MIDP: Liquefaction Mitigation via Microbial Denitrification as a Two-Stage Process. I: Desaturation

This paper focuses on desaturation due to the microbially mediated dissimilatory reduction of nitrogen, or denitrification, for mitigating the potential for earthquake-induced soil liquefaction. Denitrification has the potential to mitigate earthquake-induced liquefaction as a two-stage process referred to as microbially induced desaturation and precipitation (MIDP). In MIDP, desaturation provides mitigation in Stage 1, and microbially induced carbonate precipitation (MICP) provides mitigation in Stage 2. Denitrifying bacteria, when stimulated, have the ability to rapidly desaturate a saturated soil by producing nitrogen and carbon dioxide gases. Small amounts of desaturation can significantly increase the cyclic resistance of saturated soil. As this desaturated condition may not last indefinitely, desaturation is relied upon only to provide temporary mitigation. However, in addition to desaturating the soil, denitrifying bacteria can induce MICP by increasing the pH and carbonate alkalinity of the pore fluid. Interparticle cementation, void filling, and particle roughening induced by MICP improve the cyclic resistance and dilatant behavior of granular soil, thereby providing long-term mitigation of liquefaction. This paper describes the use of desaturation via denitrification for short-term mitigation of earthquake-induced liquefaction. The use of MICP via denitrification as a long-term solution is presented in a companion paper. (C) 2017 American Society of Civil Engineers.