Vertical headwalls and wing walls for precast arch bridge construction

Sept. 24, 2015

When developers turn blighted properties into high-end developments, they need infrastructure to support it and provide access. Several years ago, a former rock quarry in Dartmouth, Nova Scotia, was selected for a $300 million development project. This unlikely site is now home to a beautiful, high-end shopping center with impressive access roads and bridges.

The challenge

Several years ago, a blighted piece of land in Dartmouth, Nova Scotia was selected for a $300 million development project. This unlikely site is now home to a beautiful, high-end shopping center with impressive access roads, bridges and infrastructure to support it.

“The development started out as an old rock quarry; we called it a hole in the world,” explained Doug McLean of Duracast. “It was a big mess of rock and gravel and debris everywhere. Then North American Real Estate Group decided they were going to turn the 150 acre site into a higher end shopping development and they were going to re-invigorate Grassy Brook.”

Designers needed a way to create several crossings over Grassy Brook that would keep the creek corridor relatively natural. “Part of the redevelopment of the quarry was to make a green space for local residents. A  fairly good sized subdivision is right nearby, so the residents use this as a walking and natural area. They tried to incorporate that natural feel as much as possible with the bridges and retaining walls,” McLean said.

The project required a total of four crossings over Grassy Brook. Two required precast arches that were 40 ft at the base, and another required a precast arch that was 60 ft at the base. To keep these arches looking natural, designers needed a solution for the wing walls and headwalls.

The solution

Stantec Engineering designed the bridges using a precast arch system which combines cast-in-place footings and precast concrete arches. After learning that Redi-Rock could provide zero degree batter wing walls and headwalls to work in conjunction with the precast system, Stantec specified Redi-Rock for the job.

“The arch and the walls were put in to protect the beauty of the brook here at Dartmouth Crossing,” explained Michael Cameron of Dexter Construction. “The Redi-Rock gave it a more natural look than just a concrete poured wall. The whole goal of the project was to keep everything original and keep the woods feel so you don’t feel like you’re in an urban jungle; you feel like you’re shopping in a country setting.”

Redi-Rock is a large block retaining wall system that uses massive precast concrete blocks that stack up like giant Legos. Multiple batter options and textures are available, plus the shape of the blocks makes it easy to build corners and curves. These Redi-Rock blocks were manufactured locally by Duracast in Dartmouth.

The wing walls and headwalls were constructed using Redi-Rock Limestone texture blocks reinforced with geogrid. From the footings to grade level, the walls stand 24 ft tall with 3 ft of freestanding walls on top plus caps to finish off the look of the bridge.  The freestanding walls were J-bolted in place to act as a pedestrian rail.

A crew of four to six from Dexter Construction unloaded the blocks using a loader with forks and installed the blocks using a 20-ton excavator.

“We built this wall over 10 years ago, and it’s stood the test of time in the fact that everything is still exactly where I laid the blocks 10 years ago,” explained Cameron in 2015. “There’s some weathering, and that makes everything look more natural.”

In total, this project required 1,500 blocks equaling 8,625 sq ft of walls.

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