Collaborative Research: Use of Microbially-Induced Calcium Carbonate Precipitation to Improve Seismic Behavior of Saturated Sands

该奖项支持必要的基础研究，以量化微生物诱导胶结对砂的工程性质的改善，以便这种方法可用于减轻地震引起的液化损害。 液化是指饱和土壤存款在地震震动过程中从固体迅速转变为粘性流体。 地震中基础设施损坏的一些最引人注目和代价最高的例子，如1964年威廉王子湾阿拉斯加地震，1971年圣费尔南多地震和2010-12年基督城地震都是由液化引起的。 利用天然微生物改良土壤工程性质的生物调解技术可能是一种有前途的液化预防技术。 细菌过程可用于在饱和砂沉积物的颗粒内产生自然胶结作用，从而提高土壤的抗液化性。 此外，生物调解可能比传统的化学土壤改良技术更环保，更可持续。 这项研究的结果将使美国的基础设施和住房更能抵御地震破坏，从而降低未来地震中的财产和生命损失。 这项研究涉及多个学科，包括土木工程，环境工程，生物化学和可持续发展科学。 多学科的方法将有助于扩大在研究中代表性不足的群体的参与，并积极影响工程和科学教育。本项目的目的是测试的假设，即微生物诱导的碳酸钙沉淀在动态加载饱和砂的效果是由微观结构的变化，在颗粒间胶结取决于循环应变加载幅度，大应变加载周期数，和胶结密度。 不同的生物胶结密度的有效性将被量化的体积循环阈值应变和剪切模量，阻尼比，和过剩孔隙水压力的函数循环应变大小和数量的大应变载荷循环。将与未处理标本一起制备具有不同MICCP密度的饱和生物介导实验室标本。 弯曲元件、共振柱和应变控制动态循环三轴试验将用于测量不排水、不固结条件下生物胶结密度和动态加载条件的影响。 微生物强化的扫描电子显微镜图像将用于识别宏观行为的微观结构来源。 这项工作的智力价值在于：（1）识别微结构变化的微生物引起的胶结在不同的密度，由于动态加载条件和（2）量化的宏观剪切模量和阻尼比的饱和砂土，这是必要的动态力学性能的预测模型的动态加载土壤系统的影响。微观结构的机制，负责变化的动态力学性能和行为的变化，在可变的负载条件下将被确定，推进机械的理解如何生物胶结物理演变和强化饱和砂在动态负载下。

This award supports fundamental research necessary to quantify the improvements made to the engineering properties of sand by microbially induced cementation, so that this method can be used to mitigate against earthquake-induced liquefaction damage. Liquefaction is the rapid transformation of a saturated soil deposit from a solid to a viscous fluid during seismic shaking. Some of the most dramatic and costly examples of infrastructure damage in earthquakes such as the 1964 Prince William Sound, Alaska earthquake, the 1971 San Fernando earthquake, and the 2010-12 Christchurch earthquakes were caused by liquefaction. Bio-mediation, the use of naturally occurring microbes to modify the engineering properties of soils, may be a promising technology for liquefaction prevention. Bacterial processes can be used to generate natural cementation within the grains of saturated sand deposits, improving the soil's resistance to liquefaction. Bio-mediation may additionally be a more environmentally friendly, sustainable option than traditional chemical soil improvement techniques. Results from this research will make US infrastructure and housing more resilient to earthquake damage, resulting in lower loss of property and life in future earthquakes . This research involves several disciplines, including civil engineering, environmental engineering, biochemistry, and sustainability sciences. The multi-disciplinary approach will help broaden participation of underrepresented groups in research, and positively impact engineering and science education.The objective of this project is to test the hypothesis that the efficacy of microbially induced calcium carbonate precipitation in dynamically loaded saturated sands is governed by microstructural changes in interparticulate cementation dependent upon cyclic strain loading magnitude, number of large strain load cycles, and cementation density. The effectiveness of varying bio-cementation densities will be quantified in terms of volumetric cyclic threshold strains and shear moduli, damping ratios, and excess pore water pressures as functions of cyclic strain magnitudes and number of large strain load cycles. Saturated bio-mediated laboratory specimens with varying MICCP densities will be prepared alongside untreated specimens. Bender element, resonant column, and strain-controlled dynamic cyclic triaxial tests will be used to measure the effects of bio-cementation densities and dynamic loading conditions under undrained, unconsolidated conditions. Scanning electron microscopy images of microbial reinforcement will be used to identify microstructural sources of macroscopic behaviors. The intellectual merit of this work is in: (1) identification of microstructural changes in microbially induced cementation at varying densities due to dynamic loading conditions and (2) quantification of their effects on the macroscopic shear moduli and damping ratios of saturated sand, which are necessary dynamic mechanical properties for predictive models of dynamically loaded soil systems. The microstructural mechanisms responsible for the changes in the dynamic mechanical properties and behaviors under variable loading conditions will be identified, advancing a mechanistic understanding of how bio-cementation physically evolves and reinforces saturated sands under dynamic loads.