Making SFO Safer: Graniterock Completes Installation of Engineered Materials Arrestor System (EMAS)

Posted by Rose Ann Woolpert on Mar 18, 2015

For three months this summer, the pounding of compactors, shrill of back up alarms and reverberation of rollers and excavation equipment competed with the roar of jets taking off and landing at San Francisco International Airport. Graniterock Team Members and joint venture partner DeSilva Gates Construction were busy installing new Engineered Materials Arrestor System (EMAS) safety devices on two of the airport’s four major runways.

Although air travel is the safest mode of transportation available today, commercial aircraft runway overruns during takeoff or landing remain a safety concern. The FAA calls for 1,000-foot-long runway safety areas, but airports surrounded by highways, waterways or buildings simply do not have the room to meet this requirement. Two of the main runways at SFO are bordered by Highway 101 and the San Francisco Bay, with not enough space to meet the FAA rule.  The EMAS system, intended to stop aircraft that have overshot a runway, is now required by the FAA when there is insufficient area for a standard safety runway space.

EMAS involves placement of lightweight, crushable concrete blocks in a very specific grid pattern. The four-foot cubes are made of a specially designed concrete aggregate infused with a foaming agent, which creates air bubbles to give the cubes a low density and allows them to collapse on impact. The number of air bubbles can be adjusted to create different strengths depending on whether an airport caters to larger or smaller aircraft. Individually numbered blocks are set into place, scanners on each block verify the correct location, special emulsions are applied, and the blocks are finished with a coating that is taped in place. 

EMAS is similar in concept to a runaway truck ramp - the aircraft is slowed by the loss of energy required to crush the EMAS material. As a plane hits the cubes, they break apart and friction between the cubes and the plane’s wheels ultimately slows the plane to a stop. The system can safely stop a Boeing 737 traveling at 65 miles per hour in fewer than 300 feet. Ground crews placed 22,532 collapsible cubes in the SFO system, which was paid for through federal grants and airport revenue bonds. Tolerances for the FAA are very tight and base material compaction, an extremely level grade and accurate block placement require a high level of professionalism and proficiency.

When the project began mid-May, up to 300 people were on the job shutting down run-ways, constructing safety fences, setting up plants and equipment, demolishing and grinding old runways, stockpiling materials, and readying the site for this major reconstruction. Two runways were closed, which pushed all of SFO’s air traffic to the two remaining runways. “They don’t shut down these runways very often,” said Graniterock’s Dave Olivas, “so now is the time to get everything done at once.” With reduced runway availability, alternate scheduling was required at airports around the country, but Team Members worked around the clock to finish the job. Under budget and a month ahead of schedule, the runways and the new Runway Safety Areas were open for business at 12 Noon on Sunday, August 10, 2014.

For more information on how EMAS works, please see this video clip:

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