ATC engineers develop groundbreaking Solo-Driver method for transmission line construction
American Transmission Co. is helping keep the lights on through a revolutionary approach to utility pole foundation installation. New transmission structures are springing up throughout ATC’s service area thanks to a new invention that is faster, more economical and more environmentally friendly than other methods.
ATC has a patent pending with the U.S. Patent and Trademark Office for its new Solo-Driver™ method.
Before Solo-Driver, ATC and the rest of the transmission industry relied on two popular foundation installation methods for utility poles when a concrete base is not needed – direct bury and traditional vibratory installation.
The direct bury method involves drilling a hole and placing a pole in it before backfilling the hole. This method requires roughly two and a half hours to install one foundation.
Traditional vibratory installation is a newer technique. It uses a vibratory hammer to drive the pole into the earth. This method typically requires one hour for setup and roughly 15 minutes to install the foundation.
ATC first used the traditional vibratory method in high volume to rebuild a 69-kilovolt transmission line between the Monroe County Substation near Sparta, Wis., and the Council Creek Substation near Tomah, Wis., in 2014. Next, ATC used the method to rebuild a 138-kV transmission line between Waukesha, Wis., Concord, Wis., and St. Lawrence, Wis.
Todd Maersch, consultant transmission line engineer, and Mark Sanzenbacher, senior project manager, were both involved with the 138-kV transmission line rebuild project. While they appreciated the environmental and timesaving benefits that accompanied the traditional vibratory installation method, they wanted a method that was more efficient.
“We watched the guys struggle with setting up the equipment every time,” said Maersch.
With traditional vibratory installation, a crew must wrangle the foundation into position using taglines. Taglines are removable ropes that attach to a foundation while it is suspended above ground by a crane. Crews use the taglines to align the foundation as it is lowered to the ground. Then, the crew must situate the vibratory hammer, which runs off a power pack, over the foundation to drive it into the ground.
“Every time the crew moved to the next foundation, they had to disassemble and reassemble everything. It would take an hour of setup to do five to 20 minutes of work,” said Sanzenbacher. “So our conclusion was that there had to be a better way to set this up.”
The two started brainstorming. They hoped that if they could eliminate the crane, they could significantly reduce setup times. They also wanted to power the vibratory hammer with excavator hydraulics instead of relying on the large power pack. They found a few techniques used in other industries, but nothing that would work specifically for transmission poles.
“I started reaching out to various companies that I found on the internet asking whether they’ve done anything where they’ve tried to install a transmission pole,” said Maersch. “Most of the answers were that they had tried to grab the actual pole, but were never able to make it work.”
“That’s when we started thinking that we could design a tab that’s integral in our transmission pole,” said Sanzenbacher.
The two found a vibratory hammer manufacturer who worked with them to retrofit poles with side tabs. The vibratory hammer would be able to lock on to the tabs and maneuver the caisson.
The whole process works like this:
1) Attached to an excavator, a vibratory hammer grips tabs affixed to a caisson. 2) The hammer lifts, rotates and drives the foundation into the ground. 3)Then, the hammer grasps a tab on the top of the caisson to drive the foundation to the required depth.
With the initial design complete, Maersch and Sanzenbacher were ready to test their invention. They tried five installations in five different soil types. It worked.
Today, Solo-Driver is the new normal for 69-kV and 138-kV foundation installation at ATC.
Solo-Driver requires just two to three crew members compared to five for traditional vibratory installation and direct bury. The method is very safe for the crew on site since there are no taglines, and no manual maneuvering of the foundation is required. Safety interlock jaws on the excavator prevent the foundation from being dropped during installation, even if the hammer loses power.
Since Solo-Driver requires just one excavator for installation, the weight of the equipment is much lighter than the equipment required for traditional installation methods, which reduces environmental impacts. The new method also requires reduced overhead clearance compared to other methods. This allows foundations to be installed in closer proximity to existing overhead lines.
Taken together, the lighter equipment and reduced overhead clearance required means Solo-Driver can be used in locations where direct bury and traditional vibratory installation methods are not options. For example, while traditional vibratory installation and direct bury methods are not typically viable options in wetlands, Solo-Driver is. Additionally, Solo-Driver does not produce any spoils, whereas the direct bury method can result in five to 50 yards of spoils per pole.
Field studies have shown that in optimal conditions, Solo-Driver could cut costs by as much as half compared to traditional installation methods due to reduced labor costs, reduced equipment costs and reduced project risk dollars due to a smaller construction window and expedited timeline.
Maersch and Sanzenbacher say they’re thrilled to see a more efficient method already at work in the field.
“We know that a lot of things in the utility industry are done because that’s the way they’ve always been done. We knew that there were probably some opportunities to improve our projects in terms of finding better ways to do things,” said Maersch. “It seemed like the right thing to do to find another way.”