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CHAPTER 3 Dams and Spillways

CHAPTER 3 Dams and Spillways. Ercan Kahya. Department of Civil Engineering, I.T.U. Figure uses by courtesy of Prof. Recep YURTAL. Embankment (Fill) Dams. Environmental Effects of Dams. Social and economic effects E cologic effects Regional climate effects Vegetation effects

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CHAPTER 3 Dams and Spillways

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  1. CHAPTER 3Damsand Spillways Ercan Kahya Department of Civil Engineering, I.T.U. Figure uses by courtesy of Prof. Recep YURTAL

  2. I.T.U., Department of Civil Eng.

  3. I.T.U., Department of Civil Eng.

  4. Embankment (Fill) Dams I.T.U., Department of Civil Eng.

  5. Environmental Effects of Dams • Social and economic effects • Ecologiceffects • Regional climate effects • Vegetation effects • Fishery • Navigation effects • Upstream and downstream navigation effects • Tourism effects

  6. 3.1 Classification of Dams • According to dams height • If crest elevation and foundation level greater than 15 m Large Dam • If dam height less than 15 m Small Dam • If dam height greater than 50 m High Dam • More specifically • The height of the dam > 15 m • The crest width of the dam > 500 m “LARGE DAM” • The storage volume of the dam > 106 m3

  7. Classification of Dams • According to construction purpose • Single purpose ■ Storage Dams ■ Diversion Dams ■ Detention Dams ■ Hydropower Dams • Multiple purpose • (Serves for all or most of the above purposes)

  8. Drinking water Irrigation Flood control Energy Navigation Recreational purposes I.T.U., Department of Civil Eng.

  9. Classification of Dams • According to Hydraulic Design ■ Overflow Dams (i.e., diversion dams) ■ Non-overflow Dams (i.e., earth fill & rock fill dams)

  10. Classification of Dams • According to Materials of Construction ■ Embankment Dams • Earth-Fill Dams • Rock-Fill Dams ■ Masonry and Rubble Dams ■ Concrete Dams ■ Steel and Timber Dams

  11. Classification of Dams • According to Structural Design • Gravity Dams • Arch Dams • Buttress Dams • Earth-Fill • Rock-Fill • Pre-stressed Concrete Dams

  12. According to Structural Design

  13. Ç.Ü., İnş.Müh.Böl.

  14. Ç.Ü., İnş.Müh.Böl.

  15. www.altunkaynak.net Ç.Ü., İnş.Müh.Böl.

  16. Embankment (Fill) Dams

  17. 3.2 Parts of Dams Structural components: - Body - Spillway - Outlet Facilities (i.e., sluiceways & water intake tower) - Others (i.e., hydropower stations, roads, fish ladder, etc.)

  18. 3.3 Planning of Dams • Three steps: • - Reconnaissance surveys • (Infeasible alternatives eliminated) • - Feasibility study • - Planning study

  19. Planning of Dams  3.3.1 FEASIBILITY STUDY A) Determination of water demand B) Determination of water potential C) Optimal plans ◘ Check out the relation D (demand) versus S (supply).

  20. Planning of Dams FEASIBILITY STUDY • D)Determination of dam site • ◘ Factors should be taken into consideration: • Topography • Geology and dam foundation • Available of construction materials • Flood hazard • Seismic hazard • Spillway location and possibilities • Construction time • Climate • Diversion facilities • Sediment problem • Water quality • Transportation facilities • Right of way cost

  21. Planning of Dams • E) Determination of type of dam • ◘ Comparative characteristics of dams should be considered • F) Project design • ◘ involves the computation of dimensions of the dam. • - Hydrologic design (max. lake elevation + spillway cap. + crest elevation) • - Hydraulic design (static & dynamic loads + spillway profile + outlet dimensions) • - Structural design (stress distribution + required reinforcement) ◘ Failure of the dam  “Dam Break” It is rapid for a concrete dam. See the textbook for the examples.

  22. Planning of Dams • 3.3.2 PLANNING STUDY • ◘ Followings need to be done in planning certain type of dam, since dimensions are already determined: • Topographic surveys (1:5000 scaled map) • Foundation study (seepage permeability etc. tests) • Materials study (quantity of materials) • Hydrologic study (measurements of hydrologic parameters) • Reservoir operation study (is to be performed periodically)

  23. 3.4 Construction of Dams Four principal steps are followed during the construction: 1) Evaluation of Time Schedule and Equipment ◘ a work schedule is prepared using CPM. (characteristics of dam site; approx. quantities of works; diversion facilities; urgency of work) 2) Diversion ◘ before the construction, river flow must be diverted from the site ◘ see the below figure for two possible ways to divert water:

  24. (b) Cofferdam Upstream (a) Diversion tunnel Construction zone Cofferdam Flow in stream bed Construction zone First stage Cofferdam Flow through sluiceway Downstream Diversion tunnel Construction zone Diversion by tunnel (c) Completed portion of dam Second stage River Diversion facilities

  25. 3) Foundation Treatment ◘ Concrete & Rock-fill dams  hard formations Earth-fill dams  most of soil conditions ◘ Highly porous foundation  excessive seepage, uplift, settlement “Grouting Operation” is applied to solidify the foundation & to reduce seepage

  26. Formation of the Dam Body For Concrete Gravity dams: • Low-heat cements  to reduce shrinkage problem • Concrete is placed in “blocks” • “Keyways”are built between sections to make the dam act as a monolith Upstream face Upstream face Keyways Downstream face Downstream face

  27. “Waterstops”are placed near upstream face to prevent leakage Copper strip Copper strip Waterstops “Inspection galleries” permit access to the interior of concrete Dams and are needed for seepage determination, grouting operations and etc.

  28. For Earth-fill dams • Constructed in multi-layer formation • (Layers: impervious, filter and outer) • First place the materials in layers of 50 cm and then compact these materials. • For high dams, horizontal berms are constructed to enhance slope stability • Protect the upstream face of dam against wave action • (i.e., concrete or riprap) • Protect the downstream face against rainfall erosion • (i.e., planting grass or riprap)

  29. Cross section of typical earth dams 1 on 2.5 1 on 2 Silt Sandy gravel Silt clay (a) Simple zoned embankment 1 on 2.5 1 on 2.5 Clay core Silt Rock-fill toe Silt Pervious strata Transition zone Pervious foundation (b) Earth dam with core extending to impervious foundation

  30. Cross section of typical earth dams 1 on 2 1 on 3.1 1 on 3.8 Clay blanket Sandy gravel Silt Silt clay Pervious material Concrete cutoff wall (c) Earth dam on pervious material

  31. For Rock-fill dams: • Core and filter zones are similarly constructed as the earth dam • Due to heavy rocks on the sides, these dams • have steeper slopes • have less materials • are economic • Construction period is shorter and easy to increase the crest elevation • Width of dam crest: There are two traffic lanes • Elevation of dam crest: There is no overtopping during design flood • Freeboard: See the table for recommendations

  32. Select Compacted Rock Rolled Medium Size Rock 1.3 1.3 1 1 Coarse Dumped Rock Reinforced Concrete Membrane Cutoff wall (a) Impermeable face Cross-section of typical Rock-fill dams Graded transition sections 1.4 1.4 1 1 Clay core Dumped or Rolled rock Dumped Rock Rolled rock (0.2m) (1.5m) Grout curtain (b) Impermeable earth-core

  33. GRAVITY DAMS Recep YURTAL Ç.Ü. İnş.Müöl.

  34. Concrete Gravity Dams Resist the forces by their own weight Ç.Ü. İnş.Müöl.

  35. Concrete Gravity Dams Ç.Ü. İnş.Müöl.

  36. Concrete Gravity Dams Ç.Ü. İnş.Müöl.

  37. Concrete Gravity Dams Ç.Ü. İnş.Müöl.

  38. Concrete Gravity Dams • Why & Where we prefered? • Sağlam ve geçirimsizliği sağlanabilecek yeterli kalınlıkta kaya temellerin uygun bir derinlikte bulunduğu orta genişlikteki vadilerde • Yeterli miktarda ve istenen özellikte agrega malzemesinin bulunduğu, çimento naklinin ekonomik olduğu yerlerde • Büyük taşkın debilerinin baraj gövdesi üzerinden mansaba aktarılması gereken durumlarda • Baraj üzerinden bir ulaşım yolu geçirilmesi gereken durumlarda tercih edilir • Savaş ve sabotaja karşı daha dayanıklı olması da ayrıca bir tercih nedeni olabilir. Ç.Ü. İnş.Müöl.

  39. Concrete Gravity Dams • Types: • Straight Gravity Dams • Arch Gravity Dams • Baraj ekseni, iki yamaç arasındaki en kısa bağlantıyı sağlayacak şekilde bir doğru ile birleştirilir. • Temel kayasının yapısına, derzlere veya emniyet ihtiyacına bağlı olarak kavisli de yapılabilir. Ç.Ü. İnş.Müöl.

  40. Concrete Gravity Dams • Design Criteria: • En uygun kesit, etki eden en önemli dış kuvvet olan haznedeki hidrostatik su basıncı dağılımına uyum sağlayan, tabana doğru genişleyen üçgen kesit seçilir. Üçgenin tepesi genellikle haznedeki en yüksek su seviyesidir. • Memba yüzeyi düşey veya %10 ‘u geçmeyecek şekilde eğimli yapılır. • Baraj boş haldeyken çekme gerilmelerini önlemek, dolu haldeyken kayma ve devrilme emniyetini artırmak için yüksek barajlarda memba yüzeyi genellikle eğimli planlanır. • Üçgenin tepe kısmında, duvar kalınlığını artırmak, yamaçlar arası ulaşımı sağlamak gibi nedenlerle dikdörtgen kesitli bir başlık bulunur. Ç.Ü. İnş.Müöl.

  41. Concrete Gravity Dams Design Criteria: Ç.Ü. İnş.Müöl.

  42. H b Concrete Gravity Dams Design Principles: • Ağırlık barajı hesaplarında üçgen profil gözönüne alınır. • Üçgen kesitin minimum boyutları, barajın kendi ağırlığı, hidrostatik su basıncı ve taban su basıncının etki ettiği normal yükleme durumunda çekme gerilmeleri meydana gelmeyecek şekilde belirlenir. • Bunun için: Ç.Ü. İnş.Müöl.

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