How are bridges built over water?
There are basically 3 techniques use for constructing over water:-
The techniques depend on site conditions,i.e what type of sand under the water,clay,sandy,etc,technology of that country,water type(fresh water,salty water),depth of water.
How Bridges built over water having not much depth?
In shallow waters, foundation of bridge are laid by filling the particular location for a temporarily period, over which piers(a type of piller can be built) .
Otherwise when the soil is not favourable in the top layer for constructing a bridge , temporarily rigs are erected and piles are constructed deep inside the river bed.
Then the bridge can be built either by taking support from the already constructed piers, or by temporary platforms / mud-islands in the water, or through barges (though rarely in shallow waters).
Bridges usually made in this condition are
How Bridges built over water( large rivers or Sea)?
when the water body is large and the water is very deep
the technique used here he cofferdam technique -a wall enclosing an area inside a water body)is first built, inside which water is constantly pumped out and dry working conditions have to be maintained.
The foundation is then constructed inside the cofferdam.then pillars are created
therefore it is important to keep check on the pressure of water outside the box.
towers build using this technique are very technique.
3rd technique used to built Bridges over water is Case Drilling.
This is the most advanced technique used
In this there is a water tight chamber which keeps the water away with the help of air pressure.
In this a sealed tube chamber is fitted into water .
Then a long drill is put into the tube and then the drilling process starts,whatever water is filled is pumped out.
After that case is inserted into the hole which have been drilled which gives extra support and stable frame is created.
Then this frame is filled with concrete and left over and over which pillers are built
Now this is done with advance drilling machine but in olden days human work were used.
after tower are created bridge links are created.
Bridge links are of many types-
ex -Pamban Bridge
ex-Golden gate bridge
Cable stayed bridge
ex-Bandra worli Sea link
For better understanding please watch this video:-