Stories
How Engineers Build Massive Bridges Across Flowing Rivers
- •Constructing bridges over rivers requires overcoming unique challenges like water pressure and unstable riverbeds.
- •The cofferdam technique uses a temporary watertight enclosure to create a dry working area for excavation.
- •Engineers drive interlocking sheet piles into the riverbed and pump out the trapped water to begin foundation work.
- •Deep foundations and piles are utilized when the riverbed soil is weak, transferring the load to stronger rock layers below.
- •The caisson technique is employed in exceptionally deep waters where conventional cofferdams are impractical.
Key Questions Answered
A cofferdam is a temporary, watertight enclosure built around a proposed bridge foundation site in a river. It keeps surrounding water out, allowing pumps to clear out trapped water and create a dry working space for excavation and foundation construction.
Engineers drive long steel plates known as sheet piles into the riverbed using specialized equipment like hydraulic impact or vibratory hammers. These plates are interlocked to form a sealed enclosure, and pumps are continuously used to remove any trapped or seeping water.
When water is particularly deep or a conventional cofferdam is impractical, engineers utilize the caisson technique. A caisson is a large, specially designed watertight structure used to construct foundations safely below the water level or within the ground.
