Box culverts weighing 61,600 pounds each form the largest 4-sided, wet-cast box sections ever manufactured in Colorado.
By Bridget McCrea
Over a seven-day period during the summer of 2013, record rainfall in northern Colorado affected 14 counties, killed 10 people, damaged 26,000 houses and destroyed 2,000 homes. When the flooding finally subsided, it left behind an estimated $2 billion in housing, road and infrastructure damage across multiple communities.
Many mountain roads were damaged and deemed impassable. Among them was Buckhorn Road (LCR 44H) in Larimar County, which couldn’t stand up to the force of a 100-year flood event. There, the flood damaged one bridge, destroyed seven large culvert installations and inflicted a range of damage to the adjacent roads.
“The massive flooding washed out a lot of roadways and underpasses, including CR 44H’s multiple crossings,” said Tyler Brookhart, president at SEMA Precast in Brighton, Colo.
To prevent this from happening again in the future, Larimar County’s Road and Bridge Department initiated the County Road 44H (Buckhorn Road) Flood Repair Project. With a construction budget of $7.3 million, the project included raising more than 10 miles of road to pre-2013 flood elevations and replacing six culvert crossings with precast box culverts ranging in size from 15 feet by 7 feet to 25 feet by 8 feet. The county reported that final approval for the project was given by FEMA in September 2020 and that Flatiron Constructors Inc. of Denver started work in January 2021.
ANSWERING THE CALL WITH PRECAST
When the CR 44H Flood Repair Project was put out to bid, SEMA Precast answered the call. The county engineer specified precast for the project, which would require a four-sided precast box culvert made from 8,000 psi concrete. The overall length of the box was 88 feet, and it was made up of 4-foot sections (for a total of 22 pieces), each weighing 61,600 pounds.
The precast top and floor slabs were 18 inches thick, and the walls were 14 inches thick. Brookhart said precast was selected for several reasons, including the need to expedite construction, work within the tight confines of the installation site and minimize the amount of time that the road was closed to traffic.
“It’s a winding road with homes on both sides; cast-in-place would have taken weeks to install,” he said.
The job site also was heavily wooded with tall trees and situated in a canyon, which made communications difficult. Because of unreliable cell phone connectivity, employees had to use walkie-talkies to communicate with one another.
“The goal was the get in and out quickly and to keep the traffic flowing,” Brookhart said. “Once the boxes were set at a pace of one every 15 minutes, they were able to start constructing the roadway on top of them right away.”
SPECIAL MOLDING EQUIPMENT
To make the huge culvert, SEMA Precast obtained special molding equipment and modified its existing molds to accommodate the culvert’s huge size and heavy weight.
“The span was bigger than anything we’ve made before,” Brookhart said, “and we had to modify our molds to accommodate the 14-inch wall thicknesses.”
Using its Mi-Jack® Travelift® crane and two hooks to support the product’s heavy weight and load its transports, SEMA Precast delivered the culvert to the job site in February 2021. The culvert was in place and functional within a day thanks to the contractor being able to set one piece (of a total of 22) every 15 minutes.
The project also required intricate logistics on the installation side. Trucks were driven in a straight line right to the job site and then unloaded by crane. Then, the trailer had to be detached, raised in the air by the crane, spun 180 degrees (while the truck itself turned around), reattached and driven away.
“That’s the only way we could exit the job site,” said Bookhart.
ATTENTION TO DETAIL
Because of the span’s length and heavy weight, SEMA Precast used more reinforcing steel in the products and also braced them in the center for extra support during storage, handling and shipping.
To speed up the installation process, SEMA Precast pre-installed rubber profile gaskets on the culvert sections at its plant. That way, when the pieces arrived on-site, the contractor could put them together and ensure that they were watertight without the need to spend time installing mastic or joint sealant.
Matt Tolsma, project manager for Flatiron Constructors, said his company was the lowest bidder on the County Road 44H Flood Repair Project. The contractor has completed multiple bridge, drainage improvement and roadway rehab projects in the region, and this one was a typical run-of-the-mill county roadway project, according to Tolsma.
“It was in a remote area with little room to get trucks in and out of the job site,” Tolsma said, “but nothing that we’re not used to handling. The logistics of getting trucks and cranes in and out of there was really the most difficult aspect of the job.”
PRECAST: THE MATERIAL OF CHOICE
As bridge builders who “pour their own concrete whenever it’s feasible,” Flatiron Constructors saw the value in using precast for this particular project.
“In my mind, precast made the most sense,” Tolsma said. “We were up against the weather and runoff coming down the creek, so being able to get in there, dig it out, set precast boxes, get it backfilled and get the roadway fully opened quickly was huge. I think precast was definitely the right option there.”
The contractor considered cast-in-place for the larger 8-foot-by-25-foot culvert but later abandoned that idea because of the time it would require for cast-in-place construction versus precast concrete.
“SEMA Precast was able to figure out how to cast that box locally, so we went that route instead,” said Tolsma, who was pleased with the results. “Everything went well and looks good. The joints on the boxes were good.”
Brookhart said Larimar County provided positive feedback the day after the installation was complete.
“They just couldn’t believe how fast the box was installed,” he said. “I’m sure it also saved them money on installation, which I believe they were anticipating would take three to four days, versus just one.”
Bridget McCrea is a freelance writer who covers manufacturing, industry and technology. She is a winner of the Florida Magazine Association’s Gold Award for best trade-technical feature statewide.