Collaborative Research: Laboratory-to-Field Scaling and Geophysical Monitoring for Soil Bio-Improvement

世界各地大量城市人口的增长以及与之相关的在土壤问题场地上建设的需要，增加了对低噪音/低能量地基改良技术的需求，以阻止土壤沉降，增加土壤强度，并防止地下土壤不稳定，如液化。微生物诱导碳酸盐沉淀(MICP)是一种很有前途的土壤改良技术，因为能够引起碳酸钙沉淀的微生物在地球系统中普遍存在，而且自然发生的生物地球化学反应可以增强和工程实现。然而，MICP面临固有的土壤类型限制和空间变异性问题，需要充分的质量控制/适应，必须满足所需的“永久性”，并可能造成不希望看到的环境后果。将成功的实验室结果推广到现场条件方面的经验有限，而且新技术本身就存在较高的早期成本。这项研究的目标是将新兴的地球物理技术与现有的土壤加固技术相结合，首先在实验室中调查MICP法的可行性，然后在实地研究案例中提升结果。MICP是一种很有前途的生物介导型土壤改良技术。碳酸盐沉淀可以通过生物刺激工程实现，通过将选定的养分注入土壤，并使用本地土壤微生物催化整个沉积物多孔网络的碳酸盐沉淀，这是细胞生长或活跃新陈代谢过程中形成的副产品的直接结果。胶结作用对土体性质的影响取决于胶结剂的用量和类型、土壤的颗粒分布、密度和胶结时的约束程度，即应力胶结历史。碳酸盐沉淀减少了孔隙度，使土体变硬和加强，改变了内部组构对应力变化的响应，增加了剪切时的膨胀趋势。质量控制是任何土壤改良工作的关键组成部分。可以实时定量地检查这一过程，以评估生物处理的演变和空间范围，并对其进行调整/优化以提高其效率。这项研究将探索互补的、实时监测的概念。为这项研究选择的非侵入性地球物理工具将在实验室中开发和优化，然后将扩大到现场条件。这项研究将包括以下活动：(1)探索环境安全的最佳部署战略；(2)确定将空间变异性降至最低的条件，并开发控制技术；(3)测试补充的过程监测技术(利用当地和层析测试条件以及实地渗透CPTU测试弹性剪切波速度和电谱激发极化)，以及(4)扩大实地的实验室研究。

The growth of large urban populations worldwide and the associated need to build on sites with problematic soils has increased the need for low-noise/low-energy ground improvement techniques to hinder soil settlements, increase soil strength, and prevent subsurface soil instabilities such as liquefaction. Microbial-induced carbonate precipitation (MICP) has emerged as a promising technique to improve soil sites because microorganisms capable of causing calcium carbonate precipitation are ubiquitous in earth systems, and naturally-occurring biogeochemical reactions can be augmented and engineered. However, MICP faces inherent soil type limitations and spatial variability issues, requires adequate quality control/adaptation, must satisfy required "permanency," and may pose unwanted environmental consequences. There is limited experience with upscaling successful laboratory results to field conditions, and there are high early costs inherently related to new technology. The goal of this research is to combine emerging geophysical technologies with established soil strengthening techniques to first investigate the feasibility of MICP in the laboratory and then upscale the results in a field study case. MICP has emerged as a promising bio-mediated soil improvement technique. Carbonate precipitation can be engineered by biostimulation, whereby selected nutrients are injected into the soil and indigenous soil microorganisms are used to catalyze carbonate precipitation throughout the sediment porous network as a direct consequence of byproducts formed during cell growth or active metabolism. The effect of cementation on soil behavior depends on the amount and type of cementing agent, grain size distribution of the soil, density, and degree of confinement at the time of cementation, i.e., the stress-cementation history. Carbonate precipitation reduces porosity, stiffens and strengthens the soil mass, alters the response of the internal fabric to stress changes, and increases the dilative tendency upon shear. Quality control is a critical component of any soil improvement effort. The process can be quantitatively examined in real time to assess the evolution and spatial extent of the bio-treatment and to adapt/optimize it to increase its efficiency. This research will explore complementary, real-time monitoring concepts. The non-invasive, geophysical tools selected for this study will be developed and optimized in the laboratory, and then will be scaled up to field conditions. This research will include the following activities: (1) explore environmentally-safe, optimal deployment strategies, (2) identify conditions to minimize spatial variability and develop control techniques, (3) test complementary process-monitoring techniques (elastic shear wave velocity and electrical-spectral induced polarization using both local and tomographic test conditions and penetration CPTu in the field), and (4) scale up laboratory studies to the field.