Higher Tech Manhole Rehab Solution in Historic Boone, North Carolina
Boone is a small town (population 19,000) surrounded by forest, located in the Blue Ridge Mountains of western North Carolina. Incorporated in 1872 and named for Daniel Boone, who made camp several times within what is now town limits, Boone prizes its heritage and, in fact, works hard to preserve the historic look and feel of downtown.
That’s just one of the challenges that public utilities superintendent Mike Trivette has dealt with since he took the job in 2005.
One particular challenge Trivette faces is familiar to anyone responsible for maintaining public infrastructure — raising utilities to grade after paving lifts. In Boone, this must be done in a way that preserves the character of town, but that doesn’t mean that ‘old fashioned’ technology has to be used.
“We used to use concrete rings to raise utility rims to grade, and the risk of injuries from heavy lifting or foot drops was always a problem — they seemed like a problem we should get rid of, if we could,” says Trivette.
Fortunately, eight years ago, Trivette was at a conference and saw a demonstration of Cretex PRO-RING technology, a manhole grade adjustment system based on rings made from high-strength lightweight expanded polypropylene (EPP), a material first used commercially in the highly regulated automotive industry. After confirming that the EPP rings were approved for use by the N.C. Department of Transportation, he decided to try them out in Boone. His department has been using the solution ever since, installing five to 10 of the stacked ring assemblies annually. For Trivette, the immediate attraction was safety, but he soon realized that the PRO-RING system also represented major efficiency gains and labor savings.
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“We used to raise manholes with a three- or four-person crew, and it could take hours,” he explains. “Now, we use a two-person crew, and it takes half the time. Actual material costs are a wash, but time and labor savings are huge for us.”
For a small public works department, it’s hard to overestimate the advantages of faster installation with a smaller crew. Not only is it safer for employees, it’s also appreciated by the public because road closures, even when multiple rims are being raised, take place in just a few off-peak hours, not days.
Much of this savings and efficiency is due simply to the lighter weight of the EPP rings — a typical ring weighs 14 lbs and can safely and easily be transported and installed by one person. By comparison, 6-in. concrete rings of the type used in Boone weigh about 240 lbs. Worse, concrete rings are surprisingly fragile, despite their mass; they break if dropped and so they must be moved about carefully by two crewmembers, who both expose themselves to injuries, particularly back strain and smashed toes.
Trivette also appreciates the angled rings that are part of the PRO-RING system because they simplify a tricky situation he often must deal with. “For example, we raised the grade of the street near one of our classic old hotels, and kept the sidewalks as they were,” he explains. “That created a slope of 8 in. that we had to match with the raised rim.”
Rather than rebuild the utility chimney completely, Trivette was able to stack four EPP rings and angle rings to raise the manhole precisely and exactly match the new slope. When it comes to matching the grade of new paving, Cretex PRO-RINGs are not only a safer and more efficient solution, they also provide a higher quality finish.
Durable and “No Issues”
It really wouldn’t matter if Cretex PRO-RINGs were safer, more efficient to install, and provided a higher quality roadway service if they weren’t also a durable and long-lasting solution. And in Boone, PRO-RINGs have proved to be reliable for eight years and counting. “We’ve had no issues at all,” says Trivette. “Even when we’ve installed them in open air, in flood plains or out in fields, with up to 5 ft exposed, I’ve seen no wear or degradation.”
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For agencies that maintain public infrastructure, expanded polypropylene is desirable material compared to concrete, when it is possible to substitute. EPP PRO-RINGs are lighter, easier to have on hand and work with and, like concrete, have a 50-year lifecycle and don’t degrade or deform under load or when exposed to harsh conditions — this has been demonstrated by tens of thousands of installations in the United States and Canada over decades.
Building sturdy, durable utility chimney extensions that precisely raise rims to grade and slope of new roadway surfaces is a simple process with the PRO-RING system. Using hand tools and non-shrink grout, extension rings, angle rings, and finish rings of the desired diameter and height are stacked and secured as needed to create a good fit and smooth surface and backfilled as needed. No potholes or raised edges are created, and Trivette says that snowplows don’t damage correctly installed raised manholes. PRO-RING installations also meet or exceed AASHTO HS-25 load requirements, and ASTM vacuum testing and exfiltration requirements.
Because EPP rings are light and can be stacked as high as needed, PRO-RINGs are convenient to store in warehouses or equipment yards — most years, Boone orders a large pallet of the EPP rings for use during the paving season and restocks if needed.
Lighter, safer, and better suited to purpose than concrete rings, the Cretex PRO-RING utility raising system has been a dependable success for Boone and Trivette. He’s happy to recommend the system to his counterparts in North Carolina and really, to any municipal public works department anywhere.
