Biogrout, ground improvement by microbial induced carbonate precipitation
Biogrout, ground improvement by microbial induced carbonate precipitation
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发表时间：
2009-10
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通讯作者：
L. Paassen
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作者：
L. Paassen
生物土工法是一种基于微生物诱导碳酸钙沉淀（MICP）的新型地基处理方法。当提供合适的基质时，微生物可以催化地下的生物化学转化，导致无机矿物质的沉淀，从而改变土壤的机械性质。本研究的重点是这些生化转换之一：微生物催化水解尿素诱导碳酸钙沉淀砂。该Biogrout方法包括以下步骤：培养巴氏孢子八叠球菌，一种含有大量尿素酶的细菌物种，注入地下并提供含有尿素和氯化钙的溶液。尿素酶催化尿素转化为铵和碳酸盐，并且所产生的碳酸盐与钙一起沉淀为碳酸钙晶体。这些晶体在砂粒之间形成粘着的楔形物，增加了沙子的强度和刚度。剩余的氯化铵被提取和处置。该论文包括必要的步骤，从实验室实验到实际应用，最终在一个前所未有的100立方米的现场规模的实验中，40立方米的沙子生物胶结在12天内延伸超过5米的距离。工程工具的建立，如CaCO3含量和强度或刚度之间的经验相关性，这使得设计处理程序的几个强调的应用，如增加刚度的铁路路基或提高石灰石房和支柱矿山的稳定性。该Biogrout工艺的一些剩余问题包括需要去除氯化铵和使用无菌培养的好氧生物体，由于地下缺氧，脲酶活性会随着时间的推移而衰减。为了避免这两个问题的其他可能的MICP过程的适合性进行评估，最有前途的替代品，反硝化，在实验室实验中显示的潜力。
Biogrout is a new ground improvement method based on microbially induced precipitation of calcium carbonate (MICP). When supplied with suitable substrates, micro-organisms can catalyze biochemical conversions in the subsurface resulting in precipitation of inorganic minerals, which change the mechanical soil properties. This study focuses on one of these biochemical conversions: microbially catalyzed hydrolysis of urea inducing calcium carbonate precipitation in sand. This Biogrout process comprises the following steps: Sporosarcina pasteurii, a bacterial species containing a large amount of the enzyme urease are cultivated, injected in the ground and supplied with a solution containing urea and calcium chloride. Urease catalyzes the conversion of urea into ammonium and carbonate and the produced carbonate precipitates with calcium as calcium carbonate crystals. These crystals form sticking wedges between the sand grains increasing the strength and stiffness of the sand. The remaining ammonium chloride is extracted and disposed. The thesis comprises the necessary steps to develop this process from a laboratory experiment to a practical application, culminating in an unprecedented 100 m3 field scale experiment in which 40 m3 of sand was biologically cemented within 12 days stretching over a distance of 5 m. Engineering tools are established such as empirical correlations between the CaCO3 content and strength or stiffness, which enable to design treatment procedures for several emphasized applications, such as increasing the stiffness of railroad embankment or improving the stability of limestone room and pillar mines. Some of the remaining issues of this Biogrout process include the required removal of ammonium chloride and the use of axenically cultivated aerobic organisms with consequent decaying urease activity in time due to a lack of oxygen in the subsurface. To avoid both these issues the suitability of other possible MICP processes for ground improvement is evaluated and the potential of the most promising alternative, denitrification, is shown in laboratory experiments.