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Important Details of a Buttress Dam.
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Introduction• Roman engineers, often erroneously,
judged the stability of a dam wall to be inefficient, they backed it up by irregularly spaced buttresses.
• A third of the Roman dams in the Iberian peninsula were buttress dams.
• The most remarkable of the Roman buttress dams is the one near the village of Esparragalejo. This is the first multiple arch dam
Evolution of the Modern Buttress Dam
Today buttress dams as derivations from the massive gravity type with the introduction of intermediate spaces.
These spaces allows the discharge of water seeping through the dam and its foundation, thus greatly reducing uplift pressures.
Given the absence of uplift, more substantial savings were possible by inclining the
upstream face, thereby mobilizing the vertical water load on the upstream face for sliding stability.
Classifications OF BUTTRESS DAMS
Massive head buttress dams Deck slab buttress dam Multiple arch buttress dam
• Massive round head
• Massive flat head
Massive head buttress damsMassive head buttress dams
Deck slab buttress dam1. Simple slab deck
2. Continuous slab deck
Multiple arch buttress damThe first multiple arch dam of reinforced concrete had been completed in 1908. It impounded the Hume Lake fluming reservoir on the Ten Mile creek in the California Sierra Nevada Mountains. The dam was designed and supervised during constuction by John S. Eastwood (1857-1924).
DESIGN CONSIDERATION1. Geologic investigation for the foundation
2. Assessment of the area to be inundated by the upstream lake (also called a reservoir) and its associated environmental and ecological impacts
3. Selection of materials and construction techniques
4. Designation of methods for diverting stream flow during construction of the dam
5. Evaluation of the potential for sediments to accumulate on the reservoir bottom and subsequently reduce storage capacity
6. Analysis of dam safety and failure concerns.
Forces on the buttress dams
WATER
F1
R1R2P
F2
R0 R1
w
Prestessing is used to minimize the quantity of concrete and counteract tensions.
Prestressing can be applied in at least three manners to a buttress dam.
» To 'pull down' the upstream face » To 'jack up' the downstream face » To compact the buttress on to the foundation
CONSTRUCTION PROCESSStream must be diverted or blocked from
flowing through the site.
CONSTRUCTION PROCESSCONSTRUCTION PROCESS
• A coffer-dam (a temporary structure to
impound the water) must be built.• Another small coffer dam is built to block
the leakages.
CONSTRUCTION PROCESS Contd…CONSTRUCTION PROCESS Contd…
• Pumps are used to remove the water from
site.• Compact the site.
CONSTRUCTION PROCESS Contd…CONSTRUCTION PROCESS Contd…
• Foundation area - must be cleaned before the first concrete is placed.
• Form work-Modern steel formwork is of cantilever design.
• Forms made of wood or steel are constructed.
CONSTRUCTION PROCESS Contd…CONSTRUCTION PROCESS Contd…
• May be necessary to install extensive systems of rock bolts or anchor bolts.
• Instruments has to be installed:
» monitor groundwater levels» joint movement» potential seepage» slope movements» seismic activity
FOUNDATIONFOUNDATION PREPERATIONPREPERATION
Excavation in bedrock. Construction on un consolidated deposits. Grouting. Pour the concrete.
CONCRETE HANDLINGCONCRETE HANDLING Pre-cast reinforced concrete planks &
reinforced concrete piles are used.
CONCRETE HANDLING Contd…CONCRETE HANDLING Contd…
Steel reinforcing rods are cast into the body.
Buttresses also poured with reinforcing rods.
Functional Importance of Functional Importance of Elements of the Buttress DamElements of the Buttress Dam
Structure of a Buttress DamStructure of a Buttress Dam
Crest
Heel
Gallery
Toe
Spillway(inside dam)
NWLNormalwater level
MWLMax. level
Free boardSluice way
Upstream Down stream
Buttress
ButtressButtress
NWLNormalwater level
MWLMax. level
Upstream Down stream
Buttress
ButtressButtress
A thin, erect, tabular concrete supporting member used in construction of slab and buttress dams. Also a projecting structure providing lateral support to a rock face or a portion of a dam.
HeelHeel
NWLNormalwater level
MWLMax. level
Upstream Down stream
Heel
HeelHeel
The upstream contact of a dam with its foundation.
ToeToe
NWLNormalwater level
MWLMax. level
Upstream Down stream
Toe
ToeToeThe downstream contact of a dam with its foundation.
CrestCrest
NWLNormalwater level
MWLMax. level
Upstream Down streamCrest
CrestCrest
The top of a dam.
Dam PavementsDam Pavements
The top part of the dam can be designed as a road.
Same time it can act as a bridge.
SpillwaySpillway
NWLNormalwater level
MWLMax. level
Upstream Down stream
Spillway(inside dam)
SpillwaySpillwayThe structure on or at the side of a dam that contains and guides the flow of the excess water supplied to a reservoir. Spillways inside the reservoir are called glory holes and consist of a vertical shaft a tunnel which exits below the dam.
SpillwaySpillwaySpillwaySpillway
Controlled SpillwayControlled Spillway
Water flow control by using gates
Uncontrolled SpillwayUncontrolled Spillway
The elevation of spillway crest use to control the water flow.
Spillway TypesSpillway Types
Auxiliary Spillways/Emergency Spillways
Primary Spillways
Side Channel Spillways
Siphon Spillways
Shaft Spillways/Morning Glory Spillways
SluicewaySluiceway
NWLNormalwater level
MWLMax. level
Upstream Down stream
Sluice way
Sluice waySluice wayAn opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side.
GalleryGallery
NWLNormalwater level
MWLMax. level
Upstream Down stream
Gallery
GalleryGallery
A long, narrow passage inside of a dam used for inspection, grouting, or spillway.
Free boardFree board
NWLNormalwater level
MWLMax. level
Upstream Down stream
Free board
FreeboardFreeboardThat portion of a dam maximum water level in a reservoir.
PenstockPenstockA conduit, commonly steel pipe, leading from the reservoir to a power generating plant downstream from the reservoir.
Usage of PenstockUsage of Penstock
Turbine
FishFish LaddersLaddersA structure built at the side or up the face of a dam to enable migration of fish upstream and downstream.
MaterialsMaterials Depend OnDepend On
Construction Method
Size of Construction
Type of Project
Soil Condition
Nature
Durability
TypesTypes of Materialsof Materials
Reinforcement AggregateAdmixturesWater proofingPozzolanCement
CementCementCementCement
For massive hydraulic structures, Ordinary Portland cement has been used
Proper chemical composition of cement is
important
PozzolanPozzolanPozzolanPozzolan This is a type of a cement replacement
The heat producing and cost of cement is lead to use pozzolan to reduce the cement content of mass concrete structures.
Natural pozzolan materials- Clays
May be used to improve the workability & quality of concrete
AggregatesAggregatesAggregatesAggregates
Coarse AggregateCoarse Aggregate Materials within the range of 5 to 150mm in
size for hydraulic Should be made of clean, hard, durable,
uncoated rock fragments
Fine AggregateFine Aggregate Can be natural or crushed Grading of fine aggregate has much greater
effect on workability Sea sand, suitably graded may be used
ReinforcementReinforcementReinforcementReinforcement
Used according to the structural requirements
Different diameter of tor steel and mild steel bars used
WaterWaterWaterWater
Should be free from materials that affect the hydration of Portland cement
Where choice is available, the cleanest and the purest source of water has to be selected
AdmixturesAdmixturesAdmixturesAdmixtures Accelerators Accelerators CaCl2 (2% by weight of cement) for cold
weather
Air entraining agents Air entraining agents Improve workability
Water reducing and set controlling agentsWater reducing and set controlling agents Native gypsum from 2.5%-5% weight of cement
WaterproofingWaterproofingWaterproofingWaterproofing
The water leakage should be prevent perfectlyThe water leakage should be prevent perfectly
Water Stops: Provided in transfers joints for stopping the Provided in transfers joints for stopping the
flow of water into the jointsflow of water into the jointseg:-- Copper (20mm gauge)- An alloy of Nickel & Copper- Stainless Steel
PLANT & EQUIPMENTPLANT & EQUIPMENT
EXCAVATORSEXCAVATORS
• Dragline
• Backhoe
• Bulldozers
•Scraper
• Dumpers
CRANES
CONCRETE EQUIPMENTCONCRETE EQUIPMENT
ADVANTAGES
• Less material required.
• Strong rock foundation not required (as for arch dams)
• Strength of the dam is high.
• uplift forces acting on the dam are minimal.
DISADVANTAGES
• Height limitations.
• Construction difficulty.
• Time consuming construction.
Examples
Bartlett DamVerde River, AZ
Examples
Bartlett DamVerde River, AZ
Cost analysis
• Materials 25%
• Formwork 20%
• Plant Purchase 19%
• Plant Operation 19%
• Placing and consolidation of concrete 4%
• Precooling concrete 3%
• Concrete Treatment 3%