Thanks to its speed and cost-effective nature, precast concrete is a key component for U.S. infrastructure.
By Mark Crawford
Precast concrete is an essential and cost-effective building solution for maintaining U.S. infrastructure, particularly sanitary and storm sewer systems. For instance, Utility Concrete Products of Morris, Ill., recently completed a massive combined sanitary and storm sewer junction chamber for the Village of Lombard, Ill., that took a mere 2.5 hours to install. This vital piece of infrastructure allows easy access for municipal employees and engineers to the intersection of three sanitary/storm sewer lines as part of the Gatz Pond Outfall Improvements. The chamber measures 23 feet by 16 feet by 17 feet and weighs 193,000 pounds.
“Precision and timing were key since many of these sewers were active during installation,” said Tom Heraty, vice president of sales and engineering for UCP.
Taking this challenge into account, UCP and contractor Martam Construction selected a precast solution to replace the original cast-in-place design. The precast solution minimized disruptions and impacts to area residents.
Efficient and speedy design
Design challenges for the junction chamber included pipe diameters, pipe orientations and pipe supports. The pipe diameters intersecting the structure range from 48 inches to 92 inches.
Pipe orientations provided challenges due to their angles. A traditional rectangular or circular structure could not accommodate the large pipe diameters and their associated angles. In plain view, the shape of the resulting chamber design consists of six custom precast units, the heaviest of which weighs 74,150 pounds, and resembles that of home plate. The 48-inch pipe, which passes through the chamber, required a precast pipe support at mid-point. The crew maintained proper elevations for positive pipe flow during and after installation.
“We made sure to maintain balance at the lifting points, despite the odd shapes of these units,” Heraty said. “We also utilized bolts and bolt pocket formers to easily connect these units. The use of self-consolidating concrete ensured a uniform pour around the extensive reinforcement grid in each unit, with a final concrete compressive strength in excess of 6,000 psi.”
Well planned, well executed
Installation of the junction chamber went off without a hitch. UCP performed a mock installation at its plant to ensure proper fit between all units. This resolved any issues that could have arisen for the contractor during installation in the field.
“PVC sleeves in the roof slabs for dowel bars to be drilled and grouted in the field solidified the connection between the base and wall units and roof slab units,” said Heraty.
The contractor certainly appreciated the ease of installation – the entire process took about half a day, compared to the multiple days that would have been required for cast in place.
A group of municipal engineers, public-works employees, village employees and local officials watched the installation.
“Seeing the satisfaction on their faces was very rewarding,” Heraty said. “The chamber now gives city workers easy access to this important juncture of the sanitary and storm sewers, making it easier for the village to take care of the system.”
Mark Crawford is a Madison, Wis.-based freelance writer who specializes in science, technology and manufacturing.