Transcript
Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
Cross Drainage Works 1. Aqueducts: If the bed level of the channel is higher than H.F.L. of t he drain, the structure is an aqueduct. aqueduct. Otherwise, the structure is either syphon or culvert. 2. Culvert If there is no restriction downstream, the structure will have two slopes S1 and S2, then, the structure will be a culvert. 3. Syphon If there is any restriction downstream the structure will have three slopes, therefore the structure is a syphon.
Hydraulic Design of Syphon Design a syphon with the following data a. Canal Discharge
= 40 cumec
Bed width
= 18 m
Full supply depth
= 2.1 m
Bed level
= 250 m
Side slope
= 1½ H: 1 V
b. Drain Flood discharge
= 100 cumec
Bed level
= 251.8 m
Depth
= 1.45 m
H.F.L.
= 253.25 m
Roadway
16 m
Drain
44.5 m
1
Roadway
8m
Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
Design 1. Drainage waterway
Lacey’s Formula P 4.83 Q
, P wetted perimeter
4.83 100 48.3 m Total length of barrels 8 44.5 16
68.5 70 m Provide bed width of the drain at crossing
44.5 m
High flood level of the drain= 253.25 m 2. Canal waterway
Velocity of approach
Q A
40 2
1.5 2.1 18 2.1
0.9 m s
Maximum fluming is 40%, 0.4 18 7.2 m Let the canal waterway be reduced from 18 m to 7.3 m such that two barrels each 3.5 m with 0.3 m thick wall.
3.5 m
0.3 m
Let the height of the barrel = 2.5 m
V
Q A
Fr
40
2.29 m s
3.5 2.5 2 V 2.29
gD
9.81 2.5
V 2 ~ 3 m s
0.46 1
~ 0.6 Fr 1, 0.4
The flow is subcritical in the barrel. 3. Head loss and bed levels at different sections:
Provide 2 in 1 splay in contraction, and 3 to 1 splay in expansion, and 3 in 1 splay in expansion: Length of contraction Length of expansion
18 7.3 2
18 7.3 2
2 10.7 m
3 16.05 m
At section 4 Velocity head ha
V a2
2g
0.92 2 9.81
R.L. of bed = 250 m 2
0.041m
2.5 m
Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
R.L. of water surface = 250+2.1=252.1 m R.L. of T.E.L. = 252.1+0.041 = 252.141 m At section 3 Provide water depth = 3 m Area of section 3 7.3 21.9 m
2
Velocity
Q A
Velocity head
40 21.9 V 32
2g
1.83 m s
1.83
2
2 9.81
0.17 m
Loss of head in expansion from section 3 to section 4
V32 V 42 1.832 0.92 K2 0.3 0.039 m g 2 2 9.81 El. of T.E.L. at section 3 252.141 0.039 252.18 m R.L. of water surface 252.18 0.17 252.01m R.L. of bed 252.01 3 249.01m L V Head loss through barrels 1 f1 f 2 R 2 g 2
where, f 1= constant for syphon mouth
=0.08 for bell mouthed syphon
f 2 a 1
b where a and b are constants depending on the R
material of the surface of barrels. For cement plaster, a = 0.00316 and b = 0.1. R
A P
2 3.5 2.5
3.5 2.5 2 2
f 2 0.00316 1
0.1 0.036 0.729
Assume length of syphon barrels L= 70 m 2
70 2.29 h L 1 0.08 0.0036 0.729 2 9.81 0.381m At section 2
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Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
R.L. of T.E.L. R.L. of T.E.L. @ section 3 + head loss through barrels
252.18 0.381 252.561m R.L. of water surface 252.562 0.17 252.39 m R.L. of bed 252.39 3 249.39 m
say 249.40 m
At section 1
V22 V 12 h L in contraction transition K 1 2g 1.832 0.92 0.2 0.026 m 2 9.81 R.L. of T.E.L. 252.561 0.026
252.587 m R.L. of water surface 252.587 0.041
252.546 m R.L. of bed 252.546 2.1 250.446 m
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Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
4. Transitions
Because the depth is varying through the transition, Metra’s and Chutervedi’s formulae for transitions are not applicable, therefore Hinds’ method shall be used.
The expansion transition is explained in more details, please refer to section 4.b. a. Contraction transition y C x 2 y1
x1
w.s. @ sec.1 - w.s. @ sec. 2 2 252.546 252.4
0.073 m
2 length of transition 2
10.7 2
5.35 m
Substitute y1 and x1 in the equation to find C 0.073 C 5.35
2
C 0.0026 y 0.0026 x 2 Contraction Transition
[1]
[2]
Dist.
y ( m)
0.0026 x 0.00
0.0000
[3]
[4]
[5]
El. of W.S. ( m)
El. of T.E.L. ( m)
Velocity head hv ( m)
Linear Interp.
[4]-[3]
(2g hv)
252.500
0.017
1.83
2
252.400
[6]
[7]
Velocity
V ( m/s) 1/2
Side slope s
[8] Area 2 A ( m )
[9] Bed level ( m)
Linear Interp. 0:1
21.86
249.40
[10]
[11]
Depth
Bed width
D ( m)
B
[3]-[9]
A / D - s D
3.0
7.30
2.50
7.53
5.35
9.06
8.00
14.56
10.70
0.0000
252.546
252.587
0.040
0.90
b. Expansion transition y1
252.1 252.01 2
x1
16.05
C
y1
2 x
2
0.045 m
8.025 m 0.045
8.025
2
y 0.0007 x 2
5
1.5:1
44.44
250.45
2.1
18.00
Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
252.1 y1
w.s. El. 252.01
PROFILE 8.025 16.05
Bed level
m h t d i w d e B
x
0 0 3 . 3 . 7 7
0
3
9 0 . 8
6
6 1 . 9
0 7 . 0 1
8.02 10
2 9 . 3 1
0 0 . 8 1
13
16.05 m
PLAN
Expansion Transition
[1]
[2]
Dist.
y ( m)
0.0007 x
[3]
[4]
[5]
El. of W.S. ( m)
El. of T.E.L. ( m) Linear Interp.
Velocity head hv ( m)
[4]-[3]
(2g hv)
2
[6]
[7] Side slope s
Velocity
V ( m/s) 1/2
[8]
[9]
Area 2
A ( m )
Bed level ( m)
Linear Interp.
[10]
[11]
Depth
Bed width
D ( m)
B
[3]-[9]
A / D - s D
0.00
0.0000
252.010
252.180
0.170
1.826
0:1
21.86
249.01
3.00
7.30
3.00
0.0063
252.016
252.173
0.157
1.753
0.28:1
22.73
249.20
2.82
7.29
6.00
0.0252
252.035
252.165
0.130
1.596
0.56:1
25.48
249.38
2.66
8.09
8.02
0.0450
252.055
252.161
0.106
1.442
0.75:1
28.37
249.50
2.56
9.16
10.00
0.0252
252.075
252.156
0.081
1.262
0.93:1
31.75
249.63
2.44
10.71
13.00
0.0063
252.094
252.150
0.056
1.051
1.21:1
38.10
249.81
2.28
13.92
16.05
0.0000
252.100
252.140
0.040
0.886
1.5:1
44.44
250.00
2.10
18.00
5. Pucca floor
Provide pucca floor in half the transition length in the upstream and 3/4 the length of the expansion transition in the downstream. Length of pucca floor u.s.
10.7 2
5.35 m say 6.0 m
6
th
Pucca Floor
Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
6. Uplift pressure on the barrel floor and pucca floor
a. Static uplift pressure i.
At the bottom of barrel floor Level of bottom of barrel floor 251.8 0.6 0.3 2 2.5 248.1 m Static head 250 248.1 1.9 m of water
ii.
At the downstream end of barrel
Floor level 249.01m Assume floor thickness 249.01 1.5
247.51 m Static head 250 247.51 2.49 m of water b. Seepage head on the barrel floor and the pucca floor Seepage head H.F.L. in the drain
W.T. in the region (canal bed level) 253.25 250 3.25 m Total seepage path 0.6 2 0.3 2 2.5 1
8 13 13 11.3 m i.
At the bottom of barrel floor Seepage path to bottom of barrel floor 0.6 2 3.11 4.3 m H 1
11.3 4.3
3.25 11.3
, H1 2.01m of water
Total uplift in the barrel 1.9 2.01
3.91m of water
Max. Seepage 3.25 head
H 1 H 2
4.3 6.97 Total seepage length = 11.3 m
ii.
At d.s. end of barrel floor
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Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
Seepage path 0.6 2 3.1
8 3
6.97 m H 2
4.3
3.25 11.3
, H 2 1.25 m of water
Total uplift 2.49 1.25 3.74 m of water Floor thickness
3.74 2.2
1.7 m say 2.0 m
The remaining length of transition shall be provided with
0.8 m 0.8 m 0.6 m C.C. blocks over 0.6 m inverted filter. 4 rows of blocks resting on 1.2 m deep toe wall at ends.
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Hydraulic Structures – Hydraulic Design of Syphon
February 1, 2011
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