Construction of Dams.pptx

This is ppt file is a construction of dams and define parts of dams , types of dams and design of dams

1. Punjab Tianjin University Technology, Lahore Group Members Khawar Ijaz (20CT009) Arslan Ahmed (20CT010) M. Mudassar (20CT018) Talha Iqbal (20CT028) Naeem Akram (20CT040) Subject Name Construction & Hydraulic Machinery .LAB Topic Construction of Dams semester 5th Submitted to Sir Munawar Hussain .Sb

2. Dams : A dam may be defined as an obstruction or a barrier built across a stream or a river. The pool of water is formed at upstream and which is used to turn the blades of a turbine to generate electrical power. 1

3. Purpose of dams : Generation of hydropower electricity For agricultural and irrigation purposes For fishery To prevent the flooding during high water flows at high PMP To diverse the water maintaining required heights. 2

4. Various Types o f Dams: Earth Dams Rock-fill Dams Solid Masonry Gravity Dams Hollow Masonry Gravity Dams Timber Dams Steel Dams Arch Dams 3

5. Structure of Dam: He el Gallery T o e Spillway (inside dam) C re st N WL Normal water level MWL Max. level Free board Sluice way Upstream Down stream 4

6. Heel : contact with the ground on the upstream side Toe : contact on the downstream side Abutment : Sides of the valley on which the structure of the dam rest • Galleries : small rooms like structure left within the dam for checking operations. Diversion tunnel : Tunnels are constructed for diverting water before the construction of dam. This helps in keeping the river bed dry. Spillways : It is the arrangement near the top to release the excess water of the reservoir to downstream side Sluice way : An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side. 5

7. Crest : The top of the Dam. These may in some cases be used for providing a roadway or walkway over the dam. Pa r apet w all s : Lo w P r ot e c ti v e w a lls on e ither s ide o f the roa d w ay or walkway on the crest. Free board : The space between the highest level of water in the reservoir and the top of the dam. Dead Storage level : Level of permanent storage below which the water will not be withdrawn. Diversion Tunnel : Tunnel constructed to divert or change the direction of water to bypass the dam construction site. The dam is built while the river flows through the diversion tunnel. 6

8. Dams Chosen In Project To Build : Construction of concrete gravity dams : Concrete gravity dam is such a dam that is designed in such a way that its own weight resists the external forces. 7

9. Factors In Site Selection: Topography : A narrow site will minimize the amount of material in the dam thus reducing its cost, but such a site may be adaptable. Geology : The foundation of the dam should be relatively free of major faults and shears. If these are present, they may require expensive foundation treatment. Appurtenant : While the cost of these Structures is usually less than the cost of the dam, economy in design may be obtained by considering their effect at the time of site selection. Local condition : Site of availability of water supply, sewage disposal, electric power for construction purposes, telephone service should be chosen. Access : Accessibility of the site has a very definite effect on the total cost. Easy excess is required for the contractor’s plant and equipment near the site. 8

10. General Design Consideration: Local condition Availability of public facilities or utilities such as water supply, sewage disposal, electric power for construction purposes, telephone service, construction camp; and need for permanent buildings for operating personnel should be well available. Maps and photographs Map should show existing towns, highways, roads, railroads, and shipping points Ground & aerial photographs and general area map should be obtained locating the general area within the State, together with county and township lines. 9

11. Hydrological data Stream-flow records, Stream-flow and reservoir yield, Flood studies, Sedimentation and water quality studies ,ground-water conditions are to be collected. Reservoir capacity A topographic map of the reservoir site is to be collected, annual periodic fluctuations of reservoir levels , Area-capacity curves for storage of the spillway design flood are to be calculated. Climatic effects Weather Service records of mean monthly air temperatures, river watertemperatures at various times, Wind velocities and prevailing direction, Amount and annual variance in rainfall are to be collected. 10

12. Construction materials Concrete aggregates and properties Availability of suitable aggregates usually processed from natural deposits of sand, gravel, and cobbles in sufficient quantity to construct the dam and its appurtenant structures. Concrete mix having high cement content and admixtures like pozzolans, fly ash etc. are prepared from hydraulic laboratory model studies & environmental studies. Water for construction purposes An adequate supply of water for construction purposes such as washing aggregates and cooling and batching concrete should be assured. The water used in the concrete mix should be reasonably free of silt, organic matter, alkali, salts, and other impurities and objectionable amounts of chlorides or sulphates. 11

13. Procedure To Build A Dam: Step I : Dewatering the part of river valley at selected site of dam which is achieved by diverting the river through a tunnel . Provision of diversion tunnel is made. Construction of dams in two stages. Construction of galleries in gravity dams 12

14. Step II: Work is started at river during summer i.e. when river flow is low. Earth-moving equipments is used to build small dam(cofferdam) on upstream of main construction area. Pumping is regularly done to remove water that may seeps through the cofferdams. Diversion tunnels are not required in case of concrete gravity dams and only if water is channeled through a water pipe is satisfactorily. 13

15. Step III : Removal of loose rock and rubble from the valley walls and river bed. Concrete-faced rock-fill dams require a footing to be constructed around their upstream edge. The plinth is made from concrete and serves as a foundation or connection between the dams and valley walls & floor. The area under plinth is waterproofed by drilling holes and pumping cement grout into cracks in the rock. 14

16. Step IV : During dam construction, the associated power station and intake works are also being built if hydropower generation is to be generated. Once, dams is completed, diversion tunnel is closed and lake begins to fill. 15

17. F o u n d a t i o n I n v e s t i g a t i o n s Field investigations Appraisal investigations It includes a preliminary selection of the site and type of dam using geologic and topographic maps, photographs of the site area, and data from field examinations of natural outcrops, road cuts, and other surface conditions. Feasibility investigations The location of the dam is usually finalized. The geologic mapping and sections are reviewed and supplemented by additional data such as new surveys and additional drill holes. 16

18. c) Final design data A detailed foundation investigation is conducted to obtain the final design data. This investigation involves as many drill holes as are necessary to accurately define : Strike , dip, thickness, continuity, and composition of all faults and shears in the foundation . Depth of overburden. Depth of weathering throughout the foundation. Joint orientation and continuity. Lithologic variability. Physical properties of the foundation rock, including material in the faults and shears 17

19. Foundation treatment : Excavation: Adequate attention is to be paid during blasting operation to assure unnecessary shattering of rocks, loosening of bed of foundation. Foundations such as shales, chalk, mudstones require protection against air and water slaking. a) Shaping of canyon profile: If canyon profile for a dam is relatively narrow with steep sloping walls, dam section will be deflected by reservoir load and result torsional effect. To counteract this, uniformly varying profile is to be shaped. b) Dental treatment: The procedure of reinforcing and stabilizing weak zones during driling action and final excavation is called “dental treatment .” c) Proper Protection against piping should be made for dam stability. 18

20. Grouting: Holes are drilled at shallow as well as deep and cement grouting is filled to establish an effective barrier to seepage under the dam and to consolidate the foundation. Consolidation grouting Low-pressure grouting to fill voids, fracture zones, and cracks at and below the surface of the excavated foundation is accomplished by drilling and grouting relatively shallow holes. Curtain grouting Construction of a deep grout curtain near the heel of the dam to control seepage is accomplished by drilling deep holes and grouting them using higher pressure. 19

21. T o Decide Whether Dam is L o w or High : The height of gravity dam, H < f /[Yw(Sc+1)] Where, f = permissible compressive stress of the dam material and Sc= Sp. Gravity of the dam material Then, dam will be a low gravity dam. otherwise, high gravity dam. 20

22. Design o f L o w Concrete Gravity Dams: 21

23. Design o f High Concrete Gravity Dams : 22

24. Force acting on Gravity Dams: Water pressure Uplift pressure Pressure due to earthquake forces Silt pressure Wave pressure Ice pressure Stabilizing force i.e. weight of dam itself 23

25. Modes o f Failure a nd Criteria f or Structural Stability o f Gravity Dams: By overturning( or rotation) about the toe By crushing By development of tension, causing ultimate failure by crushing By shear failure called sliding 24

26. M a j o r I s s u e s T e m p e r a t u r e C o n t r o l O f C o n c r e t e 26 Methods of temperature control a) Pre-cooling Restricting concrete placement during the hotter part of the day or the hotter months of the year, to a full treatment of refrigerating the various parts of the concrete mix to obtain a predetermined, maximum concrete placing temperature. one method is to chill the aggregate in large tanks of refrigerated water for a given period of time.

27. b) Post-cooling Artificially cooling mass concrete by circulating cold water through embedded cooling coils on the top of each construction lift will materially reduce the peak temperature of the concrete Low heat producing cement and modified cement as per site requirements should be used . Use of pozzolans 27

28. Design considerations for temperature treatment : a)Shallow construction lifts b)Retarding agents Surface cooling It can be accomplished by circulating water in closed spaced embedded cooling-pipe coils placed adjacent to and parallel with the exposed surfaces, by use of cold water sprays Size of construction blocks Concrete cooling systems Lift thickness Delays between placements 28

29. Problems in Construction of Dams : Fish problem Cracking of concrete in concrete gravity dams Submergence problem Pressure problem in hydroelectric power 29