Construction Without Disruption: Installing Fiber Optic Cables Underground

Published On
Jul 16, 2018

Recently, the Fiber Optic Association (FOA) has worked with and, at times, even trained city planners and traffic engineers. After talking to people responsible for municipal networks, it’s clear why they are so harried. They are being bombarded by demand for new services, some immediate like the proliferation of video surveillance cameras, smart traffic signals, small cells for cellular wireless service and sometimes fiber to the home. Some of the pressure is also long term—or just hype—such as automated vehicles and the ubiquitous internet of things.

But the demand for fiber under the street is real. Everybody I have met has projects going on now or planned for the near future, and everyone has similar problems. Budgets, of course, are the biggest issue, and training personnel is near the top of the list as well. When the FOA talks about updating or installing fiber, we find these people are really interested in new techniques for construction that minimize the disruption of typical underground utility construction.

The fiber optic industry and its suppliers have not ignored the nature of their concerns. Today’s projects are no longer limited to bringing in the backhoe and digging up the streets. New techniques have made projects easier and prevented the need to endlessly repeat work for upgrades.

The first thing we ask these people is if they have spare conduit space. The least disruptive way to install fiber is with no construction at all. If they have spare ducts or conduits, installation can be simple, fast and not disruptive. But, many times, their conduit is already filled up. Sometimes, that’s not a reason to look into reuse of existing conduits.

New techniques have been developed to add cables to conduits that would normally be considered full. In the past, it was common to have a 4-inch conduit with three to four plastic innerducts, each of which had one cable. Pulling additional cables into a duct was considered potentially harmful to the existing cable. Cables no longer in use can obviously be removed and make space for new cables, but that’s a rare occurrence.

However, several new techniques make expanding capacity of conduits possible. One is to add microducts for blown cable to a conduit. Microducts are so small, sometimes they can be pulled into conduit along with the existing innerducts. Ducts only about a ½-inch in diameter will accommodate 144- or 288-fiber microcable. Another option is fabric innerduct. They take up practically no space and can sometimes be installed without disturbing existing innerducts.

If needed, there is a possibility of removing the existing innerducts without removing the cable inside them. A machine grabs the innerduct, splits it and pulls it out, leaving the cable in place. As this machine pulls the existing duct out, it pulls in fabric ducts, making it possible to pull several cables in.

Another method being used involves unused CATV coaxial cable, the type called “hardline.” The technique is to attach a machine that pressurizes the cable and fills it with lubricant, then grabs the center conductor and pulls the conductor and the insulation out of the cable. The remaining part of the cable is a hollow tube into which a new fiber optic cable can be blown or pushed.

Sometimes, none of these techniques work, so some construction is necessary. First, it’s important to understand the “dig once” concept. This is something I learned 20 years ago from personal experience in the suburbs of Boston, watching a road I used daily be torn up several times by different contractors installing fiber optic cable for different service providers. The Massachusetts Turnpike figured out the solution. The next company wanting to run fiber along the Turnpike had to install about 10 ducts when they opened a trench, guaranteeing future installs would not necessitate construction.

“Dig once” is now a U.S. policy; whenever you do underground construction, you should install many ducts for fiber. Doing that is easy, especially with microcables and micro–ducts; although, if a large trench is open, installing full-size conduits and ducts is possible.

Another technique that can work well in cities is directional boring, especially when crossing roads, driveways, sidewalks and even creeks. The biggest problem with directional boring seems to be running into buried utilities. In Nashville, Tenn., a contractor punctured seven water mains in one year. Knowing how to locate buried utilities is very important with boring. See my column from last month, “What Lies Below."

About the Author

Jim Hayes

Fiber Optics Columnist and Contributing Editor

Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at

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