Mitigation of Earthquake-Induced Liquefaction via Microbial Denitrification: A Two-Phase Process

Abstract

Microbial denitrification, or dissimilatory reduction of nitrate, offers the potential of a sustainable and cost-effective method for mitigation of earthquakeinduced liquefaction. Carbonate precipitation via microbial denitrification is a slow process and may take years to precipitate enough carbonate to provide the desired degree of mitigation. Fortunately, large amounts of nitrogen gas are generated immediately upon the onset of denitrification. As desaturation by biogas generation is in itself a liquefaction mitigation mechanism, liquefaction mitigation via microbial denitrification may be viewed as a two-phase process: an initial phase wherein desaturation via biogas generation provides mitigation and a second phase in which sufficient carbonate precipitation has occurred to provide mitigation via particle cementation and/or an increase in dilatancy. Microbial denitrification is suitable for remediation under and around existing facilities because it is non-disruptive. An advantage of microbial denitrification compared to hydrolysis of urea (ureolysis), another technique for microbial precipitation of carbonate, is that its primary byproducts are benign (non-toxic). Another advantage of microbial denitrification is that denitrifying bacteria are ubiquitous in the subsurface. Laboratory test data demonstrates the ability of microbial denitrification to both desaturate the soil and induce carbonate precipitation, leading to an increase in strength and dilatancy, substantiating the concept of microbial denitrification as a two-phase process for mitigation of earthquake-induced liquefaction.