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Design of surplus weir. Estimation of Flood discharge entering the tank. Flood discharge entering the tank in question is determined by the formula Type formula here. Where C may be assumed as 9. Length of the surplus weir. Water is to be stored upto level of Submersion of foreshore lands is limited to Since temporary regulating arrangement are to be made on top of the weir, to store water at times. The weir may be assumed as a broad crested weir. So the discharge per meter length of the weir is given by.
Where Cd is 0. Since the dam stones are to be fixed on top at 1 meter clear intervals, the number of openings will be So the number of dam stones required is 62 Nos. Size of dam stone 15cms x 15cms. And the projecting length above crest will be 75cms. Therefore the overall length of surplus weir between abutment s is However provide an overall length of Crest level. Level where hard soil at foundations is met with 9. Taking foundations about 0. Crest width. Generally the crest width is assumed as equal to 0.
This gives a crest width of about 1. This width may be adopted. Base width. Check the stability of the weir such that the resultant thrust due to overturning water pressure.
In such cases the maximum overturning moment due to wataer. The slope of weir on either side being the same , the restoring moment M of the weir due to the weight of masonry is. The weir will have a trapezoidal profile as shown in figure. Abutments, wings, and returns. The top width of abutments, wings, and returns will all be uniformly 0. Length of the wing walls must be enough to completely encase the tank bund as shown in.
Portion AB is called the abutment. It has its top level same as that of the tank bund at The bottom width required is about 4. The section indicated in figure. The wall BD is called upstream wing wall. The section of the wing wall at B is same as the section of the abutment.
This wing wall start sloping down from B till it reaches about 30cms. Above MWL i. So , the portion of wing wll BC will be having its top sloping down from Section of the wing wall at C. Height of wall above top of foundation The top width from B to C is the same as 0. Level wing and return. Since the level wing and return i. Upstream side transition. In order to give an easy approach , the upstream side wing wall may be splayed as shown.
Downstream side wings and returns. As the water after passing over the weir goes down rapidly to normal MFL in the water course,. The wing wall from A to F. The section of wing wall at A will be the. The top wing wall at F may be fixed at The base width required is 1. The same section is continued for the return FG also.
Downstream transition. The downstream side wings are given a splay of 1 in 5 as shown in figure 4. Aprons of the weir. The ground level at site of weir is Upstream Aprons. Generally no apreons are required on the upstream side of the weir.
Howeverit is desirable to provide puddle apron as shown in figure 4. It is also sometimes provided with nominal rough stone apron 30cms. Thick packed well on puddle clay apron. In case where the head of percolation is great, in order to reduce the length of aprons on the. This apron is. However this acts in considerably. Downstream aprons. Since the ground level is falling down to The aprons may be designed for a hydraulic gradient of 1 in 5 so that the residual gradient at the.
Maximum uplift pressure are experienced on the down stream aprons when the water level in the tank is upto Top of dam stone level i. However assume that the downstream water elevation is ta The upstream water has to percolate under the. The possible path of. Assuming the puddle apron formed on the upstream of the weir to be not impervoius , the water. From here, it will follow the least path D to E under the end cut-off and.
So the total length of percolation. This length must not be less than The total lengh to of solid apron from the body wall as provided in the drawing is 8 meters and. These can be reduced if the upstream side puddle clay apron is really. To ensure safety, the whole upstream side apron can be packed with stone and well. At the end of the second apron retaining wall of the downstream side apron , a nominal 3 to 5 meter length of talus with a thickness of 50cms.
May be provided as a safety device. Thickness of solid apron. The maximum uplift on the apron floor is felt immediately above point D in the sketch. Total creep length from point A on the upstream side upto the point above D under the solid apron is 1. Since the bottom of apron is above the assumed tail water elevation , the weight of concrete fully takes care of the uplift, as there is no loss of weight in concrete due to buoyancy.
Each meter depth of concrete can withstand a head of 2. Allowing an extra 20percent thickness to withstand any variations, the thickness of apron required.
So, provide the first solid apron as 80 cms thick. The second apron can be similarly checked and a thickness of 50cms. Learn more about Scribd Membership Home.
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Home Login Register Search. Report this link. Length of the surplus weir. Water is to be stored upto level of Size of dam stone 15cms x 15cms. However provide an overall length of And the projecting length above crest will be 75cms.