Mitigation of liquefaction hazards using the combined biodesaturation and bioclogging method

Conventional soil improvement methods for mitigation of liquefaction can be costly for large-scale applications. A study to establish a more cost-effective method for mitigation of liquefaction hazard is presented in this thesis. The so-called "combined biodesaturation and bioclogging method" is to produce biogas (N2) in sand to reduce the degree of saturation of sand and sustain the desaturation by immobilizing the gas bubbles through bioclogging. The biogas is produced via a denitrification process and bioclogging is from a microbial induced calcium carbonate precipitation (MICP) process. Shaking table model testing results indicate that as the degree of saturation reduces to less than 90 percent, the generation of pore pressure and potential to liquefaction is largely contained. This phenomenon is also observed in the triaxial compression test. Seepage flow in sand may lead to the mobilization of biogas bubbles in sand. Introduction of a weak bioclogging effect may reduce considerably the tendency for gas bubbles to be displaced. Permeability measured using the sand column tests indicate that when the bioclogging is applied together with the biogas method, gas bubbles generated in sand can sustain for the whole testing duration under a seepage flow. CT images illustrate that gas bubbles are either in the single bubble form or in the form of gas pocket with small gas bubbles aggregating together. SEM images reveal that for sand with low calcium carbonate content produced through the bioclogging method, majority of the calcite precipitation is formed as a single crystal on the surface of sand grain.