This a question for a curious mind.
How can columns or pillars be built underwater?
Where is their foundation laid, and how is it even possible to do such a thing?
Today we are going to make a sincere attempt at answering these questions.
Construction over waters is done by employing 3 techniques broadly.
These techniques are governed by the pertaining conditions on site.
e.g. Type of Sand underwater, Type of Water, Weather conditions of the area and Depth of water.
In case of shallow waters, a temporary foundation is made on which piers (a type of pillar) is constructed to support the upper structure. No rocket science is employed here and things are in general, Simple.
What if the water is deep, very deep and the soil conditions are not supportive?
In that case, Engineers employee different techniques to raise the piers.
Here comes the Cofferdam Technique:
Technically Cofferdam is a structure that retains water and soil in a particular area. No matter how deep the water is cofferdam can be built. Now in a cofferdam, an underwater bounded room type structure is constructed which is enclosed with soil and water. Then the water and excess soil are pumped out to make the area dry. It requires constant pumping out of the water and other undesirable materials.
Cofferdam walls are generally made up of sheet piles supported by wailers, internal braces, and cross braces. Cofferdams are temporary structures and are removed after the piers are constructed to support the bridge. Owing to their temporary nature cofferdams construction materials are available in template form.
Cofferdams are of three types :
It is a single wall of sheet piles that is put in to the excavated site on the ground. This is used for relatively shallow waters which are about 12 meters deep.
They are used where the site does not allow the use of cross braces.In this case, the cofferdam is stable due to the forces acting on it.
Double walled sheet piled cofferdam:
They have two parallel rows of sheet piles driven to site ground and attached to each other with tie rods. The gap is then filled with a material like sand or gravel to get the work done.
Here the water is not driven out. In this case, the chamber is watertight and uses air pressure to keep the water away. Then a sealed tube chamber is fitted into the water.A special drill is then used to make a hole on the site. Wherever water fills up the air pressure is used to remove it.
Then the drilled hole is filled with concrete and left to set. The pillars or piers for the bridge have then constructed atop these columns. Earlier lots of human labor was employed to do this work. Now in modern engineering, the same work is done by using sophisticated machines and equipment.
So here is the basic mechanism used to construct columns underwater. Hope this article has enhanced our reader’s knowledge by some percentage.