March 9, 2012A key 48-in. transmission water main in the City of Columbus, Ohio, was accidentally punctured last summer, causing a heavy loss of water through a 4-in. hole. City officials turned to trenchless technology — specifically the use of a carbon fiber lining solution — to address the damaged main using the least invasive means possible.
Columbus is the state capital of Ohio and is also the state’s largest city, with a population of more than 787,000. Water service to the city and several surrounding communities is handled through the Columbus Department of Public Utilities’ (DPU) Division of Power and Water, which maintains 2,516 miles of water mains inside the city and 969 miles outside, as well as three major water treatment plants, which serves 1.1 million customers in the central Ohio region.
The water main that was damaged provides water to the Port Columbus International Airport, a hospital and most of the east side of Columbus. Having this main out of service for any amount of time would create even more of a headache for the DPU than it already had with puncture hole.
The pipe was damaged last June when a directional drilling contractor accidentally bored through the 48-in. pre-stressed concrete cylinder pipe (PCCP) while trying to install a cable across a stream, leaving approximately a 4-in. diameter hole for the water to gush through. The main is located along Hamilton Road under Big Walnut Creek and there is an incline of 60 degrees on the south bank of the creek, which would factor into how main would be repaired.
“We wanted to shut down the main right away but we couldn’t because we would have been taking a large chunk of people out of service, including the airport,” says Brian Haemmerle, acting manager for the Water Distribution Engineering Section of the DPU’s Division of Power and Water.
But in the midst of all the bad luck, a little good luck emerged. The department was fortunate enough to have a redundant 48-in. PCCP water main a few miles away that runs parallel to the damaged main, enabling it to be used to service the affected area. “That redundant main was our savior,” Haemmerle says. “We had to change the way we flowed water to get it where it was needed to compensate for the loss of water but were able to shut down that [damaged] main without impacting service to all the customers. ”
Having that redundant main also allowed the DPU to take a breath to explore its options to repair the main. The main, installed in 1973 by the Ohio Department of Transportation (ODOT), was in good condition otherwise; however, access to the main and the location of the damage were problematic. Access issues at the location made replacement and rehabilitation of the punctured pipe using conventional methods extremely challenging and costly. Environmental considerations associated with Big Walnut Creek caused further problems for any rehabilitation method that required trenched excavation or disruption of the creek or adjacent regions.
“There were a lot of issues we were battling…The Hamilton Road bridge is next to the main with bridge abutments located to the west, a concrete thrust block near the top of the embankment to the south and the creek to the north. We were also dealing that steep slope and water existing in the stream,” Haemmerle says.
Haemmerle says DPU considered four options: 1) repair it using a sleeve, 2) replace the pipe section, 3) use cured-in-place pipe (CIPP) and 4) use a carbon fiber lining system. Option 1 was rejected due to the access issues and environmental concerns associated with Big Walnut Creek as was Option 2, which would have also resulted in taking out part of the parking lot of a nearby city golf course. DPU’s staff seriously considered CIPP but decided against it due to its inexperience of using the trenchless method on such a large diameter water main.
“We recently finished our first CIPP water project this past year and are just becoming familiar with using CIPP on water mains,” Haemmerle explains. “We found that not many 48-in. water mains have been rehabbed using CIPP and given the slopes and bends involved with our situation, we were concerned about how it would be done. We had only done 6- and 8-in. water mains with CIPP. We weren’t ready to make that jump.”
Haemmerle says DPU opted to repair the pipe section by installing Fibrwrap’s internally applied carbon fiber structural liner. Safety was still a concern as workers would need to be lowered into the main using a harness. “We would be putting people inside of a pipe that has a 60 degree slope. We weren’t sure if water was coming into the pipe from the river because we had no access to the pipe,” he says. “But this option eliminated working in the stream, removing trees for access and other environmental issues.”
With Fibrwrap, the pipe can be rehabbed without excavation and installed by crews utilizing existing manholes or entryways for access. Material advantages of its use include high strength-to weight ratios, corrosion resistance, material flexibility and relative ease of installation. The material can be designed to provide full structural rehabilitation for a wide range pipe diameters (36- to 201-in. (diameter) and construction (PCCP, RCP and metallic).
Carbon Fiber Liners
In July, Pure Technologies was brought in to assess the condition of the pipe and pinpoint the location of the damage. Using its Sahara Leak Detection device, which was equipped with a video camera, Pure performed an internal video and leak detection inspection. Pure inserted the device through a 2-in. air relief valve near the top of the north creek bank. The inspection was cut short due to the turbulence of the water flowing into the pipe., causing the camera to exit through the hole.
“We expected [the inspection] to show a 4-in. hole and that’s what was found. What did surprise us was that we thought the damage was located above river level but it wasn’t. It was under the river,” Haemmerle says.
Having the damage located under river level meant that water was flowing into the pipe through the 4-in. hole. Due to the issues related to rehabbing this pipe, DPU needed a contractor to install the carbon fiber lining that was experienced in difficult projects. Fibrwrap Construction Services was recommended to DPU as a company that was experienced in doing challenging pipeline rehabilitation projects.
To gain access into the main and to provide ventilation for the workers, DPU constructed two manways, one being located about 150 ft from the section to be repaired. Fibrwrap Construction designed special rigging to insert into the pipe, allowing its crew to patch the hole and apply the carbon fiber liner. “The rigging allowed us to lower them in, suspending them inside the pipe so we had access to the entire pipe all the way around that segment,” says Jason Alexander, vice president and general manager of Fibrwrap Construction. “When applying the carbon fiber to the pipe segment, it is essential to wrap circumferentially all the way around it in one continuous wrap.”
After the pipe was dewatered, Fibrwrap Construction was able to patch the hole, using a special grout and welded a new plate onto the steel cylinder. The concrete was replaced on top of the plate. In designing the carbon fiber lining portion of the project, Fibrwrap Construction worked closely with Fyfe Co. manufacturer of the Tyfo Fibrwrap system and Simpson, Gumpertz & Heger (SGH). Together, they designed an internally bonded carbon fiber reinforced polymer (CFRP) strengthening repair as a standalone system inside the pipe. The carbon fiber system would assume all of the internal pressure and external loads with no reliance on the host pipe.
The carbon fiber wrap was saturated with epoxy outside the pipe and the saturated material was conveyed into the pipe on a spool and adhered to the pipe’s surface, covering about a 20-ft section. The design required three layers of the Tyfo Fibrwrap System, and was completed in four eight-hour shifts. The repair was completed in two weeks, costing the city $250,000.
“Use of the carbon fiber in this pipe is basically the same as replacing that section, given the proven durability of the Fyfe Co. Tyfo systems” Alexander says. “Life expectancy of the repair is 50 years.”
Haemmerle says the DPU is more than pleased with the results of the carbon fiber repair and is confident in its use for future projects, noting the DPU has expanded its use of trenchless technologies in recent years. “Over the last few years, we have started looking at different alternatives and technology,” he says. “We recently completed our second and third HDD projects using ductile iron pipe and last year completed our first CIPP project on a water main. We’ve used CIPP on the sewer side for many years.”
Sharon M. Bueno is managing editor of Trenchless Technology.