The nearly 100-year-old pipe serving Monroe, Mich., drinking-water customers aren't at the end of their service life, but by last year tuberculation was causing leaks and breaks and degrading water quality.
It was time for an overhaul. The Monroe Engineering Department is lining 2.5 miles of 8-inch cast-iron pipe and installing 230 service connections using cured-in-place pipe technology. The department contracted with St. Louis-based Insituform Technologies USA Inc. to perform the work using the company's “Blue” products — Thermopipe and iTAP.
“We decided to go with the lining method because the pipe's still good; it just needed to be cleaned out and shored up,” says Engineering Director Patrick Lewis. “Second, there aren't a lot of leads along the line. This method provides minimal disruption to the area's traffic, so that alone results in at least a 20% cost savings — and even more in densly developed areas where open cut becomes more costly.”
Thermopipe is a reinforced polyethylene liner for pipe up to 12 inches in diameter. Supplied in a factory-folded “C” shape, it's winched into the host pipe from a reel and reverted with air and steam. Once inflated and heated, the liner forms a close fit within the host pipe, creating a jointless, leak-free structural lining that independently carries the full system's internal design pressure. It's expected to extend the life of the city's water infrastructure by 50 years.
More than 14,000 linear feet of water main are being lined. Along the pipeline, the main is being accessed from 120 to 140 times, wherever there's a hydrant, tee in the line, or valve.
Even though the main is only 5 to 8 feet deep, making multiple excavations in a busy area raises unique challenges. Crews need to access the host pipe for cleaning, lining, and post-rehabilitation inspection, so multiple pits — as many as 21 at once — must be dug. Some are cut directly into the middle of busy roads, requiring lane closures and other traffic redirects.
Each pit is dug with a rubber-track Komatsu PC78US compact excavator. The trench shoring for the pits is also installed with smaller equipment.
Rachel Excavating, the subcontractor responsible for all excavations, shoring, and plumbing on the project, is using the modular Build-A-Box aluminum trench shielding system made by Efficiency Production Inc. of Mason, Mich. It can be assembled into two-, three-, and four-sided configurations, plus three-way tee configurations. Custom-accessorized barrier posts integrate seamlessly into the corner posts of each unit to keep crew members from falling in.
Where the water main is accessed, the pits are kept relatively tight. Crews connect 2-foot-tall aluminum panels and 8-foot-tall corner posts to create a 5x10-foot, four-sided trench shield. The panels are secured in the corner posts with a series of pins and keepers.
“There've been places where we've needed to add depth, so we've simply added another panel to the top of the box, and in some places we've needed to leave out a panel near the bottom to get around a cross utility,” says Scott Weaver, foreman with Rachel Excavating.
After installing and reverting the liner, service connections are renewed using the robotic iTAP system that enables an operator to remotely locate and cut through the liner at each service opening. The robotic unit then taps each corporation valve. As a final step, a sealing nut and gasket are installed in each threaded corporation valve to create a watertight seal.
The pipe lining is part of a larger, $2.5 million water main restoration that began in October and is expected to be completed in early July.
— James McRay (email@example.com)