Precast concrete allowed a Virginia construction company to lay a solid foundation while building a foot-and-bike bridge over a park pond.
By Joe Frollo
There’s a common thread throughout the precast concrete community.
People in the industry love their jobs and are proud of the structures they create. They drive past buildings and down highways, seeing precast concrete seemingly everywhere, knowing they helped bring it all to life.
That can be a hard concept for children to understand. Kids can be tactical rather than conceptual and learn by touching things, feeling them with their own hands and feet.
For Alex Burkhart, projects manager at Virginia-based Smith-Midland, a recent venture offered both a challenge and a personal reward. A new foot-and-bike bridge at Ben Brenman Park in Alexandria, Va., combines not just form and function, it serves as the centerpiece to an enjoyable afternoon for the entire family, including Burkhart’s.
“It was a fun project,” he said. “Most projects I’ve done are along a roadway, but with this one, I could take my kids and have them walk along what went up. It’s a little different than our typical experience with construction jobs.”
Starting from the bottom up
Smith-Midland supplied the precast concrete footers, posts, panels and hammerhead piers for the bridge that sits above two weirs designed to facilitate water runoff.
Work began with Avon Construction dredging the affected portion of the 290-acre pond and relocating the wildlife in and around the water to other locations. With all the runoff during decades of weather, animal and human interaction, a lot of debris had settled at the bottom of the basin.
A $1.75 million grant from the Virginia Department of Environmental Quality, which required finding new homes for all the fish and other wildlife, funded the project.
“We hired a biologist to remove all the turtles and fish, even frogs,” said Kurt D. Lorenz vice president of Avon Construction. “Then they restocked everything afterward. This is a pond that kids frequent, so we were pleased to see all that happen.”
Once Avon drained the affected portion of the pond, they began setting the foundation. With the surface areas being so wet, the contractor determined that it was more cost- and time-effective to use precast concrete to construct the base and the weir wall.
Avon dug an open area to put the base and precast footings down, then locked everything together with panels and piers.
Some major wet work
The weirways allow water to spill safely away between the pond’s three cells and prevent flooding. They serve as dams designed specifically to impound water behind a wall while the weir alters and directs the flow.
In essence, Smith-Midland and Avon diverted 35 acres of water to build two concrete weir walls that control the pond’s water level, one of which has a bridge on top of it.
The biggest complications, both Burkhart and Lorenz said, was keeping everything dry during the project and maintaining watertight seals after the job was done.
“It was a little unique,” Burkhart said. “I hadn’t been part of anything like this before. All of the work would eventually be underwater. We’ve made walls before but never for that purpose.”
Even after dredging and partially draining the pond, Avon still had to contend with a lot of swampy, wet conditions. To solve that, crews laid large inflatable bladders that served as temporary portable dams that spanned the entire distance of the pond.
“At one point, I got to walk across the inflatable dam,” Burkhart said. “It was like walking across a waterbed. You needed a cable to hold on to as you did it or else down you went. The bladders were 20 feet wide and 100 feet long. Several of those stacked on top of each other to make the dam.”
Everything remains watertight
Precast footings sit spaced out at the bottom of the pond with columns attached to them. Wall panels then slide down into the footings. One weir was just that, Burkhart said – footings, columns and the weir wall. The other weir, with the bridge on top of it, required hammerheads on top of the columns and abutments, serving the spans within the bridge.
Because much of the precast concrete would spend its time underwater, the architect and Smith-Midland created watertight joints and connections.
“The connections had to be pretty precise and, at the same time, give us the strength required,” Lorenz said. “What they came up with was a bolted, grouted connection. That was a pretty unique part of the job.
“The other thing they came up with that was different and job-specific had to do with the weir wall. The joints used above ground in similar jobs are not typically watertight, so we used a water stop that applied to the panels to stop the water from leaking through.”
Even with all of the precautions and preplanning, Avon Construction’s biggest challenge remained being at Mother Nature’s mercy. After four months from contract to casting, it took an additional two months to put it together. Heavy rain led to runoff refilling parts of the pond, and additional time was needed to pump the site dry.
“They got down there with the sump pumps and buckets getting everything out that would spill into there, including fish, frogs and turtles,” Burkhart said. “It was more than I expected, but Avon has done this kind of thing before, so they were prepared.”
A design to be proud of
The final pieces of precast to be installed were the hammerheads, designed to match the look, feel and style seen throughout Alexandria.
“The city liked the architectural features you get with precast,” Lorenz said. “You’ve seen these traffic overpasses with hammerhead tops to them, spanning out in a big triangular shaped piece. They used the same thing on the bridge, and it looks very nice. We even put it up for some awards.”
The project was a decade in the planning for the city of Alexandria, and officials are happy.
“They got a lot of great feedback from the community,” Lorenz said. “They’d been wanting his bridge for 10 years, and they could not be more pleased with the outcome.
“Smith-Midland is tops in the industry. They did a great job. Their engineers and project management were very clear and in constant contact with me.”
City leaders got their bridge, and Burkhart’s then 3-year-old son finally got a first-hand look at what daddy does for a living.
As a second-generation precaster, Burkhart hopes one day to watch his children follow in his footsteps, taking the same pride in the ways precast concrete helps build the world around us.
Truth be told, though, Burkhart admitted that his son Ridge probably would have been happier right now with one of the turtles.
Joe Frollo is NPCA’s Acting Director of Communications and Public Affairs and editor of Precast Inc. magazine.
Photos Courtesy of Smith-Midland Corp.
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