Cured-in-place pipe Technique Renews Wastewater Lateral While Sparing Landmark Bridge

The motherhouse of the Dominican Sisters of Peace was becoming a frequent stop for The Waterworks, a residential and industrial plumbing firm based in Columbus, Ohio. At about 100 years old, the wastewater lateral from the motherhouse to the street was well past its life expectancy. Continued treatments for backups due to root intrusion in the lateral’s widening joints were becoming too much for the antiquated pipe to bear.

Scott Steiner, project coordinator for The Waterworks, said crews used a jet vac and tractor cam to get a clear video of the problem area. Upon seeing it, he said, “We recommended it was time to look into a long-term solution to this problem. They agreed.”

The Waterworks proposed rehabilitating the lateral with cured-in-place-pipe (CIPP) technique, which would create a durable, impervious pipe with improved flow. They could make the repair in a single shift at a fraction of the cost of open-cut replacement.

They consulted Mike Moore of Source One Environmental. Headquartered in Davison, Mich., Source One is HammerHead Trenchless Equipment’s authorized distributor of HydraLiner CIPP tools and consumables.
No Trenching

Open-cut replacement had been ruled out for a number of reasons, including the need to preserve a historic deck-arch bridge. Most of the 135-ft long manhole-to-manhole run of original line was 8-in. diameter vitrified clay pipe. But one section was a 50-ft length of 8-in. cast iron that ran through the foundations of the bridge’s century-old stonework at each side of the creek. To cross the creek at continuous grade, the iron pipe had been suspended from brackets attached to the bridge’s underside.

Trenching would not only damage the lawns and gardens of the motherhouse’s property, but it would require partial demolition of the bridge, irreparably degrading its status as a perfectly preserved artifact of the institution’s past. The bridge’s deck supports the only two-way access to the motherhouse. That meant demolition would also reroute all traffic to a one-way drive past the Dominican’s retirement center, the site’s only other access.

“Early estimates to repair the damaged area by closing and trenching the road, partially dismantle the bridge, replace the damaged pipe and then put everything back together were well into six figures,” Steiner said. “And the work would have taken several months. The project was a great candidate for pipe lining through the CIPP technique.”

Equipment & Consumables

HammerHead provided a Super Hydra Inversion Drum, electric wet out table and lining trailer for the installation, as well as a water boiler. Both the drum and boiler were mounted in pickup truck beds, providing ease of transport and good on-site mobility. “The setup of that large inversion machine is spot on — easy to move around, user friendly, and holds up to 330 ft of 8-in. felt for mainline work. For this job it was just perfect,” said Jim Mathews, The Waterworks vice president of operations.

The CIPP consumables consisted of HammerHead HH felt liner, extended cure resin and extended cure hardener.
HammerHead CIPP specialist Cory Steckmann explained the product choices: “Every job and every jobsite can be different, so liner and resin combinations offer different choices. This job provided good access at both ends, running from one manhole to another, so they chose HH Liner, which can withstand pressure even while unsupported outside the pipe. That way they didn’t need a calibration tube.”

Calibration tubes are flexible sleeves cut to length and closed off at one end before inverting them inside an installed liner. The calibration tube is then inflated to mate the liner to the existing pipe and is maintained at a specified pressure while it cures. Cure times vary. When the CIPP has fully set, the calibration tube is deflated and removed, leaving the new pipe ready for use.

In this application, however, the liner itself was simply tied off at one end after it was installed. Pressure during the cure was maintained with the force of hot water instead of a calibration tube. Thermal-setting resins have a shorter cure time, which was activated in this application by the water’s heat.

Site Prep

Mathews said success in this application depended on thorough preparation. “We really did our homework prior to the job, making sure we knew what that system involved. We didn’t rush it, even though it could be seen as an urgent project, since there’s a stream right there we wanted to protect.”

Installers arrived on the site at 8 a.m. Wastewater from the lateral was bypassed to a pumper truck at the run’s upstream manhole. The motherhouse adjusted workflow of its onsite laundry and food service to minimize effluence during the installation. Service continued throughout the installation, however, with minimal disruption to the facility’s normal routines.

The line was cleaned with high-pressure jetting before sending the tractor cam in to inspect it for any changes that would pose a problem and to document the condition of the existing pipe immediately prior to rehabilitation.

Wet Out

To begin the wet out process, the crew laid the lining out onto the ground and cut it to length. They mixed the epoxy resin’s components to the manufacturer’s specified ratio for this job. Then, the crew carefully impregnated the liner with the resin, working it from one end to the other with the electric press on the wet out table, ensuring consistently optimum saturation of each felt fiber.

Use of an extended resin formula gave the crew up to four hours of open working time, since the run was so long. Should an unexpected difficulty arise that required a longer installation window, the delay would not impact the quality of the installation.

Inversion

The impregnated lining was sent inside the existing pipe in a CIPP “inversion process.” The crew first wound the liner, fresh from wet out, onto the Hydra Drum spool. They sealed the drum, fastening the free end of the felt to the inversion collar through the drum nozzle.

When the drum was pressurized with air from a trailer-mounted compressor, it forced the resin-impregnated felt to push out through the nozzle, turning itself resin-side out as it entered the lateral, inverting itself outward until it reached the opposite opening. Inversion began just before 11 a.m., taking only 30 minutes to complete.

Thermally Activated Curing

The far end of the liner was tied off. The crew now filled the liner with water heated to 176 F. Hydraulic pressure inside the pipe forced the lining firmly against the sides of the pipe, holding it there throughout the cure. The HH liner held its shape even under pressure to bridge past fractures and joints, eliminating deformities. To monitor pressure, the installation crew set the inversion drum regulator and opened the air intake. Pressure from the combination of water and compressed air could be read directly from the inversion drum’s gauges.

The resin being used for this project requires thermal assistance to properly cure. Minimum temperature for activation is 130 F. Maintaining water temperature at 176 F throughout the curing process shortened the cure time. Once activated, the resin’s cure time as calculated for this project’s combination of products and jobsite conditions was just two-and-a-half hours.

Once cured, the closed end of the liner was cut off and water was drained from the pipe. The tractor cam was used again to inspect the installation, providing video documentation of the rehabilitated pipe.

The liner had been installed directly into the existing lateral without and cuts or excavation. Service was restored simply by removing the bypass pump truck and an inflatable 8-in. plug from the line. No restoration work was required.

The new 8-in. CIPP rehabilitation has added at least 50 years to the lateral’s service life and ended any need to deal with root intrusion and backups until at least 2064.

Joe Bradfield is senior writer for Ellenbecker Communications, an international communications firm specializing in the drilling, mining, and construction.