RAPID: Biostimulation for Biocementation at Field Scale Treatment Depths

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Soil improvement is often required when the soil supporting the foundations for structures, or soil used for embankments, and other earthworks lack sufficient strength and stiffness to perform satisfactorily. Current engineering practice relies primarily on the use of chemical grouts and mechanical methods to improve soils, despite environmental concerns regarding high embodied energies and documented groundwater contamination incidents. Microbially Induced Calcite Precipitation (MICP) offers an environmentally conscious bio-mediated soil improvement alternative that can improve a soil's engineering properties through the precipitation of calcite at soil particle contacts (biocementation). Although researchers have extensively demonstrated the ability of MICP to improve soils, the need for cultivation and injection of specialized non-native bacterial strains has restricted the technology from becoming a cost-competitive and environmentally permissible soil improvement technique. This award supports research critical to the advancement of the technology, by assessing the feasibility of using native bacteria to complete the process at depths relevant to practical engineering application. Stimulation of native bacteria will eliminate cultivation costs and potential long-term environmental and ecological impacts by forgoing the introduction of non-native bacteria into native soil ecosystems. This advancement would provide industry with financial and environmental incentives for adoption of the method into practice and therefore attain important societal and environmental benefits. This research will involve interdisciplinary expertise in microbiology, geotechnical engineering, and geology by engaging an international collaboration of researchers. The feasibility of stimulating native bacteria at depths typically required for mitigation of geotechnical hazards such as liquefaction is unknown. This research will provide important and unprecedented insight about the distributions, relative abundances, and feasibility of stimulating native bacteria in natural soil deposits to complete biocementation with depth. Previous experiments have successfully demonstrated the ability of stimulated native bacteria to enable biocementation, but these studies have only involved surficial soils. Total concentrations of native soil microorganisms are expected to decrease with depth however, due to reductions in total soil organic matter and oxygen availability. In this study, a drilling and sampling program will be conducted to obtain samples from discrete depths up to 15 meters within a natural soil deposit for microbiological characterization and geotechnical testing. Batch experiments will be performed on obtained samples to optimize stimulation treatments using microbiological analyses and timed measurements of process biogeochemistry. Column experiments will be also performed to evaluate the effectiveness of stimulation techniques to enrich for native bacterial populations and improve soil geotechnical properties with depth through microbiological, biogeochemical, and geotechnical monitoring.