With the road in Austin ballooning from 10 lanes to 15, the team had to rethink how to deal with all the extra runoff.
Balfour Beatty, as apart of Colorado Constructors (CRC) joint venture, recently celebrated the partial opening of Central Texas Regional Mobility Authority’s (Mobility Authority) new US 183 South tolled expressway in Austin.
The expanded expressway presented a problem in terms of drainage, because the roadway’s surface area would increase drastically from 10 lanes to 15, and the traditional concrete box culvert structure along the corridor was deemed insufficient to meet the increased drainage requirements.
So, CRC used an innovative solution of installing an arch culvert bridge system to better convey hydraulic flow along the expressway’s corridor to neutralise the heightened risk of flooding.
As Balfour Beatty explains here, the solution was arrived at after a false start, and the final, successful approach required two crawler cranes working in tandem to set 42 precast concrete arch culvert segments in a short space of time.
- See how they did it
Move the utilities?
CRC initially proposed a design that would add an additional barrel to each side of the existing box culvert located along the US 183 corridor. But the team realised this approach and larger structure would likely interfere with the existing utility mains that run parallel to the drainage canal.
Relocating utilities on the corridor could solve the problem but would risk the project’s cost and schedule. This plus existing high-pressure gas and wastewater mains running parallel along each side of the box culverts caused them to abandon the idea.
Precast concrete arch culverts to the rescue
"Instead of spending several million dollars to relocate the existing utilities and running into the possibility of delaying the project’s schedule with our initial design, we quickly pivoted and devised a plan to install a precast, concrete arch culvert bridge system along the new expressway," said Brendan McGrath, Balfour Beatty general superintendent on the US 183 South project. â€¨â€¨Work began with the excavation and construction of two 168-foot long, by six-foot tall concrete footings, which had to be done with care because existing utilities were only a few feet away.
During this process the team kept the existing box culvert in place so storm water could pass directly through the work area, keeping the site dry.
Tag team crawler cranes
Once both footings were constructed, CRC demolished the existing concrete box culvert, creating a solid base for two crawler cranes to set 42 new precast concrete arch culvert segments.
The 62,000-pound arches were shipped lying flat on their sides, which allowed one crawler to flip the arch segments vertically and the other to grab the upright arch, track it in place and set each structure in its permanent location.
Within two shifts, all precast arches were set in place, and backfill operations quickly embanked to the roadway grade just in time for the structure’s first storm.â€¨â€¨"With the delivery of the arch culvert bridge system, conveying hydraulic flows for all new lanes of SH 71 at 183 South overpass intersection has been a success," said McGrath.
"From fitting the unique design parameters to saving time and money, the installation of the arch culvert bridge system was a major milestone for our project teams. I commend our workforce for their resiliency in providing an innovative solution for the Mobility Authority and the 60,000 drivers who travel on the expressway every day."
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Image: Installing an arch culvert bridge system would better convey hydraulic flow (Balfour Beatty)