Cofferdam


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What is a Cofferdam


“A cofferdam is a temporary structure designed to keep water and/or soil out of the excavation in which a bridge pier or other structure is built.”


Braced Cofferdams


Formed from a single wall of sheet piling
Drive into the ground to form a box around the excavation site
The “box” is then braced on the inside
Interior is dewatering
Primarily used for bridge piers in shallow water.


Earth-Type Cofferdams


Simplest Type of Cofferdam
Consists of an earth bank w/a clay core or vertical sheet piling enclosing the excavation.
Used for low-level waters with low velocity
Easily scoured by water rising over the top

Timber Crib Cofferdam


Usually consists of 12’ x 12’ cells
Used in rapid currents or on rocky river beds
Must be properly designed to resist lateral forces such as:
Tipping / Overturning
Sliding

Cellular Cofferdam

Two main types are circular and segmental.
Can be used on a temporary or permanent basic.
Force are resisted by the mass of the cofferdam.