Building teams for successful quality projects

An innovative technology is helping to preserve the past, while saving time and money at DPR Portland’s Newberg City Hall project in Oregon. The job includes the historic renovation and seismic retrofit of the original city hall built in 1914 and construction of a new 6,000-sq.-ft. addition.

At the outset of the $2.5 million project, DPR considered several configurations to give the city the 18,000 sq. ft. of finished space it requested. After reviewing a dozen options, the City of Newberg decided to convert the unusable existing 4,000-sq.-ft. basement, with a six-ft., eight-inch-high ceiling into a fully usable lower level. This meant lowering the existing basement floor by almost five feet. The as-built plans for the building indicated that the existing basement walls had a footing of two feet and initial inspection appeared to confirm the as-builts. However, as DPR began mass excavation, it became evident that most of the original walls were placed directly on the ground.

“After initial excavation, we realized that there was no footing,” explains DPR’s Bruce Reid. “The concrete walls were poured on top of dirt, which placed excessive loads on the existing soil. We couldn’t continue basement excavation without additional support of the concrete walls.”

The two most common solutions to this problem, excavating and increasing the depth of the foundation in four-foot segments or demolition and reconstruction of the entire building, would have added three-and-a-half months to the schedule and $400,000 to the budget. Neither the cost impact nor time impact was acceptable.

After researching alternatives, DPR discovered a foundation anchor technology developed by Missouri-based AB Chance Co. With this system, helical piers, two-inch galvanized steel square shafts with helices at the bottom, were installed 40-ft. deep under the building walls. The helical piers were screwed into the soil with a hydraulic jack, six ft. on center all around the building. Resisting compression or uplift loads, the piers provided temporary foundation support and allowed DPR to continue its excavation of the basement. “The result was incredible,” commented Reid. “We saved $300,000 and had only a six-week impact to the schedule.”

The City of Newberg appreciated DPR’s efforts. “DPR was chosen for this project because of their experience with public buildings and remodels,” stated Duane Cole, Newberg City manager. “DPR came up with an innovative solution that saved us time and money.”