HOW BRIDGES ARE BUILT OVER WATER?
Almost everyone travel everyday and you must pass any bridge along your way. Bridges are the connecting link between two lands separated with water body. Do you ever think how the pillars are build in the water bodies to construct the bridge?
Bridges are built over water by different methods (depending on the level of water and quality of soil).
First method is used for bridges which are build in low depth water. In low depth water, foundation of bridge are laid by filling the particular location for a temporarily period, over which piers (a type of pillar can be built). Otherwise when the soil is not favorable 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 less depth waters).
Cofferdam technique: bridges
Next method is for the bridge build over deep water body (river or sea). Cofferdam technique is used in this case. In this method, a wall enclosing an area is build inside the water and water is continuously pumped out from the area. After that, foundation of the bridge(the pillars) is constructed inside the cofferdam. As the construction place is sea or river itself. Therefore, 24 hour monitoring is required outside the cofferdam to check high tides of water. Bridges build using this technique are strong and carry heavy loads.
Case Drilling
And the last technique is called Case Drilling. This is the most advance technique. In this technique, a water tight chamber keeps the water away with the help of air pressure. Then a sealed tube chamber is fitted inside the chamber. After that a long drill is put inside the tube and then drilling process starts. Water filled during this process is pumped out. After that a case is inserted into the hole which is drilled inside to give extra support. In this way a stable frame is created. This frame is filled with concrete. Then pillars are build and hence the bridge.
