buttress Dam

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%