In the early 1800’s, Alexander Mitchell developed power-installed helical foundations. These power-installed foundations were used in conjunction with the construction of several lighthouses in the English tidal basin.
In the 1920’s, light-load-capacity, manually installed helical screw anchors began to be used by the electric power industry for guy wires and as anchorage for utility poles.
In the 1950’s, the electrical power industry began to use power-driven helical screw anchors for tension loads to 36,000 pounds of guy anchorage for towers and utility poles worldwide. The primary use of these anchors was to resist tension or guy loads.
In the 1960’s, the use of helical screw anchors was extended by the electrical power industry for guy anchorage of transmission towers with loads exceeding 100,000 pounds. Engineers were beginning to explore other applications of helical screw anchors, including foundations. It became apparent that helical screw anchors could resist compression loads as well as tension loads.
In the 1970’s, helical screw anchors became the preferred method for guying electrical transmission towers and utility poles. Load capacity relationship began to be recognized as a major advantage of helical piles.
In the 1990’s, helical piles became an accepted method of providing deep foundations. Applications include, but are not limited to, foundation retrofits, new construction, marine moorings, boardwalks, department of transportation projects, and as tiebacks for all types of earth retention systems.
Currently, the use of helical piles includes temporary and permanent earth retaining systems (tieback anchors), underpinning systems for structures subject to settlement, pipeline supports, buoyancy control for underwater pipe lines, equipment mounts, street light foundations, and new construction projects with soil conditions that typically would not permit suitable capacities.
In addition to providing deep foundation solutions to residential foundations, MacLean Dixie helical piles have been used to entirely support a nine-story commercial building.
Terzaghi’s General Bearing Equation is now recognized as an effective method of predicting helical pile capacity. The accepted industry use of Terzaghi’s General Bearing Equation is coupled with torque-to-load-capacity relationships; these have proven to be two of the most important developments in the helical screw anchor industry.
With the wide acceptance of helical screw anchor technology, the international code council has now created industry-wide standards under ICC-AC358. ICC-AC358 establishes product testing and evaluation criteria for helical pile foundation underpinning systems.
These new standards will give engineers and local building code officials the ability to compare products from different manufacturers without comparing raw materials, allowing them to choose the best product for each project.
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