KERNERSVILLE — The bright orange sign is usually greeted with dread from motorists: UTILITY WORK AHEAD.
It often means delays for people wanting to get to their destination. But such delays become much more meaningful when the broader context of the work is brought to mind.
“People don’t really understand or appreciate it until their sewer backs up or they don’t have water one day,” said Channin Bennett, project manager for HDR, a Winston-Salem engineering firm overseeing the replacement of about 5½ miles of aging sewer pipes in Kernersville.
“Generally people take it for granted, the availability of good infrastructure,” Bennett said.
The $3.2 million project in Kernersville involves several roads downtown, including such main thoroughfares as Mountain and Cherry streets. HDR and contractor KRG Utility Inc. are working to replace 29,795 linear feet of sewer pipes, many of which are 60 to 80 years old.
Recently, they were working in the area of Armfield and North Cherry streets.
The work involves a mix of old-fashioned human muscle, powerful equipment and computer technology.
“It all starts with data collection,” Bennett said.
That data is gathered by cleaning the inside of the sewer pipes and running a camera on wheels through them.
Engineers then scrutinize that footage, looking for defects in the pipes and scoring them according to their risk of failure.
However, Bennett said the main focus of the Kernersville project is not so much looking for defects. Much of the work going on is to increase the level of service — specifically, installing bigger pipes.
“We’re fixing a lot of pipes and in a small area, and that increases the overall effectiveness of that system to handle more wastewater efficiently,” Bennett said.
Along Armfield Street recently, workers replaced a 6-inch terra-cotta pipe with an 8-inch high-density polyethylene pipe. The original 230-foot-long pipe likely was put in place 60 years or more ago, workers said.
But they didn’t have to tear up the road by digging a trench the entire length of the pipe.
Instead, KRG used a technique called “pipe bursting,” which only requires a small trench to be cut.
The existing sewer pipe is cut inside that trench and workers muscle a fiberglass rod with a rope attached through the pipe, fishing it through until it reaches a manhole at the other end.
Then, in a process workers call “stringing the mole,” a steel winch line is attached to the rope, brought back to the trench and attached to a pneumatic bursting head, or mole, as workers call it.
The new high-density sewer pipe — 20-foot lengths that were heat-fused together to the length needed — is attached to the back end of the mole.
“It’s all welded together so it’s one continuous pipe,” Bennett said, “so we don’t have issues of joint separation or roots being able to get into a joint and open that joint up.”
The cone-shaped, steel mole is lifted into the trench at the opening of the pipe. Once it is lined up correctly, a winch pulls it through the old pipe, breaking it apart as it travels and laying down the new pipe in its wake.
“Because (the mole) is pneumatic, there’s air pressure that hits the head and it creates impact, and it helps to go through the pipe as it’s being pulled,” Bennett said. “It’s almost like a pneumatic hammer.”
Though the vibration is felt in the immediate roadway, it doesn’t affect the overlying pavement or surrounding buildings.
When the pipe-laying is complete, it is then tied into the manholes and any service lines.
Bennett said pipe bursting is a cost-effective way of replacing the pipes.
“It’s typically cheaper than if you had to dig up the entire pipe and replace it by one pipe at a time,” Bennett said.
It’s faster, too.
“They’re going to replace two lines in two days,” Bennett said. “Whereas if they had to completely dig up and replace the pipe, it would take them several days just to do one pipe.”
And that means less time, too, for those UTILITY WORK AHEAD signs to stay up.
Contact Kenwyn Caranna at 336-373-7082 and follow @kcaranna on Twitter.