Fixed From Within
Subdivision incorporates trenchless methods in storm sewer system update
Atlantic Beach is a coastal community of 13,000 people in Duval County, Fla. As the name implies, it has a beach; the nearby ocean affects every aspect of life, including the infrastructure. Royal Palms—Atlantic Beach’s biggest subdivision, built in the early 1960s—did not take that into account.
The majority of Royal Palms’ storm sewer system, which also serves a large drainage area north of the subdivision, is comprised of corrugated metal pipe (CMP), according to Public Works Director Rick Carper. The salt, tidal influence and sandy soil have caused major problems, such as leaks, corrosion, subsidence and even collapses. The city was shocked that it had spent $200,000 on spot repairs with no end in sight. So, Atlantic Beach embarked on a $3.2-million storm sewer rehabilitation project.
Most of the rehabilitation was done by replacing CMP with reinforced concrete pipe or high-density polyethylene pipe, which required excavation. But for a substantial percentage of pipe, excavation or trenching was not a viable solution.
“Several areas of buried line fell outside of roadways or right-of-ways, in easements,” Carper said. “We don’t do that anymore because of the problems it creates.”
In this case, large construction easements near homes were required for excavation, and homeowners were unwilling to grant those easements.
“We were able to realign around some of the problem CMP,” Carper said, “but some simply had to stay in place and excavating wasn’t really an option. So we looked at trenchless methods.”
Cured-in-place pipe (CIPP) was used for most of the smaller-diameter pipe that needed rehabilitation. But for two long runs of 106 and 119 ft, CIPP was not considered a good option.
“These were large elliptical pipes, with cross-sections of 40 by 65 in. and 44 by 72 in.,” Carper said, “and the size meant that CIPP would simply cost too much.” The added cost came to $76,000, and that amount of funding was not available.
Putting off repair was not an option. “We inspected the pipes by closed-circuit TV and saw leaks and holes at the springline,” Carper said. “And we also observed subsidence. We had to do something because more rotting might have led to a complete collapse.”
Carper asked the lead contractor to look into alternatives, particularly a relatively new solution called CentriPipe.
An Attractive Alternative
CentriPipe is a centrifugal compaction system from AP/M Permaform that was pioneered in manholes and now is being used in horizontal pipe. It works well on large pipe.
Carper was impressed by a Florida Department of Transportation project that had successfully used the CentriPipe system on a 13-ft-diameter pipe. The spincaster is inserted into pipe and withdrawn at a predetermined speed while special mortar pumps to the spincaster for centrifugal compaction in thin layers to form a completely structural liner. The finished product is smooth and tightly bonded, and it does not reduce inner diameter or flow significantly.
Permacast PL-8000, distributed by Coastal Construction Products Inc., was used. It is a high-strength, fiber-reinforced packaged cement mixture that is mixed on site with water and then pumped to the CentriPipe spincaster. It can be applied to most substrates (brick, concrete, metal, etc.), and it is waterproof, corrosion resistant and structurally sound even in relatively thin layers.
The advantages of CentriPipe on the Atlantic Beach project were apparent. Because runs of up to 400 ft are possible by insertion and withdrawal, no trenching is needed. The final product is a completely sound and smooth structural liner with no seams or joints while maintaining maximum flow capacity. And it is cost-effective, especially when used in larger-diameter pipe.
“We figured we saved $30,000 on this part of the sewer rehabilitation compared to CIPP,” Carper said.
The CentriPipe work was subcontracted to T.V. Diversified Inc., a south Florida-based trenchless rehabilitation contractor that is licensed by AP/M Permaform for the centrifugally cast concrete pipe system. Owner Tom Vitale, Jr. said that excavation would have been especially difficult on these sewers.
“The lines ran between houses on a narrow easement with a curb inlet,” Vitale said. “Excavation would have put the houses at risk of settling.”
Working from the inlet, Vitale dewatered the system with bypass pumps. He spent three days cleaning the sewer with high-pressure jet streams and repairing holes and gaps in the metal pipe with PL-8000. He also sprayed PL-12,000 along the pipe invert to fill in the damaged pipe and give it a smooth “floor” so that the CentriPipe spincaster could be withdrawn without excess vibration or shaking. The CMP’s elliptical shape was not a problem.
“We ended up with a bit less coverage at the 3-o’clock and 9-o’clock positions,” Vitale said, “but honestly it wasn’t a big deal.” With just one pass, the CMP was coated with a smooth liner that was 1.75 in. thick at the top and bottom and 1.5 in. thick at the sides.
Another advantage of the centrifugal compaction system is the minimal staging area needed. “We only needed enough space to park a 25-ft trailer and a 20-ft box truck, so it was basically like parking on the street,” Vitale said. Traffic disruption was minimal, as the Atlantic Beach Public Works Department needed to close only one lane.
To ensure quality, Atlantic Beach scheduled continuous inspections during work and will follow up with an inspection at five years. So far, city staff members are pleased with the results.
“This really solved a problem for us and helped us to complete an important project,” Carper said.
There are more trenchless repair options than ever before, and CentriPipe—also known as centrifugally cast concrete pipe—fills an important niche. It is cost-effective, structurally sound, has minimal impact on flow and requires less staging area than other options. For municipalities making tough decisions on big projects, it is likely to be a useful solution.
Challenge: The storm system of a major subdivision in Atlantic Beach, Fla., was comprised largely of corrugated metal pipe. When faced with the elements of its coastal environment, the system suffered leaks, corrosion, subsidence and even collapses.
Solution: A $3.2-million storm sewer rehabilitation project included a centrifugal compaction system on larger-diameter pipe for which the cured-in-place method would yield too high a cost.
Conclusion: The solution proved to be cost-effective and structurally sound, with minimal impact on flow.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/7_8.11_Pipe_1.jpgThe spincaster is inserted into pipe and withdrawn at a predetermined speed.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/7_8.11_Pipe_2.jpgThe finished product is smooth and tightly bonded.
http://www.wwdmag.com/sites/default/files/imagecache/article_slider_big/7_8.11_Pipe_3.jpgIt does not reduce inner diameter or flow significantly.