ppt on design of a aqueduct- cross drainage work

PROJECT ON COMPARATIVE STUDY OF CROSSINGS OF DRAINAGES BY THE IRRIGATION CHANNELS WITH SPECIAL REFERENCE TO

DESIGN OF A PROTOTYPE C.D. WORK: AQUEDUCT

Cross drainage works are structural elements which are constructed at the crossing of a canal and a natural drain, so as to dispose of drainage water without interrupting the continuous canal supplies.

NECESSITY OF CROSS DRAINAGE WORK:  The water shed canals do not cross natural drainages. But in actual

orientation of the canal network, this ideal condition may not be available and the obstacles like natural drainages may be present across the canal. So, the cross drainage works must be provided for running the irrigation system.

 At the crossing point, the water of the canal and the drainage get

intermixed. So, for the smooth running of the canal with its design discharge the cross drainage works are required.

 If the site condition of the crossing point may be such that without any

suitable structure the water of the canal and drainage cannot be diverted to their natural directions, cross drainage works must be provided to maintain their natural direction of flow.

TYPES OF CROSS DRAINAGE WORKS AND THEIR SALIENT FEATURES: A: By passing

the canal over the drain. They are of three types: 1. Aqueduct 2.Syphon aqueduct 3.Drainage syphon

AQUEDUCT & SYPHON AQUEDUCT

B: By passing the canal below the drainage. They are of two types: 1.Super-passage 2.Canal syphon

SUPERPASSAGE AND CANAL SYPHON

C: By passing the canal through the drain. They are of two types: 1. Level crossing 2.Inlets And Outlets

LEVEL CROSSING & INLET AND OUTLET

A)-FSL of Canal in relation to HFL of Drainage Channel B)-Suitable Canal alignment C)-Topography of Terrain: D)-Regime of Drainage Channel E)-Foundation Strata F)-Dewatering Requirements G)-Ratio of Design Flood in Drainage Channel to the Discharge in Canal H) - Envisaged Head Loss

A) Topographical / physical/contour data: B) Hydraulic Data: C) Cross section D) Longitudinal section

FLUMING  Reduction of width of waterway of canal  CD works become economical  Possibility of hydraulic jump

 To avoid this we have to control velocity of water.

TRANSITION  Provides smooth change  Avoid sudden transition and formation of eddies  At U/S section splay of 2:1 and at D/S splay of 3:1

Three methods for design of transition:1.Mitra’s transition method 2.Chaturvedi’s method 3.Hind’s methods

MITRA’S TRANSITION METHOD

Bn=Bed width of the normal channel section Bf=Bed width of the flumed channel section Bx=Bed width at any distance x from the flumed section Lf= Length of transition

CHATURVEDI’S TRANSITION METHOD

Bn=Bed width of the normal channel section Bf=Bed width of the flumed channel section Bx=Bed width at any distance x from the flumed section Lf= Length of transition

CUTOFF WALL  Built under the floor of hydraulic structure  Reduces uplift pressure  Reduces seepage of water  Depth of cut-off is decided from the scour

depth

 From lacey’s Normal regime scour Depth*=

R =0.473(Q/f)1/3  From Lacey’s Normal Scour depth*= R=1.35(q²/f)1/3

Where Q= Discharge w.r.t drainage f= slit factor , normally taken as 1 q= intensity=max. velocity*max. depth  At U/S cut-off 1.5 R and D/S cut-off 2R

FLOOD ESTIMATION: The various methods for estimation of design flood are broadly classified as under:  Maximum Probable flood/Application of suitable factor of safety  Return period  Rational method  Empirical flood formulae

DESIGN CONSIDERATION I) SELECTION OF TYPE OF C.D WORK II) HYDRAULIC DESIGN  Estimation of flood.  Design of drainage Section.  Estimation of HFL.  Design of drainage waterway.  Design of canal waterway.  Scouring  Head loss and bed level at different levels.  Design of transitions

III) STRUCTURAL DESIGN  Design of Trough .  Design of Pier.  Design of Abutment.  Design of Retaining wall.

Cont…

HYDRAULIC PARTICULARS OF THE CANAL AND DRAIN             

CANAL DATA Design discharge Bed width Bed level Full supply level Free board Left bank top level Right bank top level Left bank width Right bank width Velocity Side slope Water surface slope

U/S 4.905cumecs 5.30m 285.596m 286.846m 0.50m 287.346m 287.346 5.00m 1.50m 0.662m/sec 1 in 1.50 1 in 4000

D/S 4.905cumecs 5.30m 285.382m 286.632m 0.50m 287.132m 287.132m 5.00m 1.50m 0.662m/sec 1 in 1.50 1 in 4000

DRAIN DATA  Catchment area

28.67km2

 Observed high flood level

282.930m

 Deepest bed level

280.500m

 Average bed level

281.600m

 Left bank level

286.46m

 Right bank level

283.74m



90degree

Angle of crossing

 Direction of flow  Type of soil/Foundation  Safe bearing capacity

Right to left Hard soil/DI/Rock Foundation 35t/ m2

C/S OF DRAIN AT VARIOUS RDS

I) SELECTION OF TYPE OF C.D WORK  Terms  Discharge  F.S.L  H.F.L  Bed level

Canal 4.905m3/s

Drain 198.23m3/s

286.846m _

-284.3m

285.596m

281.75m

 Velocity 0.662m/s 1.5m/s  On the basis of above discussion, it can be concluded

that the best and most economical structure that can be built is AQUEDUCT.

II) HYDRAULIC DESIGN Step1: Estimation of flood in drain:Dickens’s Formula says, Q = CA3/4 Let us assume C = 16 Design Discharge, Q = 16×28.673/4 =198.23cumecs

Step2: Design of Drainage selection: Area of cross-section at crossing from graph is 24.8 m²≈ 25m² Velocity of flow at crossing in the drain = 198.23/25 = 7.92m/s ≈ 8 m/s Let us restrict the flow of water up to 1.5 m/s New area, A = 198.23/1.5 = 132.2m² Lacey’s regime perimeter (water way) is given by, W=4.75√Q

=4.75×√198.23=66.83m Average waterway required=50.56m

Step3: Estimation of High Flood level (HFL) Stage discharge curve was plotted at crossing point for drain and will adopt HFL according to our Qp (198.2 cumecs) Stage-Discharge curve at C.D site 284.5

284

Stage

283.5

283

y = 0.0131x + 281.72

282.5

282

281.5 0

50

100

150 Discharge

200

250

Step4: Design of drainage waterway We have lacey’s regime waterway =4.75√Q Clear span between piers be 9m and thickness be 0.7 m Using 7 bays of 9m each, clear waterway= (9×7) m=63 m Using 6 piers of 0.7m each, we have got length occupied by piers =6×0.7 m=4.2 m Total length of waterway=67.2 m.

Step5:- Design of canal waterway. • Providing a splay of 2:1 in contraction, the length of contraction transition =( (5.3-3)/2)x2 = 2.3

• Providing a splay of 3:1 in expansion, the length of expansion transition = ( (5.3-3)/2)x3=3.45 m

Step6:- Scour a)Scour in Drain (i) From lacey’s Normal regime scour Depth*= R’r =0.473(Q/f)1/3 . From this formula we found safe scour level at RL 277.58m which is 2.92m below deepest nallah bed. (ii) From Lacey’s Normal Scour depth*= R’=1.35(q²/f )1/3 q= maximum velocity × maximum depth of flow From this formula we found safe scour level at RL 278.1m which is 2.4m below deepest nallah bed.

(b)Scour

in canal

Upstream:Assume scour factor=1.25 Safe scour depth below FSL= SF×R Safe scour level=284.096m So, the bottom R.L of upstream cut-off is fixed at 284.096 Downstream:Assume scour factor =1.50. Downstream cut off 1m below NSL i.e. =282.882m

Step7: Head loss and bed levels at different sections

Fig- Plan and Section of Canal Trough

Step9:-Design of transitions (a) Contraction transitions:-Since the depth is kept constant, the transition can be designed on the basis of Mitra’s hyperbolic transition equation given as BX= (Bn .Bf. Lf)/Lf. Bn –x (Bn-Bf) where Bf=3m, Bn=5.3m, Lf=2.3m (b) Expansion transitions: - In this case, Bn=5.3, Bf=3, Lf=3.45m Using above equation, we have, calculated BX

DESIGN OF PIER            

LOADING CONSIDERATION: Length of trough=9.7m Load on each beam=5.871t/m Load of trough/meter run=2×5.871=11.742t/m Total load on each pier=113.897tons Loads to pier from each span =56.95tons Dl of trough =2× (17.25+9.38+3.45+1.00) =62.16 tons Dl of tie beam =0.6 tons Total DL =62.76 tons Wt of water and slit =2× (26.25+1.38) =55.26tons Total DL+ water and slit =118.02tons @0.5t/m2 live load =15 tons.

ANALYSIS OF PIER  1) Pressure developed at the foundation level: 2) Stress at the pier bottom, i.e., R.L.277 metre

a) Stress due to live load, dead load and self weight b) Stress due to buoyancy effect c) Stress due to eccentricity of live load and dead load d) Stress due to longitudinal force 1. Due to tractive effort or breaking force 2. Due to resistance in bearings e) Stress due to wind load f) Stress due to water current

Factors

When dry

When floods

Max (t/m²)

Min (t/m²)

Max (t/m)²

Min (t/m)²

live load, dead load and self weight

66.33

66.33

66.33

66.33

Buoyancy

-

-

-7.3

-7.3

Eccentric loading

10.62

-4.67

10.62

-4.67

1. Tractive effort

39.79

-39.79

39.79

-39.79

2. Bearing resistance

88.87

-88.87

88.87

-88.87

Wind load

9.492

-9.492

9.492

-9.492

Water current

-

-

36.253

-36.253

Total

215.102

-76.492

244.055

-120.045

Longitudinal forces

REINFORCEMENT DETAILS OF PIER

3)-STABILITY ANALYSIS OF ABUTMENT  Assumptions:  1. Unit weight of soil=2.08 t/cum  2. Unit Weight of wing wall=2.3 t/cum  3. Unit Weight of R.C.C= 2.5t/cum  4. Angle of Repose of soil=30o  5. Coefficient Of Friction between concrete and

concrete= 0.75  6. Coefficient of Friction between concrete and soil=0.6

Structural details of Abutment

4)-STABILITY ANALYSIS OF GRAVITY RETAINING WALL  Assumptions:  Unit weight of soil=2.08t/cu m

 Unit weight of wing wall= 2.3t/cu m  Unit weight of RCC=2.5t/cu m  Angle of repose of soil(φ) =30°

 Coefficient of friction between concrete & concrete =

0.75  Coefficient of friction between concrete & soil= 0.6

Structural details of Gravity Retaining Wall

CONCLUSION  The comparative study for the project reveals that not only

the selection of type of CDs for a particular crossing plays a vital decisive discriminatory role, but also the design of the structural with various alternatives with respective to (i) suitability of foundation vis-à-vis various foundation strata, (ii) transitions (iii) u/s and d/d protection works (iv) post construction operation and maintenance etc. does equally challenge the hydraulic engineers exposure to the veracity of the job’s complex nature.  The aqueduct which we have designed is found to be the most stable and economical structure as compared to the any other cross drainage work. Here we have not provided any inspection road but in future, if required, then we can design and provide an inspection road.