In most areas today, fiber optic cables are installed underground. Traditional underground cable construction involving digging trenches, installing conduits and then pulling fiber optic cables through the ducts is disruptive, however. New techniques have been developed that are less disruptive but may make location more complicated and future construction more hazardous.
DIRECTIONAL BORING
Directional boring has been used for many years to install cables underground in urban and suburban areas. Directional boring requires especially good documentation and location in cities where there may be a century’s worth of undocumented underground utilities.
Directional boring can cause major damage if the operator is not experienced and very careful. One fiber optic contractor punctured seven water mains, two in one week, in a southern city. In a northern city, a fiber optic contractor punctured a high-pressure gas line, leading to the destruction of several buildings nearby and causing several deaths.
But properly done, directional boring is effective and safe, like the contractor working down Santa Monica Blvd. in downtown Santa Monica, with a member of the crew working ahead to locate the boring tool and buried utilities (see photo A).
MICROTRENCHING
Microtrenching is gaining proponents for fiber optic installation in both urban and rural areas. Instead of digging a trench to bury fiber optic ducts, you grind or saw a groove typically 8-12 inches deep (20-30 cm) in a roadway or sidewalk and drop a cable or small duct – a microduct – into the groove. You fill in the groove with the dust vacuumed up when grinding the groove, mixed with an adhesive.
Properly done, microtrenching is almost invisible. One job site we visited cut the groove along the edge of the road at the sidewalk and even matched the color of the roadway asphalt.
At first, microtrenching was used to install traditional fiber optic cables. But cable companies and duct companies introduced smaller “microcables” and “microducts” with more fibers in smaller diameters. A regular 144-fiber cable was about 5/8th of an inch in diameter (16 mm), while a microcable is half that – about the size of a #2 pencil.
Into a groove cut with microtrenching, you can install a half-dozen microducts filled with microcables or one cable and five ducts for future installation. Microcables are also popular with directional boring installation.
Microtrenching can complicate location in several ways. Documentation on buried utilities may not indicate the type of underground installation or depth, but knowing the depth of the cable is important. Being close to the surface means that you must be careful at both ends for directional boring, of course, but it’s also important if someone else decides to do some microtrenching in the same area or just digs up the road surface for repair.
Another development in fiber optic technology can cause big headaches in a “dig-up.” Fiber optic cables have been developed for use in metropolitan areas and business parks that have 1728, 3456 and 6912 fibers in a cable around one-inch (25 mm) diameter. These cables were designed to provide the large number of fibers needed for projects like fiber to the home data centers and small cell wireless. If damaged, these cables are expensive to replace and can take weeks to splice for restoration.
Jim Hayes is a VDV writer and trainer and the president of The Fiber Optic Association. You can reach him at jim@thefoa.org.