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This approximate $500 million expansion of Concourse A/B Corridor will service Southwest Airlines (SWA) at BWI Airport and offers passenger amenities and hold rooms, and creates a new baggage basement and apron level operations area, extending the terminal toward the airfield and widening the facility some 500 feet, and completely retrofitting the existing structure for this State of the Art design.


Several unique geotechnical aspects were addressed for creative and efficient design recommendations. The Baggage Handling System (BHS) will be constructed about 15 feet below grade which requires substantial underpinning and bracing of the existing A/B Terminal and surrounding aprons and infrastructure during construction. The new Concourse and BHS will result in a realignment of the existing gates, passenger boarding bridges (PBBs), jet fuel lines, and the existing vehicle services road (VSR).

Balter, as Geotechnical Engineer of Record, provided geotechnical engineering, subsurface explorations and materials laboratory testing services for this BWI project. With close coordination among the designers, MAA, and Southwest Airlines, Balter established and provided a field investigation program distributed throughout the project limits with borings extending to depths of 100 feet in and around active gates.

A unique geologic condition was encountered and confirmed through classifications and laboratory testing. Subsurface soils sampled exhibited fine to medium-grained “clean” sands in a loose condition. The combination of these soils, shallow ground water levels, and the proposed elevation of the baggage basement resulted in a concern for liquefaction. To further evaluate this potential, Balter implemented a supplemental field program consisting of CPT tests, seismic CPT tests, and MASW geophysical testing. These supplemental methods permitted a continuous profiling of the subsurface conditions which confirmed the presence of liquefiable soils; but in much thinner layers than the borings were able to identify. This additional data was used in the final liquefaction analysis with results indicating an acceptable factor of safety against liquefaction.

Balter performed extensive geotechnical evaluations considering various structural load parameters, the field data, and the laboratory test results (performed in our highly accredited laboratory) to develop geotechnical recommendations for the project. Multiple foundation options were considered, including shallow, mat, and deep foundations. The presence of the loose, clean, saturated sands led to foundation design challenges that eliminated standard shallow foundations from consideration. As the design progressed, a mat foundation was selected for support of the BHS. Outside of the BHS, all new foundations will be supported on caissons.  Significant lateral load analyses using multiple iterations of load combinations have been performed, and Balter is also providing continual evaluations of the proposed caissons for the new PBBs. Balter continues with participation related to the geotechnical aspects.

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