Physical Investigation of Discrete Air Pocket Migration and Release in CSO Storage Tunnels
Various rapid filling scenarios lead to the formation of large discrete air pockets in below ground storage tunnel systems. The release of trapped air pockets through a vertical shaft can potentially cause a geyser event in which untreated wastewater returns to the ground surface. It is important to the design efforts of these expensive systems to estimate the potential for such events and to provide solutions to mitigate the undesirable effects. However, little is known about the behavior of discrete air pockets once they are trapped within tunnel systems. Initial laboratory experiments were performed to qualitatively assess the main contributing variables for the direction and velocity of air pockets as they migrate within nearly horizontal systems. Experimental data is collected for air pocket migration in the direction of water flow. Next, a diameter expansion within the vertical shaft was investigated as a possible design modification to mitigate geyser events. Experimental variables such as the ratio of expansion diameters and the vertical location of the expansion were investigated to optimize the proposed design. The scalability of experimental results was explored by performing tests on a 0.095 m diameter tunnel as well as a 0.203 m diameter
tunnel. Qualitative conclusions are presented and discussed from the experimental results.
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