Geotechnical centrifuge study on air flow during air sparging

Air sparging (AS) is one of the most efficient techniques to remediate saturated soils and groundwater contaminated with voltaic organic compounds. Knowledge of the extent of the zone affected by the injected air is essential in designing in situ air sparging system. In this research, the centrifuge modeling tests were conducted to simulate the air sparging process in 2D scenario. The glass beads with different size were used as soil simulant to facilitate the visual observation of air movement in saturated porous media. The air flows in micro-channel in fine porous media and in individual bubbles in coarse media. The characteristics of zone of influence (ZOI) were studied at a wide range of sparging pressures and centrifuge g-levels. The test results show that the ZOI is cone-shaped and it can be depicted by two parameters; the width at the tip of the cone or lateral intrusion and the cone angle. Increasing sparging pressure will lead to increase in both lateral intrusion and the cone angle. With further increasing in air injection pressure, the cone angle reaches a constant value while the lateral intrusion will become the main contributor to the enlargement of ZOI. The characteristics of ZOI are related with the effective sparging pressure ratio, which is defined as the difference between sparging pressure and hydrostatic pressure normalized with respect to the effective overburden pressure at the sparging point. The air flow velocity increases with the increase of the sparging pressure, and the slope of mass flow rate with effective sparging pressure ratio increases with higher g-levels. These conclusions provide valuable references for design and application of air sparging for groundwater remediation.