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Evaluating Hydraulic Roughness in Tunnels

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*by* Thomas C. MacDonald, (M.ASCE),

Ken J. Susilo, (A.M.ASCE),

**Document Type:** Proceeding Paper

**Part of:** North American Water and Environment Congress & Destructive Water: **Abstract:** Much of the data presented in the literature on measured friction losses in tunnels are given in terms of the Darcy-Weisbach

f or Manning's

n friction coefficients. Both of these coefficients vary with tunnel diameter, flow velocity, fluid viscosity, and tunnel wall roughness and, therefore, only apply to tunnel and flow characteristics used in the measurements. Use of data in the literature require engineers to research data sources, convert the data to a comparable basis, and use engineering judgment to estimate a friction coefficient for the tunnel type and flow conditions that are being designed. Considerable engineering judgment is needed to select an appropriate

f or

n friction coefficient from the data if the design flow is less than fully turbulent. The authors have collected data on prototype measurements of friction losses in tunnels and converted all usable data to a common basis for friction loss estimates, namely, absolute roughness, or rugosity (e), which is the characteristic size of the roughness element on the wetted perimeter of the tunnel (analogous to the Nikuradse sand grain diameter). Tunnel rugosity is, to some extent, a physically measurable parameter and independent of other hydraulic design variables.

**Subject Headings:** Tunnels |

Hydraulic roughness |

Friction |

Fluid flow |

Flow measurement |

Viscous flow |

Computing in civil engineering |

Fluid velocity |

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