With a population of less than 14,000, Warsaw, Indiana -- the ‘Lake City’ -- is not an especially big town, but it’s snuggled in the midst of four lakes and generates seasonally high quantities of storm water runoff to Tippecanoe River. Inflow and infiltration with its resulting erosion is a continuing challenge. So when a 48-inch storm sewer pipe, made of paving brick and mortar, appeared to be failing, the city had to take it very seriously. But the proper response wasn’t immediately obvious.
“This is a round pipe made of brick and mortar,” says Warsaw Superintendent of Public Works Lacy Francis, “It sits low in the water table and there are some issues with the bottom of the pipe and there are also long cracks running the length of a pipe -- it seemed to be cracking like an egg. We worried that if bricks started falling out, there could be a sudden collapse.”
Warsaw needed a fix that was fast and it definitely needed to be structural. Given the state of municipal budgets, it also needed to be inexpensive, too. Francis had a solution in mind…he just wasn’t sure where to find it. “I’d seen manholes rehabilitated with a ‘sling’ (centrifugally casted) method that coated the manhole with high-strength grouts,” he explains, “and I figured that it would work on horizontal pipe as well, even though I’d never seen it done.”
A New Method That’s Already Proven
Fortunately, a trade show led Francis to Iowa-based AP/M Permaform, founded by Bill Shook. AP/M Permaform has been using the centrifugally cast, high strength PERMACAST system to repair and seal manholes since 1985. Thousands of projects in challenging situations have proven that centrifugally compacted concrete is an effective and durable rehabilitation technique. And Francis’s intuition was correct; the PERMACAST system has been adapted for use in horizontal pipe and there are now hundreds of successfully completed projects in the United States.
Called CentriPipe®, this horizontal lining system is based on a computer-controlled spincaster that is pulled backwards through pipes, precisely applying thin layers of high strength grouts to build the right thicknesses engineered to seal and structurally reinforce the failing pipe. The final product is waterproof, smooth, and relatively thin so that flows aren’t restricted. It is especially cost-effective for larger diameter pipe and costs less per foot than other trenchless repair methods like cured in place pipe (CIPP).
The Warsaw rehabilitation of its critical pipe will take place over three years, for budget reasons, with the first 700 feet being lined this year. After comparing bids for lining from four companies, Warsaw selected Indiana-based ProForm Pipe Lining Inc. to do CentriPipe®. ProForm has been using the PERMACAST method to do manhole lining for more than ten years, and has just begun using the CentriPipe method for horizontal pipe rehabilitation. “I saw CentriPipe at a show -- AP/M Permaform had a section of corrugated metal pipe lined as a test piece -- and it made sense to me,” says ProForm president Marc Campbell. And after working with the system on a few projects he says, “My personal sense is that, for larger diameter pipe, this is the way to go. It’s much less expensive than CIPP, and provides a stronger, more structural solution. The client gets more for their money. This is also better than epoxy coatings -- we’ve worked with those before, and probably won’t do it again.”
How It Worked in Warsaw
The Warsaw rehabilitation took about five weeks total, but Campbell says that work with the spincaster was only about one week; “The rest of the time was spent plugging and patching the pipe.” After the pipe was plugged and dewatered, more-than-expected I&I was discovered, so ProForm sealed the bottom with underwater cement -- this also provided a smooth bottom surface for the spincaster sled to travel on. Long cracks were sealed with MS-10000, a fiber-reinforced cement from AP/M Permaform.
Working in both directions from a central manhole -- the CentriPipe spincaster can be inserted through most manholes and requires minimal staging area -- ProForm plugged holes, filled cracks, stabilized loose brick, and cleaned the pipe with high-pressure jetting. Then PL-8000, an AP/M Permaform cementitious grout designed for brick and concrete pipe relining, was applied in two passes of about 1/2-inch each. “AP/M Permaform engineers determined that a one-inch thickness of grout was right for this pipe,” Campbell explains, “and they also suggest that it be applied in two thinner layers, to avoid slumping or peeling.”
The CentriPipe spincaster guidance system controls the application thickness by adjusting the withdrawal speed according to the project requirements. Several methods are used to verify layer thickness during application. During application, a thin wire wet gauge is inserted into the grout at random points for precise spot checks of actual applied thickness. Bag counts (of PL-8000) are kept during passes to keep track of applied volume; these counts are compared to calculated volumes for the exact pipe lengths.
The passes are also videotaped from the spincaster side during application, and can be inspected visually from the other end of the pipe. “I could drop by during passes and watch the work being done, and that was reassuring,” says Francis, “And I’ll have a copy of the video for review later.”
Realistically, Francis knows that the effectiveness of the project will have to be judged in five to ten years, to see how the new lining holds up. But he says, “I’m feeling good about it.” In fact, he immediately contracted for additional CentriPipe rehabilitation of a 36-inch concrete storm sewer running underneath a railroad crossing. This is another application where the solution has to be trenchless; and, due to the pressure of the crossing, it must be structural.
The CentriPipe method received an award at the 2011 NO DIG conference in Washington DC for a major sanitary sewer pipe lining project at Westlake, Ohio. A number of state highway offices are specifying it for lining corrugated storm culverts because its saves time, money and traffic disruption. The underlying technology of CentriPipe® has been in use for decades in its patented Permacast® system for manhole lining. It’s a long term solution for a fraction of the cost of replacement!
Angus W. Stocking, L.S. is a licensed land surveyor and full-time infrastructure writer. He can be reached at www.InfrastructureWriting.com.