About 18 months ago, Nicholas A. Willis was starting his new job as Stormwater and Conservation Superintendent in Hays, Kansas. Willis decided to take a closer look at the stormwater sewers underneath the picturesque brick streets in the city’s center.
The 48″ arched corrugated metal pipe (CMP) sewer was just over 50 years old, according to city records. 50 years is near the maximum lifespan for CMP, so Willis wasn’t expecting to find the pipe in perfect condition — still, what he did find surprised him.
“Basically, it was a cave,” Willis says. “Pipe had rusted out and been washed downstream, so I was shining my flashlight at an earth void and could see the under layer of the brick street. That’s just 6 inches of mesh-reinforced concrete, and we get semi trucks and school buses in that part of town. I’m amazed it held up.”
URGENT REPAIRS to AVOID DAMAGE AND INJURY
After closing the street and initiating emergency repairs, the department inspected all of the large-diameter CMP storm pipes and culverts in the Hays’ system. “Given that this pipe was installed in the early 1950s, it’s performed pretty well,” Willis says. “We have high pH soil, so pipe wasn’t being eaten from the outside. But 50-plus years is a long time.”
The system-wide inspection revealed about 300 feet of collapsing sewer that was immediately addressed by trenching and replacement. And with that work done, there was still several thousand feet of pipe with rotted-out inverts or other significant damage. Some of it ran underneath brick streets for hundreds of feet and replacement by trenching would have been expensive — about $490/foot — and would have seriously disrupted downtown traffic.
Willis decided to evaluate several trenchless methods. “We looked at just about everything, including two types of CIPP [cured-in-place pipe],” he says. “CentriPipe was the best on price by far. For large-diameter pipe, nothing else was even close.”
APM CENTRIPIPE SELECTED TO REHABILITATE KANSAS STORMWATER PIPES
CentriPipe is a proven centrifugally cast concrete pipe (CCCP) rehabilitation method developed by AP/M Permaform. A spincaster is inserted at one end of the pipe and pulled through at a calculated speed to apply thin layers of structural grout or epoxy mortar.
The finished product is smooth, tightly bonded, waterproof, and it doesn’t significantly reduce the pipe’s inner diameter or flow capacity. It’s especially efficient and cost-effective on large diameter pipe. The Florida Department of Transportation, for example, has used CentriPipe to rehabilitate sewers up to 13 feet in diameter.
Crucially for Hays, CentriPipe is completely structural and adheres tightly to most substrates, including CMP. It’s as if a new concrete pipe is built into the sewer. The condition of the old, deteriorated pipe doesn’t affect the performance of the new CentriPipe concrete liner.
TRIAL PROJECT to TEST APM CENTRIPIPE
In 2011, Willis decided to test CentriPipe by rehabilitating 968 feet of 30 and 48 inch sewer pipe before selecting it as the prime solution for all of Hays’ failing sewers.
“We wanted to see how it performed and how it cured out over winter,” Willis explains. “It did fine — there were some hairline cracks, like you would see in any concrete work, but after a year, it is all holding up very well with no shedding.”
In 2012, Hays rehabilitated an additional 2,500 ft of pipe. Willis anticipates about 2,000 feet each year for a few more years. Costs work out to $180/lf with almost no traffic disruption. “With the amount of work that has to be done, I don’t know how else we’d be able to catch up,” Willis says. “For efficiency and cost, this has been a great solution for us.”
Since the CMP in Hays is arched and concrete is applied by a spincaster, Willis says the new concrete was thicker ‘at ten and two’ but that this doesn’t really affect performance. Most pipes required two or three passes, one to fill in and smooth out pipe corrugations, and one or two additional layers to add strength. One-inch layer thicknesses were specified, and inspection was done with a fairly low-tech method.
“We just drilled into it in a few places until we got to metal,” Willis explains. “We found that coverage was even and predictable and we didn’t need to drill into too many places.”
CITY OF HAYS, KANSAS HAPPY WITH APM CENTRIPIPE RESULTS
Finding out that you’ve inherited a sewer system with failing pipe — and some pipe that has actually crumbled and washed away — isn’t the most pleasant way to start a new job. But Willis adapted quickly and has already addressed the most critical pipe in the system.
“We’re in a lot better shape after just two years, and CentriPipe is a big part of that,” he says. “Given our time frame and revenue, I don’t see how we could do without something like this. To any city or agency on the fence about it, I certainly recommend giving CentriPipe a try.”
APM CentriPipe in Canada
APM CentriPipe and APM Permaform culvert and manhole rehabilitation products are represented in Canada by Martech. Please ask Martech to help make your culvert rehab project a success.
