Hydraulics & Waterways

Oral

394806 - Assessment and Design Optimization of Retrofitting Dropshaft with Air Circulation Pipes for Downstream Depressurization

Monday, June 4
2:00 PM - 3:30 PM
Location: Regency Room
Co-Authors: David Zhu, Canada – University of Alberta; Jiafang Wei, China – Hohai University

Dropshafts are commonly used to convey sewage to deep tunnels. Plunging flow dropshafts have been reported to cause downstream air pressurization and subsequent sewer odor issues. A trial project of retrofitting the dropshaft with an airshaft and several horizontal pipes for air circulation has been implemented in Edmonton, Canada, although there is lack of design guidelines. In the current work, physical model study, field monitoring and theoretical prediction were conducted to assess the effectiveness of this retrofit. Experiments were run with the dropshaft model connected to the airshaft with different numbers of horizontal pipes. Predictions of air pressure and air entrainment were in good agreement with the experimental data. Field monitoring program was conducted on the existing retrofitted dropshaft in Edmonton, where the amount of air entrained into the dropshaft, the air flow rate circulating inside the dropshaft/airshaft, and the upstream/downstream air pressure, were recorded and analyzed. From the experiments and the field work, the air circulation pipes were found effective in reducing the air entrainment of the dropshaft and depressurizing the downstream sewers. However, this retrofit would cost one million dollars. For this reason, a new design of dropshaft with internal air circulation formed by a divider was also tested in the laboratory, considering its construction of relative ease and cost saving. This new design performed significant reductions in the external air demand and the air pressurization along the dropshaft, by about 36% and 26%, respectively. It could potentially be employed for practical use in the future.

Yiyi Ma

Postdoctoral Fellow
University of Alberta

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