The case of the sinking building
Deep foundation stabilization saves recreation center
The neighborhood recreation center had developed an obvious and worsening problem.
After just 20 years of use, the Hillendale/Halstead PAL Center in Parkville began showing signs of severe settling. Baltimore County, the center’s owner, asked Plano-Coudon Construction to investigate the problem and propose a remedy.
“The building was essentially sinking,” said Blair Radney, Operations Manager of Plano-Coudon’s Small Projects Division. “It was differential settlement so the building was not sinking at the same rate all the way across the foundation and that was causing cracks in the building.”
“There were cracks in the slab in unusual places,” said Cheryl Zaron PE, a structural engineer with Columbia Engineering. “Where there was a column going up through the middle of the building’s interior, there were cracks all around it which meant that the column hadn’t moved, but the slab had sunk.”
Those foundation cracks were also growing.
During visits to the site over the course of several months, “I could tell just by looking at them that the cracks were getting bigger, which is really rare. With some cracks, I could stick a pencil in them,” Zaron said.
Plano-Coudon, Columbia Engineering and geotechnical engineers from KCI Technologies, Inc. began investigating the source and the severity of the structural issue. Team members tracked down the original plans and specifications for the center.
“We were even able to dig up some field reports made during construction,” Radney said.
The team took borings both outside and inside the building to assess the condition of the soil, exposed some of the building’s footing to ensure it was installed according to the original plan, and established a monitoring system to determine if the structure was still moving and how fast.
“It was still moving, but not at a catastrophic rate,” Radney said. “However, if you didn’t do something to stabilize it, you would eventually lose the building.”
Replacing the building would have burdened the county with a large expense and left the community without a recreation center for an extended period.
Instead, Plano-Coudon and project partners proposed to stabilize the building by installing 94 helical piles around the perimeter and within the interior of the building. Crews used a hydraulic drill to insert each pile into the ground between five feet and 12 feet until it reached a specified torque, ensuring that each pile could support sufficient weight. Workers – operating in trenches that exposed a limited portion of the building’s footing and piers at any one time – then bracketed each pile to the footing.
Work progressed smoothly, despite some challenges and unexpected complications, said Ed Wasilewski, Plano-Coudon’s Small Projects Foreman. At the outset of the project, crews had to spend considerable time hand digging around the building’s perimeter to expose every utility line and drain “because if we had started drilling without that precaution, we would have drilled right through them.”
Once drilling began, crews periodically hit especially hard soil and had to get revised specifications from project engineers for larger drill bits and different sized piles for those locations.
When operations moved inside, workers faced a new challenge. The space was too tight to accommodate standard equipment and, to save the county money, Plano-Coudon wanted to avoid tearing out any walls, ceilings or other interior components. Consequently, the company sourced specialized, hand-held equipment from the pile manufacturer. The interior machinery took three times as long to install a single pile – sometimes as long as half a day. The choice, however, saved money. And Plano-Coudon still completed the project on schedule.
“The guys wanted to work six days a week and I’m not going to stop anybody from working,” Wasilewski said with a chuckle. “These guys worked long days from sunup to sundown to get this project done.”
After installing the piles, crews drilled more than 300 holes in the building’s slab and pumped specialized concrete beneath the slab to fill any negative spaces and provide a completely solid foundation.
“That building isn’t going anywhere now,” Wasilewski said.
Workers then gave the center new interior finishes “so that it looks like a brand new building,” Radney said.
Ultimately, the solution to the sinking building “was a reasonably easy fix from the owner’s point of view that cost much less than replacing the building,” Radney said. “This is an important community resource that gets used for a lot of after-school activities, so it was great to be able to fix the problem and let people start using the center again within four months.”