Bacteria in Sediments: Soil Bio-engineering

微生物活动影响了地球表面的演化，将大气从还原转变为氧化，改变了地球的矿物性质(今天大多数矿物要么含有氧气，要么含有氢氧化物)，加快了岩石风化和土壤形成的速度，影响了地下水的组成，并参与了天然气和石油碳氢化合物的形成。在这项研究中，我们提出了利用生物活性的巨大转化能力在短时间内对近地表土壤进行生物工程。我们明确认识到有限的尺寸效应：虽然细菌的大小约为1微米，但土壤和土壤孔隙的范围可以从纳米到几米。因此，我们特别感兴趣的是定义土壤中生物活动的几何和力学限制(同时认识到其他潜在的限制因素，如碳、水和营养)。这项研究的具体目标是(1)开发受控的生物矿化方法，以增加颗粒骨架的小应变剪切刚性和扩张性，(2)确定与各种矿化途径相关的生物生成气体的潜在影响，以及(3)确定沉积物中新陈代谢和生物生存所需的条件，作为沉积物粒度和有效应力的函数。研究方法是基于有针对性的实验，使用精心挑选的细菌物种和沉积物来放大研究中的现象，或证伪潜在的假设。为每个任务设计了详细的实验方案。广泛的仪器和地球物理测量将能够实时监测过程的演变，包括潜在的长期可逆性。实验将与分析模型的发展相辅相成，以捕捉支配的物理和生物过程，以及扩展实验范围的离散元素模拟。结果将影响工程(例如，增强的地震性能、微裂缝的愈合，以及新的地基、挖掘和隧道施工)以及科学(例如，生物地质过程的界限、重新评估生物圈深层的生物活动或海洋沉积物中的自生碳酸盐形成)。这项研究将在生物过程的新维度推动土壤行为和岩土工程，超越今天的物理-力学-化学框架，它将探索潜在的革命性的工程实践的新方案。将编写教育单元，并将其分发给社区。

BACTERIA IN SEDIMENTS: BIO-ENGINEERED SOILSMicrobial activity has influenced the evolution of the earth's surface, converted the atmosphere from reducing to oxidizing, changed the mineral nature of the earth (today most minerals contain either oxygen or hydroxide), accelerated the rate of rock weathering and altered soil formation, influenced the composition of groundwater, and participated in the formation of gas and petroleum hydrocarbons. In this research, we put forward that the tremendous transforming power of bioactivity can be harnessed to bio-engineer near surface soils in short, engineering-time scales. We explicitly recognize limiting size effects: while bacteria are ~1 micron in size, soils and soil pores can range from nanometers to meters. Therefore, we have special interest in defining the geometrical and mechanical limits for bio-activity in soils (while recognizing other potential limiting factors such as carbon, water and nutrients).The specific goals of this research are (1) to develop controlled bio-mineralization methods to increase the small strain shear stiffness and dilatancy of the granular skeleton, (2) to identify the potential effects of bio-generated gas associated to various mineralization pathways, and (3) to determine the conditions required for metabolism and 'bio-survivability' in sediments as a function of sediment grain size and effective stress. The research methodology is based on targeted experimentation, using carefully selected bacterial species and sediments to magnify the phenomena under study, or to falsify the underlying hypotheses. Detailed experimental protocols are designed for each task. Extensive instrumentation and geophysical measurements will permit monitoring the evolution of processes in real time, including the potential long-term reversibility. Experimentation will be complemented with the development of analytical models that capture the governing physical and biological processes, and discrete element simulations that extend the experimental range.Results will affect both engineering (e.g., enhanced seismic performance, healing of microfractures, and new foundation, excavation and tunneling practices) as well as science (e.g., bounds for bio-geological processes, reassessment of bioactivity in the deep biosphere, or authigenic carbonate formation in marine sediments).This research will advance soil behavior and geotechnical engineering in the new dimension of biological processes, beyond today's physical-mechanical-chemical framework, and it will explore potentially revolutionary new alternatives for engineering practice. Educational modules will be prepared and distributed to the community.