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CROSS REGULATOR

CROSS REGULATOR

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CROSS REGULATOR

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  1. CROSS REGULATOR The cross regulator is provided to effect equitable distribution of supplies amongst the distributary and parent canal, to raise water level when supply in the parent canal is low, to release surplus water from canal, in conjunction with escapes, or to provide means for cutting off supplies to the downstream side for repairs etc. The criteria for the Hydraulic Design of cross regulators for canals is as per I.S. code: 7114 – 1973 (reprint December, 1979).

  2. 1) Driving Head: The driving head is the difference between the water levels on U/S and D/S side of the regulator. This is provided to allow the passage of required discharge on D/S through the regulator at full supply level. 2) Fluming ratio: Depending upon the driving head (fully utilizing the driving head) the regular width may be flumed up to a maximum of 50% of the canal width to economize the cost of the structure.

  3. 3) HUMP AT THE REGULATOR SRUCTURE A hump is provided below the regulator gates creating a fall on the D/S side for the following reasons. (a) To trap silt carried by the water on the U/S side of the regulator. (b) To reduce the depth of flow over the hump to increase velocity through the vents and economize the gate structure. (c) Hump is created in the glacis drops to increase the efficiency of flow of water to D/S side. (d) To negotiate the difference of levels if any in the canal bed levels on the U/S and D/S side of the regulator.

  4. 4) DISCHARGE FORMULA Q = C Bt H3/2 Where Q = D/S full supply discharge in m3 /sec C = Co-efficient of discharge Bt = Clear water way in metres. H = Head over crest i.e. Full supply level on the U/S + head due to velocity of approach – crest level. The value of ‘C’ is determined using Malikpur graph (a graph drawn between drowning ratio and co-efficient of discharge based on experiments).

  5. 5) HEIGHT OF HUMP Crest level is calculated as per CWC, Manual i.e, Crest level = U/s TEL – head over crest (H) The height of crest above up stream bed level should not be more than 0.4 H. Glacis profile is calculated as per CWC manual with 2:1 slopes to negotiate the levels and smooth curves at the junctions. The radius of curvature to be adopted is H/2 on up steam and ‘H’ on downstream as specified therein.

  6. 6) ENERGY DISSIPATION: D/s floor of the regulator is depressed to form a cistern to dissipate energy. Since the U/s and D/s C.B.Ls and F.S.Ls are almost the same in the NSP Canals and distributaries, the energy dissipation arrangement is quite simple. To dissipate energy at low flows through regulator the cistern with water cushion with a minimum length and deflector wall at the end of the cistern are provided. On main system the hydraulic jump calculations are to be done for different opening conditions i.e., ¼, ½, ¾ and full supply. Further if there are more than one vent, these calculations have to be made for different conditions of vents opening. The height and length of jump in each case is to be found. Based on these calculations the depth and length of cistern will be fixed. Refer I.S:4997–1968 or Small Dams by USBR.

  7. 7) EXIT GRADIENT AND FLOOR THICKNESS When there is no water on D/s of the regulator and water at FSL on U/s, the exit gradient is to be calculated and the thickness of floor has to be designed for the uplift pressures at various sections. The formula for exist gradient is: GE = 1 x H (π √ λ) d Where: λ = 1 + 1 + α2 2

  8. α = b d H = difference between crest level and downstream bed level in m b = length of impervious floor in m d = depth of downstream curtain wall in m 8) U/s & D/s CURTAIN WALLS Scour depths are to be calculated at the U/s and D/s transition ends and the curtain walls to be taken up to 1.5 times the scour depth.

  9. 9) PIERS Piers to be designed considering hoist loads, load due to water thrust on gates, wind pressure and water currents. Whenever a road bridge is provided the live load moments, tractive force and braking force etc., are to be considered while checking the stability. 10) ABUTMENTS Abutments to be designed with super imposed loads, live load moments, tractive force and braking force and the earth pressure behind them.

  10. 11) WINGS AND RETURNS Conventional Wings and returns to be designed for the earth pressures with T.V.A. procedure considering Ф as 32 degrees and δ as 16 degrees. 12) BED PROTECTION U/s and D/s canal bed and sides are to be protected with C.C. lining in M 15 grade concrete with profile walls at the end. The thickness of lining is normally the same as for the remaining length of the canal in the reach.

  11. 13) OPERATION PLATFORM It is in VRCC M 20 grade, designed for its self weight plus forces transmitted through the screw rod or the hoist and crowd load of 400 kg/ sqm. 14) GATES AND HOISTS Either sliding type or fixed wheel type gates are provided depending on the size of opening. Electrically or manually operated hoist arrangement is to be made to operate the gates.

  12. FIG.16

  13. CANAL FALL (DROP) The canal fall or drop is required to be provided, whenever, the natural slope of the country is steeper than the bed slope of the canal and the difference in levels is adjusted by constructing a fall or drop. Drops become necessary in the case of distributaries, which are generally aligned along the ridge for commanding the area on either side. There are two main types of falls. (i) Type I: Vertical drop: In this type of fall, the nappe impinges clear into the water cushion below. The dissipation of energy is effected by the turbulant diffusion as the high velocity jet enters the deep pool of water downstream.

  14. (ii) Type II: Glacis fall: This type utilizes the principal of standing wave for dissipation of energy. This type of fall can be divided into following three classes. • Straight glacis with baffle platform and baffle wall. • Straight glacis without baffle platform and baffle wall. • Modified glacis type. The falls are further divided into: • Flumed or unflumed falls and • Meter or non – meter falls. As per the Central Water Commission’s Manual on falls, the following table indicates the type of falls to be selected for the given discharge and height of drop.

  15. The Design Circular No. 35/1807 dated 2.2.1978 of CE., N.S.L.C. stipulated the type of drop to be adopted for different discharges and heights of drops. Glacis type drop: Design Procedure: • Clear width of throat (Bt): The fluming of Canal should not exceed the limits given below subject to the condition that over all width of throat is not more than Bed width of channel on the downstream side. Height of dropPercentage of fluming • Up to 1.0 m 66% • Over 1.0 m to 3.0 m 75% • Above 3.0 m 85%

  16. 2) Crest Level: The Crest level is fixed by working out ‘D’ using formulae Q - = C. Bt. D 3/2 Where Q = discharge in cumec C = co-efficient of discharge depending on the drowning ratio. Up to 70% fluming C = 1.84 can be adopted and above that, it is to be read from Malikpur graph Bt = Throat width in ‘m’. D = Depth of crest below U/S TEL in ‘m’ After calculating value of D from the formula, crest level is fixed with the equation: Crest level = U/S TEL – D

  17. Length of Crest: 2/3x D. 4) Height of Crest: Should not be greater than 0.4 D, above the upstream canal bed level. 5) D/S Glacis: In the case of baffle type glacis drops, glacis slope is to be 2/3: 1 joined tangentially to the crest on the U/S side and baffle platform on the downstream side with radius equal to ‘D’. In the case of straight glacis provide glacis slope of 2:1 with radius of curvature as D at the junction with the crest at the upstream end and pavement at the downstream end. 6) U/S Glacis: Glacis slope is to be ½: 1 joined tangentially to the crest with a radius equal to D/2.

  18. 7) Protection: • Length of U/S protection: 3 times F.S.D. or as per the standard fixed by the project authority. The protection is in CC M 15 grade with profile walls at the end. • Length of D/S protection: 4 (d + h) where d = d/s F.S.D. and h = difference in F.S.Ls or as per the standard fixed by the project authority. The protection is in CC M 15 grade with profile walls at the end. 8) Glacis fall without baffle: (i) The hydraulic jump is calculated to be the most efficient means of dissipating the energy. To ensure formation of the hydraulic jump, it is necessary that the depth of tail water flowing at sub–critical velocity in the canal downstream should bear the following relation to hypercritical depth of flow at the toe of glacis:

  19. dx = -d2 +√2v2² d2 + d22 g 4 Where v2 = velocity of water at the formation of jump d2= hyper critical depth at formation of jump dx = sub – critical depth in canal on downstream side The values of d2 and dx are calculated from the following formulas dxfor unflumed falls = 0.985 q0.52 x Hx0.21 For flumed falls d1x = Hx - HL + dx(unflumed) Where = Hx HL K0.152 Hx = calculated drop in m HL = actual drop in m K = fluming ratio (D/S bed width / throat width). d2 = 0.183 q0.89 x Hx - 0.35

  20. ii) Cistern: The cistern level is obtained by subtracting the value of 1.25 dx or 1.25 dx1, as the case may be, from the downstream full supply level of the canal or 1.25 Ef2 from the downstream total energy level, which ever gives the lower level. Ef2 is the energy of flow in the canal after formation of the hydraulic jump. The length of the cistern is equal to 5 Ef2. The cistern is joined to the downstream bed at a slope of 1 in 5. 9) Glacis fall with baffle: The dimensions of the baffle platform and baffle wall are determined from the relationship given below: (i) R.L of Baffle platform: D/S F.S.L. – d1x. (ii) Height of Baffle wall (Hb) = dc – d2 Where,d2 = Hyper - critical depth at the point of formation of standing wave.

  21. d2 =0.183 (q)0.89 x Hx -0.35 dc = Critical depth dc = q21/3 • g q = discharge per meter width. R.L. of Baffle wall = R.L. of Baffle Platform + Hb. (iii) Thickness of Baffle wall = 2/3 x Hb (iv) Length of Baffle Platform Lb = 5.25 (Hb) The baffle platform should join the toe of glacis with a radius equal to D and the baffle wall with a radius R = 2/3 Hb

  22. v) Cistern: • Depth of cistern: D/S FSD/10 subject to a min of 15 cm for distributaries and minors and 30 cm for main canals and branches. • R.L. of the cistern = D/S bed level – depth of cistern • Length of cistern = 5 times down stream F.S.D. • R.L. of the deflector wall = D/S CBL + D/S F.S.D/ 10 • Friction blocks and glacis blocks: (i) Glacis fall with baffle (a) If the height of drop is less than 2.0 meters, friction blocks and glacis blocks are not required. If the height of drop is more than 2.0 m, two rows of friction blocks staggered in plan are to be provided.

  23. Size of friction blocks: Height (h) = 0.262 dx, Length (L) = h Top width (W) = 2h / 3 Distance between two rows = h. The downstream edge of downstream row of friction blocks shall be provided at a distance of one third length of cistern from the end of the cistern floor. b) Glacis blocks: Single row of glacis blocks of same size as friction blocks is to be provided at the toe of the glacis. (ii) Glacis fall without baffle

  24. Four rows of friction blocks staggered in plan are to be provided in the case of flumed falls. The upstream edge of first row of blocks may be at a distance of 5 times the height of blocks from the toe of glacis. Size of friction blocks: Height (h) = D/S FSD 8 Height (L) = 3h Height (W) = 2h 3 Distance between rows = 2h 3 11) Deflector wall: In glacis falls, a deflector wall of height equal to one tenth of the downstream FSD is provided at the downstream end of the cistern. The minimum height should be 15 cm.

  25. 12) Curtain wall: i) Depth of U/S curtain wall = U/S FSD subject to minimum of 0.50 m 3 ii) Depth of D/S curtain wall = D/S FSD subject to minimum of 0.50 m 2 These should be checked with scour depth formulae with suitable factor of safety. Downstream cut off can be increased suitably to reduce the thickness of floor. 13 (i) Exit gradient and uplift pressure: H = difference between crest level and D/S CBL d depth of D/S curtain wall b = length of impervious floor d depth of D/S curtain wall

  26. After working out values of H/d and b/d, find the value of exit gradient GE from the graph in plate 16 of CWC manual on falls. The GE depends upon the soils, but it should be less than 0.30. Uplift Pressure: (a) U/S curtain wall: 1 = d = depth of D/S curtain wall α b length of impervious floor Find out corresponding value of φ E = from graph i.e., from plate 17 of CWC manual on falls. …% of residual head φ E1 = 100 - φ E b) At the d/s cut off wall 1 = d = depth of D/S curtain wall α b length of impervious floor

  27. Find out the corresponding value of φ E from graph i.e, from plate 17 CWC manual on falls. ii) Thickness of floor: The uplift pressures at toe of glacis, at the end of baffle and at the end of cistern are worked out by interpolation for fixing the thickness of floor. Thickness of floor at toe glacis: % age of pressure @ toe of glacis = φ E at D/s + (φ E1 − φ E D/s) X L/b b = total length of impervious floor. L = Length of floor up to toe of glacis from D/S end. Thickness of floor at the toe of glacis = %age of pressure @ toe of glacis x H 100 x (ρ − 1) Where ρ is specific gravity of CC i.e., 2.4

  28. FIG.17 Similar method is to be adopted for calculating thickness of floor at the end of the baffle, at the end of cistern etc.

  29. FIG.18

  30. Vertical drop: Design procedure: 1) a) Throat width Bt = B.W. of canal (If canal bed width on upstream and downstream are different, lower of the two). b) Crest Level: Crest level is obtained by working out value of D (depth of crest below upstream TEL) from the following formula. Q = C x Bt D 1/6 x D3/2 Lt Where Bt = Throat width in m C = Coefficient of discharge usually taken as 1.835 Lt = Length of crest in m D = Depth of crest below upstream TEL in m U/S T.E.L = U/S FSL + Velocity head R.L. of crest = U/S TEL – D

  31. 2) Cistern: A cistern is provided at the toe of the drop by suitably depressing the floor below the downstream bed of the canal. a) Depth of cistern = (HL x D) 2/3 in m. 4 D = depth of crest below U/s TEL. R.L. of cistern = D/s CBL – depth of cistern. b) Length of cistern = 5 (HL x D)½ in m. (3) Length of throat or crest (Lt): Lt = 0.55 √D in m subject to a min. of 0.50 m. (4) Thickness of crest wall at base: T = 0.5 x D1 in m, where D1 = RL of crest – RL of cistern

  32. 5) U/S and D/S Protections: i) Length of U/s protection= 1 ½ times the U/S FSD or as per standard fixed by the Project authority. ii) Length of D/s protection = 3 times the D/S FSD or as per standard fixed by the Project authority. 6) Exit Gradient & Uplift pressures a) Exit gradient: H = R.L. of crest – D/S CBL. d = depth of D/S curtain wall off = FSD/ 2 or as per the requirement to bring the exit gradient within the limit. b = Length of impervious Floor = Foundation offsets + width of drop wall + length of cistern + width of curtain wall.

  33. α = b/d, λ = 1 + 1 + α2 2 GE = exist gradient = 1 x H ∏ λ d b)Uplift pressures: (a) U/S face of crest wall d = U/S CBL – Bottom of foundation concrete. 1 = d α b φ E is read from ‘Plate 17’ of CWC manual on falls

  34. At the end of floor 1 = d α b. φ E is read from ‘Plate 11.1 (a) of CWC manual on fall (enclosed) Thickness of Floor at the d/s Face of drop wall is interpolated considering the pressures at the face of crest wall and at the end of floor. Absolute pressure = (% Pressure) x H m of water column. 100 • P = 75% of Absolute pressure for soils other than pervious soils

  35. Thickness of floor = P, where ρ = 2.40 ρ – 1 c) Friction Blocks: For discharge exceeding 3 cumec, two rows of friction blocks staggered in plan may be provided in cistern. The downstream edge of downstream row should be at a distance of one third the length of the cistern from the downstream end of cistern floor. Size of friction blocks: Length (L) = 1 x Downstream F.S.D. 8 Height (h) = 1 x Downstream F.S.D. 8

  36. Top width (w) = 1 x height of subject to minimum of 8 cm, joined to floor on the 4 downstream side with a slope of 1:1 Clear space between rows = height of the blocks. Vertical type core wall drop: (CE NSLC Circular No. DW.150/ 3845 – S, 3-9-1980) Various components of the vertical type drop with core wall for different ranges of discharges i.e., 1.5 cumec to 1 cumec, 1 cumec to 0.5 cumec, 0.5 cumec to 0.1 cumec, 0.1 cumec and below and for various heights of drops i.e., 0.6 m, 0.8 m, 1.0 m, 1.2 m and 1.5 m with clear over fall are given in table I and II. The same may be adopted for the drops on the distributories having discharge 1.5 cumec and below.

  37. For drops in silty or clayey soils the following modifications may be adopted (Design Circular No. 35/1807 dated 2.2.1978 of C.E., N.S.L. Canals). (a) For drops of 1.5 m and above, for all discharges, wings and returns may be provided. (b) For drops less than 1.5 m height and discharge above 1 cumec, wings and returns may be provided. Following are the recommendations of the Expert Committees on design of drops on distributary system.

  38. (a) For drops with height of less than or equal to 0.60 m and discharge of less than 50 cusec, unflumed core wall type drops may be provided. (b) For drops with height more than 0.60 m and discharge between 50 and 100 cusec, unflumed vertical drops with wings and returns may be provided. (c) For drops with discharges more than 100 cusec, straight flumed drops may be provided. Where fluming ratio as per codel provision could not be adopted for drops of height less than 0.60 m, unflumed vertical or unflumed core wall type drop may be provided.

  39. TABLE No. I DETAILS OF COMPONENTS OF VERTICAL TYPE DROPS WITH

  40. THAN 1.5 CUMEC AND HEIGHT OF DROP LESS THAN 1.5 m

  41. FIG.19

  42. TABLE No. II Table showing discharges and depth of crest below U/S T.E.L. for vertical type drops with rectangular opening and free fall. Discharge Q = 1.835 Bt (D/ Lt)1/6 D3/2 in cumec or D = {(Q/ Bt) x (Lt1/6/ 1.835)}3/5 in meters

  43. or D = {(Q/ Bt) x (Lt1/6/ 1.835)}3/5 in meter where Bt = Width of crest = Canal Bed width in meters Lt = Length of crest along axis of canal in meters Notch type drop: (Trapezoidal/ Rectangular) As per Irrigation manual by W.M Ellis. Design procedure: 1) For half discharge, find out F.S.D. Usually it is 0.7 F.S.D. 2) Calculations of no. of notches: No. of notches = Bed width 1.5 x FSD

  44. Vide – Emperical rule No.4 page No. 229 of ‘Irrigation practice & Engineering’ by Etcheverry) Find discharge per notch i.e., = Q No. of notches. Silt level of drop = U/S CBL 3) For free fall notches: Case I: For free notch, the equation used for finding out notch dimensions is Q = 2.96 C d3/2 (L + 0.4 d n) Where : Q = discharge in cumec

  45. C = The coefficient of discharge of notch = 0.70 d = depth of water in metres over sill of the not L = width of the horizontal sill of the notch in ‘m’. n = 2 tan α, where α is the angle made by each of the sides of the notch with the vertical. If ‘n’ is Zero, then it becomes a rectangular notch. Case II: For submerged notch: Q= 2.96 C√ d-E E +d L + 3 E2 + (d-E) E + 0.4 (d-E)2 n 2 4

  46. Where E = the submersion depth of tail water over the sill of the notch. Q, C, d, L, n are the same as in the case – I. Find L and n by using the above equations (free fall or submerged) for full supply discharge and half supply discharge conditions. Substitute the values of L and n to get top width of notch in the equation = L + nd. 4) Length of drop wall between abutments: Length of drop wall between the abutments should not be less than 7/8th of the canal bed width on up stream. However in practice, the length of drop wall is provided equal to upstream bed width.

  47. (5) Width of notch pier at FSL should not be less than half of upstream F.S.D. ‘d’ Top width of notch is generally 0.75 d, where notch is free and d where notch is submerged. 6) Water cushion: The depth ‘x’ of the water cushion is worked out from the following equation X + d1 = 0.91 dc √ h Where d1 = D/S F.S.D dc = Depth of water over the crest. h = height of drop (difference in FSLs).

  48. 7) Length of cistern: Length of the horizontal floor of the cushion = 2 dc + 2 √ dc h subject to a minimum of 1.2 + 2√dc h. It is to be designed on the basis of up lift pressures and exit gradient if the soil is pervious. 8) Thickness of cistern floor = 0.55√ dc + h. This should be designed on the basis of uplift pressure and exit gradient, of the soil is pervious.

  49. Drop wall: i) Top width of drop wall at sill level (0.5d + 0.15) to (0.5d + 0.3) ii) Bottom width of drop wall = H + dc+x √ ρ Where H = vertical height of the sill from the apron, dc = depth of water over the crest and x = depth of water cushion 10) Protection works: i) Length of the U/S revetment = 3dc subject to min of 3 meters