Helical
Evolution
Invented in the 1830s for marine foundation
applications, screw piles have evolved over
nearly two centuries into a capable deep
foundation alternative to driven piles
In the 1830s, a blind Belfast engineer named Alexander
Mitchell had a vision that would transform foundation
construction. His invention, the helical screw pile, has
supported countless structures since he patented the
design 188 years ago.
Initially, Mitchell devised cast or wrought iron screw
piles with a wooden shaft to permit the construction of
lighthouses, beacons and marine moorings where traditional
foundation construction was not feasible. The idea
behind the screw pile was simple: rather than hammering
piles into soft soil, they were screwed in with the help
of helices that sliced into the sandy earth with minimal
disruption, allowing the pile to be installed in dense soil.
Eventually, the technology was adopted for land-based
applications such as fence posts, tower legs, decks and
additions to residential structures. Screw or helical piles
have changed with the times; today, they are typically
made from high strength steel and feature round hollow
shafts or solid square shafts. Often, they incorporate multiple
steel screw threads – or helical bearing plates – that
allow the pile to be screwed into the soil. Sometimes,
helical piles are installed with cement grout surrounding
the shaft to increase vertical and lateral load capabilities.
The energy required to install a helical pile or anchor
is typically called installation torque. The torque is measured
in foot-pounds or Netwon-metres at a regular
By Lisa Gordon
16 Issue 4 2021 www.pilingcanada.ca
/www.pilingcanada.ca
