How does pillars are constructed in water during bridge construction?

Construction of pillars in underwater

Do you know how to construct pillars in underwater or river? Bridges are built over water by different methods (depending on the level of water and quality of soil)

The most common approach is to sink a pier down into the earth below the water–allowing for shorter bridge spans. If the water is relatively shallow, and the loads not too great, individual piles or a precast concrete pile group can be driven through the water and into the riverbed.

In cases of large bridges requiring substantial supports much more extensive foundations are needed than a few simple piles. These are inevitably cast-in-place concrete foundations. Up to a certain depth what’s called a cofferdam can be built around the planned pier foundation site. A cofferdam is a basically a three or four sided box built in the water that is made nearly watertight. The water is then continuously pumped out of the cofferdam lowering the water level inside the box until the earth is finally reached. This allows men to work on solid (well it’s usually a muddy mess) ground.

Those pieces of corrugated steel you see holding back the water around the cofferdam are called sheet piles.

 

Here are some sheet piles.

Each is driven like a pile into the earth below the water. They interlock to create a cantilevering wall or sheet of steel that serves as a dam. To keep them tightly interlocked they have a sliding joint.

The deeper the cofferdam the more shoring is required to prevent the sides from collapsing inwards under the hydrostatic pressure exerted on all sides. Shoring very broadly describes bracing–vertical or horizontal. Working inside a cofferdam is a dangerous job with millions of tons of water separated from the worker by these thin steel sheet piles.

If interested beyond you can watch this video construction of pillars underwater

https://youtu.be/fO5yYxpOsLo

These methods are used for the construction of pillars under water.

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