Bridges are marvels of engineering that stand inconspicuously amongst us we don’t think of them much even when we are passing over them nowhere of these structures more impressive than when they are built over water which brings us to the question of our bridge is built over water?
When the water is shallow construction is easy a temporary foundation is made on which piers are built to support the upper structure and the bridge is then built it’s when the water is deep that other techniques are needed. There are many methods to complete such a task in deep water. But, here we will explore the main three.
These three methods of bridge-building are called battered piles cofferdams and caissons let’s begin with battered piles these are poles that are driven into the soil underneath the water, piles are hammered into the water until they turn outward or inward at an angle this makes the piles firm and increases their ability to carry lateral loads piles are inserted in the ground using pile drivers.
These are mechanical devices that may be transported to a location on a floating pile. Driving plant pile drivers may also be cantilevered out over the water from piles that have been installed in advance with the use of pile frames. Pile hammers and winches pile drivers hammer the piles into the soil until they turn outward or inward at an angle.
The piles are now ready to carry lateral loads and can provide the foundation of support for the bridge, the next step is to construct the pile caps above the piles. Once this is done the bridge is ready to be built next up to our cofferdams. These are temporary enclosures made by driving sheet piling into the bed of a body of water to form a watertight fence, this is called the cofferdam.
There’s more to this bridge-building technique once the sheet piles have been inserted in the water to create a cofferdam the water is pumped out of the enclosure now the construction workers can build the bridge as if they are working on dry land the process then becomes relatively easy. Finally, caissons may be used there are two types of caissons open and pneumatic.
An open case is a structure that is usually shaped like a box it is open at the top and bottom the caisson is usually constructed on land then floated into position and sunk so that the upper edge is above water level the caisson has a cutting bottom edge so that it sinks through the soft silt on the bed inside is a series of large pipes or dredging.
Wells are used to dredging up the bed material as more material is dredged up the caisson sinks and more sections are added to the shaft to keep it above water once the caisson reaches the correct depth concrete is laid to seal the bottom and then more concrete is poured into the caisson to form a solid post.
A pneumatic caisson is similar to an open case on but it has an airtight bulkhead above the bottom edge this is fitted with airlocks the space between the cutting edge and the bulkhead is called the working chamber. In this space, the water is removed using air pressure.
Construction workers can then enter the chamber and excavate the soil it is important that the air pressure in the chamber be carefully monitored so the workers do not get the bends but how do engineers pick which technique to use? this all depends on the condition of the site and the technology available.
These are important decisions to make that only expert can fully handle now that you know a bit more about how bridges are built you can admire them even more after all bridge-building techniques are impressive feats of Engineering. So friends, now you know how bridges are built underwater. If you have any doubts regarding this, feel free to comment down and if you also have any doubts about anything, comment down we are here for you.. All the best.