and damage promote the exploration of new soil reinforcement technology. Since the new century, a microorganism induced calcium carbonate precipitation (MICP) technique derived from the interdisciplinary disciplines of science, chemistry and biology has been widely studied. The results show that this technique can significantly improve the strength and stiffness of soil. The properties of permeability and liquefaction resistance are more consistent with the concept of sustainable development than the traditional soil improvement technology. In this paper, the influencing factors of calcium carbonate precipitation induced by Bacillus pasteurium (Sporosarcina pasteurii) and the strength test of grouting cemented sand soil were studied, and the microstructure of microorganism solidified sand column was observed to find out the cementation mechanism. The main contents and conclusions are as follows: (1) the factors affecting the calcium carbonate deposition induced by Bacillus pasteurium were studied, and the selection of calcium source was optimized by contrast test. When the concentration of cementing solution was less than 1.0mol/L, the yield of calcium carbonate increased with the increase of concentration, but too high concentration of calcium in cementing solution inhibited urease activity greatly, and the yield of calcium carbonate decreased. The pH value between 6 and 9 had little effect on the induced calcium carbonate, but the yield of calcium carbonate increased with the increase of temperature. (2) A study on the reinforcement of sand soil with Bacillus pasteuris liquid was carried out. By using mixed injection method and step grouting method to cement sand column, it is found that step by step grouting is more favorable to the overall solidification effect of sand. The effect of single concentration, high concentration and low concentration of cementing liquid on the cementation effect of sand column was compared and analyzed. Based on the microorganism solidified sand column, the unconfined compression test was carried out, and the failure modes of different pouring methods to sand column were analyzed. Under the influence of calcium carbonate content and strength, high and low concentration of calcium carbonate can get higher intensity under less perfusion times, and the maximum strength is about 10MPa. Different pouring methods have no great effect on the failure mode and calcium carbonate content of sand column. The difference in strength of different samples is mainly due to the difference in the distribution uniformity of calcium carbonate induced by microorganism in the sand column. (3) the microcosmic test of microorganism solidified sand column is carried out by scanning electron microscope (SEM), and the cementation mode between sand particles is proved. A comparative experiment was carried out to induce calcium carbonate to reinforce sandy soil by chemical method. It was found that the microorganism induced the ball shape and the spherical aggregate calcium carbonate crystal to wrap the sand particles, and the smaller crystals interlaced each other to form the whole sand particles, and there were still some pores in the sand particles. However, the larger size of the hexahedron crystal deposited by the chemical method did not bind the sand particles into a whole.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU472

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