Study of flow transitions during air sparging using the geotechnical centrifuge

Air sparging (AS) is an in-situ groundwater remediation technique for volatile organic compounds (VOCs) in contaminated sites. Knowledge of effect of the injected air on air flow patterns and extent of the zone known as zone of influence (ZOI) is crucial for design of in situ air sparging. The two main objectives of this research are to study transition of air flow patterns and characteristics of ZOI under different air injection pressures during centrifugal tests and to find the scaling factors for centrifugal tests under different gravitational levels (N times gravitational force). In this research, the modeling of models test was first performed to validate centrifugal technique for simulating air sparging. Then, a set of two-dimensional (2D) centrifugal modeling tests were performed under various gravitational levels to study the transition of air flow patterns and characteristics of ZOI during air sparging. The centrifugal model tests showed that the observed 2D ZOI was truncated-cone under various gravitational levels. It was also observed that flow pattern for the same soil transits from channel flow under lower gravitational levels to bubble flow under higher gravitational level. If there are same air flow regimes during air sparging tests under varied gravitational levels, then the scaling factor for air sparging is N, and a formula was proposed to check the flow regime. In this research, a formula was proposed to explain the transition of air flow patterns during air sparging and determine the boundary of flow regime transition based on grain size and unit-sparging rate.