What's Underground

A new 9,000-foot runway at the Hartsfield-Jackson Atlanta International Airport in Atlanta was officially commissioned in May. This runway, said to be one of the most complex structures of its kind in the world, spans a major interstate highway and includes an 18.5 million cubic yard embankment. Here, FAA and airport officials share some insights learned along the way when it comes to putting in underground systems that can be easily traced.

Hartsfield-Jackson Atlanta is the world’s busiest passenger airport, serving more than 89 million passengers in 2005 alone. Delays at Hartsfield-Jackson can create a ripple effect across the continent and hamper airport efficiency all across the nation. Consequently, the new runway has been called the most important runway in North America.

The Southeast Region office of the Federal Aviation Administration (FAA) is responsible for installing and maintaining flight-related airport facilities for this expansion, including navigational aids, instrument landing and approach lighting systems, and the buried cables required for these functions. As new cables were buried adjacent to the new runway, approximately 1,000 discrete locations were electronically marked as a safety measure and to facilitate future maintenance.

According to FAA Project Engineer Brian Murphy, the traditional means of identifying the location of buried airport facilities has been to place 2’x2’x6” concrete markers flush with the ground, immediately above marked features. These heavy markers cost about $100 each, and require painting as well as ongoing attention to remove grass clippings and repair soil erosion. They can be easily displaced by mowing equipment, which can compromise facility records and excavation accuracy.

The traditional means of tracing buried airport facilities involves the use of locating equipment which senses an electromagnetic field created when an applied signal current flows through the buried conductive elements to a distant ground point. Murphy notes that this process is effective for tracing isolated metallic cables, but delivers ambiguous results where there is underground congestion — the technology cannot positively identify multiple adjacent buried facilities.

“We determined that a better method was required for marking and locating underground cable routes, and eventually we adopted buried markers because they are safe from surface threats, require no maintenance, and provide very precise locating,” said Murphy.

“We initially used passive markers, which indicate location only, but have settled on active identification markers that can be programmed with specific information about the location when they are placed, and then read later from the surface using an electronic locating device. Unlike traditional locating, buried markers allow the locator to easily distinguish between adjacent facilities and make it possible for crews to excavate safely even under crowded underground conditions.”

Underground Guidelines

Underground utility markers conform to a national utility color code and interrogation frequency standards for each utility type so that excavators can identify both the location and the nature of buried facilities. FAA is placing red markers for facility power cables and black/orange markers for fiber optic and other communication cables at the Atlanta location.

FAA engineers selected the 3M™ Dynatel™ 2200MiD Series Locating and Marking System for the Atlanta airport project. This marking system uses 4-inch round ball markers, each of which has a unique, preset, and remotely readable ID number. An electronic circuit in the ball is programmed with custom information, which can then be located and read remotely. Murphy explains that FAA has developed a series of scripts for ball marker programming that includes details such as the nature of the buried facility (cable type, number of conductors or fibers, etc.) and the exact depth below grade. FAA has established 30 such identifying scripts, covering every combination of details for their buried facilities at the airport. Program and placement details for each marker are archived in the locator device as they are programmed, and these records are downloaded electronically at the end of a shift for archiving.