Where the Cookie Crumbled

A cured-in-place-pipe spot-liner system saves the City of Tacoma, Wash., substantial time and inconvenience on a challenging sewer main repair

A 2 1/2-foot-deep sinkhole, 3 feet square, developed in Tacoma, Wash., when soil eroded under a 115-kV transmission tower after a cookie failed in a 10-inch sewer main. The city’s Environmental Services/Maintenance Division (ESMD) had to seal the connection before erosion threatened the tower’s stability.

Hugh Messer, assistant division manager, called Tacoma Power in preparation for excavation. “They gave me a rough estimate of $100,000 to erect a temporary power pole, remove the tower, pour a new foundation after we repaired the pipe, rebuild the tower, and re-rig the dual power lines,” he says. “It would take three to four weeks.”

Earlier, ESMD had purchased the Mainliner cured-in-place point repair system from LMK Enterprises Inc. in Ottawa, Ill. Messer wondered if it could replace the failed cookie. Cookies are wooden caps covering extra connections installed in original lines in anticipation of future development. Although still learning the technology, Messer’s crew sealed the troublesome connection and a previously unknown bad cookie in four hours.

Escalating expenses

Failed cookies are one of ESMD’s transmission system issues. The division does its own excavations down to 20 feet, but doesn’t use the spoil for backfill. “The sheer cost of hauling and disposing of the material, then backfilling with gravel to solve settling problems was crippling,” says Messer. “Repairing cookies was a low priority. We’d wait until blown or rotten cookies released dirt and large rocks into the mains before fixing them.” Excavating and capping connections could take up to one-and-a-half days.

The transmission towers run down a median strip separating the four lanes of North 41st Street. The 10-foot-deep sewer main lies directly below. Manholes, between the turn lanes, enabled the crew to keep traffic flowing, yet stay clear of it. “The city has a lot of issues with street repairs,” says Messer. “Management liked the idea that we could repair the cookie manhole to manhole instead of tearing up the roadbed.”

Besides the 28-foot turnkey trailer from LMK, Messer purchased a Yamaha Grizzly 350 ATV that pulls a trailer carrying the air compressor and liner installation equipment. “We’re hoping to buy the T-Liner system this year,” he says. “The larger liners are heavy and difficult to pull in, so we’ll use the ATV and avoid injuring someone’s back.”

Although LMK taught the men to enter manholes to position the inversion bladder, flexible launching device, hoses and cable in the pipe, Messer found that the division’s portable, expandable hydraulic manhole shoring jacks with rollers allowed the crew to do the same thing from above ground.

“Eliminating confined-space entries is a big safety issue, and it saves time and money,” says Messer. “The rollers enable us to pull our lines back and forth without chafing on the edge of the pipe.” The ATV transports the shoring jacks, too.

Kit perfect

Messer purchased LMK kits with 6-foot-long, 10-inch textile-lined tube and premeasured resin and catalyst. While part of the five-man crew cleaned the section of pipe with a Vactor truck, Bill and Mike Smith wet out the liner in the LMK trailer. They hooked a vacuum hose on one end of the tube, poured the resin into the other end, and slowly kneaded it forward. “Vacuum impregnation removes all the air and draws resin into every fiber to produce a dense, uniform, cured-in-place pipe,” says Messer.

Depending on ambient temper-ature, the resin cooks off in 90 minutes to two hours. Putting it into the on-board freezer extends the curing time. “Point repairs wet out quickly and go in easily,” says Messer.

The liner was packed into the inversion bladder, loaded onto the launching device, and centered in the pipe. A camera in front of the launching device allowed operator Steve Jackson to position it 3 feet from the connection. He then radioed Rose Ortiz to open the air valves. Pressure at 5 to 10 psi in-verted the liner/bladder assembly as it rolled through the pipe.

Once it was inflated, Ortiz adjusted the valves until 2 to 4 psi held the liner against the host pipe while the resin cured. After removing the inflation bladder, Jackson verified with the camera that everything went well. “What’s really nice about this system is that the resin fairs the edges of the liner so our jetting nozzles don’t catch on it,” says Messer. The ESMD crew now shoots 3-foot point repairs with confidence, no longer needing an additional 3 feet to compensate for inexperience.

Unending opportunities

Jackson spotted a bad cookie on a dead-end connection coming off a side street into the North 41st Street main, so the crew repaired it, too. They left the intersection four hours later. “This technology enables us to fix anything quickly and cheaply,” says Messer. “For example, we can do repairs deeper than 20 feet or under electrical vaults now. We save another $20,000 to $30,000 per job by not having to pull the vault.”

The city also has old, cracked terra cotta mains. Instead of chasing the crumbling line to find a solid section, ESMD blows in a liner at the excavation and connects the replacement pipe to it.

“We’re always looking for opportunities to use the liner system,” says Messer. “Compared with excavation, it has reduced our repair costs by 25 to 50 percent, and repairs are up to four times faster. Just the North 41st Street job paid for the LMK trailer. That’s a great advertisement to present to management.”



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