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

与地震相关的动态荷载会导致松散、饱和的砂土液化，基本上将合格的地质材料转化为流沙。存在于这些沉积物上的任何天然或人造结构都将遭受灾难性的破坏，因为与液化相关的强度损失。然而，水泥土比松散的颗粒状材料更不容易液化。由于某些矿物的沉淀，胶结可以自然发生，也可以通过化学注射诱导。最近，新的生物技术，如微生物诱导方解石沉淀(MICP)，已经在实验室中被用来模拟自然胶结过程。生物胶结技术有可能比传统的化学注入方法更具可持续性。这项工作将使用一个紧密集成的数值实验程序来探索生物粘结的影响。这项工作的预期结果是一个建模框架：如果胶结程度已知，那么生物胶结土壤的行为就可以预测。因此，作为这项工作的一部分而开发的模型将帮助工程师使用生物胶结来防止未来地震时的液化。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。MICP等生物胶结通过增加砂子的循环强度、减少产生的过剩孔压和减少动态加载引起的沉降量，有可能提高抗液化能力。胶结土的性质与胶结剂的矿物学性质密切相关。用化学试剂(如石灰、普通波特兰水泥和石膏)人工胶结的沙子与天然胶结土壤的性能不同。因此，现有的用于模拟化学胶结砂行为的模型不适用于生物胶结砂。在实施MICP用于液化缓解之前，有必要更好地了解支配生物胶结砂土本构行为的基本物理原理。用传统实验很难测量潜在的微观力学(例如，颗粒粗糙度的变化，剪切过程中方解石粉的生成)，因此离散元方法模拟将有助于在微观尺度上研究生物胶结砂。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的方式进行评估。这些试验的结果将被用来开发和校准数值模型，以预测生物胶结砂在静态和动态载荷下的整体响应。

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.