Uncontrolled air pocket release and geysering in upstream dropshafts in stormwater systems

Jose G. Vasconcelos, Leandro C. Pinto, Liriane E. Bock, Rutineia Tassi and Daniel G. Allasia


The operation of stormwater systems is severely impacted by the air phase, which may become entrapped in episodes of rapid filling. Among the effects of entrapped air in such systems, the uncontrolled release through water-filled shafts is known to create problems such as stormwater geysering and manhole cover displacement episodes. Research also have addressed the role of the system geometry on the issues created by uncontrolled air pocket release, studying the role of shaft length, diameter, alignment, and even the placement of storage and flow restrictors. One key geometric characteristic not addressed in previous research is the type of connection at the base of the water-filled shafts. Most studies to date have considered dropshafts at intermediate locations between pipes. In such conditions, it was shown that a significant fraction of air continues to move in the horizontal tunnel upon reaching the shaft during the release. This work presents an innovative apparatus in which all the air phase reaching a shaft will be released through the shaft, resembling an upstream dropshaft in stormwater systems. Experimental results collected in this work have shown that such releases can be more severe in terms of vertical displacement and velocity of the air phase initially present in the shaft. These results indicate the need for further studies and quantification of these adverse conditions in vertical shafts with similar geometries.

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