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

传统上，土工地基改良技术依赖于使用高机械能和能源密集型材料来改善土壤工程特性。最近，新兴的生物介导的土壤改良领域已经显示出自然化学和生物过程的变革潜力，以改善脆弱的，有问题的土壤，减少有害的环境和社会影响。 微生物诱导的方解石沉淀（MICP）或生物胶结，是一种利用生物介导的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特性的因素、生物胶结土壤可能随时间降解的过程以及受损生物胶结土壤可以检测和修复的方法的了解有限，限制了我们评估MICP的长期弹性，量化过程环境影响，并了解处理和现场条件对材料工程性能的影响。该项目将通过综合地球化学和岩土工程实验以及数值模拟，解决我们对生物胶结土壤改良与材料合成、降解和修复相关的生命周期性能的理解中存在的关键差距。 这项研究将提高依赖民用基础设施系统的弹性，并减轻生物胶结和类似胶结/老化地质材料失效造成的潜在经济、生命和财产损失。 材料长期性能的不确定性降低，预计将增加在工程实践中采用生物介导的地基改良替代方案，从而减少材料和能源消耗，有害的环境影响，并改善公众健康。 代表性不足的少数民族（URM）和女学生参与研究活动的增加将培养具有多学科专业知识的多样化学生群体，从而使学术界和工程实践中的生物技术领域得以持续发展。 外联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示范和展览，以及与当地K-12学校和太平洋科学中心的伙伴关系，吸引初中和高中学生。 每年将有超过500名K-12学生接触来自工程，地质学，材料科学，化学和微生物学的STEM概念，以激励新一代多学科工程师。该研究计划将利用批量和一维运输地球化学实验，三轴和土柱岩土实验室测试，反应运输数值模拟以及先进的化学，生物和材料分析：（1）研究矿物合成过程中生物地球化学条件对生物胶结作用控制长期化学和机械回弹性的影响，（2）评估生物胶结的化学持久性，包括矿物溶解度和溶解动力学，（3）检查化学和机械引起的损伤对生物胶结土壤性能的影响，包括工程性质的演变、损伤模式和降解监测方法，以及（4）开发可以保护和修复受损的生物胶结土壤同时最小化能量和材料使用的技术。 为了实现这些研究目标，将完成三个综合研究任务。 首先，将进行一系列的间歇反应器实验，以了解沉淀过程中的生物化学反应条件，生物胶结形成和沉淀物的性质之间的关系。 第二，将完成一系列地球化学和岩土工程实验室实验，以表征生物胶结作用的溶解度和溶解行为，作为沉淀物性质和地下环境条件的函数。所获得的结果将告知具体的生物胶结材料原位持久性预测的溶解动力学框架的发展。 最后，将进行岩土工程和地球物理调查，以确定检测胶结退化的非破坏性方法，开发新的修复技术，并探索生物胶结退化和修复对生物胶结土工程行为的影响，包括材料应力应变、模量退化、弹性和屈服后响应、临界状态和峰值剪切强度的变化，该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

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.