SGER: Biological Improvement of the Mechanical Properties of Soils

摘要：这一SGER项目将通过一系列小试实验，论证三种不同的微生物改良土壤物理性质的机制的可行性。虽然近年来利用微生物方法修复土壤和地下水污染的潜力已被广泛探索，但利用微生物方法改善土壤物理性质用于岩土工程应用的潜力在很大程度上还没有被探索，尽管它存在于许多自然地质过程中。工程过程中由微生物引起的潜在改进包括增加剪切强度、降低压缩性、降低水力传导性和降低液化势。该项目将涉及的三个微生物过程是矿物沉淀、矿物转化以及生物膜和生物聚合物的生长。众所周知，这些过程在地质时间尺度上改善土壤的工程性质，也已知在较短的时间内引起土壤工程性质的潜在有益变化，但在环境使这些影响变得不可取的情况下(例如，堵塞垃圾填埋场下水道和水处理厂过滤器)。在开发这些微生物过程的有益应用方面的工程挑战包括在感兴趣的工程地点的工程兴趣的时间范围内诱导所需的过程，并控制该过程以避免不想要的副作用。这项研究计划包括三个系列的小规模实验，以证明这些微生物机制在工程上感兴趣的时间框架内改善土壤物理性质的可行性。一系列实验将尝试通过三种不同的机制：硫酸盐还原、反硝化和尿素分解来诱导颗粒土壤中的碳酸盐沉淀，以增加剪切强度和降低液化潜力。第二系列实验将评估微生物将大多数膨胀土中发现的粘土矿物蒙皂石转化为伊利石的潜力，伊利石是一种明显不那么膨胀的粘土矿物，从而减轻土壤膨胀(膨胀潜力)。第三系列小试试验将评估生物聚合物堵塞对粒状土壤力学性质的影响。这些实验将一起评估微生物改善土壤物理性质的三种主要候选机制。成功地利用微生物改善土壤的物理(岩土)性质将开启岩土工程的新纪元--生物改良时代。矿物降水将在修复粒状土壤液化潜力方面提供显著的优势，特别是在现有构筑物附近或之下，传统的土壤改良技术由于相关的地面变形和/或高昂的成本而受到限制，例如稳定斜坡、控制土壤侵蚀和冲刷、减少浅层地基的沉降和提高承载能力、稳定开挖和缓解隧道中的流沙。此外，微生物矿物沉淀可以用来封堵碎裂岩层中的裂缝。矿物转化可以用来缓解与基于膨胀土壤的住宅地基和道路相关的问题，据估计，这个问题每年给美国经济造成超过50亿美元的损失。生物聚合物和生物膜的潜在应用包括暂时和永久的地下水控制，减轻液化潜力，以及可能的钢铁和混凝土结构的腐蚀保护。土壤微生物改良的成功还将促进微生物学和地球化学与岩土工程相结合的一个新的跨学科领域的创建。今天科学和工程上最大的进步来自于迄今互不相关的领域的相互作用。将微生物学和地球化学与岩土工程结合起来，是创造这样一个界面的绝佳机会，具有深远的科学和实践效益。

Abstract:This SGER project will demonstrate the feasibility of three different mechanisms for microbiologically based improvement of the physical properties of soil through a series of bench-scale experiments. While the potential for employing microbiological process to remediate soil and groundwater contamination has been extensively explored in recent years, the potential for employing microbiological processes to improve the physical properties of soils for geotechnical engineering applications is largely unexplored, despite its occurrence in many natural geologic processes. Potential microbiologically-induced improvements in the engineering process include increased shear strength, decreased compressibility, decreased hydraulic conductivity, and reduced liquefaction potential. The three microbiological processes that will be addressed by the project are mineral precipitation, mineral transformation, and biofilm and biopolymer growth. These processes are known to improve the engineering properties of soil on a geological time scale and are also known to induce potentially beneficial changes in engineering properties of soils in shorter time frames, but in situations where the context renders these effects undesirable (e.g., clogging of landfill drains and water treatment plant filters). The engineering challenges in developing beneficial applications of these microbiological processes involve inducing the desired process over a timeframe of engineering interest in the location of interest and controlling the process to avoid unwanted side effects. This research program consists of three series of bench scale experiments to demonstrate the feasibility of these microbiological mechanisms for improving the physical properties of soil over time frames of engineering interest. One series of experiments will attempt to induce carbonate precipitation in granular soil to increase shear strength and reduce liquefaction potential using three different mechanisms: sulfate reduction, denitrification, and ureolysis. The second series of experiments will evaluate the potential for microbial transformation of smectite, the clay mineral found in most expansive soils, to illite, a significantly less expansive clay mineral and thereby mitigate soil expansion (swell potential). The third series of bench scale experiments will evaluate the impact of biopolymer plugging on the mechanical properties of granular soil. Together, these experiments will evaluate three of the primary candidate mechanisms for microbiological improvement of the physical properties of soils.Success with microbial improvement of the physical (geotechnical) properties of soil would open up a new era in geotechnical engineering - the era of bio-improvement. Mineral precipitation would provide significant advantages in remediation of liquefaction potential of granular soils, especially near or beneath existing structures where traditional soil improvement techniques are limited because of associated ground deformations and/or high cost, stabilization of slopes, control of soil erosion and scour, reduction of settlement and increase in bearing capacity for shallow foundations, stabilization of excavations, and mitigation of flowing sands in tunnels. In addition, microbial mineral precipitation could be used to seal the cracks within a fractured rock formation. Mineral transformation could be used to mitigate problems associated with residential foundations and roadways founded upon expansive soils, a problem that is estimated to cost the US economy over $5 billion per year. Potential applications of biopolymer and biofilms include temporary and permanent groundwater control, mitigation of liquefaction potential, and possibly corrosion protection of steel and concrete structures. Success with microbial improvement of soil will also spur the creation of a new inter-disciplinary field that marries microbiology and geochemistry with geotechnical engineering. The greatest advancements in science and engineering today come at the interfaces of heretofore unrelated fields. Bringing microbiology and geochemistry to bear on geotechnical engineering is an exceptional opportunity for creating such an interface, one with profound scientific and practical benefits.