Exploratory Research in Microbial Remediation of Liquefiable Soils

饱和松散砂土在地震荷载作用下易发生液化，即孔隙水压力突然增大导致土体强度迅速丧失。在这些土壤上建造的结构在液化过程中可能由于地基土失去支撑而引起的过度沉降而遭受严重变形或破坏。在未开发的地方，经过验证的土壤改良方法-例如，动态压实和振冲压实-可以减少液化的可能性。然而，在已经存在结构或附近存在结构的地点，这些方法要么不可能实施，要么不切实际，因为它们可能对这些结构造成损害。本研究的目的是确定细菌的添加，无论是简单的粘附细菌还是生物成膜细菌，是否增加了可液化土壤的强度和稳定性。据推测，微生物将在颗粒之间提供一些凝聚力/胶结，从而增加它们对液化的抵抗力。很少有人研究利用微生物来提高土壤的强度。松散的沙子将分别接种两种生物，细胞噬菌U67（一种生物膜前体）和突变细胞噬菌U67（一种非生物膜前体）进行测试。细胞吞噬自然存在于饱和、低营养的环境中。微生物在固体上的附着有望在颗粒之间产生内聚/胶结，从而降低土壤沉积物在孔隙水压力快速增加时强度损失的敏感性。将使用叶片剪切试验和/或无侧限压缩试验来测量砂的内聚强度增益。该项目将提供关于微生物在可液化土壤修复中的潜在用途的信息。它还将启动拉斐特学院土木工程系和生物系之间的第一个合作研究项目。研究结果将通过海报展示和发表的研究论文向更广泛的科学界传播。

Saturated loose sand deposits subjected to seismic loads are susceptible to liquefaction, a phenomenon in which there is a rapid loss of strength of the soil caused by a sudden increase in porewater pressure. Structures built on these soils may suffer severe deformations or failure during liquefaction due to excessive settlement caused by the loss of support from the foundation soils. At undeveloped sites, proven methods of soil improvement - e.g., dynamic compaction and vibro-compaction - can reduce the likelihood of liquefaction. However, at locations where structures already exist or exist nearby, these methods are either impossible to implement or are impractical as they may cause damage to these structures.The aim of this research is to determine whether the addition of bacteria, either simple adhering bacteria or biofilm formers, increases the strength and stability of liquefiable soils. It is hypothesized that the microbes will provide some cohesion/cementation between the particles, thereby increasing their resistance to liquefaction. Very little research has been done on the use of microbes to improve the strength properties of soil. Loose sands will be inoculated in separate tests with two organisms, Cytophaga U67 (a biofilm former) and a mutant Cytophaga U67 (a non-biofilm former). Cytophaga are naturally found in a saturated, low-nutrient environment. The attachment of the microbe to the solids is expected to create cohesion/cementation between particles, thereby reducing the susceptibility of the soil deposit to loss of strength during rapid increases in porewater pressure. Cohesive strength gains in the sand will be measured using vane shear tests and/or unconfined compression tests.This project will provide information on the potential use of microbes in the remediation of liquefiable soils. It will also initiate the first collaborative research project between the civil engineering and biology departments at Lafayette College. The results will be disseminated to the wider scientific community through poster presentations and published research papers.