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在地震作用下发生的强度损失，可引起地基大变形和承载力损失，造成基础设施严重破坏。美国的主要基础设施位于易液化的淤泥土壤上，包括俄勒冈州波特兰哥伦比亚河沿着的许多燃料罐。然而，有几个可行的方法来减轻基础设施下的粉土液化，由于成本高，在许多情况下，现有的地基加固方法的侵入性。该奖项将研究微生物诱导的去饱和（MID）的有效性和耐久性，以减轻可液化的淤泥土壤。MID向地下注入一种处理溶液，刺激天然微生物。反硝化反应的主要产物是氮气，其降低土壤饱和度。众所周知，饱和度的小幅降低可显著提高砂土的抗液化性。然而，MID在淤泥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、现场测试和理论建模来解决这些未知因素。该奖项还将通过研究实习吸引来自全女子高中的代表性不足的学生。该项目旨在了解基本的土壤-水-气体相互作用，以评估MID减轻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）检查沼气在民用基础设施相关的时间尺度上的持久性，以及（iii）将空间和时间饱和度变化与该领域的基本物理学联系起来，这些物理学控制气体的流动性和寿命。将通过考虑孔隙流体压缩性和土骨架损伤的变化的室内循环试验来检查MID对液化触发的影响。将通过实验室实验研究细粒土壤中气体的形成，通过实验室规模的实验研究分层土壤中气体的扩散和再分布，通过实地规模的实验研究细粒分层土壤中地下水流的影响，从而研究气体的持久性。基于理论的气体传输模型，以检查土壤再饱和将开发和验证项目数据集。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，将MID从抽象的地基加固方法转变为可以评估为可行的长期地基加固方法。机械和制造创新（CMMI）部门和既定计划，以刺激竞争力的研究（EPSCoR）该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.