how are bridges built on water/oceans/river/sea ?

[deva888]

I always wonder how they are built, how they put concrete in the river bed which is so so deep. pls tell me if you know.

[Tim Baxter]

Foundations are the answer as with any building project.  There is concrete which will set under water.  According to Adam Heart Mother (Davis) on the Beeb, the Romans invented it.  So having surveyed (underwater) foundations are built.  This may be thousands of tons of rubble for a big bridge or 500Kgs for a small bridge.  Whichever, enough to stabilise the platform which the piers are going to be built on.  If you get the chance have a look ar the Beeb's documentary on building the Panama canal.  It shows you all about foundations and pouring concrete.  So, having established firm foundations all you have to do is span the gap between the uprights built on these foundations.  Piece of **** (cake)

[landie]

Generally the water is displaced by sinking a large collar around the point where the bridge pier will be and then pumping out the water. The contractors are then able to work below the water line and lay foundations.