Collaborative Research: Soil Improvement Through Bio-Cementation: Physical and Numerical Experiments

与地震震动相关的动态荷载可导致松散饱和砂土液化，实质上将合格的地质材料转化为流沙。任何存在于这些沉积物上的结构--天然的或人造的--都将由于与液化相关的强度损失而遭受灾难性的破坏。然而，水泥土比松散的粒状材料更不易液化。胶结作用可以由于某些矿物的沉淀而自然发生，也可以通过化学注入而诱导。最近，新的生物技术，如微生物诱导方解石沉淀（MICP）已被用于在实验室中模拟自然的胶结过程。生物胶结技术比传统的化学注入方法具有更可持续的潜力。这项工作将探讨使用紧密结合的数值实验程序的生物胶结的影响。这项工作的预期成果是一个建模框架：如果胶结水平是已知的，那么生物胶结土壤的行为可以预测。因此，作为这项工作的一部分开发的模型将帮助工程师使用生物胶结来防止未来地震中的液化。这项工作将通过课程开发和与俄勒冈州科学与工业博物馆的合作得到广泛传播。生物胶结（如MICP）具有通过增加砂土的循环强度、减少产生的超孔隙压力和减少动态荷载引起的沉降来增加抗液化性的潜力。水泥土的性能非常依赖于胶结剂的矿物学。用石灰、普通波特兰水泥和石膏等化学试剂人工胶结的砂与天然胶结的土壤表现不同。因此，现有的模型用于模拟化学胶结砂的行为是不适合生物胶结砂。在实施液化缓解的MICP之前，更好地理解生物胶结砂的本构行为的基本物理机制是必要的。测量底层微观力学（例如，颗粒粗糙度的变化、剪切过程中方解石细粉的产生）是传统实验难以解决的问题，因此将使用离散元方法模拟来帮助研究微观尺度的生物胶结砂。生物胶结砂的元素和颗粒尺度行为将通过强度测试、颗粒尺度测量和X射线计算机断层扫描相结合进行评估。这些实验的结果将用于开发和校准数值模型，以预测静态和动态载荷下生物胶结砂的体积响应。

Dynamic loading associated with earthquake shaking can lead to the liquefaction of loose, saturated sands, essentially transforming competent geological material into quicksand. Any structures - natural or man-made - that exist on these deposits will suffer catastrophic damage due to the loss of strength associated with liquefaction. Cemented soils, however, are less prone to liquefaction than loose granular materials. Cementation can occur naturally due to the precipitation of certain minerals or may be induced via chemical injections. More recently, novel biological techniques such as microbially induced calcite precipitation (MICP) have been used in the laboratory to mimic the natural cementation process. The biological cementation techniques have the potential to be more sustainable than traditional chemical injection methods. This work will explore the effects of bio-cementation using a tightly integrated numerical-experimental program. The expected outcome of the work is a modeling framework: if the level of cementation is known, then bio-cemented soil behavior can be predicted. Thus, the models dveloped as part of this work will help engineers use bio-cementation to prevent liquefaction during future earthquakes. The work will be broadly disseminated through course development and a collaboration with the Oregon Museum of Science and Industry.Bio-cementation such as MICP has the potential to increase liquefaction resistance by increasing the cyclic strength of sand, reducing the generated excess pore pressures, and reducing settlements due to dynamic loading. The behavior of cemented soil is extremely dependent on the mineralogy of the cementing agent. Sands cemented artificially with chemical agents, such as lime, ordinary Portland cement, and gypsum behave differently than naturally cemented soils. Thus, existing models used to simulate the behavior of chemically-cemented sand are not appropriate for bio-cemented sand. Before implementing MICP for liquefaction mitigation, a better understanding of the underlying physics governing the constitutive behavior of bio-cemented sands is necessary. Measuring the underlying micromechanics (e.g., changes in particle roughness, calcite fines generation during shearing) is difficult with traditional experiments, so discrete element method simulations will be used to help study bio-cemented sand at the microscale. Element- and particle scale behavior of bio-cemented sands will be assessed through a combination of strength testing, particle-scale measurements, and X-ray computed tomography. Results from these experiments will be used to develop and calibrate numerical models to predict the bulk response of bio-cemented sands subjected to static and dynamic loading.