Warner Robins, Ga., is a military town named in honor of Brigadier General Augustine Warner Robins. The city is built around Robins Air Force Base, Georgia’s largest employer.
The military background has affected Warner Robins’ infrastructure. Rapid wartime expansion meant that sewers and other assets went in quickly, with relatively little planning or inspection. As a result, the town has a lot of older corrugated metal pipe (CMP) storm sewers and struggles with major rehabilitation challenges, according to storm water management technician Krag Woodyard.
“We’ve divided our storm water system into five sectors, and we need to address one each year in order to keep up with EPA requirements,” Woodyard said. That means he has to be organized and diligent. Inspection teams pull up to 60 manholes daily inspect inlets and outlets as well. Flow direction is determined, condition assessed, and the amount of debris and blockage estimated. Using a hand-held tablet, the results are noted and later uploaded to an office GIS. The result is a good record of a failing system—Warner Robins has a lot of aging CMP and much work to be done. Priorities needed to be set.
Two main factors were considered when setting priorities: pipe condition and public safety. “If we’re comparing two sewers that pass under roads, and both are showing 50% corrosion and need repair, the one that gets more traffic is going to be a higher priority. We really can’t have pipe collapsing under roads,” Woodyard said.
Warner Robins needed a solution that was trenchless, cost-effective and, ideally, structural. Utility Asset Management Inc. (UAM), a longtime city contractor, was working with a new technology that seemed to fit the bill perfectly.
Stepping Into Cleaner Water
UAM is a certified female business enterprise. Its three principals each have about 20 years of experience in manhole and sewer rehabilitation.
“We’ve done a lot of manhole work and a lot of sanitary sewer work,” said UAM President Anita Clyne. “A year ago we were setting goals for our company and realized that storm sewer rehabilitation was an untouched area for us, mainly because we’d been waiting for good options.”
That realization set off a search for new trenchless solutions that eventually led to Centri-Pipe, a spin casting system designed by AP/M Permaform .
“We’d been thinking about spray applications, and, when we looked at the science and the engineering of this system, we realized it was a good fit with our expertise, so we got licensed,” Clyne said.
Centri-Pipe is based on a computer-controlled spin caster that is pulled back through pipes at calculated speeds, spraying on thin, precisely measured layers of high-strength cementitious grouts. It does not require backhoes or large staging areas, and costs less per foot than cured-in-place pipe, according to the Minnesota Department of Transportation. The result is a smooth layer of grout that adheres tightly to the inner surface of the rehabilitated pipe, effectively replacing the pipe from within with a new, structurally sound concrete pipe. Flow reduction is minimal.
“We had worked with spray systems on manholes, so this was an easy transition for us,” Clyne said. “We give the project specifications to AP/M Permaform , and they give us engineered thickness and layer calculations the same day. It gives us a level of comfort, especially on a project like Warner Robins’ where there’s a lot of elliptical CMP.”
Because it is a spray system, Centri-Pipe projects do not have to completely rehabilitate a pipe from end to end, which Woodyard liked.
Clyne noted another advantage of storm sewer rehabilitation: “After all the sanitary sewer we’ve worked in, it’s nice to step in cleaner water for a change.”
So Far, So Good
Video inspection allows UAM to assess the amount of damage and obtain data needed for the engineered specifications for a particular length of pipe. Bottoms often are a concern. The Centri-Pipe applicator needs a fairly smooth bottom so that it can be moved along the pipe evenly without jerking or stopping. Sometimes a new bottom is poured to provide a smooth pulling surface. Pipes also have to be dewatered and cleaned.
“A little moisture is fine,” Clyne said. “But if there’s standing water, as there often is in CMP bottoms, we go in with air hoses and blow it out.”
Manual gauges are used to confirm the thickness of each pass, and logs are kept to monitor the amount of material being applied. After a length of pipe is completed, it is videotaped again, and the city is shown before and after comparisons. “We do need man entry to do a good job,” Clyne said. “But for any pipe that’s 30 in. or bigger, we feel that Centri-Pipe is definitely the way to go.”
“We’ve been doing this for a few months, and so far, so good,” Woodyard said. “We don’t have to stop traffic; we have a structural repair, and there’s no hindrance at all for the public.”
Warner Robins is the firm’s first Centri-Pipe project, but it will be starting another soon in Macon, Ga., and already has quoted about $1 million worth of work to other municipalities.
“We know these cities well from all our work in sanitary sewers and manholes,” Clyne said. “They have been telling us for a while that storm sewers needed attention, and now we have a good way to help them out.”
