Rex Hospital Parking Garage
The construction of a four-level parking deck structure at Rex Hospital was one phase of extensive new construction, joined by a new patient tower and a new diagnostics and testing center. The completed parking deck features 446 parking spaces, with a portion of the structure below ground level.
Auger-cast in-place piles (ACIPs) were recommended initially for foundation support, but the project’s geotechnical engineer, S&ME, suggested that a Geopier solution could be a more cost effective alternative to ACIPs . When Skanska priced out the Rammed Aggregate Pier® (RAP) elements they ended up being the most cost-effective solution for support of the proposed structure.
Column loads in the parking structure exceeded 2,000 kips with a foundation design that included large, closely spaced footings with significant overlap of stresses between adjacent foundation elements. The heavy loads, large footing dimensions, and overlapping stresses pushed the depth of influence for settlement control, requiring relatively long RAP elements for adequate support. RAP design lengths of up to 44 feet below ground surface were required in order to provide adequate settlement control. Traditional Geopier GP3® elements are typically limited to depths of up to 26 feet, and therefore would not be a feasible option.
GeoStructures, Inc., opted for a design based on the use of Geopier X1™ elements, which can be installed up to 55 feet deep and for piers up to 36 inches in diameter. GeoConstructors, Inc. installed 275 Geopier X1 elements at the site, measuring 30 inches in diameter and between 8 and 32 feet in length. Although the parking garage was to have a lower level, the X1™ elements were all installed at ground level, with 8 to 10 foot overburden drilling to accommodate the lower level, resulting in total drill depths of 16 to 42 feet. By installing the piers from one level, Skanska was able to eliminate remobilization to the site for ground improvement and reduce the overall construction schedule. The parking deck was constructed with traditional spread footing foundations placed directly over the installed RAP elements. The Geopier X1 system was enabled deeper and higher capacity piers to be installed rapidly and in one mobilization helping Skanska save time and money on the project.