Tank Sluice i4m7

DDIS UNIT-IV 1. Design a sluice taking off from a tank irrigating 160 hectares at an average duty of 700 hectares/cumecs The earthen dam of an irrigation tank has the following data: Top width of bund = 2 m Side slopes of bund = 2:1 on both sides R.L of top of bund = 128.50 m Full tank level = 125.50 m Max water level = 126.50 m Average lower water level = 123.00 m Sill of the sluice at off take = 122.50 m Good foundation = 121.50 m The details of the channel below the sluice are as under Bed level : 122.00 m FSL : 122.50 m TBL : 123.50 m Side slope : 1 ½ : 1 Draw i) Longitudinal section along the c.l of the barrel. ii) Half plan at top and half at foundation. iii) Cross section of the tower head and of the rectangular barrel Design: Ayacut: 160 hectares Duty: 700hectares/cubicmeters/second Discharge= 160/700 =0.22cubic meters/second Ventway: The area of the ventway of the sluice must be such that it can draw normal supplies of water when the tank is at the low water level or a level at which the tank supply will always be available to be drawn during the normal crop period. The level of the water in the tank is given as +123.00 Sill of the sluice is +122.50. So the head of water available above the sill for drawing supplies is 123122.50=0.5 meter. However the sluice is designed to draw the normal requirements with a driving head of 0.25 meters, and when the tank water level is high the entway is throttled by means of screw gearing shutters. Assuming a driving head of 0.25 meters above the centre of the opening, we get the discharge by using the formula Q= CdA√2gh Where Cd is the coefficient of discharge of a large orifice usually taken as 0.60., A is the area of the ventway and h is the driving head in meters. Since the necessary discharge required id 0.2cubic meters/second, we have 0.22= CdA√2gh = 0.6A√2x9.81x0.25 =1.328A A=0.22/1.328= 0.165 square meters. This gives approximately a diameter of 45cms. For a circular opening. This can be adopted. But the minimum ventway to be adopted for sluice barrels is about 75cmsx60cms, so as to allow room for repairs etc; So insert a disaphragm stone with 45cms. Diameter opening in it. Thus wii be placed at the entrance

to the sluice barell with regulating arrangements in front of it. Sluice barrel: The sluice barrel is buried under the tank bund. The barrel will have masonry side walls. The roof can be either of R.C Slab laid in situ, or precast R.C slabs with a leveling course of concrete laid over it. The foundation of the two side walls is continuous in concrete 60 cms. ing the overburden. So deg for the maximum possible load i.e considering the section of the barrel at the centre of bank, the height of the earth ed by the slab is 5.10 meters.

The earth will be charged with the percolating water through the embankment. It is designed for saturated earth fill. Height of the bank over barrel = 128.50-121.40= 7.1 meters Weight of concrete/cubic meter=2400kg Weight of saturated earth per cubic meter=2240kg Assume the thickness of slab to be 15cms Effective span of slab (60+15) =75cms Taking a meter width of slab self load of slab is 2400x15x75/100x100=270kg. Weight of earth: 2240x7.1x75/100=11,928.80 kg Maximum bending moment =WL/8 = 11928.80 x 0 .75x100/8= 111,832.5 kg.cm Side walls: The side walls act like abutments. They take the side thrust due to the earth pressure and also the superincumbent weight of the surcharged earth standing directly on the wall and roof slab. Calculating the earths pressure by Rankine’s theory, the stability of one wall is checked by assuming a section as shown in the figure.

Earth pressure: The horizontal earth pressure acting on the wall at point (A) to be calculated . Height of earth fill above A= +128.50-122.50 .00=6.00 meters. Assuming the weight of earth saturated as 2240kg/m 3 and angle of repose as 300, The earth pressure at A=

wh(1 - sin f ) =2240x6x1/3=4480kg/m2 wh(1 + sin f )

Earth pressure at D=2240x7.1x1/3=5301kg/m2 Total horizontal thrust on the side wall ==4401kg. This acts at =44 cms. Above point A. Let this force be called as H. Weight transmitted by the roof slab: Load coming on each side wall=8850/2=4425kg. Let this force be called P1. This acts vertically on the side wall at a distance of 7.5 cms. From the vertical face of the abutment. Weight of earth on the top side of wall beyond the slab The width of side wall at top is 45cms. Deducting the slab bearing the portion of masonry wall remaining is equal to 45-15=30cms or 0.3 meters. The weight of earth coming down on this portion=0.30X2240X7.1=4771.2 kg. Let this force be P2. This acts vertically on the side wall at a distance of 15+30/2=30cms. From the vertical face of the abutment. Weight of earth standing on the slope of side wall

This can be split into two vertical forces a) The force representing the weight of earth of the rectangular portion B’BCD=7.1x0.55x2240=8747.2kg. Let this force be P3 acting vertically at a distance of 45cms.+55/2=45+27.5=72.5cms. from the vertical face b) The force representing the weight of earth standing on the sloping portion AB’D =

1 x0.9x0.55x240=555kg. 2

Let this force be P4 acting vertically at a distance of 45cms.+

2 x55cms, i.e 81.7 cms. 3

Weight of masonry per cubic meter=2100kg. Weight of masonry side wall P5=

(0.45 + 1) x0.9x2100=1370kg. 2

This load is P5 acts at a distance of 39cms. From the vertical face. Stability analysis: Take moments of all forces about toe Force

Force in kg.

Lever arm cms.

Moment of the force in kg.cm.

Horizontal

Vertical

P1

------

4425

7.5

3318

P2

------

4771.2

30

102810

P3

------

628

72.5

455518

P4

------

555

81.7

45344

P5

------

1370

39

53430

H

4401

------

44

(-)164120

Total

Arm of the resultant from toe is Eccentricity=

16060kg.

526170 =33cms 16060

100 - 33 = 17cms. 2

526170 kg.

So, the resultant is just outside middle third Max. compression at toe=

16060 � 6 C17 � 2 1+ � �=3.24kg/cm which is with in permissible limits of 100 C100 � 100 �

masonry. Tension at heel A=

16060 � 6C17 � 2 1� �=0.032 kg/cm . The maximum allowable tension is 100 C100 � 100 �

1.25kg/cm2. Hence the section adopted is safe and can be adopted. Tower head: The tower head consists of a masonry well as shown in the figure into which the shutter operating arrangements are fixed and can be operated from a slab on top of the well. Generally these levels are not less than 1.25 meters in internal diameter and have their top taken at least 30 cms. above M.W.L of the tank. The bottom of the well rests directly on the foundation concrete of the sluice. The well steining is designed as a thick cylindrical shell to withstand a radial earth pressure acting on the outer surface. By doing so, the masonry develops hoop compression, which shall not exceed the safe limits of stress the masonry can take. Assume a section of masonry well as shown in the figure with internal diameter 1.25 meters. The top of well is to be at least 30 cms, above M.W.L i.e keep it at+38.30