Force acting on gravity dam
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1. Dams are constructed across rivers to store flowing water for uses like hydropower, irrigation, water supply, flood control, and navigation. 2. The key forces acting on a gravity dam include its self-weight, which provides stability, and water pressure from the reservoir, which acts to overturn the dam. Uplift, earthquake loads, silt pressure, and ice pressure are other important forces that must be estimated based on assumptions and available data. 3. The weight of the dam per unit length is calculated based on the cross-sectional area and unit weight of the concrete or masonry used. The total weight acts at the centroid of the cross-section and is the main stabil
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Force acting on gravity dam
- 1. FORCE ACTING ON GRAVITY DAM DIVYA VISHNOI ASSISTANT PROFESSOR
- 2. Dams • Dam is a solid barrier constructed at a suitable location across a river valley to store flowing water. Storage of water is utilized for following objectives: • Hydropower • Irrigation • Water for domestic consumption • Drought and flood control • For navigational facilities • Other additional utilization is to develop fisheries
- 4. Structure of Dam Heel Gallery Toe Spillway (inside dam) Crest NWL Normal water level MWL Max. level Free board Sluice way Upstream Down stream
- 6. Basic definition 1. Axis of the dam: is the line of the upstream edge of the top (or crown) of the dam. The axis of the dam in plan is also called the base line of the dam. The axis of the dam in plan is usually straight. 2. Length of the dam: is the distance from one abutment to the other, measured along the axis of the dam at the level of the top of the dam. 3. Structural height of the dam: is the difference in elevations of the top of the dam and the lowest point in the excavated foundation. It, however, does not include the depth of special geological features of foundations such as narrow fault zones below the foundation. In general, the height of the dam means its structural height. 4.Maximum base width of the dam: is the maximum horizontal distance between the heel and the toe of the maximum section of the dam in the middle of the valley. 5. Hydraulic height of the dam: is equal to the difference in elevations of the highest controlled water surface on the upstream of the dam (i. e. FRL) and the lowest point in the river bed.
- 7. Basic definition 6. Heel: contact with the ground on the upstream side 7. Toe: contact on the downstream side 8. Abutment: Sides of the valley on which the structure of the dam rest 9. Galleries: small rooms like structure left within the dam for checking operations. 10.Diversion tunnel: Tunnels are constructed for diverting water before the construction of dam. This helps in keeping the river bed dry. 11.Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side 12.Sluice way: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side.
- 9. Forces Acting on a Gravity Dam • These forces fall into two categories as: a) Forces, such as weight of the dam and water pressure, which are directly calculable from the unit weights of the materials and properties of fluid pressures; and b) Forces, such as uplift, earthquake loads, silt pressure and ice pressure, which can only be assumed on the basis of assumption of varying degree of reliability.
- 10. Forces Acting on a Gravity Dam • It is in the estimating of the second category of the forces that special care has to be taken and reliance placed on available data, experience, and judgment. • It is convenient to compute all the forces per unit length of the dam.
- 11. Weight of Dam • Main stabilizing force in a gravity dam Dead load = weight of concrete or masonry or both + weight of such appurtenances as piers, gates and bridges. • Weight of the dam per unit length is equal to the product of the area of cross-section of the dam and the specific weight (or unit weight) of the material. • Unit weight of concrete (24 kN/m3) and masonry (23 KN/m3) varies considerably depending upon the various materials that go to make them. • For convenience, the cross-section of the dam is divided into simple geometrical shapes, such as rectangles and triangles, for the computation of weights. The areas and centroids of these shapes can be easily determined. Thus the weight components • W1, W2, W3 etc. can be found along with their lines of action. • The total weight W of the dam acts at the C.G. of its section.
- 12. Self weight of Dam
- 47. RTU QUESTIONS • Describe the various forces acting on gravity dam with suitable sketch. • What are the modes of failure of gravity dam? Explain.
- 48. References • Irrigation Engineering & Water Power Engineering – By Prof B.C.PUNMIA – Laxmi Publication • Irrigation Engineering & Hydraulic Structures – By Prof. Santosh Kumar Garg – Khanna Publishers • Irrigation, Water Power Engineering & Hydraulic Structures – By Prof K.R. Arora – Standard Publishers Distributions • Internet Websites • http://www.aboutcivil.org/ • http://nptel.ac.in/courses/105105110/
- 49. Thanks