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土工程性能的改善，从而使该方法可以用于减轻地震引起的液化损害。液化是在地震震动过程中饱和土壤沉积物从固体到粘性流体的快速转变。一些在地震中造成基础设施破坏的最严重和最昂贵的例子，如1964年的威廉王子湾地震、阿拉斯加地震、1971年的圣费尔南多地震和2010-12年的克赖斯特彻奇地震，都是由液化引起的。生物介导是利用天然存在的微生物来改变土壤的工程特性，可能是一种很有前途的液化预防技术。细菌过程可用于在饱和沉积物的颗粒中产生自然胶结，从而提高土壤对液化的抵抗力。此外，与传统的化学土壤改良技术相比，生物调解可能是一种更环保、更可持续的选择。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，从而在未来的地震中减少财产和生命的损失。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。多学科方法将有助于扩大代表性不足的群体在研究中的参与，并对工程和科学教育产生积极影响。该项目的目的是验证这样一个假设，即在动态加载的饱和砂中，微生物诱导碳酸钙沉淀的有效性是由颗粒间胶结的微观结构变化所控制的，这取决于循环应变加载的大小、大应变加载循环的次数和胶结密度。不同生物胶结密度的有效性将通过体积循环阈值应变和剪切模量、阻尼比和超孔隙水压力作为循环应变大小和大应变加载循环次数的函数来量化。具有不同MICCP密度的饱和生物介导的实验室标本将与未经处理的标本一起制备。弯曲单元、共振柱和应变控制动态循环三轴试验将用于测量不排水、松散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。这项工作的智力优势在于：(1)识别由于动态加载条件而引起的不同密度下微生物诱导胶结的微观结构变化；(2)量化它们对饱和砂宏观剪切模量和阻尼比的影响，这是动态加载土系统预测模型所必需的动态力学特性。将确定在可变载荷条件下动态力学性能和行为变化的微观结构机制，推进对动态载荷下生物胶结如何物理演化和强化饱和砂的机制理解。

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.