October 1, 2008Cured-in-place pipe (CIPP) became the answer to the U.S. Army Corps of Engineers’ problem earlier this year when a leaking 1,740-ft section of 30-in. storm line needed attention in Marmet, W.Va., located just outside of Charleston.
CIPP contractor US Sewer and Drain adeptly handled this tricky and somewhat unusual project in late March, overcoming several challenges, including an unusually thick liner and the Kanawha River.
Since 1934, the Marmet Lock and Dam in southern Kanawha County, W.Va., has played a key role in controlling flooding and aiding commerce on the Kanawha River. Over the last few years, the Marmet Lock and Dam has undergone a facelift of its own. The Corps is nearing the end of a project to replace the aging structure. The problematic polyethylene storm line was installed as part of that undertaking and had been in the ground for approximately a year.
The problem with the storm line, which serves residential development adjacent to the Marmet Lock and Dam and drains into the river, was extensive infiltration of soil and water through joints in the pipe. After a closer inspection, the reasons for the infiltration were clear.
“Due to the depth of the pipe, which at 30 ft is considered extremely deep, as well as the fact that it was located 100 ft adjacent to the recently constructed Marmet Lock and Dam banks, the pipe was taking on soil and water,” explains US Sewer and Drain president Jeremy Bowman. “The material that they used wasn’t holding up to the compression and they were getting a ton of infiltration at the joints.”
Something needed to be done. CIPP was the method of interest but the Corps wasn’t 100 percent sold that it would solve this pipe’s problem and last long-term.
Before the U.S. Army Corps of Engineers signed off on CIPP and put the project out for bid, which was awarded to US Sewer and Drain, Corps officials did their homework. CIPP was only deemed the method of choice after months of asking questions and doing research. “They were asking questions such as ‘Will [CIPP] work in this application?’ and ‘How long of a shot can be made at a time?’” Bowman says, noting that the Corps wanted to rehab the pipe so that the liner would serve as a stand-alone pipe in case the line completely failed.
Beyond working closely with US Sewer and Drain, the Corps also did so with resin manufacturer Composites One and liner manufacturer Applied Felts to ensure the resin and liner they wanted for the project was developed.
“The resin played a key role in the success of the project,” Bowman says. “An enhanced resin was requested by the Corps of Engineers to ultimately add more strength to the finished liner. This goes back to the fact that [the Corps] wanted this liner to be a stand-alone product if the host pipe failed completely.”
The job was completed in a few weeks’ time, with minor delays occurring when the river rose too high and prevented crews from being able to get the pipe plug in place. Before the CIPP process got under way, crews also applied a pre-liner, a very thin plastic membrane that is stretched through the pipe to help hold back any water and give the actual liner time to set up.
The 1,740-ft liner itself, wetted off site and brought to the river site in a refrigerated truck, was installed in three shots; each shot was a little more than 500 ft each. Bowman notes that it took crews three to four hours to invert the liner for each shot. Using 6 million BTU boilers, each shot took approximately 18 hours to water cure, followed by the cooling down process.
A couple of 6-in. bypass pumps, rented from Sunbelt Rentals, were mobilized and maintained during the process.
Relining a storm line may sound routine but this project brought its own set of challenges. In this case, the depth of the pipe played a part in everything that was done from cleaning the line prior to lining to liner thickness. “Any time you have a system that is deep like that, it makes for a more difficult project,” Bowman notes, adding that making sure your prep work is done properly is imperative in these cases.
One challenge was the thickness of the liner. One of the Corps’ requirements for the job was that the 30-in. liner needed to be 24.5 mm thick—which goes back to the Corps’s goal of having the liner being able to serve as a stand-alone pipe. Having the liner that thick added significant weight to it, which was a factor in doing the inversion in three shots instead of one or even two.
“That is very thick,” Bowman says. “Typically you make the liner thickness half of the diameter of the bag, in millimeters. But [the Corps] wanted a thicker liner for stability. [The Corps] became very educated with the product and helped in designing and calculating what thickness of bag was going to go in the ground. The added thickness makes the liner heavier and more cumbersome, making the application a little more difficult.”
Another challenge was getting the pipe plugged due to the high water in the manhole. Beyond the delay in attempting to plug the pipe, it took project foreman Ruben Santiago wrestling the pipe plug into place. “[Ruben] had to go into the manhole and physically put the 30-in. plug into place. The water was over the top but it was at mid-level, making it difficult. He did a great job.”
Bowman adds that crews also didn’t have the option to release the process water used to cook the liner into the river. “We had to pump out the process water into above-ground holding tanks and haul it away. That was an added dimension to the project.”
Bowman reiterated that the prep work and coordination were keys to the project’s success. “The guys did a great job with the prep work,” Bowman says. “You have to make sure everything is in order before you start inverting that liner. Because once you start inverting the liner, there’s no turning back.”
Sharon M. Bueno is managing editor of Trenchless Technology.