Mitigation of liquefaction beneath existing facilities using denitrification

Microbially mediated dissimilatory reduction of nitrate, or denitrification, offers the promise for non-disruptive mitigation of the potential for earthquake-induced liquefaction beneath existing facilities. Denitrification can mitigate liquefaction in two ways: by desaturation of the soil through generation of gas and by cementation of the soil through precipitation of calcium carbonate as calcite. Laboratory column tests demonstrate that desaturation via biogenic gas occurs almost immediately upon stimulation of the denitrifying microbes, providing short term mitigation while calcite is being precipitated. Once enough calcite is precipitated, denitrification provides long term mitigation. Laboratory simple shear testing demonstrates that a relatively small decrease in the degree of saturation, as little as 5%, and a relatively small amount of calcite precipitation, as little as 0.4 percent of the dry weight of the soil, can both provide substantial mitigation of liquefaction potential. When there is sufficient normal stress on the ground surface (mitiga t ing the potential for shallow crack development due to gas production), these processes are nondisruptive and thus provide a non-disruptive means of mitigating liquefaction beneath existing facilities.