Taggart Outfall Sewer Pipe was built in 1906 by hand with picks, axes, horses, and dynamite and now serves nearly 18,000 homes and 1,700 commercial properties in SE Portland. It is 114 years old and nearly at the end of its functional life. The design work on rehabilitation of this sewer tunnel started in 2014 with actual construction work starting in 2020.
Originally, the rehabilitation was designed with 15,000 metal tunnel liner plates that would need to be bolted together with about 200,000 bolts. With nearly 3,000 feet of tunnel to be rehabilitated, that would be very labor intensive project. In December 2019, James W. Fowler Co. (JWF) proposed a new rehabilitation method of slip-lining 108-inch fiberglass pipe, but the challenges were daunting:
There were 3 bends in the system. How can the pipe segments go through these bends?
How can the pipe segments be transported down the tunnel without damaging the old brick pipe and the fiberglass pipe?
There were areas as tight as 1-inch with existing Tunnel Liner Plate, is the clearance enough to clear the fiberglass pipe?
After carefully reviewing LIDAR data, JWF built a wood mock-up pipe made up of ten 34-inch wide sections which were lowered into the tunnel through a 36-inch manhole opening. Once inside the tunnel, the ten sections were assembled to be pulled approximately 1,800 feet through the three tunnel bends to test the theory the team designed. This provided the proof that the new fiberglass pipe could be installed with the tight tolerances.
JWF was able to negotiate and lease an are for the 20’ x 24’ x 25’ entry shaft on private property along the tunnel alignment to lower fiberglass pipe into the tunnel. Then, JWF installed a track system and the fiberglass pipe was pushed down the tunnel by an electric locomotive. The clearance around the fiberglass pipe was anywhere from 3 inches down to 1 inch at the tightest spot. It was challenging, especially at the beginning.
Since the pipe couldn’t be jacked from the shaft due to the bends in the alignment, the JWF team used their ingenuity to visualize a process using two joint testers with a hydraulic system to pull the pipe together. Some joints took more than 15 tons of pressure to “home” them. Customized joint testers were cost Prohibitive, so the team fabricated “Homer” at a fraction of the cost to help align the pipes together and also can “home” them with ease.
The team faced several challenges related to conditions that jeopardized the safety of the team. Any time that the weather forecast called for .04 inches of rain in a 24 hour period, the project had to be shut down because the pipes could flood. At one point during construction, an unknown chemical dump occurred in the tunnel. The project was shutdown until the air quality allowed staff back into the pipe.
Ultimately, the project was completed successfully with accolades from the City for our team’s effort. Over 37,500 worker hours were required to rehabilitate this segment of the tunnel. Two 25 person crews worked 24 hours a day, six days a week, while overcoming the challenges on COVID-19, flooding rains, and wildfire smoke, over the course of this past summer and into early fall to culminate with final completion at the end of October.