Not many runway designs incorporate a tunnel, or move millions of cubic yards of fill dirt to the site on a conveyor belt.
The fifth runway taking shape at Hartsfield-Jackson Atlanta International Airport boasts each of those characteristics.
The project is part of a 10-year, $5.4-billion expansion of airport facilities and infrastructure on the 3,650 acres (1,518 ha) of airport property.
The 80 million air travelers who pass through Atlanta each year are getting some fancy new facilities. But construction of the runway is something of an engineering story all by itself.
The landing and takeoff pavement will extend for 9,000 ft. (2,730 m), with an additional 3,000 ft. (910 m) of taxi and turnaround area. This being metropolitan Atlanta, a stretch of unbroken, unimpeded land that long is not easily cobbled together.
Perhaps it is not surprising then that Runway 10-28 will cross over 10 traffic lanes of Interstate 285, with two-thirds of the pavement on the west side and the rest across the way.
What links the two legs of the runway is a $159-million bridge that is just shy of 500 ft. (152 m) long and 1,200 ft. (3,640 meters) wide, one of the largest such structures in the world. Motorists passing beneath it will feel like they are in a tunnel and, as a matter of fact, they will be. Any highway bridge longer than 1,000 ft. (303 m) is officially designated NFPA 502 standard for road tunnels, bridges and other limited-access highways.
Most aircraft landing on the east side of I-285 will touch down before they cross the bridged segment of the runway. However, some smaller aircraft are expected to make first contact atop the bridge itself.
About 200 ft. (61 m) away, all taxiing planes will cross I-285 on a parallel 450-ft. (137 m) wide taxiway bridge also being constructed by Archer Western Contractors Ltd.
The company’s Atlanta office won the contract for this design-build job and David Casey is program manager. He is shepherding the project toward completion in 2006. As April arrived and a “rough winter” was behind him, Casey said the job was approximately 30 percent complete.
Decking of the two bridges will cross the interstate on the backs of precast concrete beams –– approximately 750 of them. Each beam is 82 in. (208 cm) tall and up to 130 ft. (39 me) long. They are precast to 8,000 to 10,000 psi concrete specifications, Casey noted.
The high-strength beams will rest on cast-in-place concrete walls more than 3 ft. (91 cm) thick. Allied RMC of Atlanta has a concrete batch plant operating on site.
Pumps supplied by Pioneer Concrete Pumping out of Smyrna, GA, are filling the wall forms until more than 100,000 cu. yds. (76,000 cu m) of concrete form a rigid structure. Bridge decking will consume another 37,000 cu. yds. (28,100 cu m).
The integrity of supporting structures is an even greater concern than usual in this project because tolerances are so tiny and expectations so high.
The bridge will be expected to withstand a load of up to 606,271 tons (550,000 t). That specified load level, not coincidentally, is slightly more than the weight of wide-bodied airliners like the Boeing 747 and new Airbus A380.
Add to their weight all the stresses that these hurtling airliners bring to bear as they roughly reunite with Mother Earth and the need for the runway’s massive undergirding is clear.
The height of the runway bridge might especially impress drivers passing under it. The interstate climbs gently at that point, so the rise of the level bridge above the traffic lanes will range from 30 ft. (9 m) on up to 70 ft. (21 m).
Because the taxiway structure is narrower, it might be the more impressive sight to highway travelers. Airliners moving slowly across it will be more visible to them.
Both structures are designed to accommodate an eight-lane widening of the interstate.
Casey said he will use Manitowoc models 888 and 2250 cranes to lift the beams in place when the walls are ready to support them. Piles were driven and forms were hoisted for the support wall in the center using Sumitomo Link-Belt LS138 and 238 cranes; Grove 760 units also were involved.
The bridge surfaces must seamlessly join with adjacent runway and taxiway segments. Because the elevation for the runway is considerably higher than the embankment on either side of I-285, fill dirt is being hauled in to elevate the abutting segments.
In fact, about 1 million cu. yds. (760,000 cu m) of fill are being transported. This presents another challenge, Casey noted: The fill dirt must not settle. If the earth is less stable than the bridge, the earth-bound runway can sag, with potentially catastrophic consequences for landing jetliners.
Archer Western is contractually obligated to prevent such slippage. To that end, Casey employed a Liebherr crane with a 40-ton (36 t) ball and compacted the first 470 ft. (148 m) of dirt off each end of the bridges.
The plummeting weight squeezed down the earth approximately 2 ft. (61 cm) to a density considered stable for at least 20 years.
To bring the bridge project home on schedule, Casey has up to 200 people working two-shift days.
The other major contractor on site will have up to 300 people working this summer. 5R Contractors is moving approximately 27 million cu. yds. (20.5 million cu m) of earth to the path of the eventual runway.
5R is an Atlanta consortium comprised of C.W. Matthews Contracting Co., APAC-Georgia and Thrasher Trucking Co. After the combined company won the $350-million earthmoving contract, it began moving dirt in earnest in December 2002.
The work has gone well. Project Manager and Vice President Roy H. Jump said in early April that his crews are running several months ahead of schedule.
Some of the speed of the project might be credited to the innovative way the dirt is being moved: It is riding a belt seven eighth of an inch (2 cm) thick to the site from borrow pits 5 mi. (8 kg) away.
“We couldn’t do it by conventional methods,” Jump said of his company’s unusual conveyor system.
5R engineers first figured the job using trucks, perhaps as many as 150 of them. It then re-figured the task using the conveyor belt system designed especially for the site.
Result: The unconventional and enclosed conveyor belt was projected to complete the job two and a half to three years sooner and with much less disruption to traffic.
Said Jump, “It has worked out the way it worked out on paper.”
The fill loaded onto the front of the conveyor is overburden stripped from commercial quarries and contiguous property. The borrow site is separated from the airport property by three major roadways, including I-285.
The nine-section conveyor assembly –– the longest section being approximately 8,000 ft. (2,427 m) –– moves the dirt 3 mi. (4.8 km) on belts that are 72 in. (153 cm) wide and the remainder of the distance on belts 48 in. (122 cm) wide. The speed of the transfer is approximately 800 ft. (243 m) a minute.
Jump said the top transfer rate is approximately 8,000 tons (7,200 t) an hour, but the system averages 6,000 tons (5,400 t) an hour, hour after hour. Crews handle all that dirt in 16-hour shifts.
Powering the system are series of electric motors that, combined, generate the equivalent of 20,000 hp (14,908 kW), Jump said.
To scrape up and spread all this earth, the company turned to an Atlanta Caterpillar dealer, Yancey Brothers Co. Yancey supplies and largely maintains the fleet under the terms of a unique contract.
Consequently, Caterpillar equipment is everywhere. Moving the earth at various points in the conveyor-loading and unloading process are D8 and D9 dozers, Cat 773 trucks, No. 16 graders and Cat 345 and 5110 backhoes.
The mounded earth is shaken down and compressed by Cat 825 rollers and 563 vibrating rollers. Cat 769 water trucks with a capacity of 9,000 gal. (34,200 L) suppress the dust kicked up by the rest of the equipment.
The belt actually delivers dirt into four 100-ton (90 t) hoppers spaced along the future runway. Driven under the hoppers are 100-ton (90 t) Cat 777 trucks, which are loaded at the rate of approximately one a minute. This figures out to 6,000 tons (5,400 m) an hour.
All these millions of cubic yards of dumped and spread dirt are necessary because the rolling topography of the property must be evened out. The elevation established by the Federal Aviation Administration has meant slight cuts in some rises and deep fills at other points.
Some of the fill points are 100 ft. (30 m) deep, Jump said. The average fill is approximately half that.
Contracts for eventual pavement of the runway have not been put out for bidding.