A next-generation biogeochemical model was developed to explore the impact of the native water source on microbially induced desaturation and precipitation (MIDP) via denitrification. MIDP is a non-disruptive, nature-based ground improvement technique that offers the promise of cost-effective mitigation of earthquake-induced soil liquefaction under and adjacent to existing structures. MIDP leverages native soil bacteria to reduce the potential for liquefaction triggering in the short term through biogenic gas generation (treatment completed within hours to days) and over the longer term through calcium carbonate precipitation (treatment completed in weeks to months). This next-generation biogeochemical model expands earlier modeling to consider multi-phase speciation, bacterial competition, inhibition, and precipitation. The biogeochemical model was used to explore the impact of varying treatment recipes on MIDP products and by-products in a natural seawater environment. The case study presented herein demonstrates the importance of optimizing treatment recipes to minimize unwanted by-products (e.g., H2S production) or incomplete denitrification (e.g., nitrate and nitrite accumulation).@en

Desaturation by biogenic gas formation can significantly affect the hydro-mechanical behaviour of soil. The high compressibility of the gas dampens pore pressure build up during both monotonic and cyclic undrained loading. Stimulating biogenic gas production therefore has potential as a ground improvement method to mitigate the risk of both static liquefaction and earthquake induced liquefaction. However, gas generated below the ground water table at shallow depth may also constitute a hazard for offshore foundations and terrestrial deposits, as a sudden release of trapped gas may cause instability. In order to evaluate the potential use of biogenic gas for geotechnical applications it is essential to be able to predict gas production and assess its effect on the hydro-mechanical behaviour of a soil. A basic theoretical framework to estimate the volume of gas produced by a biogenic process and the related degree of saturation, experimental results on the rate of gas generation, and its impact on soil behavior are presented herein.

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