Caisson (8/7/2011)

Altered photo of Chesapeake Bay Bridge taken from Sandy Point State Park in MD

Ever stare out at a bridge over water and wonder about the foundations in the water? The Chesapeake Bay Bridge (pictured above) spans over 4.3 miles and is a beautiful sight to see as it curves over the bay. I'm always amazed by structures that make you wonder how they were built and all the design and planning that went into making it happen from the initial sketches to figuring out the balance on the structure and acquiring the material and labor to get it built. I would love to work on a huge project like that from start to finish. 

Today I learned how the foundations are made in the water. The piers on bridges that are sunk into the water are made by using caissons. Caissons provide an airtight chamber in the water which can be used to work on construction underwater. A caisson is basically a hollow structure which is sunk into the water. Cranes are then used to dig at the bottom until a solid grounding can be found. The caisson structure provides an airtight chamber to dig under the the water and once solid ground is found the base foundation can be built. The box mold is then filled with cement and anchors to prevent the structure from floating off. Once these piers are built then the construction on the rest of the bridge can be built. This process is similar to piers made on land in which the soil is drilled down until bedrock or suitable strong ground is found before pillars are placed in position. It's kinda cool to think about all the engineering that goes behind the structures we use everyday!

Check out this super short video of an explosion of a caisson under water: