Safety, environmental pressures
Part of the mile-long installation was under high-tension electrical transmission wires.
Thanks to Maine's tough bedrock, some blasting was required.
Finally, the last half of the installation occurred in an area identified by the Maine Department of Inland Fisheries and Wildlife and state EPA as an inland wading waterfowl habitat, which limited construction to between Aug. 1 and Oct. 15. The travel corridor for reaching the area to install the new pipe in depths to 22 feet was only 30 feet wide.
“We went with the ADS pipe because we could set it in place simply with our backhoes and wouldn't need cranes,” says Ken Grondin of R. J. Grondin & Sons Inc., which was awarded the installation contract. “Plus, there were logistic issues.
“If we used concrete pipe that comes just in 8-foot lengths, we'd have had nearly 200 truckloads to coordinate to the holding site and then have to move again piece by piece to the trench. That's a lot of extra handling and traffic control. There were essentially three times fewer trucks required with the 20-foot lengths of the ADS pipe.”
Another benefit of choosing the pipe was that ADS had recently acquired the Inserta Tee line of fittings, which can be used to connect corrugated, solid wall, profile wall, and concrete pipe regardless of manufacturer to provide a watertight lateral service connection for wastewater and stormwater systems. About 200 feet of the ADS pipe in diameters ranging from 24 to 48 inches was used for laterals that were connected to the main trunk using Inserta Tee fittings and fabricated fittings.
“What I like about the pipe as well as the company is that ADS was open-minded and provided a good product and good service,” Grondin says. “They offered us options to make the pipe at the length we required and T-bases.
“So, for instance, in the shallower areas where we needed to use smaller equipment under the power lines, we used 16-foot lengths with a smaller backhoe and smaller trench box. But in the more accessible areas where we could use a larger backhoe for a wider and longer trench, we went back to the standard 20-foot lengths. Then when we got into the deeper areas, we asked for some more 16-foot lengths even though we were using the big backhoes and didn't have any overhead hazards.
“ADS did a wonderful job on fabricating the fittings. They went through pain-staking efforts to make sure we got what we needed, such as special tees and bells; and everything was made very accurately and fit perfectly.”
Manholes made from the same material as the pipe also helped the contractor meet deadline.
The original design called for concrete structures. But instead of heavy, 8-foot precast concrete manholes that would've been cumbersome to move, each of the 21 manholes were individually designed for H-20 load rating and fill heights at the ADS factory. Once in place on the jobsite, each T-base was encapsulated in concrete with a field-placed steel reinforcing cage.
“We saw the benefit of making them out of the SaniTite pipe instead of concrete and worked with the city to gain approval,” says Robbie Chadwick of E.J. Prescott Inc., which provided logistics and system design support for the project. “In the past you'd have the pipe from ADS, then the concrete structures from another company, etc. Instead, this is a turnkey operation. We live here, so we want what's best for our community. This interceptor will probably last for more than 100 years.”
The T-bases made the contractor's job easier as well.
“They were ideal because essentially you plug them in and at the end of every night you can open up the line installed that day and go home, not worry about flows or your bypass pump as opposed to a precast concrete structure,” Grondin says. “We did have four precast concrete manholes on the job for various reasons. But for those you end up having a space underneath the inlet and outlet of the manhole that requires a brick channel. You have to get back in there and do that brickwork.
“The T-base is superior in 90% of applications because it's a plug-and-go solution with no brickwork. They're lighter, so you can use smaller equipment to set them. The concrete would've required a crane, and we were working under high-voltage power transmission lines. It was just safer all around.”
Gorrill-Palmer Consulting Engineers Inc. monitored construction and provided continuity between the engineering design firm, the city, and the contractor.
“We kept track of quantities, payments to the contractor, and were also the go-between for Grondin & Sons and Woodard & Curran,” says Paul Ostrowski, PE. “If the contractor had a question I'd try to answer it first. But if it was too technical, I'd go back to Woodard & Curran. Our goal was to simplify and keep the project moving because we had a tight timeline.”
In fact, the contractor brought in another crew as the construction deadline loomed to split the park segment of the installation in half: one crew started upstream, the other downstream, and they met in the middle.
“It was pretty much a perfect fit,” Ostrowski says. “They hit it right on grade. The Grondin crew had to be a little creative in making the connection because it was a tight fit. They picked up both pipe sections, let them touch, and then lowered both into place. They used a steel band coupler and did a concrete collar around it.
“The ADS pipe definitely increased productivity. Once, they put in about 320 feet in one day.”
To backfill the trench most of the material used was existing native soil. Crushed stone was laid as a bed for the pipe and about 1 foot of cover directly over the top the pipe.Post-installation assessment: positive
A Mandrel test was performed several months after installation to determine to what degree, if any, the pipe had deflected.
Grondin & Sons pulled the mandrel through the pipe using ropes, hauling it from manhole to manhole without any issues. The pipe, which had been buried in depths ranging from 8 to more than 20 feet, maintained shape regardless of the depth.
—Cooper (firstname.lastname@example.org) is a freelance writer based in New York City.