Collaborative Research: Efficacy and Durability of Microbially Induced Desaturation to Mitigate Liquefaction in Fine-grained Soils

地震液化是指饱和土体在地震作用下强度的严重损失，它会引起地基的大变形和承载能力的丧失，从而对基础设施造成严重的破坏。美国的主要基础设施位于易液化的粉质土壤上，包括俄勒冈州波特兰哥伦比亚河沿岸的许多燃料箱。然而，由于现有地基加固方法的成本较高，而且在许多情况下具有侵入性，因此几乎没有可行的方法来缓解基础设施下粉土的液化。该奖项将检验微生物诱导减饱和(MID)缓解可液化粉土的有效性和耐久性。MID将一种能刺激天然反硝化微生物的处理溶液注入地面。反硝化反应的主要产物是氮气，这会降低土壤饱和度。已知，饱和度的小幅降低可以显著提高砂土的抗液化能力。然而，MID在粉土中的有效性和寿命仍然是主要的未知数。本研究通过实验室实验、实地测试和理论建模来解决这些未知数。该奖项还将通过研究实习吸引全女生高中中代表性不足的学生。该项目旨在了解土壤-水-气的基本相互作用，以评估MID缓解细粒可液化材料液化的潜力。这项研究的具体目的是：(I)检查由于MID引起的周期性引起的超孔隙水压力的变化，以防止液化触发，(Ii)检查与民用基础设施相关的时间尺度上的沼气的持久性，以及(Iii)将现场的空间和时间饱和度变化与支配气体流动性和寿命的基本物理联系起来。MID对液化触发的影响将通过考虑孔隙流体可压缩性变化和土体骨架损伤的室内循环试验来检验。通过室内实验研究气体在细粒土壤中的形成，通过小规模实验研究气体在成层土壤中的扩散和再分布，通过野外实验研究细粒成层土壤中地下水流动的影响，以研究气体的持久性。将开发基于理论的气体运移模型来检查土壤再饱和度，并用项目数据集进行验证。这项工作将产生丰富的数据集和对土壤-水-气相互作用的理解，需要将MID从抽象的地基改良方法转变为可评估为可行的长期地基改良方法。该项目由土木、机械和制造创新工程(CMMI)部门和既定的激励竞争研究计划(EPSCoR)共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earthquake liquefaction is the severe loss of soil strength due to earthquake shaking in saturated soils, which can cause significant infrastructure damage from large ground deformations and bearing capacity loss. Major infrastructure in the US is on silt soils vulnerable to liquefaction, including many fuel tanks along the Columbia River in Portland, Oregon. However, there are few feasible methods to mitigate liquefaction of silt soils beneath infrastructure due to the high cost and, in many cases, the invasive nature of existing ground improvement methods. This award will examine the effectiveness and durability of microbially induced desaturation (MID) to mitigate liquefiable silt soils. MID injects into the ground a treatment solution that stimulates native denitrifying microbes. The primary product of the denitrification reaction is nitrogen gas, which reduces soil saturation. A small reduction in saturation is known to substantially increase liquefaction resistance in sands. However, the effectiveness and longevity of MID in silts remain major unknowns. This research addresses these unknowns through laboratory experiments, field testing, and theoretical modeling. This award will also engage underrepresented students from an all-girls high school through research internships. The project seeks to understand fundamental soil-water-gas interactions to evaluate the potential for MID to mitigate liquefaction of fine-grained liquefiable materials. This research specifically aims to (i) examine changes to the cyclically induced excess pore water pressure due to MID to prevent liquefaction triggering, (ii) examine the persistence of biogas on time-scales relevant to civil infrastructure, and (iii) link spatial and temporal saturation changes in the field to the fundamental physics governing gas mobility and longevity. The effects of MID on liquefaction triggering will be examined through laboratory cyclic tests considering both changes in pore fluid compressibility and soil skeleton damage. Gas persistence will be investigated by examining the formation of gas in fine-grained soils through laboratory experiments, gas diffusion and redistribution in layered soils with bench-scale experiments, and the effects of groundwater flow in fine-grained stratified soils through a field-scale experiment. Theory-based gas transport models to examine soil resaturation will be developed and validated with the project dataset. This work will generate a rich data set and understanding of soil-water-gas interactions required to move MID from an abstract ground improvement method to one that can be assessed as a practicable long-term ground improvement method.This project is jointly funded by the Engineering for Civil, Mechanical and Manufacturing Innovation (CMMI) Division and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.