Underwater construction Civil engineering Download: http://skillcruise.com/academics/civil-engineering/

1. Underwater ConstructionUnderwater ConstructionUnderwater ConstructionUnderwater Construction

2. ContentsContents
• IntroductionIntroduction
• Underwater construction techniquesUnderwater construction techniques
• CaissonsCaissons
• TypesTypes
• AdvantagesAdvantages
• Dangers encounteredDangers encountered
• CofferdamsCofferdams
• TypesTypes
• ComponentsComponents
• AdvantagesAdvantages
• Underwater lying of concreteUnderwater lying of concrete
• Tremie methodTremie method
• Pump methodPump method
• Toggle bagsToggle bags
• Bag workBag work
• ConclusionConclusion

3. Introduction:Introduction:
• During the construction of brides , dams or any other structure whereDuring the construction of brides , dams or any other structure where
the foundation part of the structure is most likely to lie underwater,the foundation part of the structure is most likely to lie underwater,
we have to opt for underwater constructionwe have to opt for underwater construction
• Construction in water poses many difficulties especially in the placesConstruction in water poses many difficulties especially in the places
where there the depth is considerable.where there the depth is considerable.
• During underwater construction our main objective is to createDuring underwater construction our main objective is to create drydry
and water freeand water free environment for working in such a manner that theenvironment for working in such a manner that the
structural stability of the structure is not compromised.structural stability of the structure is not compromised.

4. UNDERWATER
CONSTRUCTION
Construction
techniques
Caissons
Cofferdams
Methods of
Placing of
concrete
Tremie method
Pump method
Toggle bags
Bag works

5. Underwater construction techniquesUnderwater construction techniques
CaissonsCaissons
•Watertight retaining structure .Watertight retaining structure .
•Permanent in nature.Permanent in nature.
•Used to work on foundation of bridge pier, construction of concrete dam or for theUsed to work on foundation of bridge pier, construction of concrete dam or for the
repair of ships.repair of ships.
•Constructed in such a manner so that the water can be pumped out.Constructed in such a manner so that the water can be pumped out.
•Keeps working environment dry.Keeps working environment dry.

6. Working inside a caisson

7. Control post
pontoon
Ballast water
grab
Ground
water level
Circumferential gap
shoe
Box caissonBox caissonOpen caissonOpen caisson
TYPES OF CAISSONSTYPES OF CAISSONS

8. PNEUMATIC CAISSONPNEUMATIC CAISSON

9. • More suitable for off shore construction.More suitable for off shore construction.
• Upturned bucket embedded in marine sediment.Upturned bucket embedded in marine sediment.
• Embedment achieved by pushing or by creating negative pressure.Embedment achieved by pushing or by creating negative pressure.
Suction caissonSuction caisson

10. ADVANTAGES OF CAISSONSADVANTAGES OF CAISSONS
• Economic.Economic.
• Slightly less noise and reduced vibrations.Slightly less noise and reduced vibrations.
• Easily adaptable to varying site conditions.Easily adaptable to varying site conditions.
• High axial and lateral loading capacity.High axial and lateral loading capacity.
• Minimal handling equipment is required for placement of reinforcing cage.Minimal handling equipment is required for placement of reinforcing cage.
• Placement is sometimes possible in types of soil that a driven pile could notPlacement is sometimes possible in types of soil that a driven pile could not
penetratepenetrate

11. Dangers encounteredDangers encountered
• Caisson diseaseCaisson disease is so named since it appeared in construction workers when is so named since it appeared in construction workers when
they left the compressed atmosphere of the caisson and rapidly re enteredthey left the compressed atmosphere of the caisson and rapidly re entered
normal (decompressed) atmospheric conditions.normal (decompressed) atmospheric conditions.
• Construction of the Brooklyn Bridge, which was built with the help of caissons,Construction of the Brooklyn Bridge, which was built with the help of caissons,
resulted in numerous workers being either killed or permanently injured byresulted in numerous workers being either killed or permanently injured by
caisson disease during its construction, including the designer's son and Chiefcaisson disease during its construction, including the designer's son and Chief
Engineer of the project.Engineer of the project.

12. CofferdamsCofferdams
• Temporary structureTemporary structure
• Built within or in pairs across a body of waterBuilt within or in pairs across a body of water
• Allows the enclosed space to be pumped out, creating a dry workAllows the enclosed space to be pumped out, creating a dry work
environmentenvironment ..
• Enclosed coffers are commonly used for construction and repair of oilEnclosed coffers are commonly used for construction and repair of oil
platforms, bridge piers and other support structures built within or overplatforms, bridge piers and other support structures built within or over
water.water.
• A cofferdam involves the interaction of the structure, soil, and water.A cofferdam involves the interaction of the structure, soil, and water.
The loads imposed include the hydrostatic forces of the water, asThe loads imposed include the hydrostatic forces of the water, as
well as the dynamic forces due to currents and waves.well as the dynamic forces due to currents and waves.
• Used for shallow constructions having depth less than 10m.Used for shallow constructions having depth less than 10m.

13. Working inside a cofferdamWorking inside a cofferdam

14. Components of cofferdamComponents of cofferdam
• Sheet pilingSheet piling
Sheet piling is aSheet piling is a
manufactured constructionmanufactured construction
product with a mechanicalproduct with a mechanical
connection “interlock” atconnection “interlock” at
both ends of the section.both ends of the section.
These mechanicalThese mechanical
connections interlock withconnections interlock with
one another to form aone another to form a
continuous wall of sheeting.continuous wall of sheeting.
• Brace pilingBrace piling
• Concrete sealConcrete seal BracingBracing
frameframe
SheetSheet
pilespiles

15. COFFERDAM CONSTRUCTION SEQUENCECOFFERDAM CONSTRUCTION SEQUENCE
1.1. Pre-dredge to remove soil or soft sediments and level the area of the cofferdamPre-dredge to remove soil or soft sediments and level the area of the cofferdam
2.2. Drive temporary support piles.Drive temporary support piles.
3.3. Temporarily erect bracing frame on the support pilesTemporarily erect bracing frame on the support piles
4.4. Set steel sheet piles.Set steel sheet piles.
5.5. Drive sheet piles to grade.Drive sheet piles to grade.
6.6. Block between bracing frame and sheets, and provide ties for sheet piles at theBlock between bracing frame and sheets, and provide ties for sheet piles at the
top as necessarytop as necessary
7.7. Excavate inside the grade or slightly below grade, while leaving the cofferdamExcavate inside the grade or slightly below grade, while leaving the cofferdam
full of waterfull of water
8.8. Drive bearingDrive bearing
9.9. Place rock fill as a levelling and support course.Place rock fill as a levelling and support course.
10.10. Place Tremie concrete seal .Place Tremie concrete seal .

16. ADVANTAGES OF COFFERDAMADVANTAGES OF COFFERDAM
• Allow excavation and construction of structures in otherwiseAllow excavation and construction of structures in otherwise
poor environment.poor environment.
• Provides safe environment to work.Provides safe environment to work.
• Contractors typically have design responsibility.Contractors typically have design responsibility.
• Steel sheet piles are easily installed and removed.Steel sheet piles are easily installed and removed.
• Materials can typically be reused on other projects.Materials can typically be reused on other projects.

17. UNDERWATER CONCRETINGUNDERWATER CONCRETING
It is a process in which the prepared concrete is poured below the water surfaceIt is a process in which the prepared concrete is poured below the water surface
by using suitable methods.by using suitable methods.

18. TREMIE METHODTREMIE METHOD
•A Tremie is a watertight pipeA Tremie is a watertight pipe
•Generally 250mm in dia.Generally 250mm in dia.
•Funnel shaped hopper at its upper end and a loose plug at theFunnel shaped hopper at its upper end and a loose plug at the
bottom.bottom.
•It is supported on a working platform above water level.It is supported on a working platform above water level.

19. Laying of concrete by using TremieLaying of concrete by using Tremie
Basic principle behind Method of underwaterBasic principle behind Method of underwater
concreting - Tremie methodconcreting - Tremie method
Method of underwater concreting— Tremie methodMethod of underwater concreting— Tremie method
(inside view)(inside view)

20. Specifications of concrete to be used in TremieSpecifications of concrete to be used in Tremie
method:method:
•Coarse Aggregate: Gravel of 3/4” (20mm) max. size. Use 50-55 % of the total aggregateCoarse Aggregate: Gravel of 3/4” (20mm) max. size. Use 50-55 % of the total aggregate
by weight.by weight.
•Sand, 45-50% of the total aggregate by weight.Sand, 45-50% of the total aggregate by weight.
•Cement: Type II ASTM (moderate heat of hydration), 600 lbs./yd3Cement: Type II ASTM (moderate heat of hydration), 600 lbs./yd3
•Water/Cement Ratio: 0.42 (0.45 Maximum).Water/Cement Ratio: 0.42 (0.45 Maximum).
•Water-Reducing Admixture (preferably it is also plasticizer): Do not use super plasticizers.Water-Reducing Admixture (preferably it is also plasticizer): Do not use super plasticizers.
•Air-Entrainment Admixtures: To give 6% total air.Air-Entrainment Admixtures: To give 6% total air.
•Retarding Admixture: To increase setting time to 4-24 hours, as required.Retarding Admixture: To increase setting time to 4-24 hours, as required.
•Slump: 6 1/2" ± 1"Slump: 6 1/2" ± 1"
•This mix will develop compressive strength in the range of 5,600 – 7,000 psi at 28 days.This mix will develop compressive strength in the range of 5,600 – 7,000 psi at 28 days.

21. PUMP METHODPUMP METHOD
• Pumping concrete directly into itsPumping concrete directly into its
final position, involving bothfinal position, involving both
horizontal and vertical delivery ofhorizontal and vertical delivery of
concrete.concrete.
• Pumping concrete has thePumping concrete has the
advantage of operationaladvantage of operational
efficiency with potential savings ofefficiency with potential savings of
time and labour.time and labour.
• For massive underwater concreteFor massive underwater concrete
construction of navigationconstruction of navigation
structures, the pump methodstructures, the pump method
should be prohibited.should be prohibited.
PUMP METHOD OF LAYING CONCRETEPUMP METHOD OF LAYING CONCRETE

22. TOGGLE BAGSTOGGLE BAGS
• Toggle bags are ideal for smallToggle bags are ideal for small
amounts of concreteamounts of concrete
placement.placement.
• The bag is filled in the dry withThe bag is filled in the dry with
wet concretewet concrete
• Used for repair work.Used for repair work.
• The concrete is squeezed out byThe concrete is squeezed out by
a diver.a diver.
BAGWORKBAGWORK
• Bags are made of open weaveBags are made of open weave
material.material.
• Diver-handled bags are usuallyDiver-handled bags are usually
of 10 to 20 litres capacity butof 10 to 20 litres capacity but
1cub.m bags can be placed1cub.m bags can be placed
using a crane.using a crane.
Used only in special cases like repair works, etc.Used only in special cases like repair works, etc.

23. CONCLUSIONCONCLUSION
• Cofferdams are temporary structures and used in cases where the plan area ofCofferdams are temporary structures and used in cases where the plan area of
foundation is very large, depth of water is less and for the soft soils, where soils allow easyfoundation is very large, depth of water is less and for the soft soils, where soils allow easy
driving of sheet piles.driving of sheet piles.
• Caissons are permanent structures and becomes economical in cases where the planCaissons are permanent structures and becomes economical in cases where the plan
area of foundation is small, large depth of water and for loose soils.area of foundation is small, large depth of water and for loose soils.
• Suction caisson anchors are gaining considerable acceptance in the offshore industry.Suction caisson anchors are gaining considerable acceptance in the offshore industry.
• At present, the Tremie placement method is the standard way of placing high-qualityAt present, the Tremie placement method is the standard way of placing high-quality
concrete underwater. The other placement method are not able to reliably place high-concrete underwater. The other placement method are not able to reliably place high-
quality underwater concrete for major structures, although they may find application inquality underwater concrete for major structures, although they may find application in
special cases.special cases.
• For massive underwater concrete construction of navigation structures, the pumpFor massive underwater concrete construction of navigation structures, the pump
method should be prohibited.method should be prohibited.

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