What It Takes (Geostructurally) to Extend the Plane Train Tunnel Under the World's Busiest Airport-Technical Paper Upload

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Hartsfield-Jackson Atlanta International Airport extended its underground Plane Train tunnel about 600 feet west to reduce train wait times by approximately 13 seconds. The work required tunneling beneath the domestic terminal, where 19 column footings were close to the planned alignment and, in places, had less than seven feet of clearance above the excavation.<br /><br />Keller North America designed and installed temporary underpinning, dewatering, and excavation-support systems as part of a progressive design-build team. Forty-eight micropiles, installed in low-headroom conditions, supported steel beams and grillage that transferred terminal column loads away from the tunnel excavation. After tunneling and initial support were complete, most loads were returned to the original footings and the temporary frames removed. One column received a new footing and another a permanent micropile-supported pile cap.<br /><br />The tunnel crossed variable ground, including fill, residual soil, partially weathered rock, and competent gneiss. A dewatering system of parallel well rows lowered groundwater through a challenging mixed-face section; a minority of wells supplied most of the extraction. Dewatering enabled tunneling without ground-instability incidents. Braced soldier-pile systems supported the tunnel breakthrough and the separate cut-and-cover egress and ventilation structures.<br /><br />Automated instrumentation provided real-time monitoring of micropile strain and construction effects. The work also demanded close coordination around airport utilities and critical systems, restricted access, stringent micropile installation tolerances, and pandemic-related supply constraints. Despite these challenges, the underpinning was completed in about four months, faster than initially anticipated, after the airport permitted longer daytime work shifts. The project demonstrates how coordinated geotechnical systems can enable underground construction beneath an operating airport while protecting existing structures and maintaining airport operations.

Keywords

Hartsfield-Jackson Atlanta International Airport

Plane Train tunnel extension

underpinning

micropiles

dewatering

excavation support

soldier-pile system

geotechnical engineering

tunnel construction

airport operations