No Vibrations are Good Vibrations in Des Moines

When Foundation Service Corp. accepted a job working on an urban renewal project in Des Moines, Iowa, the contractor agreed to abide by a strict requirement: No vibrations on the site. With the help of Hammer & Steel, and the PVE 2316VM high frequency variable moment driver / extractor system, the job went without a hitch - and without vibrations.

The job site occupied about half a city block at 9th and Walnut streets, where Wells Fargo Bank planned to erect a new structure in place of an old building. The area was surrounded by 100-plusyear- old, all-masonry structures that, according to Ron DeHart, project manager with Foundation Service Corp., were sensitive to vibrations. An equally old and vibration-sensitive six-foot brick sanitary and storm sewer line ran along the northern edge of the site, and a power cable that supplied electricity to a good portion of downtown Des Moines was right next door. "There were a number of critical utilities we had to deal with," DeHart said.

Weitz Corp., the general contractor on the project, approached Foundation Service about doing foundation work under some tight stipulations. "One of the parameters that was critical was that, because of the sensitivity to vibration in the area, there could be no vibrations. Another important consideration was that there was no tieback easement to the street, so we knew we were in a sheeting mode," DeHart recalled.

Weitz Corp. and Foundation Service Corp. considered several options for shoring up the area, from soldier pile and wood lagging to a soil stabilization technique that would freeze the sandy soil like sandstone. In the end, company officials decided the right choice was using a high-frequency variable moment vibratory hammer to drive Hoesch 1700K steel sheet piling, both supplied by Hammer & Steel.

Foundation Service Corp. owns two conventional vibratory hammers; however, they operate at a frequency that transmits vibrations through the soil. "We needed to rent a high-frequency hammer because those vibrations don't carry in the soil," DeHart said.

Hammer & Steel's president, Joe Dittmeier, suggested the PVE 2316VM driver/extractor system would be the best machine for the job. The variable moment driver/extractor completes its startup and stopping cycles with no vibrations. At 2300 cpm, the driver/extractor vibrates well above the natural frequency of all soil types, greatly reducing the vibrations transmitted through the ground. And with 389 horsepower, the Dutchmade unit can maintain high frequency vibrations at all times, efficiently driving pile.

"The system worked extremely well. It did exactly what we needed it to do," DeHart said. He used a seismograph to monitor vibrations in the sensitive downtown area as work progressed. "I measured all around the perimeter of the site. I'd stand right in front of a historic building. The vibrations were 1/20th of what would be damaging. The peak particle velocities (which indicate potentially damaging vibrations) were very small."

That was DeHart's first experience with the PVE 2316VM, but as more construction projects involve putting up new buildings in old areas, he'll likely use it again. Foundation Service Corp. operates in 28 states, including many in the northeastern United States where old buildings are being replaced by new construction. "Conditions similar to the Wells Fargo job are becoming more and more the norm as construction grows in downtown areas," said DeHart.

Foundation Service Corp. has been a Hammer and Steel customer for many years, noted DeHart. "I've personally been a customer for 10 years," he said. "I really like their service orientation and their response to customer needs."

In the case of the Wells Fargo project and the PVE 2316VM driver/extractor system, he might have said, "Hammer and Steel gives its customers 'good vibrations.'"