February 11, 2013

The History of Helical Piles

Helical piles and design consideration
What would happen if helical piles were installed under the Leaning Tower of Pisa?

Chances are, we wouldn't call it the leaning tower.

A little history...
Helical piles were not used as a foundation system until the 1830s;  and then they were primarily used to stabilize lighthouses.

The helical pile was invented by Alexander Mitchell, an Irish engineer, as a method to stabilize lighthouses and other structures that were built on mud and sand. Originally called a screw-pile, the piers were made of cast or wrought iron and were screwed into the ground. The design and installation method provided more stability in the mud and sand than straight piers.

The first helical pile installed in the US was at Brandywine Shoal in the Delaware Bay. The tops of the helical piles were interconnected, which created an ice breaker, protecting the lighthouse from the heavy ice floes.

After the Civil War, helical piles quickly caught on in the United States after the Lighthouse Board decided to replace the interior waterway (bays, sounds and rivers) lighthouse vessels with screw pile lighthouses. Over 100 helical pile lighthouses were constructed to replace the older vessels.

Many of these screw pile lighthouses have withstood the test of time. The Roanoke River Light, which was built in 1877, is the last screw pile lighthouse standing in North Carolina. And the Carysfort Reef Light, located four miles outside of Key Largo, FL and constructed in 1852, is the oldest screw pile lighthouse still in service in the United States.

Want to learn more about helical pile history? Read the history of helical foundation systems.

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