Lake Tillery Bridge has served as a vital economic link and community landmark near Albemarle, North Carolina since 1927. When it needed rehabilitation, the North Carolina Department of Transportation chose a design-build project model with one key requirement: preserve the bridge’s iconic appearance.
The design-build bridge rehabilitation presented three challenges PCL’s design-build team overcame.
Although this was a design-build project, the team was handed finalized design documents at the outset. Any innovations or alternatives proposed by the team needed to be signed and sealed by the engineer of record (EOR). Our construction team worked with the client’s engineering firm, AECOM, and PCL’s engineer, Modjeski and Masters, who served as joint EORs. AECOM led the structural engineering and Modjeski and Masters supported the approach roadway portion of the project and structural modifications during construction.
Keeping communication clear and chain-of-command conflicts to a minimum is tough on any complex bridge project. Achieving that with two different EORs was an added challenge, but through proactive consultation and strong teambuilding, everyone came together to minimize risk and achieve successful construction.
The second challenge was maintaining the historic appearance of the bridge—especially its iconic arches, under which generations of North Carolinians had passed while enjoying the waters of Lake Tillery and the Pee Dee River that drains it.
Most of the rest of the bridge needed replacing, including the bearings, expansion joints, deck overlay and approach slab. To make sure the historic arches were not damaged during this extensive bridge rehabilitation, the project team installed strain gauges to monitor their stress and movement. Precise cutting and careful resequencing of the demolition schedule kept stresses on the arches well below the allowable limits for reinforced concrete, yielding no damage to the existing structure.
The final challenge was minimizing the project’s impact on the surrounding water.
This was easier said than done. The rehabilitation required a two-foot-thick layer of concrete to be cast around the footing of some piers, more than 20 feet below water.
To contain the concrete silica plume during this, the team designed and built a special reinforced fabric formwork that encased the pier and projected above the waterline. This provided an effective containment system for the silica plume and sped up the overall installation.
The team showed its care for the water in other ways, too — like using slag cement, which is more resistant to flaking underwater, and eliminating the longitudinal saw cutting called for in the demolition plan. This stopped concrete slurry from falling into the lake.
Today, unless you knew where to look, you’d never know that the Lake Tillery Bridge has undergone such extensive repairs. (We like to think even the fish in the lake can’t tell the difference.) Its four arch spans look virtually the same as they did when the project began, just as the client was looking for in a historic bridge rehabilitation.
The arches support what is nearly a brand-new bridge, designed and built with the scrupulous care that could see it last another century.
And when that time comes, PCL will be ready to rehabilitate it once more.