Compositional and geoenvironmental factors in microbially induced partial saturation

Introducing gas bubbles in saturated soils, even by very small amounts, will increase the liquefaction resistance, particularly useful around existing structures. Biodenitrification through dissimilatory reduction of nitrate to nitrogen gas has been recently implemented as an alternative desaturation technique. In this study, a number of compositional, mechanical and environmental factors were examined to assess their effects on the efficiency of the treatment system and the retainability of gas bubbles in the soil. Results from denitrification gas generation tests with different initial nutrient concentrations were compared with the expected values predicted from bioenergetic calculations. Soil density, fines content and overburden stress affected the treatment efficiency and retainability of gas bubbles. Lower degrees of saturation with higher efficiencies could be attained in soils with higher density, fines content or overburden stresses. However, the results suggested that gas accumulation in pore space is not unlimited. Substantial gas loss from the soil surface resulted in reduction in treatment efficiency, explained through the effects of potential gas transport mechanisms – that is, capillary invasion and fracture opening.