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

世界范围内大量城市人口的增长以及在有问题的土壤上建造的相关需求增加了对低噪音/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性，如液化。微生物诱导的碳酸盐沉淀（Microbial-induced carbonate precipitation，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，并且可以增强和工程化自然发生的生物地球化学反应。然而，中等收入国家方案面临着固有的土壤类型限制和空间变异问题，需要适当的质量控制/适应，必须满足所需的“持久性”，并可能造成不必要的环境后果。在将成功的实验室结果推广到实地条件方面经验有限，而且新技术必然会带来高昂的早期成本。 本研究的目标是将联合收割机新兴的地球物理技术与现有的土壤加固技术相结合，首先在实验室中研究MICP的可行性，然后在现场研究案例中升级结果。MICP已成为一种很有前途的生物介导的土壤改良技术。碳酸盐沉淀可以通过生物刺激来工程化，由此将选定的营养素注入土壤中，并使用土著土壤微生物来催化整个沉积物多孔网络中的碳酸盐沉淀，这是细胞生长或活性代谢过程中形成的副产物的直接结果。胶结作用对土壤特性的影响取决于胶结剂的数量和类型、土壤的粒度分布、密度和胶结时的约束程度，即，应力-胶结历史。 碳酸盐沉淀降低孔隙度，硬化和加强土体，改变内部结构对应力变化的反应，并增加剪切时的膨胀趋势。质量控制是任何土壤改良工作的关键组成部分。可以在真实的时间内定量地检查该过程，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概念。 本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）确定最大限度地减少空间变异性的条件并开发控制技术，（3）测试补充过程监测技术（使用局部和层析成像测试条件以及现场穿透CPTu的弹性剪切波速度和电频谱激发极化），以及（4）将实验室研究扩大到实地。

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.