Microbially-Induced Cementation of Sands by Denitrification

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The research team will investigate the use of oxidation of organic compounds by denitrifying bacteria (?denitrification?) to induce carbonate cementation in sand. Microbially induced carbonate precipitation (MICP) offers the promise of a sustainable, non-disruptive and energy efficient engineering solution to a variety of important infrastructure development and geologic hazard mitigation problems, including remediation of liquefaction potential, improving foundation bearing capacity, and reducing (or even eliminating) excavation and tunnel support requirements. MICP through ureolysis is being investigated by several research groups in the U.S. and abroad. However, denitrification is potentially superior to ureolysis as a MICP process in that denitrifying bacteria are ubiquitous in the subsurface and the process works under anaerobic conditions, e.g. below the water table, while ureolysis requires oxygenation. Denitrifying bacteria and nutrients will be introduced into a laboratory soil column with pore water containing calcium carbonate in solution. Carbonate precipitation will be monitored by mass balance measurement of calcium concentrations in the pore fluid and the development of cementation will be monitored by shear wave velocity measurements in the soil column. These column experiments will be used to refine a biogeochemical model for denitrification, establish an optimal nutrient mix for denitrification, and establish precipitation and cementation rates for MICP by denitrification. Triaxial and simple shear tests on specimens from the column experiments will be used to evaluate the relationship between the amount of MICP and changes in the strength, stiffness, and liquefaction potential of the specimens. The proposed research has the potential to transform geotechnical practice, not only by development of a new, sustainable approach to ground improvement but also by advancing the emerging field of biogeotechnical engineering. This work is a continuation of work initiated under a National Science Foundation Small Grant for Exploratory Research (SGER).