On Final At SeaTac

Story by Carl Molesworth | September 28, 2010

As a massive concrete paving machine inches its way along a 1.6-mile-long strip of real estate at Seattle-Tacoma International Airport, Port of Seattle officials are entering final approach on their long journey to add a third runway for the Northwest's biggest airport.

What a long, sometimes strange, trip it's been.

SeaTac's new runway will run parallel to the existing runways on the west side of the airport. It will help reduce flight delays at the airport by giving SeaTac the capability of operating at full capacity in nearly every type of weather. The total cost of the runway is estimated at $1.2 billion, making it the most expensive public works project ever undertaken at SeaTac.

Construction of the third runway at SeaTac has been two decades in the making. Transportation planners recognized the limitations on bad-weather operations imposed by SeaTac's current two runways as long ago as the 1980s. Because the existing runways are only 800 feet apart, FAA regulations limit the airport to operating only one runway for both incoming and outgoing aircraft when visibility is limited. That's a big deal, considering the airport served about 29 million travelers last year.

After a thorough investigation of possible alternatives to expanding SeaTac came up empty, the Port of Seattle filed an Environmental Impact Statement for building the Third Runway in February 1996. Permitting and legal wrangling with neighboring communities consumed more time, and work on the preliminary phase of construction began in 1997.

In 2002, contractors for the port began the first of several projects that ultimately would consume 13 million cubic yards of earth to fill a slope on the north end of the airport. Three giant retaining walls, the tallest 130 feet high, were built to hold the dirt in place (see PB&E, Nov. 7, 2005). It wasn't until the middle of 2004, however, that the port won final approval to construct the runway.

More Than A Runway

ICON Materials, with headquarters in Kent, Wash., won the job to pave the runway with a bid of $79.8 million in January 2007. Ironically, the paving project constitutes just 6 percent of the total cost that the Port of Seattle is spending to build the runway.

The centerpiece of the project is, of course, the runway. It measures 8,500 feet long by 150 feet wide and is 17 inches thick. Eight concrete taxiways, each 100 feet wide, will connect it to the rest of the airport, said Bruce Harjehausen, construction manager for ICON Materials.

"It's not complicated at all," Harjehausen said in jest. "Just get the concrete down, grade the shoulders and land the plane."

Actually, there is a lot more to the project than simply paving a big strip of concrete. It also involves installing 70,000 linear feet of duct banks and 25,000 linear feet to 30,000 linear feet of storm sewer and water lines, plus extending the safety area by 40,000 square feet for the airport's existing 16C runway (which will become SeaTac's center runway in the new configuration) by placing about 1 million tons of fill at the north end of the airport. In addition, the runway and taxiway shoulders will be paved with 35,000 tons of asphalt, 1,500 runway and taxiway lights will be installed in fixtures cast into the concrete, and 500,000 square yards of airport property will be seeded.

Work began early this year when mass excavation subcontractor SCI Infrastructure did the cut for the runway. ICON followed, starting late March, with 320,000 cubic yards of cut and fill work to shape the infields between the taxiways. ICON also is doing earthwork, grading, crushed rock, and asphalt paving, plus trenching and backfill for the duct banks, Harjehausen said.

Meanwhile, work on the Runway 16C extension got under way. ICON is supplying fill and topsoil from its site in nearby Auburn, Wash., running 75 trucks in a 24-hour operation. To ease their impact on the busy roadways around the airport, ICON is running 45 trucks at night and just 30 during the daytime, Harjehausen said. The fill area will be held in place by a 60-foot-high MSE wall supplied by Reinforced Earth Co., he added.

In addition, subcontractor Harbor Pacific Contractors Inc., Woodinville, Wash., is building a 12,000-square-foot lighting vault on the far side of the runway that will serve the entire airport.

Batch Plant On-Site

Gary Merlino Construction, the Seattle-based runway and taxiway paving subcontractor, set up a mobile batch plant at the north end of the airport to produce the 133,000 cubic yards of concrete needed for the project. With the plant no farther than 1.6 miles from the site of the paving, it has been no problem to deliver concrete in open dump trucks. The concrete mix includes fly ash, port officials have reported.

Concrete paving began with the taxiways on July 19, and then moved on to the runway itself on Aug. 6, starting on the south end. Harjehausen said the Merlino crew is able to pave three or four days a week, depending on the cure times.

The preparations for paving included rolling the subgrade to 100-percent compaction and then placing an 8-inch layer of crushed rock, which was hauled from Washington Rock Quarries Inc. in Graham, Wash., Harjehausen said. ICON used three graders and eight rollers for this work, he added.

Merlino Construction is using a Gomaco GHP2800 slipform paver for the project. Because the dowel bar cages and light cans are prepositioned ahead of the paver, Merlino is feeding concrete to it with two Gomaco 9500s placed on either side of the section to be paved. Trucks deliver concrete to the hoppers of the 9500s, and their conveyers dump the material in front of the GHP2800 as the three machines move in unison.

A crew from Arizona-based T.L. Smith follows after the concrete takes its initial set to saw cut it into 20-foot-by-20-foot panels for the expansion joints. Merlino Construction also is using a Gomaco TC 600 surfacer to create a rough texture on the runway.

Likely starting in January, a crew from Pennsylvania-based Cardinal Grooving will spend 12 working days cutting runoff slots in the runway that will allow rain water to dissipate. The slots, measuring 1/4-inch wide and 1/4-inch deep and placed 1-1/2 inches apart, will run perpendicularly across the runways. After that, Apply-A-Line Inc., Pacific, Wash., will stripe the runway.

Harjehausen said ICON expects the runway paving to be completed early this fall. Then another year of work will remain to tie the new runway into the existing airport facility.

"This is different and interesting," Harjehausen said of the project. "But basically it's earthwork, grading and paving when it comes right down to it. It's just that the scope is huge."

Port of Seattle officials expect the new runway, designated Runway 16R, to open in November 2008.