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<p>This study investigates the impact of air entrainment on operational safety in large-diameter water transmission pipelines, employing hydraulic simulations (SewerGEMS) of a critical case study: Obour City’s 1.8 m raw water conduit (Q = 360,000) with slopes reaching 0.026. We quantify crucial thresholds for maintaining pressurized flow, identifying a critical slope (S<sub>crit</sub>) = 0.0013 for standard conditions (D = 1.8 m, <i>n</i> = 0.014, and Q = 360,000 m<sup>3</sup>/day), beyond which flow transitions to free-surface (water depth/pipe diameter (d/D) decreased from 100% to 68% at S = 0.014) with a 42% velocity surge (2.05 to 2.91 m/s) elevating scour risk. Results demonstrate diameter-dependent stability (D<sub>crit</sub>  = 1.8 m at S = 0.0013) and establish slope-diameter interdependence (S<sub>crit</sub> ∝ D − 1.2). Steep sections (S &gt; S<sub>crit</sub>) exhibit chaotic air–water interfaces where hydraulic jumps entrain microbubbles (&gt; 0.1% Q<sub>air</sub>/Q<sub>wate</sub>r), amplifying transient pressures and corrosion. To mitigate these risks, we propose the following: (1) 30° oblique weirs stabilizing mild slopes (S = 0.003) via optimized discharge coefficients (Cd = 0.85) and (2) triple-orifice air valves (d<sub>orifice</sub>  = 0.04 D) at summits for rapid venting. These deterministic criteria enable the reliable design of air-resilient conduits in challenging topography.</p>

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Study of crucial slopes in pressurized conduits case study: Obour raw water transmission line, Egypt

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年10月24日

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  • Mohamed Elsayed Gabr,
  • Ehab M. Fattouh,
  • Hesham N. Farres

摘要

This study investigates the impact of air entrainment on operational safety in large-diameter water transmission pipelines, employing hydraulic simulations (SewerGEMS) of a critical case study: Obour City’s 1.8 m raw water conduit (Q = 360,000) with slopes reaching 0.026. We quantify crucial thresholds for maintaining pressurized flow, identifying a critical slope (Scrit) = 0.0013 for standard conditions (D = 1.8 m, n = 0.014, and Q = 360,000 m3/day), beyond which flow transitions to free-surface (water depth/pipe diameter (d/D) decreased from 100% to 68% at S = 0.014) with a 42% velocity surge (2.05 to 2.91 m/s) elevating scour risk. Results demonstrate diameter-dependent stability (Dcrit  = 1.8 m at S = 0.0013) and establish slope-diameter interdependence (Scrit ∝ D − 1.2). Steep sections (S > Scrit) exhibit chaotic air–water interfaces where hydraulic jumps entrain microbubbles (> 0.1% Qair/Qwater), amplifying transient pressures and corrosion. To mitigate these risks, we propose the following: (1) 30° oblique weirs stabilizing mild slopes (S = 0.003) via optimized discharge coefficients (Cd = 0.85) and (2) triple-orifice air valves (dorifice  = 0.04 D) at summits for rapid venting. These deterministic criteria enable the reliable design of air-resilient conduits in challenging topography.