Fort Drum in Jefferson County, N.Y., is home to the U.S. Army’s 10th Mountain Division and, with a population of nearly 13,000 on 107,265 acres, is one of the most active military bases in the country. Like any municipality, Fort Drum deals with infrastructure challenges caused by population growth and aging facilities, and also has to contend with winter temperatures as low as -30°F (-34°C). But unlike most municipalities, Fort Drum roadways, culverts and bridges also have to contend with heavy military equipment—tanks are common sights at Fort Drum, as are mine-resistant ambush protected vehicles (MRAPs), which weigh between 14 and 18 tons each.
In July 2016, all these factors came together when a 56-ft-wide, road-supporting culvert needed rehabilitation. The culvert, laid in a trout stream, consisted of four 142-by-91-in. corrugated metal pipe (CMP) arches laid parallel to one another with a separation of 3 ft between each barrel and only 3 ft of cover over the barrel crowns.
“This was a very good example of what I call a ‘buried bridge’,” said Norman (Ed) Kampbell, P.E., president of Rehabilitation Resources Solutions. “With relatively little cover, the CMP barrels really had to do a lot of structural work, so any rehabilitation technique used had to be structural itself, which, along with the big diameters of these culverts, ruled out cured-in-place pipe (CIPP) and most of the other techniques usually used in culvert rehabilitation.”
This was especially true given the military loading classification that applied—the existing buried bridge structure was classified for wheeled traffic of 41 tons for one-direction traffic and 27 tons for two-direction traffic; for tracked vehicles, it was classified as 37 tons and 25 tons, respectively.
Two other complications applied: The buried bridge is set in the Black River, a recognized trout stream, and the military roadway needed to stay open. So the structure could not simply be torn out and replaced, and river diversions had to be limited and carefully managed.
Kampbell has been working with both manufacturers and suppliers of various rehabilitation solutions for many years, developing rehabilitation approaches for challenging situations like this.
“Here in Fort Drum, it really seemed like CentriPipe, a solution from AP/M Permaform, would be perfect,” he said. “CentriPipe is a centrifugally cast concrete pipe (CCCP) technology that uses a spin-caster to apply thin layers of concrete to pipe interiors. The spin-caster is great in itself because it casts a very smooth and even pipe. And the material used, PL-8000, was just what this project needed—completely structural, and it adheres well to most surfaces, including CMP.”
The Right Concrete
PL-8000 is a fine aggregate composite concrete (FACC) distributed by AP/M Permaform and used with the CentriPipe process, and in other situations where very high strength is needed along with good adherence. It relies on precisely graded quartz sands, non-metallic fibers and other complex admixtures to achieve a unique blend of strength and other desirable properties that make it suitable for horizontal pipe and sewer rehabilitation.
“The sophistication of this fine aggregate concrete should not be taken lightly by the design engineering community,” Kampbell said. “And it’s not just its strength characteristics, which dramatically exceed those of most concrete products. Low permeability, good freeze/thaw characteristics, the right thixotropy and thin shell toughness—AP/M Permaform has really got all these right with PL-8000, and that makes it a great choice for culverts and buried bridges like this one.”
Arold Construction Co.—based in Kingston, N.Y.—has been in the paving and construction business since 1973, when Gary Arold started the firm as a 17-year old. Arold Construction is the region’s licensed CentriPipe contractor.
“We’ve been doing CentriPipe projects since 2011, mostly municipal and some for [the New York State Department of Transportation (NYSDOT)], and I think we’re at the point where it’s recognized that this really is the right technology for many large-diameter culvert and sewer rehabilitations,” said Arold Construction Vice President Ryan Arold. “We’re excited to be taking on more and bigger projects.”
Some of those projects are very long culvert rehabilitations for NYSDOT, including an October 2015 rehabilitation of a 9-by-14-ft-diameter culvert with a total length of 500 ft. Still, the Fort Drum buried bridge rehabilitation was a challenge.
“This was four big pipes, side by side,” said Arold Operating Superintendent Nathan Baldwin. “And because the Black River is a trout stream, we had to be careful about dewatering and diverting the stream, and the project also called for a fish ladder to be installed.”
To handle diversion efficiently and safely, Arold decided to work on two culverts at a time—water was diverted from two of the arched CMP culverts, and these two were completely rehabilitated before the process was repeated with the final two. Diversion was accomplished with cofferdams and bypass pumping, and diverted water was filtered through large bio-bags before being reintroduced to the river. Dewatering also required some CMP repair before lining began.
“The pipes weren’t exactly failing, but some of the CMP was rotting out,” Baldwin said. “That meant water was coming up through the bottom of the pipes, and also leaking out of the headwall in places.”
To stop active water flow before doing CentriPipe work, Arold filled voids with pea gravel and PL-8000, poured some new invert sections (the CentriPipe spin-caster is sled-mounted and needs a smooth invert for even withdrawing) and patched some headwall areas. Pipe interiors were scoured, and the remains of a thick rubber layer were chipped off to ensure a smooth finish. That completed all preparation, except that most mornings “snake and turtle patrol” was needed before work started.
“Some of the snapping turtles could be 3 or 4 ft across their backs,” Baldwin said.
Actual rehabilitation work began with some spraying and troweling of PL-8000 into the lower “corners” of the arched CMP.
“The spin-caster works best with a smooth invert,” Baldwin said. “So we did some filling before inserting the spin-caster—that helped us spray even concrete layers and monitor thickness.”
Arold Construction uses a five-man crew for CentriPipe work, and one of its more interesting jobs is manning the CentriPipe sled.
“Yes, there is a man on the actual sled, and he’s an important part of the work,” Baldwin said. “He has a radio, and the rest of the crew has microphones mounted so we can hear his directions—he observes the casting and tells us to slow down or speed up as needed. This keeps the layers even.”
Working from a staging area adjacent to the buried bridge, PL-8000 was mixed on site for pumping to the spin-caster. On each culvert, a total of nine passes were needed, spraying thin layers to accumulate a total thickness of a little more than 2 in. over the corrugations. As a testament to PL-8000’s strength characteristics, this thickness was enough to meet the military loading requirements. Consistent layer thickness was assured three ways: visual inspection during application, the use of simple depth gauges prior to curing and monitoring the amount of PL-8000 bags used per pass (which provides the total volume of material used per pass). The finished and cured pipes were smoothly finished, and look very much like brand-new circular pipes.
Total time on site for rehabilitation of all four pipes plus the installation of a fish ladder (also made with PL-8000) was a month and a half.
“It’s true that a lot of features made this rehabilitation an unusual challenge,” Arold said. “But really, this is just the kind of project CentriPipe is made for, and once we got down to the actual application of PL-8000, it all went quickly. We’re very happy to have worked with Fort Drum on this, and also happy this outstanding rehabilitation technique is available in New York.”