Contractors Weave PHX Sky Train Construction Through Active Airport
More than 40 million passengers fly in and out of Sky Harbor International Airport in Phoenix every year. City officials couldn't risk stifling this sizable economic engine during construction of a much-needed passenger train project.
To stay out of the way of planes, PHX Sky Train's guideway design takes it 90 ft over an active taxiway—billed by airport officials as a worldwide first—and then dips underneath two more taxiways before rising up to pass over a passenger concourse.
To build it, construction crews have to keep a low profile, too. "The priority is operating the airport," says James Kyle Kotchou, special projects administrator at the City of Phoenix Aviation Dept. for the $1.5-billion project. "Sometimes that's hard, but we've laid that out early on before construction started, and it's disseminated down to the subs so the bids include it."
Multiple Phases
The project, designed by Gannett Fleming, Phoenix, is being completed in three phases. The many contractors, engineers and subcontractors involved hold frequent coordination meetings and keep lines of communication open to aid with the many hand-offs between project components.
Phase 1, totaling $644 million, connects Terminal 4 to Phoenix's light rail with 1.7 miles of elevated guideway. Construction included a maintenance facility built by Phoenix-based Weitz Co.; three train stations and concrete superstructure for the guideway built by Hensel Phelps Construction Co., Phoenix; and guideway fit-out by Weitz under a contract with Montreal-based automated train supplier Bombardier.
Phase 1 construction was completed earlier this year, and systems testing began last month to prep for passengers in early 2013.
The $244-million Phase 1a began construction last year and will add 0.6 mile of guideway and a single station serving both Terminals 2 and 3. Although not initially planned to be constructed until 2020 along with a longer extension to the Rental Car Center, the airport was able to accelerate this portion through "higher-than-expected passenger levels in recent years combined with operating budget reductions," says Jay DeWitt, deputy aviation director for financial management.
The third phase to the rental car facility is still in the early planning stages, so exact costs aren't set.
The overall project is funded using airport bonds, which rely on various airport revenue sources. Along with maintaining a good credit rating to access favorable financing terms, DeWitt says a key financial strategy was the timing of the bond sale. "The airport established a commercial paper program with its banking partners to provide the short-term financing until the time was right to sell the long-term 30-year bonds," he says.
Phase 1a Extension
Built by a joint venture between the Tempe, Ariz., office of McCarthy Building Cos. and the Phoenix office of Kiewit Corp. under a construction manager at-risk contract, the Phase 1a extension will be supported by 55 caissons at depths of 60 to 125 ft. Crews will demolish several small buildings and perform extensive potholing to ensure the extensive site utilities and old foundations are accounted for, says Mason Williams, McCarthy-Kiewit JV deputy project manager.
Two existing taxiways need to be extended by 80 ft to allow the new guideway to pass underneath. Each taxiway will be demolished, excavated and rebuilt separately, each under a tight six-month time constraint to prevent any delays to air traffic and to ensure both aren't closed at any one time. In addition, the first taxiway needs to reopen by November before the second is begun so that both taxiways are open for the busy holiday travel season, Kotchou says.
"Once we get the substructure up with the two abutments, we will backfill and pour a waste slab to build the bridge extension on soffit dirt to accelerate the construction process, instead of doing the traditional method of digging the whole thing out and doing falsework," Williams says. Once the new structure is tied in with the existing taxiway, crews will excavate the temporary dirt to release the new bridge extension.
The new guideway will tie into an existing abutment from the first phase, to continue a 6% grade descent to about 30 ft below taxiway level, parallel to an existing roadway. Once past the taxiways, the guideway rises 40 ft above grade to pass over the passenger concourse. Since the terminal is open 24 hours, construction of the track over the gate connector can only occur in brief three-hour windows each night.
High Security
The entire new length of track runs parallel to an active runway and taxiway, so timing and sequencing of work is essential. "The closure of a taxiway or any interruption to airport operations requires a higher level of communication beyond just scheduling the work—it must also be integrated with ongoing airside operations," says Dennis Tucker, McCarthy vice president.
Every construction worker has to submit to a background check before being issued an ID badge, and is bussed in each day to specific security checkpoint gates to access the jobsite. If there's an emergency, they can't call 911—the airport has its own rescue station. Fortunately, the job has had zero incidents or recordables to date, says Joseph Brunsman, McCarthy-Kiewit project manager. The project will see 300 to 350 workers on site at peak.
The airport allowed the taxiway S construction zone to temporarily become 'land-side', meaning outside of the high security area. "it's a more efficient way to construct at an airport, saving time and most likely money," Kotchou says. A perimeter fence approved by FAA security was erected around the entire taxiway construction zone.
The City of Phoenix mandates LEED certification when the project opens in early 2015. Sustainable efforts include the use of certified wood products, separating trash and the use of building materials incorporating recycled content. These efforts, along with recycling concrete and asphalt from the demolition as fill, has helped the team reach the cusp of LEED-Gold, Brunsman says. The site is situated on an old river bed, so excavated cobble is also being crushed on site for reuse as fill.
