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

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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.