Overview
Our work on the optimization of MICP for upscaling has been ongoing for nearly a decade. Our activities in recent years has primarily been focused on:
- developing a biostimulation treatment technique for MICP at depth
- optimizing the treatment formula for maximum effectiveness and minimum cost/environmental impact
- evaluating the effect of biocementation on cone penetration resistance
- improving the ability to control the direction and uniformity of treatment
This has occurred through field sampling and testing, small column tests, beaker tests, and large tank tests.
Current Year ’15-’16 Focus
TITLE: Stimulation of Native Bacteria for Bio-cementation at Field-Scale Treatment Depths
RESEARCHER: Mike Gomez (mkgomez@ucdavis.edu)
ADVISOR(S): Prof. Jason DeJong (jdejong@ucdavis.edu), Prof. Doug Nelson
COLLABORATOR(S): Charles Graddy, Prof. Michael Tsesarsky
THRUST: Hazard Mitigation
USE-CASE: Loose granular soil materials at depths up to 15 meters, which may experience liquefaction during earthquake ground motions.
TRANSFORMATIVE CONTRIBUTION: The ability to effectively stabilize loose weak soils to mitigate liquefaction at depths relevant to practical engineering application with significant reductions in environmental impacts.
GAPS:
- What is the role/effect of sodium acetate in the stimulation solution?
- What percentage of the total microbial population in stimulated soils is ureolytic?
- What are the relative amounts of attached and aqueous bacteria in soils during stimulation? cementation? What other factors influence this?
- What is the maximum amount of yeast extract that can be added and assimilated/respired by microbes while maintaining aerobic conditions?
BARRIERS:
- Robust methods that can identify ureolytic cells are not known, and the accuracy of existing gene specific primers is questionable.
- Attachment and detachment of bacteria to soil particle surfaces as a function of surface charge, ionic strength, soil mineral type, and chemotaxis is not well understood.
- Methods to effectively and non-selectively remove attached microorganisms from soil particle surfaces have not been identified.
RESEARCH APPROACH:
- Batch and column experiments to assess feasibility of stimulating native ureolytic bacteria using soil samples obtained from an excavation at various approximate depths
- Monitoring using total cell counts and chemical measurements to determine stimulation effectiveness and optimize treatment solutions
- Application of optimized stimulation solutions to treat soil samples obtained from different depths using sterile sampling and a geotechnical boring.
- Assess final improvement and stimulation feasibility at depth with UCS, calcite content, biogeochemistry, and microbial methods.
IMPORTANCE TO STAKEHOLDERS:
- Owners: Ability to mitigate liquefaction at comparable performance levels as traditional ground improvement, with additional environmental and cost-reduction incentives.
- Society: Reductions in greenhouse gas emissions, which help mitigate climate change, reduce energy demands, and improve public health.
- Regulators: Reduction of negative ecological impacts and elimination of permitting associated with the introduction of non-native bacteria into native soil ecosystems.
- Academia: Increased opportunities to investigate MICP for ground improvement and contaminant immobilization due to increased practicality of the treatment process (reduced treatment costs, reduced negative environmental impacts).