We have been building bridges on rivers for decades.
A usual method followed in the construction of bridge is..
We cannot divert sea till the time we build pillars on the sea bed. Also, there is no dry-time for a sea. I always had question.. how 'The Worli-Bandra Sea link' is built ? Have done some R&D about this recently.
For this... a Caisson is used.
A caisson is a watertight structure which is used to work on the foundations of bridges, dams, repair of ships etc. In simple terms, these are suspensions into the sea bed. When we throw an object into water.. the upward acting force caused by fluid pressure opposes the weight. So, the object never gets a proper grip on the sea bed. Hence, after caissons are suspended, compressed air is pumped into it so that the it gets a firm hold of the ground. Then, the water is pumped out, keeping the working environment dry. These huge steel caissons are towed out, then gradually filled with concrete and water, and sunk. Then, beams will be placed over these pillars and bridge will be constructed.
A Caisson looks like this:
First thing is.. the workers work at extreme conditions as the pressure at sea bed is very high. In addition to that, we pump high pressurized air into the chamber. So, workers who work here without taking necessary precautions, are quite often affected by a disease called as 'Caisson Disease' which is also known as decompression sickness. Affected workers may even be paralyzed for life. So absolute care is supposed to be taken by the construction companies.
A usual method followed in the construction of bridge is..
- Start constructing the pillars in summer when the river is almost dry.
- Divert the water flow at the point where we intend to raise a pillar using some means
- Raise the pillars
- Assemble beams
- Finish it.
But, what about the bridges on sea?
We cannot divert sea till the time we build pillars on the sea bed. Also, there is no dry-time for a sea. I always had question.. how 'The Worli-Bandra Sea link' is built ? Have done some R&D about this recently.
For this... a Caisson is used.
A caisson is a watertight structure which is used to work on the foundations of bridges, dams, repair of ships etc. In simple terms, these are suspensions into the sea bed. When we throw an object into water.. the upward acting force caused by fluid pressure opposes the weight. So, the object never gets a proper grip on the sea bed. Hence, after caissons are suspended, compressed air is pumped into it so that the it gets a firm hold of the ground. Then, the water is pumped out, keeping the working environment dry. These huge steel caissons are towed out, then gradually filled with concrete and water, and sunk. Then, beams will be placed over these pillars and bridge will be constructed.
A Caisson looks like this:
Problems associated with this...
First thing is.. the workers work at extreme conditions as the pressure at sea bed is very high. In addition to that, we pump high pressurized air into the chamber. So, workers who work here without taking necessary precautions, are quite often affected by a disease called as 'Caisson Disease' which is also known as decompression sickness. Affected workers may even be paralyzed for life. So absolute care is supposed to be taken by the construction companies.
thanks badri.. doubt cleared.. and i'm aware of that disease.. read it somewhere recently...
ReplyDeleteThanks to you Mahesh... for making me think about this topic :-)
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