The Eastern Iowa Airport serves nearly one-million passengers annually for the city of Cedar Rapids and the surrounding region. For 2012, renovations were planned within the terminal and baggage screening areas. This phase of construction included the installation of three new interior columns within the lower level baggage screening area to support new loads from the terminal renovations above. A deep foundation system was proposed to support the design service load of 30 kips per column. There was no soil information available to assist with the design of the deep foundation, and it was determined that an adequate (deep) geotechnical investigation could not be conducted within the functioning mid-sized airport.
There were many challenges to consider with installing deep foundations within the baggage screening area. The installation would be completed in tight spaces, limited access required smaller installation equipment, the installation equipment could not emit exhaust fumes within the building, and the work could not disrupt daily operations of the airport. The presence of private utilities within the work area also demanded that the foundation installation proceed slowly and cautiously. All that said, the tight construction schedule still only allowed two days for the installation of the deep foundations.
Helical piles were selected as the ideal deep foundation solution for this project. Each column would be supported by three helical piles cast into a three-foot square concrete pile cap. Nine (9) Model 287 (2.875-inch OD by 0.203-inch wall) hollow round shaft helical piles with an 8”-10” double-helix lead section were selected to support the design working load of 10 kips per pile. Handheld hydraulic equipment, with power source outside the building, was used to install the helical piles to at least 2,300 ft-lb of torque to correlate to ultimate pile capacities of at least 20 kips (FOS ≥ 2). The piles were installed to depths of 12 to 17 feet. The three piles within each cap were installed at a slight batter away from each other to allow the tops of the piles to fit within the pile cap and also allow adequate pile separation at the helix plate bearing depths. New construction brackets were bolted to the tops of the helical piles. The nine helical piles were installed in one day.
Architect: Miller Dunwiddie Architecture, Inc.
Structural Engineer: Foth Infrastructure and Environment, LLC
Certified Pile Installer: MidAmerica Basement Systems
Products Installed: (9) Foundation Supportworks® Model 287 Helical Piles, 8"-10" Lead Section, Installed to Depths of 12 to 17 feet, Design Working Load of 10 kips