Stories
How Bridges Are Built In The Middle Of A Roaring River
- •Engineers use a temporary waterproof structure called a cofferdam to block water and create a dry space for the foundation.
- •Sheet piles made of steel are driven into the riverbed to form a wall, and pumps remove the water from inside.
- •For very deep water where cofferdams are unsuitable, open caisson and pneumatic caisson techniques are employed.
- •The construction process is extremely dangerous and requires continuous monitoring of water levels and strict safety measures for workers.
Key Questions Answered
A cofferdam is a temporary waterproof structure built in a river to block water and create a dry workspace for laying a bridge foundation. Engineers drive long steel sheet piles into the riverbed using hydraulic hammers to form a watertight circular or square wall, after which the trapped water inside is pumped out.
When the riverbed soil is weak or very wet, engineers use a pile foundation method where long steel pillars are driven deep into the ground to support the bridge's weight. A concrete structure is then built on top, utilizing vibrators during pouring to minimize internal air and maximize structural strength.
The caisson technique is utilized in places where water is extremely deep or standard cofferdams are unsuitable. Open caissons are lowered and sunk by digging from within, while pneumatic caissons use compressed air inside an air chamber to prevent water entry for underwater foundation preparation.
