The document details the design and calculations for a trapezoidal canal fall, including the specifications for the crest wall and cistern design. It discusses various parameters such as discharge rates, heights, widths, and uplift pressures, presenting formulas and values for determining structural thickness and pressure conditions. Key elements include the elevation of the crest wall, assumed dimensions, and factors affecting uplift pressure, with comprehensive calculations throughout.

1. DROP STRUCTURE
DESIGN OF TREPEZOIDAL
CANAL FALL
3/19/2014 1
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

2. 3/19/2014 2
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

3. 1. Crest wall :
As the discharge Q = 50 cumecs > 14
cumecs, a trapezoidal crest wall is
provided
Length of crest wall = d/s bed width
L = 35 m
Assume B = 1 to 1.5 m.3/19/2014 3
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

4. R.L. Of crest = u/s HFL – H
= 203.50 – 0.83 = 202. 67
Height of crest above d/s bed,
d = crest level - d/s bed level
= 202.67 – 200
= 2.67 m
3/19/2014 4
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

5. a trapezoidal crest wall with top
width 1.00 m, u/s slope 1 : 3 and d/s
1 : 8.
Base width B1 =
= 1 + (1/3) 2.67 + (1/8) 2.67
= 2.22 or say 2.5 m
3/19/2014 5
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

6. D = 2.67 M
1.0 M
(1/3)2.67
1.00 (1/8)2.67
3/19/2014 6
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

7. Cistern design :
3/19/2014 7
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

8. 3/19/2014 8
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

9. D = 2.67 M
1.0 M
(1/3)2.67
1.00 (1/8)2.67
5.6 M
0.3 M
3/19/2014 9
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

10. 3. CUTOFF :
3/19/2014 10
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

11. D = 2.67 M
1.0 M
(1/3)2.67
1.00 (1/8)2.67
5.6 M
0.3 M
0.7 m
1.0 m
0.3 m to
0.6 m
0.3 m to
o.6 m
3/19/2014 11
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

12. 4. Impervious floor :
Exit gradient,
3/19/2014 12
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

13. IF not given assume 1/5 to 1/7 .
3/19/2014 13
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ASSISTANT PROFESSOR, DIET

14. 3/19/2014 14
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

15. = b – ld – b1
3/19/2014 15
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

16. D = 2.67 M
1.0 M
(1/8)2.67
5.6 M
0.3 M
35.90 m
25.50 m
7.9 m
3/19/2014 16
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

17. Thickness of floor
T = h / G – 1
Where h = residual head at any point
= Depth of cistern
+
(RL of crest – d/s bed level) uplift
pressure
Where uplift pressure =
3/19/2014 17
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

18. Uplift pressure = at toe =
+ (distance from
d/s cutoff)
φc1
φe1
φd1
φe
φd
φc
φe
oorlengthoffl
ec  1
7.9 m
3/19/2014 18
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

19. All must be corrected before put in
equation
Corrections are thickness, mutual
interference of pile and slope where
slope correction is neglected.
φc1φe1 φd1
3/19/2014 19
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

20. U/S PILE INTERMIDIATE
PILE
DOWNSTREAM PILE
3/19/2014
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ASSISTANT PROFESSOR, DIET
20

21. 3/19/2014 21
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ASSISTANT PROFESSOR, DIET

22. Uplift Pressure Calculations :
(a) u/s cutoff wall
d1 = 0.70 m, b = 35.90 m
b = • d1
3/19/2014 22
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ASSISTANT PROFESSOR, DIET

23. 3/19/2014 23
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ASSISTANT PROFESSOR, DIET

24. 3/19/2014 24
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ASSISTANT PROFESSOR, DIET

25. Corrections for interference of
d/s pile
3/19/2014 25
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ASSISTANT PROFESSOR, DIET

26. 3/19/2014 26
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ASSISTANT PROFESSOR, DIET

27. 3/19/2014 27
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ASSISTANT PROFESSOR, DIET

28. 3/19/2014 28
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ASSISTANT PROFESSOR, DIET

29. 3/19/2014 29
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

30. Uplift pressure = at toe =
+ (distance from
d/s cutoff)
φc1
φe1
φd1
φe
φd
φc
φe
oorlengthoffl
ec  1
7.9 m
3/19/2014 30
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

31. Uplift pressure = at toe =
+ (7.9)
φc1
φe1
φd1
φe
φd
φc
12.15
90.35
15,1273.89 
7.9 m
3/19/2014 31
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

32. Thickness of floor
T = h / G – 1
Where h = residual head at any point
= Depth of cistern
+
(RL of crest – d/s bed level) uplift
pressure
Where uplift pressure =
3/19/2014 32
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

33. Thickness of floor
Where h = residual head at any point
= 0.3 + (2.70) 0.29= 1.08
T = h / G – 1 = 1.08/2.24 – 1
= 0.87 say 0.90
3/19/2014 33
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

34. Uplift pressure = at 3 m
from toe =
+ (4.9)
φc1
φe1
φd1
φe
φd
φc
T
=
h
/
G
–
1
12.15
90.35
15,1273.89 
4.9 m
3/19/2014 34
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET
T
=
h
/
1

35. Thickness of floor
Where h = residual head at any point
= 0.3+ (2.7) 0.227 =0.913
T = h / G – 1 = 0.913/ 1.24
= 0.73 say 0.80
3/19/2014 35
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

36. Uplift pressure = at 5.6 m =
+ (5.6)
φc1
φe1
φd1
φe
φd
φc
12.15
90.35
15,1273.89 
2.3 m
3/19/2014 36
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

37. Thickness of floor
Where h = residual head at any point
= 0.3+ (2.7) 0.17 =0.76
T = h / G – 1
= 0.76/ 1.24
= 0.61 say 0.70
3/19/2014 37
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

38. Uplift pressure = at end of
floor =
φc1
φe1
φd1
φe
φd
φc
12.15
3/19/2014 38
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

39. Thickness of floor
Where h = residual head at any point
= 0.3+ (2.7) 0.1215 =0.328
T = h / G – 1
= 0.328/ 1.24
= 0.26 say 0.40
3/19/2014 39
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET

40. 3/19/2014
PREPARED BY VIDHI H. KHOKHANI
ASSISTANT PROFESSOR, DIET
40