September 2024 Vol. 79 No. 9
Features
From routine to novel: HDD installation in Waukesha pipeline project
(UI) — Among several different contracts for the Waukesha, Wisc., 36-mile pipeline and stations, one included 8.5 miles of water supply pipeline, with three horizontal directional drilling and eight tunnel crossings. Contractor Super Excavators sub-contracted the HDD work to ECI Contracting while Lithos Engineering/GEI Consultants provided engineering support.
One of the HDDs was 1,610-feet of 36-inch diameter high-density polyethylene (HDPE).
“It was fun being able to help the city and my hometown with a sustainable water source and return water back to Lake Michigan. But there was nothing particularly unusual about the HDD,” commented Matthew Olson, Lithos engineer. At least, that was the initial thinking.
That all changed early on, when an unlocated 48-inch sanitary sewer, unknown to the project team, was discovered directly in line with the bore path. Sanitary flow from the damaged sewer caused a nearby sinkhole. After setting up a bypass, repairing the sewer and backfilling the sinkhole, the team went back to the drawing board.
“We knew the crossing would have to be re-designed, deeper and longer to avoid the recently repaired sewer,” said Rob Hotz, general manager, ECI contracting.
This required additional geotechnical exploration to extend the borings sufficiently deep for the modified profile. Lithos recommended boring locations, depths and laboratory testing.
“The revised design was approximately 2,117 linear feet – 507 linear feet longer than the original – with 2,000-foot bend radii, and 10-degree entry/exit angles,” said Olson. “The re-design was also 45-feet deep to pipe crown, versus 26 feet in the original.”
The project now also faced an environmental challenge.
“When the drill was extended, it meant going through contaminated soils, where ductile iron pipe (DIP) would be required,” said Hotz.
If the contaminated soils were shallow, the HDD could have been installed with HDPE pipe and the DIP pipe installed via open cut through the contaminated zone. In this case, the contaminated zone was deep and would have required an expensive and time-consuming deep excavation extending approximately 470 feet or changing the HDD pipe to DIP for the entire length. And the HDPE product was already on site.
“In the end, changes are expensive,” said Olson. “We always have Plan ‘A’ with a reasonable contingency plan, but this was far beyond that.”
Unique solution
Now the project represented a prime example of all stakeholders (owner, contractor and their engineers) working together to innovate a reasonable solution to meet project goals and minimize change cost.
“The project team worked together in an efficient manner to keep the project moving, which has obvious cost advantages,” said Hotz.
The solution was novel: pull both types of pipe (HDPE and DIP) at the same time. But it would be restrained joint (RJ) DIP to enable the pipe to curve, acting like a chain.
“It was designed to include HDD engineering analysis for pulling back approximately 1,646 feet of HDPE pipe connected to approximately 477 feet of RJ-DIP,” said Olson.
The contracting team decided to devise a connection appurtenance to join the HDPE to RJ-DIP above ground and pull the entire pipe string in with the HDD rig. This combined HDPE/RJ-DIP pull would be a much more economical and environmentally friendly way to install the DIP where required.
The team also collaborated on the different components/fittings to transition from HDPE to RJ-DIP; none of them were “off-the-shelf” fittings.
And there were no hybrid pipe design standards to follow.
“We modified pull force and pipe stress calculations from standard approaches for the separate pipe types to estimate factors of safety on pull force and pipe stress – not just on the pipe but also the fittings,” explained Olson.
It was a novel engineering approach.
“To our understanding, this is the first occurrence of pulling a pipe string combined of HDPE and RJ-DIP in an HDD application,” said Hotz.
Novel construction
It was unique from the construction perspective, too.
“I have been involved in pipe pulls of HDPE and steel pipe, but never both pipe pulls at the same time,” said Mike Schibursky, ECI project manager.
While novel, no one hesitated.
“Everyone was eager to try something new,” he added. “We saw it as a great opportunity to prove what we could do.”
The contractor team also modified standard approaches to reduce risk pulling in this unique pipe string and employed several construction risk mitigation techniques.
A Prime Drilling PD 300/900 RP drill rig drill was set up on the west (left) side of the bore, which was also the lower elevation end of the alignment.
“We did this to reduce probability of inadvertent returns (IR) and so the rig would be in position for pullback after reaming of the borehole. Product pipe was lined up to the east/right,” Schibursky explained. “We set up a turbidity curtain in the Root River to capture any IR should it occur.”
Pipe was pulled in using water for ballast to reduce installation stresses.
ECI brough a variety of reamers for multiple soil conditions and fabricated eight different fittings.
“One of the most important risk-mitigation tactics was the steel sleeve constructed around the connection appurtenance to prevent any protrusions from grabbing or catching on the borehole wall,” he added.
Another example of great coordination and cooperation was road and lane closure for the pullback. “The city was fantastic in helping make the operation successful,” said Schibursky. “We were bringing pipe down the center of the roadway and were able to keep the flow of traffic and maintain access to businesses and residential areas.”
Construction started in April 2023 and took 62 days to complete.
FOR MORE INFORMATION
ECI Contracting, (888) 527-2294
Lithos Engineering/GEI Consultants, (303) 625-9502
Comments