Across the United States, cities are fighting the battle against deteriorating infrastructure. While the power grid often steals the headlines, the infrastructure carrying one of the most precious resources, potable water, is also in need of serious attention.

The city of Sioux Falls, South Dakota, experienced firsthand the issues with aging infrastructure when corrosion forced the replacement of an important segment of water transmission line. The city contracted with Siteworks Construction in Sioux Falls to provide a solution through trenchless pipe bursting.

“They’ve had a couple of water transmission main failures due to corrosion near a tower. Two corrosion-related breaks over a five-year period. And it led them to believe that there were bigger problems with them,” says Jason Wilson, Siteworks president. “We have pockets of acidic, corrosive soils here. Some parts of town don’t have a problem, but in other parts of town, it’s a big problem. One of the mains was ductile iron, the other cast iron. The cast iron was from the early ’60s and very brittle. Some of the issue is purely an age thing with the mains being 60-plus years old.

“The mains ran under 41st Street in southwestern Sioux Falls, which is all concrete pavement, 9-10 inches thick. It would be extremely expensive to dig up and replace. The city had no intention of replacing that. And that’s why they chose a trenchless method, pipe bursting, for the project. It’s a low-impact approach. An opencut job would have had a higher public impact.”

The project included bursting 2,000 feet of 16-inch cast iron main and 2,200 feet of 20-inch ductile iron main and replacing them with 16- and 20-inch fusible PVC from (Underground Solutions) respectively. Siteworks used a 1900G Grundoburst static pipe bursting system from TT Technologies to complete the work.

According to TT Technologies pipe bursting specialist Mark Dorn, the project was significant considering some of the host pipe material.

“Ductile iron is a difficult host pipe to work with. And this was some of the largest ductile iron pipe bursting in terms of pipe diameter and total feet that’s been done,” Dorn says. “It was definitely a challenging project, but Siteworks and specifically Jason had the experience to make it happen.”

That level of experience would prove invaluable for the project in Sioux Falls.

Bursting cast iron

The Siteworks crew started with the 16-inch cast iron main at the east end of the project and worked west. Before any bursting could begin, temporary water service needed to be established for several businesses and residential areas.

“We had to do temporary water services for a couple of strip malls, restaurants, a gas station and an apartment complex,” Wilson says. “So, there were 6-inch and 2-inch temporary services feeding all those buildings. We came off fire hydrants from a block away with a 6-inch Yellowmine pipe. We crossed one driveway and did a temporary asphalt patch across the driveway at an apartment complex.”

Dividing up the bursting runs and establishing entry and exit pits was, in large part, dictated by side streets or mainline valves and fire hydrants along the length of the 16-inch main.

“The bursting pit locations depended on the street layout and where your major tie-in points were,” Wilson says. “For the machine pit we used two 16-foot trench boxes. You need to make the new pipe entry pit long enough to accommodate the bend of the pipe to reach the depth of the existing pipe. We needed that length, 34 to 36 feet.”

Despite being limited by side streets and tie-in areas, the Siteworks crew completed the bursting runs. The city rerouted the flow of water in a few areas allowing for longer runs over 500 feet.

“Crews were very efficient at bursting the cast iron main,” Dorn says.

The Siteworks crew was able to complete the 16-inch portion of the project in the fall. The 20-inch fusible PVC pipe was delivered in winter but since temporary water services can’t be laid out in cold climates, bursting began in late spring after school was out of session. 

Bursting ductile iron

The entire project, almost a mile in length, took place along a five-lane road. Siteworks blocked off two lanes, creating a narrow work area. The city landfill was located just to the west of bursting operations, adding to the already high-traffic area.

Bursting the 20-inch ductile iron main required a similar approach, layout and configuration as the 16-inch cast iron main. But in order to reach the depth of the existing ductile water main with the 20-inch-diameter fusible PVC pipe, pits needed to be between 50 and 60 feet in length. The extra pit length was needed to accommodate the bend radius of the fusible PVC product pipe. Once the product pipe was accommodated, bursting the ductile iron host pipe presented its own set of challenges.

According to Dorn, static bursting is one of the few trenchless methods that can handle ductile iron host pipe.

“Static pipe bursting is able to burst ductile iron pipe for several reasons,” Dorn says. “First is flat-out pulling power. The right systems have the hydraulic pulling muscle to tackle these pipes.  However, that is just part of the equation. Specialized bursting heads along with wheeled cutting blades that are specifically designed for ductile iron pipe are needed to make bursting this pipe possible. The third component is knowledge. You must understand how the pipe reacts and can react in the bursting environment. Missing any of those pieces, bursting ductile iron pipe can be a frustrating experience, let alone costly.”

Wilson added, “There are so many unknowns and variables, and you don’t really know until you get started. If you’ve ever cut wet cardboard with a slightly dull box knife, the cardboard tears uncontrollably away from the blade versus dry cardboard that cuts cleanly, right where the blade goes. That’s kind of the concern with bursting ductile iron pipe. If the existing pipe has such low integrity, it’s not breaking where the cutter cuts it. It can telescope and fold up inside. And after you telescope two or three sections of pipe together, you can’t pull it anymore. You’ve got to go dig down and spend a day cutting off all these sections of pipe that have stacked up on each other.” 

With the bursting runs established and the knowledge of the potential issues they faced, the Siteworks crew took a measured approach to the first few bursts in case crews ran into anything unexpected.

“As it turns out, the pipe was conducive to bursting,” Wilson says. “The first couple runs we did, we were a little nervous with this larger-size pipe. I think our first one was only 180 feet, but it went really well. The next one was like 240 feet, and we also did a 380-foot burst. The first 95% of the pullback goes in in about 2 hours, but you still have another 2 hours of technical work to finish it up and get the last 20 feet into the pit. But everything came together.”

The experience of TT Technologies and Underground Solutions with their fusible PVC created a successful project. Additionally, Joe and Alex at Banner & Associates played a key role in designing this first-of-its-kind project in Sioux Falls. 

“The final key element is the open-minded engineering staff at the city of Sioux Falls,” Wilson says. “Nick Borns is very progressive at new technologies and methods to effectively serve the growing city and its taxpayers.”