Laboratory Investigation of Air Flow Patterns in Saturated Sands during Air Sparging

A series of tests was performed to investigate the air flow patterns in saturated sands during air sparging. Test results show that air flow patterns are affected by the particle size of the sand as well as the air flow rate. Two types of gas-phase flow patterns have been observed, namely, channel flow and bubble flow. Basically, the channel flow pattern develops when the sand particle diameter is less than 1.0 mm; whereas, the bubble flow pattern occurs when the sand particle size is larger than 2.0 mm. It has been observed that a transition flow state exists when the sand particle size changes from 1.0 to 2.0 mm. The results indicate that air-phase saturation degree of the sand mass increases with the increased air flow rate. When the air flow rate exceeds a certain threshold value, the air phase saturation tends to reach a steady state. Given that the other conditions remain unchanged, the air-phase saturation of the soil mass increases with the decrease of the soil particle size. A pretty good linear relationship was found between air flow rate and air pressure. Based on the extrapolation method, the minimum air injection pressure is derived, which is an important parameter in design practice. Finally, the effect of sand particle size on the estimated capillary pressure is discussed.