Great River Energy crews installed 11 special foundations known as “helical bucket piles” on the Portage Lake to Palisade power line project due to the lines crossing swampy land.
Typical wood pole construction entails drilling a large hole, about 3 feet wide by 15 to 20 feet deep, and setting the pole in the open excavation. With soft soil, it can be difficult to keep the hole from collapsing.
The helical bucket piles are long vertical screw anchors bolted to the base of a large steel cylinder. Once they’re screwed into the ground, crews can follow typical construction practices and place rock backfill and wood poles as they would for any other foundation.
The Portage Lake to Palisade project consists of a new 69-kilovolt transmission line serving Great River Energy member-owner cooperative Mille Lacs Energy Cooperative. It connects the Palisade Substation with the new Portage Lake Substation, creating redundancy in the system.
“We have used these a couple of times in the past, but the last time was about five years ago, so they had been relatively rare,” said Molly Pruess, senior engineer at Great River Energy. “These pilings allow us to work faster, safer and with fewer environmental impacts.”
Advantages of using helical bucket piles include faster installation, no risk of an excavation collapsing and no need to hold the hole open by a temporary casing. In addition, there is no unnecessary material left over from an excavated hole, less disturbance to the surrounding area and the steel bucket protects the pole from future road construction planned in the area.
Pruess said these special foundations will be used more in the near future, including a project in the New Prague area in early 2025.
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