Ever Wondered How Bridges Are Grounded In the Water?


| LAST UPDATE 06/04/2021

By Eliza Gray
cofferdams underwater bridge building
Wikimedia Commons via Martin Kraft

Despite being around for centuries, for many, bridges have remained an architectural mystery. Sure, the principles of construction were pretty basic if you were discussing building one on land... But how were the pillars secured down to the bottom of a body of water? One viral video brought the topic back to our minds. And we decided to take a look.

how build bridges underwater
Wikimedia Commons via Martin Kraft

The Youtube channel, #Mind Warehouse, posted a video outlining the process from start to finish. The account, which has amassed almost 8 million subscribers, racked in tons of traffic with their explanation: The video sat with over 2 million views and counting. So what was so viral-worthy about their explanation? Well, it boiled down to one incredibly important building technique: Cofferdams. This crucial structure was likened to the barrier device used by dentists to keep teeth free from saliva during procedures. Like the protective plate, cofferdams provided builders with a safe building space while they worked away.

cofferdam bridge building technique
Wikimedia Commons via MassDOT

The video went on to describe how the aquatic infrastructure worked. "First, piles are driven into the bottom of the reservoir," the narrator outlined. "And then they're covered in a waterproof frame." Once secured, powerful pumps were able to expel the unwanted water from the area. In the end, a near bone-dry environment was sustained for the entirety of the building process. Seemed simple right? Well, there were some downsides. For one, the cofferdams came at an enormous cost. And, they weren't suited for reuse. Luckily, the technique dated back many years and has improved in efficiency over time.

building in water
Cci via Shutterstock

The video went on to describe one particular time that cofferdams were used in civil engineering projects in American history. The Stillwater Bridge, a connecting bridge between Minnesota and Wisconsin, was in disarray and in need of a fix. The St. Croix river, which ran between the two states, proved a challenge for builders, as they balanced environmental and governmental interests. In the end, the cofferdam proved a valuable solution for the project, as it minimized habitat damage for endangered animals. And the nearly one-mile-long bridge owed a great deal of its success to the building technique.

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So the next time you find yourself puzzled by the architectural feats of bridges (or sitting mouth-open at the dentist), hopefully, you would have learned a little more about their unique building process...