Impact of Bacteriogenic CO ₂ on Pore Pressure Generation and Cyclic Resistance of Sand

Gases within soil voids are known to increase pore fluid compressibility, hinder pore pressure development, and enhance cyclic resistance of soils. Soil microorganisms within void spaces produce CO2, extracellular polymeric substances (EPS), minerals such as CaCO3, and other metabolic products depending on specifics of metabolic processes. Bacteriogenic CO2 can therefore influence pore fluid compressibility, pore pressure development, and deformation response of soils during rapid loading. However, this issue remains relatively unexplored. Amounts of free and dissolved CO2 within soil voids are expected to depend on the types of soil microorganisms, their metabolic processes, and solubility in pore water. Influence of CO2 produced by two species of aerobic soil bacteria on pore pressure potential of sand samples was experimentally investigated in this study. Measurements were within about 10% of analytically derived relationships between CO2 content and pore water pressure. Pore pressure was also found to relate closely to volume of free CO2 and bacterial population size. Data obtained in this study further indicate that cyclic resistance of sand containing live bacterial populations is correlated with Skempton’s pore pressure parameter, B, and amounts of EPS and CaCO3 through a relationship independent of bacterial species or metabolic pathway.