Investigating the Life Cycle Performance of Bio-cementation Soil Improvement: Synthesis, Degradation, and Repair

岩土地基改良技术传统上依赖于使用高机械能和高能量密集型材料来改善土壤工程性质。最近，生物介导的土壤改良这一新兴领域显示了自然化学和生物过程的变革潜力，可以改善脆弱的、有问题的土壤，减少对环境和社会的不利影响。微生物诱导方解石沉淀(MICP)，或生物胶结，是一种利用生物介导性碳酸钙沉淀来改善土壤工程性质的技术。尽管取得了重大进展，但对控制生物胶结材料性能的因素、生物胶结土壤可能随时间退化的过程以及检测和修复受损生物胶结土壤的方法的了解有限，限制了我们评估MCP的长期弹性、量化工艺环境影响以及了解处理和现场条件对材料工程性能的影响的能力。这个项目将通过综合的地球化学和岩土实验和数值模拟，解决我们对生物胶结土壤改良生命周期性能的关键空白，这些性能与材料的合成、降解和修复有关。这项研究将提高独立的民用基础设施系统的弹性，并减少由于生物胶结和类似胶结/老化的岩土材料失效而造成的潜在经济、生命和财产损失。材料长期性能不确定性的降低有望在工程实践中更多地采用生物介体地基改良替代方案，从而减少材料和能源消耗、有害环境影响和改善公众健康。代表不足的少数群体(URM)和女学生更多地参与研究活动，将培养一批具有多学科专长的学生，从而使生物遗传技术领域在学术界和工程实践中继续发展。外展活动将侧重于通过在华盛顿大学工程探索日等活动中的动手演示和展览吸引初中生和高中生，并与当地K-12学校和太平洋科学中心建立伙伴关系。每年将有500多名K-12学生接触到工程、地质、材料科学、化学和微生物学的STEM概念，以激励新一代多学科的工程师。这项研究计划将利用批量和一维传输地球化学实验、三轴和土柱岩土实验、反应传输数值模拟和先进的化学、生物和材料分析来：(1)调查矿物合成过程中生物地球化学条件对控制长期化学和机械弹性的生物胶结特性的影响；(2)评估生物胶结的化学持久性，包括矿物溶解和溶解动力学；(3)考察化学和机械诱导的破坏对生物胶结土壤性能的影响，包括工程性质、破坏模式和退化监测方法的演变。以及(4)开发能够保护和修复受损的生物胶结土壤的技术，同时最大限度地减少能源和材料的使用。为实现这些研究目标，将完成三项综合研究任务。首先，将进行一系列间歇反应器实验，以了解沉淀过程中的生物地球化学反应条件、生物胶结形成和沉淀材料性质之间的关系。其次，将完成一系列的地球化学和岩土实验室实验，以表征生物胶结的溶解度和溶解行为随沉淀性质和地下环境条件的变化。所获得的结果将为开发特定于生物胶结的溶解动力学框架提供信息，以预测材料的原位持久性。最后，将进行岩土和地球物理调查，以确定检测胶结降解的非破坏性方法，开发新的修复技术，并探索生物胶结降解和修复对生物胶结土壤工程行为的影响，包括材料应力-扩容、模数退化、弹性和屈服后响应、临界状态和峰值剪切强度以及孔压和应变累积的变化。

Geotechnical ground improvement technologies have traditionally relied upon the use of high mechanical energy and energy-intensive materials to improve soil engineering properties. Recently, the emerging field of bio-mediated soil improvement has shown the transformative potential of natural chemical and biological processes to improve weak, problematic soils with reductions in detrimental environmental and societal impacts. Microbially Induced Calcite Precipitation (MICP), or bio-cementation, is one such technology that uses the biologically-mediated precipitation of calcium carbonate to improve soil engineering properties. Despite significant advances, limited understanding of the factors that control bio-cementation material properties, the processes by which bio-cemented soils may degrade over time, and the methods by which damaged bio-cemented soils can be detected and repaired, has restricted our ability to evaluate the long-term resilience of MICP, quantify process environmental impacts, and understand the implications of treatment and site conditions on material engineering performance. This project will address critical gaps remaining in our understanding of the life cycle performance of bio-cementation soil improvement related to material synthesis, degradation, and repair through integrated geochemical and geotechnical experiments and numerical modeling. This research will improve the resiliency of dependent civil infrastructure systems and mitigate potential economic, life, and property losses resulting from failure of bio-cemented and similar cemented/aged geomaterials. Decreased uncertainty in material long-term performance is expected to increase adoption of bio-mediated ground improvement alternatives in engineering practice thereby reducing material and energy consumption, detrimental environmental impacts, and improving public health. Increased participation of under-represented minority (URM) and women students in research activities will develop a diverse cohort of students with multidisciplinary expertise, therefore enabling continued development of the biogeotechnics field in academia and engineering practice. Outreach activities will focus on engaging middle and high school students through hands-on demonstrations and exhibits at events including the University of Washington Engineering Discovery Days and partnerships with local K-12 schools and the Pacific Science Center. Over 500 K-12 students will be exposed annually to STEM concepts from engineering, geology, material science, chemistry, and microbiology to inspire a new generation of multidisciplinary engineers. This research program will leverage batch and 1D-transport geochemical experiments, triaxial and soil column geotechnical laboratory tests, reactive transport numerical modeling, and advanced chemical, biological, and material analyses to: (1) investigate the effect of biogeochemical conditions during mineral synthesis on the properties of bio-cementation controlling long-term chemical and mechanical resilience, (2) assess the chemical permanence of bio-cementation including mineral solubility and dissolution kinetics, (3) examine the effects of chemically and mechanically-induced damage on the performance of bio-cemented soils including evolution of engineering properties, damage patterns, and degradation monitoring methods, and (4) develop techniques which can protect and heal damaged bio-cemented soils while minimizing energy and material usage. To achieve these research objectives, three integrated research tasks will be completed. First, a series of batch reactor experiments will be performed to understand relationships between biogeochemical reaction conditions during precipitation, bio-cementation formation, and precipitate material properties. Second, a series of geochemical and geotechnical laboratory experiments will be completed to characterize the solubility and dissolution behavior of bio-cementation as a function of precipitate properties and subsurface environmental conditions. Obtained results will inform the development of a dissolution kinetic framework specific to bio-cementation for prediction of material in-situ permanence. Lastly, geotechnical and geophysical investigations will be performed to identify non-destructive approaches for detection of cementation degradation, develop novel repair techniques, and explore the effect of bio-cementation degradation and repair on the engineering behavior of bio-cemented soils including changes in material stress-dilatancy, modulus degradation, elastic and post-yielding response, critical-state and peak shear strength, and pore pressure and strain accumulationThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.