設計仮排水路設計における Flood Routine の活用（１）

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概要

仮排水路トンネル断面寸法と仮締切堤高さを決定するための設計検討を行う。具体的には、トンネル径を変化させ、Flood Routine により、洪水流入波形、流出流量、貯水池水位の関係を求める。

Conditions for Flood Routine Analysis

For flood routine analyssis, following conditions are required.

Hydrograph as unflow characteristic.
Reservoir storage capacity curve as storage characteristics
Discharge capacity curve of diversion tunnel as outfow characteristics

Hydrograph

Following hydrograph for 20 years return period flood is used as a given condition.

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Reservoir Storage Capacity Curve

Following reservoir capacity curve is used as a given condition.

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Discharge Capacity Curve of Diversion Tunnel

In this project, two lanes diversion tunnels are planed, and the characteristics of alignments and standard tunnel shape are shown below.

Information of Diversion Tunnel Alignment
Items	Inside	Outside
Length	L=400m	L=450m
Invert level of entrance	EL.64.0m	EL.64.0m
Invert level of exit	EL.62.5m	EL.62.5m
Gradient	i=0.00375	i=0.00333
Curve-1	Bending radius: $\rho$ =230m Bending angle: $\theta$ =39.5deg.	Bending radius: $\rho$ =260m Bending angle: $\theta$ =39.5deg.
Curve-2	Bending radius: $\rho$ =200m Bending angle: $\theta$ =48.2deg.	Bending radius: $\rho$ =230m Bending angle: $\theta$ =48.2deg.
The distance between tunnels are set to 30m (center to center)

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The assumptions for the calculation of flow capacity curve of diversion tunnels are shown below.

In case that the reservoir water level is lower than or equal to the crown level of the diversion tunnels, the water flows down with uniform flow state.
In case that the reservoir water levei is higher than the crown level of diversion tunnels, the water flows down with pressured tunnel flow state.
The discharge capacity of diversion is defined as the sum of the discharges of two tunnels.

Calculation of Discharge Capacity for Uniform Flow

$\begin{equation} Q=A\cdot v \qquad v=\cfrac{1}{n}\cdot R^{2/3}\cdot I^{1/2} \end{equation}$

$Q$	discharge
$A$	flow section area
$v$	average velocity
$n$	manning's roughness coefficient (=0.015)
$R$	hydraulic radius
$I$	invert gradient

Calculation of Discharge Capacity for Pressued Tunnel Flow

$\begin{gather} Q=A\cdot v \qquad v=\sqrt{\cfrac{2 g \Delta H}{f_e+f_o+f_{b1}+f_{b2}+f\cdot L\;/\;R}} \\ f_b=\left\{0.131+0.1632\cdot\left(\cfrac{D}{\rho}\right)^{7/2}\right\}\cdot\sqrt{\cfrac{\theta}{90}} \\ f=\cfrac{2 g n^2}{R^{1/3}} \end{gather}$

$Q$	discharge
$A$	section area of diversion tunnel
$v$	average velocity
$\Delta H$	difference of water head between upstream and downstream of diversion tunnel
$f_e$	head loss coefficient of entrance (=0.25)
$f_o$	head loss coefficient of exit (=1.00)
$f_{b1}$	head loss coefficient of bending for curve-1
$f_{b2}$	head loss coefficient of bending for curve-2
$f$	friction head loss coefficient
$n$	Manning's roughness coefficient (=0.015)
$L$	length of tunnel
$R$	hydraulic radius of tunnel
$D$	internal diameter of tunnel
$\rho$	radius of curvature of bending
$\theta$	inter angle of bending
$g$	gravity acceleration (=9.8 m/s $^2$ )