Over the years the subtle wear had worn down the original timber piles supporting a busy piece of off-shore roadway in Seattle, WA. It was determined that a complete replacement of the bridge was the best solution, but in order to reach the locations to remove the bridge segments, a temporary work trestle would have to be established for the heavy equipment to walk across. To make matters more complicated, the bridge was located adjacent to overhead utilities and a large historic building overlooking the harbor, and the strictest vibration restrictions were in place in order to not disturb the surrounding environment. No impact or vibratory pile installation methods would be allowed. The contractor needed a fast, noiseless, vibration-free solution that could support the loads of the heavy equipment for the duration of the project, one that could also be removed completely once the task was complete and return the natural surroundings to normal. One solution was offered to them by American Piledriving Equipment: use helical piles as the foundation for the off-shore heavy equipment trestle. They were directed to us at Pileworks, where we designed for them a massive 80ft long, 22-inch diameter helical pile with a 36-inch diameter helical flight. APE designed a custom crane-mounted pile installer which was able to generate sufficient torque & crowd force to install each pile to its target depth. Once the pile is secured in the driver and positioned for install, typical installation time has taken between 5-12 minutes per 80ft. pile. This is the first of its kind, a major advancement in off-shore projects with the use of large diameter helical piles.
Original rotted bridge timber foundation
Pileworks 80ft. Bolt-on Helical Pile Secured in the custom crane-mounted APE HD™ Driver
Crane resting on top of the work trestle, supported by Pileworks Helical Piles
Pileworks 80Ft. Pile being installed off-shore by APE’s HD™ Driver
We had a chance to interview the Superintendent and On-site Engineer for this project, who were both pleased and optimistic about the final pile results. “I think this is gonna be something that changes a lot of things!” said Superintendent Jason Tarver. “It’s awesome for what we’re doing in the ground right now… it’s quiet… it’s controlled.” When asked about the cost of helical piles compared to the other pile solutions, he said, “I think it saved us money… we got a very good deal on the pipe [pile] we’re using.” And, “It was a substantial savings to drilled shafts.” One of the biggest advantages was that each 80ft. pile was a solid length section instead of segmenting smaller piles to be welded or added on-site. Tarver mentioned that they chose solid-length sections because it significantly saved time and cost by eliminating the extra work required to splice piles together.
Engineer Iqbal Sarip echoed the cost benefits as well during a separate interview. He said, “The helical piles are much cheaper than other alternatives, such as drilled shafts. This method provides similar functions as conventional steel piles that allows us to meet the project’s strict environmental and vibration requirements.” With regards to the installation performance of the large-diameter helical piles on the jobsite, Tarver said, ” These seemed to go in just as fast as a driven pile.”
With a veteran foundation construction crew pioneering into new territory, they were able to save both time and money using innovative, modern solutions offered to the Industry, today. Combined with the powerful capabilities of APE’s multi-use HD Driver system, this crew now has a new edge in the Industry which they intend to utilize in future projects.