PHX Sky Train Phase 1—The Interaction of Structural and Geotechnical Design Considerations

The PHX Sky Train project is a key linkage in the City of Phoenix, Arizona, Department of Aviation’s multimodal facility which integrates Phoenix Sky Harbor Airport with the City’s eastern transit (Valley Metro) hub. This local project consists of a series of different bridge types, built to support the operation of the airport’s new transit system, as it stretches from the multi-modal center and 44th St. to the Phoenix Sky Harbor Airport Terminals 3 and 4. These include: (1) steel girder superstructures, (2) cast-in-place post-tensioned, (3) a precast, pre-stressed post-tensioned, pedestrian bridge along with (4) a signature cast-in-place structure spanning an airport taxiway. Along with these differing bridge types, came complex geotechnical requirements and in-situ conditions. The design of the large diameter drilled shafts supporting the elevated guideway was complicated by space constraints, due to the elevated guideway alignment being situated adjacent to existing buildings, retaining walls, a baggage cart tunnel, and between an existing retaining wall and an existing high-pressure jet fuel line, all of which had to remain in service during construction. The foundation system supports relatively high axial loads, lateral loads and moments due to the height of the guideway above the ground surface, where it needs to pass over existing concourse walkways, bridges, a taxiway and buildings. The extreme design requirements, together with difficult ground conditions at the site, resulted in several challenges in the design of the deep foundation system. Built under the construction manager-at-risk (CMAR) contract structure, the project was built in multiple phases to accommodate the schedule of the METRO opening in winter 2008. Its design was a puzzle of a series of separate contracts that required tight coordination between multiple designers and stakeholders. Multiple system and design coordination meetings were held by the designers in conjunction with the client (City of Phoenix, Department of Aviation) and the selected contractor. Attendees will take away both technical and managerial lessons-learned from this complex transportation project. Complex environmental demands required a series of innovative design solutions. Moreover, the tight, multi-phase schedule and CM@R design paradigm presented many management challenges which will be discussed.