Sliplining a Brick Stormwater Tunnel

Portland levels up against challenging stormwater tunnel rehab project

Sliplining a Brick Stormwater Tunnel

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There are large-diameter pipeline projects in which huge and heavy sections of pipe are wrestled and fitted into place. Then there are confined-space, close-tolerance pipe-laying projects where exactness and precision are paramount
engineering concerns. 

The Portland Bureau of Environmental Services simultaneously undertook both. The Oregon city’s extraordinary $11 million rehab project in 2020 was a test of engineering imagination, administrative expertise and the cooperative spirit of municipal and private sector organizations.

“It was a toughy,” says BES construction manager Don Poletski. “The pipe fought us every step of the way.”

“All the way” constituted about 4,000 feet through a 100-plus-year-old brick tunnel that was less than an inch larger in places than the sliplined pipe, contained several challenging curves and was under a
constant flood watch.

The good news: Despite an onslaught of expected and unforeseen challenges, the undertaking was completed on schedule, under cost and without loss of life. Three years later, the rehabbed segment of the city’s stormwater system is functioning “exceptionally well. We knew if we could get it in there that it would perform really well,” Poletski says of the liner pipe. “And it has.”

Getting lucky

It’s called the Taggart Outfall and is a 6-mile-long section of stormwater pipe constructed of brick 115 years ago in a southeast section of Portland. The area was undeveloped in 1908 when construction crews tunneled through it, loosening soil with dynamite and hauling it away with horse-drawn carts. In places, the tunnel resembled a mining shaft a hundred feet deep with an air shaft running down to it to make it breathable.

In this underground space, the original construction crew methodically laid three concentric circles of brick against a wood form, working in groundwater that infiltrated the tunnel constantly. This is verdant Oregon, after all, in a city that annually receives 36 inches of rain.  

The subterranean storm sewer meandered with the topography and, as it approached its terminus with the Willamette River, almost doubled in size to nearly 10 feet in diameter. The 4,000-foot section most urgently needing repair was in this larger-diameter portion of the pipe. 

“A hundred years is a long time,” Poletski notes. “The pipe had heavily deteriorated. It was safe enough to put workers inside it, but it was near the end of its service life.”

Planning to rehabilitate the pipe began in 2014 when the city selected a design consultant, Jacobs Engineering. Over the next half dozen years, engineering work on the project was split about 50-50 with the bureau’s in-house engineering staff.

Fourteen different methods of repairing the pipe were considered by the team. Because the area above the sewer had fully developed in the intervening century — populated with 18,000 homes and 1,500 industrial properties — open trenching was out of the question. One possible solution — bolting together short sections of curved steel plating inside the brick sewer — was possible, but not a popular option.

“Nobody wanted to do that,” Poletski says. “It was a 20th-century solution and had we chosen that method, we would still be there bolting plates together.” Furthermore, the thick steel plating would have reduced the diameter of the sewer, lowering the flow capacity of a line already running full at times.

Then the project team had some luck. A commercial property that straddled a segment of the pipe and had been scheduled for development unexpectedly became available. “We were able to use it after all and it totally changed the picture,” Poletski says.

This good fortune let the engineers pursue a first-choice method of repair: sliplining the brick pipe with short sections of fiberglass-reinforced pipe inserted through a hole opened on the property. The low-bid contractor, James W. Fowler Co., acquired a lease on the land and went to work. Removing some 40 feet of soil above the pipe, the contractor exposed the three-ply brick sewer and sawed open the top of it.

A sliplined pipe, of course, raised the same concerns among engineers as bolted steel plating — that is, a reduced flow in the sewer. For 18 months, the issue was researched using flow monitors and computer modeling, a period Poletski recalls with evident exasperation.

Finally, it was determined that, though the diameter of the pipe would be less, the interior surface of the fiberglass-reinforced pipe was slicker than that of the brick face of the old sewer. Consequently, the flow rate would be slightly increased, offsetting the lessened capacity. Reassured, engineers pressed on.

Slow process

With the old sewer ready to receive the new pipe, things got interesting. The issue was tightness. A $200,000 laser scan of the sewer had determined how long a section of fiberglass-reinforced pipe could be maneuvered through the old brickwork. The answer was an 8-foot-long pipe with an outside diameter of about 108 inches. 

To test this premise, a wood mock-up of the pipe was constructed, assembled inside the old brick sewer and winched through the sewer. “Pinch points” were painstakingly navigated, including the curves. The biggest issue was a 270-foot section where brickwork had been reinforced using the aforementioned bolted-together curved steel plating. The internal strengthening was required when an industrial building was constructed in 1959 on the property above the sewer.

Clearance of the mock-up through this steel section was less than an inch. It required the grinding down of the heads of some bolts to allow passage, yet it did pass through, giving a final green light to engineers. In due course, a full week was spent moving the first fiberglass-reinforced pipe section through the narrowed area.

How to move the pipe sections through the old sewer then became the problem. The contractor had planned to use a modified telehandler. However, even an expert equipment operator could find it daunting to maneuver a three-ton, eight-foot-long section of pipe through a tunnel just a few inches larger in diameter without periodically ramming the leading edge of the pipe into the brickwork. 

The solution? A locomotive. Specifically, Fowler suggested using a battery-powered mining locomotive that would run unerringly on two-inch tubular steel tracks bolted and grouted into the bottom of the brick sewer. A lidar scan determined exact placement of the tracks to keep the locomotive and sections of pipe centered and away from surrounding brick walls. A month was required just laying the track.

The locomotive solution was especially appealing because this process of transporting pipe sections would have to be replicated 300 times — that’s how many individual sections were to be installed. “The locomotive gave us a solution that was repeatable,” says Poletski. 

A battery-powered locomotive, instead of diesel-powered, was necessary because of the confined space in which it would be operating.

Insertion of the fiberglass-reinforced pipe began apace, with crews working 24/7. It was a slow process. Poletski says 14 sections of pipe were the most installed in any one day. The curves in the line required shorter sections of pipe — the shortest being 3 feet in length — and with different bevels on inside and outside edges. “It was a tremendous challenge fitting the pipes together,” Poletski recalls. Ends of pipe were seated securely using a jacking system.

Every 100 feet, grout was inserted between the outside of the sliplined pipe and the old brick sewer, effectively bonding the two structures for extra stability. “If you put too much pressure in the grouting, you collapse the inner pipe,” says the construction manager, another ticklish dimension of the project. It never happened. The tracks, incidentally, were buried in grout. They had been laid with spaces under them so the grout could penetrate the whole area. 

Coming together

Completed three years ago, the project continues to be satisfying for everyone involved with it, including the 46-year-old Poletski, who has worked at the bureau for 15 years. He expresses a lot of confidence in the fiberglass-reinforced pipe the team installed. “It has been around a long time and is a very robust and highly engineered pipe. I’ve put tens of thousands of feet of it under the city.”

The Taggart Outfall project experience was made more intense for everyone by the arrival of COVID just as actual construction began. The immediate impact was limitations on gatherings by engineering staff and some virtual management of team members. The pandemic also sequestered many residents in their homes, which led to more construction noise complaints than usual. Generally, however, Portland residents were supportive of what they came to understand was not a typical utility project.

The construction manager, who was a consulting engineer before joining the city staff, is currently overseeing other sewer repair work in the city, including a $25 million rehab project under a stretch of Interstate 5. Though 99% of Portland’s sewer and wastewater maintenance is performed in-house, any big or deep work on the system is contracted out.

Of all the challenges that had to be overcome in the Taggart project, the most satisfying to Poletski was surprising. “The most impressive accomplishment was the teamwork we all developed. We all wanted the best solution given the constraints. We believed in each other. When you have a team that has bought in, everything is solvable.

“It was really, really important to come up with the best technical solution, one that would give the best service life and so on. We accomplished that despite an incredible amount of adversity. The pandemic. A massive log fire at one point when air quality was bad. We succeeded through teamwork, trust and talent, the three Ts. It’s said you can’t have all that in a low-bid environment. We proved that you can.”


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