COFFERDAM [Compatibility Mode]

7/28/2019 COFFERDAM [Compatibility Mode]

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Prepared By:-

Mohamed Rizal Mohamed

Building DepartmentUiTM Perak

Definition:

- A temporary box structure constructed inearth or water to exclude soil and/ or waterfrom a construction area.

-Roy Chudley

- A cofferdam is a temporary structuredesigned to keep water and/or soil out ofthe excavation in which a bridge pier orother structure is built.

---- Standard Handbook of Heavy Construction


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It is usually formed to enable the formationof foundation to be carried out in safeworking conditions.

Usually sheet piling are used to form thecofferdam.

And any material which can fulfil the same

function such as timber piles, precastconcrete piles, earth-filled crib walls andbanks of soils and rocks.

Braced

Earth-Type

Timber Crib

Double-Walled Sheet Pile

Cellular

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It is formed from a single wall of sheet piling which isdriven into the ground to form a box around theexcavation site.

The box is then braced on the inside and the interioris dewatered.

It is primarily used for bridge piers in shallow water

(30 - 35 ft depth)

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It is the simplest type of cofferdam.

It consists of an earth bank with a clay core or

vertical sheet piling enclosing the excavation.

It is used for low-level waters with low velocity andeasily scoured by water rising over the top.

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Internal Baffle system: One of the innovation on earth type cofferdam.


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Constructed on land and floated into place. Lowerportion of each cell is matched with contour of riverbed.

It uses rock ballast and soil to decrease seepageand sink into place, also known as soldier-piletype.

It usually consists of 12x12 cells and is used in rapidcurrents or on rocky river beds.

It must be properly designed to resist lateral forcessuch as tipping / overturning and sliding.

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They are double wall cofferdams comprising twoparallel rows of sheet piles driven into the groundand connected together by a system of tie rods atone or more levels.

The space between the walls is generally filled withgranular material such as sand, gravel or brokenrock.

Three principle types:Box: Consists of straight flush wallsSemicircular cells connected bydiaphragmsCircular cells connected with tie-rods ordiaphragms

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Cellular cofferdams are used only in thosecircumstances where the excavation size precludesthe use of cross-excavation bracing.

In this case, the cofferdam must be stable by virtueof its own resistance to lateral forces.

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Skyline Steel, Parsippany, New Jersey


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Items needed for installation Pile driving hammer

Vibratory or Impact

Crane of sufficient size

Steel sheet piles are typically used

H-piles and/or wide-flange beams for wales andstringers

Barges may be required

***A Barges = is a long, narrow boat with a flat bottom

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Sheet piling

Bracing frame

Concrete seal

Bearing piles

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For a typical cofferdam, such as for a bridge pier,the construction procedure were as follow:-

1. Pre-dredge to remove soil or soft sediments and

level the area of the cofferdam.

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2. Drive temporary support piles

3. Temporarily erect bracing frame on the

support piles.

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4. Set steel sheet piles, starting at all four corners andmeeting at the center of each side

5. Drive sheet piles to grade.

6. Block between bracing frame and sheets, and

provide ties for sheet piles at the top as necessary.

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7. Excavate inside the grade or slightly below grade,while leaving the cofferdam full of water.

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8. Drive bearing piles.

9. Place rock fill as a leveling and support course.

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***tremie concrete seal.

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***tremie concrete seal.

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11. Check blocking between bracing and sheets.

12. Dewater.

13. Construct new structure.

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13. Construct new structure.

14. Flood cofferdam.

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15. Remove sheet piles.16. Remove bracing.17. Backfill.

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Z-Type (Z)Used for intermediate to deep

wall construction

Larson / U Type (U)Used for applications similar to Z

- Type

Flat / Straight Type (SA), (S)Used for filled cell construction

Arch shaped & lightweightUsed for shallower wall

construction


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Typical typesof interlocks

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Ball & Socket (BS)

Single Jaw (SJ)

Double Jaw (DJ)Hook & Grip (HG)Thumb & Finger

one point contact (TFX)

Double Hook (DH)Thumb & Finger

three point contact (TF)

AdvantagesAdvantages DisadvantagesDisadvantages

Allow excavation and

construction of structures in

otherwise poor environment

Provides safe environment to

work

Contractors typically have

design responsibility

Steel sheet piles are easily

installed and removed

Materials can typically be

reused on other projects

Special equipment required

Relatively expensive

Typically very time consuming

& tedious

If rushed, sheets can be driven

out of locks or out of plumb

When in heavy flowing water,added more stress on structure

which lead to structure

collapse

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COFFERDAM [Compatibility Mode]

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