UNIT-II-Gravity DAM.pdf

College of Science and Technology CST Royal University of Bhutan UNIT-II: Gravity Dam Leki Dorji A centre of excellence in science and technology enr...

College of Science and Technology CST Royal University of Bhutan UNIT-II: Gravity Dam Leki Dorji A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Classification of Dams A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Classification of Dams A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Classification of Dams Rockfill Dam Earthen embankment Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Advantages & Disadvantages of gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Components of a Dam What is a Dam? ✓ A dam is a structure built across a stream, river or estuary to retain water. ✓ Dams are made from a variety of materials such as rock, steel, concrete, earth and wood. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Components of Dam o Abutment: Sides of the valley on which the structure of the dam rest o Galleries: small rooms like structure left within the dam for checking operations. o Dam constructed to divert the water in Diversion Tunnel is called …... ….Coffer Dam o Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side o Sluice way: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side. o Heel of dam: The junction of the upstream face of a gravity or arch dam with the foundation surface o Toe of Dam (Toe of Embankment) – The junction of the downstream face of a dam with the ground surface, also referred to as the downstream toe. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan o A diversion tunnel is either a permanent or temporary tunnel built essentially for the purpose of diverting something away from something PHP-I A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Six important Components A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Components of a Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan 7 Factors governing selection of types of dam Topography-Valley Shape A Narrow V-Shaped Valley : Arch Dam A Narrow or Moderately with U-Shaped Valley : Gravity/Buttress Dam A Wide Valley : Embankment Dam Geology and Foundation Condition Solid Rock Foundation : All types Gravel and Coarse Sand Foundation : Embankment/Concrete Gravity Dam (H≤15 m) Silt and Fine Sand Foundation : Embankment/Gravity Dam (H≤8 m) Clay Foundation : Embankment /Earthen Dam after special Treatment A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan 7 Factors governing selection of types of dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan 7 Factors governing selection of types of dam Other Consideration Other factors such as life a dam, width of the road way to be provided over the dam top, Problems of skilled labours Legal and aesthetic point must be considered Over all cost and maintenance and the funds available will finally decide the choice of a particular dam at a particular palce A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Forces Acting on Dams To design a dam, various forces must be considered to insure the safety of the dam. The most important forces are: 1. Stabilizing forces is the Weight of dam itself 2. Water Pressure 3. Uplift 4. Wave pressure 5. Earthquake forces 6. Ice Pressure 7. Silt Pressure A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Weight of Dam The weight of the dam is calculated as follows: W =  m xVolume Where γm is the specific weight of the dam’s material. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Water Pressure Water pressure acts perpendicular to the surface of the dam and is calculated per unit width as follows: Where γw is the specific weight of water and h is the height of water. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Water Pressure When u/s face is partly vertical and partly inclined, the resulting forces can be resolved into Horizontal and Vertical Forces. (Ph and Pv) Similarly, if there is a tail water in d/s side, it will have horizontal and vertical components A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Uplift Dams are subjected to uplift force under its base. Uplift acts upward. 1 U =  w hB 2 Where, B is the width of the base of the dam. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Wave Pressure The upper part of the dam (above the water level) is subjected to the impact of waves. The maximum wave pressure per unit width is: Pv = 2.4 w hv The total wave force Pw, (in kN) hw = 0.032√VF + 0.763 + 0.271(F)3/4 for F < 32 km Where hw is the wave height. V – wind velocity in km/h, F – straight length wave expands in km A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Forces Acting on Dams Earthquake Forces ✓ Dams are subjected to vibration during earthquakes. ✓ Vibration affects both the body of the dam and the water in the reservoir behind the dam. ✓ Vibration forces are function of both the intensity (Rechter Scale) and its duration. Acceleration can be solved in two components into vertical and hozontal. ✓ The most danger effect occurs when the vibration is perpendicular to the face of the dam. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Earthquake Forces Earthquake Forces Body Forces: Water Force: Body force acts horizontally at the center of gravity and is calculated as Water vibration produces a force on the dam acting horizontally; Pem = W Where α is the earthquake coefficient and W is the weight of the dam. α is taken 0.2 for practical Where Ce is another coefficient (0.82) and reasons. h is the height of the water A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Kh=Hydrodynamic Coefficient A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Ice pressure The ice which may be formed on the water surface of the reservoir in the cold countries, may sometimes melt and expand: This force may act linearly along the length of the dam and at the reservoir level. The magnitude of this forces varies from 250 to 1500kN/m2. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Silt pressure ✓ Silt gets deposited against the upstream face of the dam. If h is the height of silt deposited, then the force exerted by this silt in additional to external water pressure. It can be represented by Rankine’s formula. A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Calculate the forces on given dam if; γm = 2.5 t/m3, γw =1 t/m3, hw = 1.5 m A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Design of Hydraulic Structures 1. Load Combinations 2. Stability requirement Modes of failure of a gravity dam Overturning Sliding Crushing Tension Elementary and Practical Profile A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Load Combinations Gravity dam design should be based on the most adverse load combination A, B, C, D, E, F or G given below using the safety factors prescribed ✓Load Combination A (Construction Condition) -Dam completed but no water in reservoir and no tailwater. ✓Load Combination B (Normal Operating Condition) - Full reservoir elevation, normal dry weather tailwater, normal uplift; ice and silt (if applicable). ✓Load Combination C (Flood Discharge Condition) - Reservoir at maximum flood pool elevation, all gates open, tailwater at flood elevation, normal uplift, and silt (if applicable ) A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Load Combinations Gravity dam design should be based on the most adverse load combination A, B, C, D, E, F or G given below using the safety factors prescribed ✓Load Combination D -Combination A, with earthquake. ✓Load Combination E -Combination B, with earthquake but no ice. ✓Load Combination F -Combination C, but with extreme uplift (drains inoperative). ✓Load Combination G -Combination E, but with extreme uplift (drains inoperative). A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Requirements for Stability Modes of failure of a gravity dam: Overturning Sliding Compression or Crushing Tension. The design shall satisfy the following requirements of stability: The dam shall be safe against sliding on any plane or combination of planes within the dam, at the foundation or within the foundation; The dam shall be safe against overturning at any plane within the dam, at the base, or at any plane below the base; and The safe unit stresses in the concrete or masonry of the dam or in the foundation material shall not be exceeded A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Overturning A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Sliding Resistance A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Sliding Resistance A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Compression or Crushing A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Compression or Crushing A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Compression or Crushing A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Compression or Crushing A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Compression or Crushing A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Tension A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam Effect of Freeboard 1. Freeboard is the margin provided between the top of dam and H.F.L in the reservoir to prevent splashing of the waves over the Non-flow sections a) IT takes A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan Elementary Profile of a Gravity Dam A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan PROVISION OF Diverting the Water A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan PROVISION OF Diverting the Water A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan QUESTIONS A centre of excellence in science and technology enriched with GNH values  College of Science and Technology CST Royal University of Bhutan THANK YOU Any Questions? 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