Soldier Field Renovation On Tight Schedule
No timeouts are allowed when you're working on a fast-paced project like the new Soldier Field in Chicago. "This was an extremely fasttrack job with a critical schedule," said Dr. Michael Wysockey, vice president of Thatcher Engineering Corp., piling subcontractor on the project.
When the Chicago Bears made it into the playoffs and needed the stadium for additional games, the start of the project had to be delayed. Work began in January 2002 and the entire project had to be completed by August 2003 so the Bears could play the 2003-04 NFL season there. Thatcher Engineering completed piling work on the stadium in late spring.
The massive renovation of the venerable sports stadium involved removing all but the historic Greco-Roman style exterior of the facility, which was constructed in the early 1920s. The façade, built of concrete and faced with granite-textured cast stone - and the signature 100-foot tall, classic Doric colonnades - remained as a shell in which a new, modern facility was erected.
"We replaced the old foundation, going deeper with high-strength steel," Wysockey noted. Old Soldier Field was built on 10,000 wood piles driven an average depth of 60 feet through landfill to bedrock. In its place, Thatcher drove about 2,200 HP 14x89 piles, from 85 to 114 feet long. "The new structure is much taller. The new foundation has higher loads designed to higher stress levels."
Working within the historic façade presented special challenges, Wysockey noted. "We were working next to old masonry structures, driving beams with big hammers. Huge beams were brought to the site through doors in the old façade. It was very difficult; much worse than tearing it down and starting over."
But an even bigger challenge was the timeframe, Wysockey added. "We couldn't afford a breakdown. We needed backup plans, backup equipment and backup people. We needed standby parts and equipment as well as a mechanic on call at all times." To ensure productivity under those conditions, Thatcher decided to use Delmag D46-32 hammers from Hammer & Steel.
In a pre-construction test program, the company compared air hammers, hydraulic hammers and diesel models. "The Delmag looked the best from a reliability standpoint," Wysockey said. "It was the biggest hammer we looked at. We did dynamic testing using a pile driving analyzer to judge performance. The energy delivered to the top of the piles was highest with the Delmags." The company continued to monitor the performance of the hammers throughout the project in the course of testing engineering and design assumptions, "and the energy delivered to the piles was better than advertised," he said.
Another factor that went into selecting the Delmags was the relative simplicity of the diesel hammer. "If they break down, you can fix them very quickly," Wysockey noted. During the Soldier Field project, Thatcher kept three hammers running, sometimes working two shifts and six or seven days a week. An additional hammer was available on standby at all times and only pressed into service on one occasion.
Soil conditions at Soldier Field were a final consideration in selecting the Delmags. "It's 40 to 60 feet of very soft material on top. Under that, it's about 30 feet of hard material, followed by extremely hard soil to rock. A lot of the piles are on rock. We chose the Delmags because they did the best job of penetrating the hard soils," Wysockey said.
The Gary, Indiana-based subcontractor also had a good experience working with Hammer & Steel on this project. "Hammer & Steel responded quickly to our questions," Wysockey said. "Mike Ormsby helped us solve some unique issues involving the guiding on the hammers and drive caps. We have some lead systems which aren't standard, and Mike came up with some good solutions."
Teamwork is a hallmark of Hammer & Steel's relationship with its customers. Somehow, such teamwork seems especially appropriate when the end result is the renovation of a landmark sports palace like Soldier Field.