DEPT. OF CIVIL ENGINEERING GCET JAMMU

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Presented by:

Ajita Pandey Sachin Mansharamani

Construction Underwater...

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Construction in water poses many difficulties especially in the places where there the depth is considerable.

During underwater construction our main objective is to create dry and water free environment for working in such a manner that the structural stability of the structure is not compromised.

Introduction:

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UNDERWATER CONSTRUCTION

Construction techniques

Caissons

Cofferdams

Methods of Placing of concrete

Tremie methodPump methodToggle bagsBag works

DEPT. OF CIVIL ENGINEERING GCET JAMMU

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Underwater construction techniques:

Caissons: Watertight retaining structure . Permanent in nature. Used to work on foundation of bridge pier,

construction of concrete dam or for the repair of ships.

Constructed in such a manner so that the water can be pumped out.

Keeps working environment dry.

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Working inside a caisson

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Control post

pontoon

Ballast watergrab

Ground water level

Circumferential gap

shoe

Box caisson

Open caisson

TYPES OF CAISSONS

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PNEUMATIC CAISSON

• Large inverted box on which pier is built.• Compressed air is used to keep the water and mud out.

• Used to work on riverbed or quicksand's.

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Economic. Slightly less noise and reduced vibrations. Easily adaptable to varying site conditions. High axial and lateral loading capacity. Minimal handling equipment is required for

placement of reinforcing cage. Placement is sometimes possible in types of

soil that a driven pile could not penetrate

ADVANTAGES OF CAISSONS

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Temporary structure Built within or in pairs across a body of water Allows the enclosed space to be pumped out,

creating a dry work environment . Enclosed coffers are commonly used for construction

and repair of oil platforms, bridge piers and other support structures built within or over water.

A cofferdam involves the interaction of the structure, soil, and water. The loads imposed include the hydrostatic forces of the water, as well as the dynamic forces due to currents and waves.

Used for shallow constructions having depth less than 10m.

Cofferdams:

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Working inside a cofferdam

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Sheet piling Sheet piling is a manufactured construction product with a mechanical connection “interlock” at both ends of the section. These mechanical connections interlock with one another to form a continuous wall of sheeting. Brace piling Concrete seal

Components of cofferdam:

Bracing frame

Sheet piles

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1. Pre-dredge to remove soil or soft sediments and level the area of the cofferdam2. Drive temporary support piles.3. Temporarily erect bracing frame on the support piles 4. Set steel sheet piles.5. Drive sheet piles to grade. 6. Block between bracing frame and sheets, and provide ties for sheet piles at the top as necessary7. Excavate inside the grade or slightly below grade, while leaving the cofferdam full of water 8. Drive bearing 9. Place rock fill as a levelling and support course.10. Place Tremie concrete seal .

COFFERDAM CONSTRUCTION SEQUENCE:

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PLACEMENT METHODS:

Tremie method.

Pump method.

Toggle bags. Bags work.

UNDERWATER CONCRETINGIt is a process in which the prepared concrete is poured below the water surface by using suitable methods.

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A Tremie is a watertight pipe Generally 250mm in dia. Funnel shaped hopper at its upper end and a loose plug at the bottom.

It is supported on a working platform above water level.

TREMIE METHOD

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Laying of concrete by using Tremie 18

Basic principle behind Method

of underwater concreting -

Tremie method 

 

Method of underwater concreting— Tremie method (inside view)

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Pumping concrete directly into its final position, involving both horizontal and vertical delivery of concrete.

Pumping concrete has the advantage of operational efficiency with potential savings of time and labour.

For massive underwater concrete construction of navigation structures, the pump method should be prohibited.

PUMP METHOD:

PUMP METHOD OF LAYING CONCRETE

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TOGGLE BAGS: BAGWORK:• Toggle bags are ideal

for small amounts of concrete placement.

• The bag is filled in the dry with wet concrete

• Used for repair work.• The concrete is

squeezed out by a diver.

• Bags are made of open weave material.

• Diver-handled bags are usually of 10 to 20 litres capacity but 1cub.m bags can be placed using a crane.

Used only in special cases like repair works, etc.

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Cofferdams 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 easy driving of sheet piles.

Caissons are permanent structures and becomes economical in cases where the plan area of foundation is small, large depth of water and for loose soils.

Suction caisson anchors are gaining considerable acceptance in the offshore industry.

At 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-quality underwater concrete for major structures, although they may find application in special cases.

For massive underwater concrete construction of navigation structures, the pump method should be prohibited.

CONCLUSION:

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THANK YOU!!