4 Embankment (Fill) Dams I.T.U., Department of Civil Eng.
5 Environmental Effects of Dams Social and economic effectsEcologic effectsRegional climate effectsVegetation effectsFisheryNavigation effectsUpstream and downstream navigation effectsTourism effects
6 3.1 Classification of Dams According to dams heightIf crest elevation and foundation level greater than 15 m Large DamIf dam height less than 15 m Small DamIf dam height greater than 50 m High DamMore specificallyThe height of the dam > 15 mThe crest width of the dam > 500 m “LARGE DAM”The storage volume of the dam > 106 m3
7 Classification of Dams According to construction purposeSingle purpose■ Storage Dams■ Diversion Dams■ Detention Dams■ Hydropower DamsMultiple purpose(Serves for all or most of the above purposes)
8 I.T.U., Department of Civil Eng. Drinking waterNavigationFlood controlRecreational purposesIrrigationEnergyI.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 DamsEarth-Fill DamsRock-Fill Dams■ Masonry and Rubble Dams■ Concrete Dams■ Steel and Timber Dams
11 Classification of Dams According to Structural DesignGravity DamsArch DamsButtress DamsEarth-FillRock-FillPre-stressed Concrete Dams
25 3.2 Parts of Dams Structural components: - Body - Spillway - Body- Spillway- Outlet Facilities(i.e., sluiceways & water intake tower)- Others (i.e., hydropower stations, roads, fish ladder, etc.)
26 3.3 Planning of Dams Three steps: - Reconnaissance surveys (Infeasible alternatives eliminated)- Feasibility study- Planning study
27 Planning of Dams 3.3.1 FEASIBILITY STUDY A) Determination of water demandB) Determination of water potentialC) Optimal plans◘ Check out the relation D (demand) versus S (supply).
28 Planning of Dams D) Determination of dam site FEASIBILITY STUDYD) Determination of dam site◘ Factors should be taken into consideration:TopographyGeology and dam foundationAvailable of construction materialsFlood hazardSeismic hazardSpillway location and possibilitiesConstruction timeClimateDiversion facilitiesSediment problemWater qualityTransportation facilitiesRight of way cost
29 Planning of Dams E) Determination of type of dam F) Project design ◘ Comparative characteristics of dams should be consideredF) 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.
30 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)
31 3.4 Construction of DamsFour 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:
32 Completed portion of dam Construction zone Flow through sluiceway Flow in stream bedConstruction zoneCofferdamDiversion tunnelFirst stageSecond stageUpstreamDownstreamCofferdamConstruction zoneDiversion tunnelDiversion by tunnel(a)(b)Completed portion of damConstruction zoneFlow through sluiceway(c)River Diversion facilities
33 3) Foundation Treatment ◘ Concrete & Rock-fill dams hard formationsEarth-fill dams most of soil conditions◘ Highly porous foundation excessive seepage, uplift, settlement“Grouting Operation” is applied to solidify the foundation& to reduce seepage
34 Formation of the Dam Body For Concrete Gravity dams:Low-heat cements to reduce shrinkage problemConcrete is placed in “blocks”“Keyways” are built between sections to make the dam act as a monolithUpstream faceUpstream faceKeywaysDownstream faceDownstream face
35 “Inspection galleries” permit access to the interior of concrete “Waterstops” are placed near upstream face to prevent leakageCopper stripWaterstops“Inspection galleries” permit access to the interior of concreteDams and are needed for seepage determination, grouting operations and etc.
36 For Earth-fill damsConstructed 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 stabilityProtect 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)
37 Cross section of typical earth dams SiltSilt clay1 on 2.51 on 2Sandygravel(a) Simple zoned embankmentClay coreSilt1 on 2.5Transition zonePervious strataPervious foundationRock-fill toe(b) Earth dam with core extending to impervious foundation
38 (c) Earth dam on pervious material Cross section of typical earth damsSiltSilt clay1 on 3.11 on 2Sandygravel1 on 3.8Clay blanketConcrete cutoff wallPervious material(c) Earth dam on pervious material
39 For Rock-fill dams:Core and filter zones are similarly constructed as the earth damDue to heavy rocks on the sides, these damshave steeper slopeshave less materialsare economicConstruction period is shorter and easy to increase the crest elevationWidth of dam crest: There are two traffic lanesElevation of dam crest: There is no overtopping during design floodFreeboard: See the table for recommendations
46 Concrete Gravity Dams Why & Where we prefered? Sağlam ve geçirimsizliği sağlanabilecek yeterli kalınlıkta kaya temellerin uygun bir derinlikte bulunduğu orta genişlikteki vadilerdeYeterli miktarda ve istenen özellikte agrega malzemesinin bulunduğu, çimento naklinin ekonomik olduğu yerlerdeBüyük taşkın debilerinin baraj gövdesi üzerinden mansaba aktarılması gereken durumlardaBaraj üzerinden bir ulaşım yolu geçirilmesi gereken durumlarda tercih edilirSavaş ve sabotaja karşı daha dayanıklı olması da ayrıca bir tercih nedeni olabilir.Recep YURTALÇ.Ü. İnş.Müöl.
47 Types: Straight Gravity Dams Arch Gravity Dams Concrete Gravity DamsTypes:Straight Gravity DamsArch Gravity DamsBaraj 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.Recep YURTALÇ.Ü. İnş.Müöl.
48 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.Recep YURTALÇ.Ü. İnş.Müöl.
50 Design Principles: Concrete Gravity Dams 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:bHRecep YURTALÇ.Ü. İnş.Müöl.
51 For the dam dimensions: Check out the safety for Concrete Gravity DamsFor the dam dimensions:Check out the safety forOverturningShear & slidingBearing capacity of foundationNo tensile stresses are allowed in the dam body
64 3.5.1 FORCES ON GRAVITY DAMSFree body diagram showing forces acting on a gravity dam
65 The following loads should be considered: A) WEIGHT (WC): Dead load and acts at the centroid of the sectionB) HYDROSTATIC FORCES:Water in the reservoir + tailwater causes Horizontal Hu Hd &Vertical Fh1v Fh2vC) UPLIFT FORCE (Fu): acts under the base as:
66 D) FORCE OF SEDIMENT ACCUMULATION (Fs): Determined by the lateral earth pressure expressionwhereFs : the lateral earth force per unit width,γs : the submerged specific weight of soil,hs : the depth of sediment accumulation relative to reservoir bottom elevation,θ : the angle of repose. This force acts at hs /3 above the reservoir bottom.
67 E) ICE LOADS (Fi): considered in cold climate Ice force per unit width of dam (kN/m) can be determinedfrom the following table:Thickness of ice sheet (cm)Change in temperature (oC/hr)2.557.52530609550589015075115160100140180
68 F) EARTHQUAKE FORCE (Fd): Acting horizontally and vertically at the center of gravityk (earthquake coefficient): Ratio of earthquake acceleration to gravitational acceleration.
69 G) DYNAMIC FORCE (Fw) :In the reservoir, induced by earthquake as below Acts at a distance h1 from the bottomFw : the force per unit width of damC : constant given byθ’ : angle of upstream face of the dam from vertical (oC)For vertical upstream face C = 0.7'
70 H) FORCES ON SPILLWAYS (∑F): Determined by using momentum equation btw two successive sections:ρ : the density of waterQ : the outflow rate over the spillway crestΔV: the change in velocity between sections 1 and 2 (v2-v1) Momentum correction coefficients can be assumed as unity.
71 Considered when a long fetch exists I) WAVE FORCES :Considered when a long fetch existsLOADING CONDITIONS:Usual loadingB &Temperature Stresses at normal conditions + C + A + E + DUnusual loadingB & Temperature Stresses at min. at full upstream level + C + A +DSevere loadingForces in usual loading + earthquake forces
72 Dam must be safe against 3.5.2 STABILITY CRITERIADam must be safe against(1) Overturning for all loading conditions resisting moments overturning momentsSafety factor:F.SO 2,0 (usual loading)F.SO 1,5 (unusual loading)
73 STABILITY CRITERIA(2) Sliding over any horizontal planef = friction coef. btw any two planesSafety factor:FSS 1,5 (usual loading )FSS 1,0 (unusual or severe loading)
74 (3) Shear and sliding together STABILITY CRITERIA(3) Shear and sliding togetherA : Area of shear plane (m²)τs : Allowable shear stress in concrete in contact with foundationSafety factor:FSss 5,0 (usual loading)FSss 3,0 (unusual or severe loading)
75 STABILITY CRITERIA(4) Between foundation and dam contact stresses (σ) > 0at all pointsThere are two cases for the base pressure:
76 Base Pressure Check CASE 1: e B/6 Ph s Pt ΣV B Ph DAM BASE e Pt sPh sRecep YURTALÇ.Ü. İnş.Müöl.
77 Base Pressure Check CASE 2: e > B/6 Pt Pt s ΣV B e DAM BASE Recep YURTALÇ.Ü. İnş.Müöl.