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A Special Foundation Approach

A geostructural solution to this challenging redevelopment project.

The PPL Center in Allentown, PA, consists of a 7-story hotel, multi-level office buildings, two parking garages, and a state-of-the-art arena to house the Phantoms, an American Hockey League affiliate of the Philadelphia Flyers. Built as a redevelopment project in the central business district, it sits on the site of the Corporate Plaza Building, which was severely damaged by sinkholes shortly after it was built in 1994.

A special foundation approach was required in this vulnerable location. A joint effort between Martin/Martin, Inc., Force Drilling, and Nucor Skyline utilized a threaded bar micropile foundation to allow for the building and structural loads to be transferred to more competent rock formations deep underground. The initial timetable was very tight, however, the difficult sub-surface ground conditions caused numerous design changes which required Nucor Skyline to supply threaded bars within a 24 to 48 hour timeframe.

David Borger from Nucor Skyline noted that “Force Drilling installed over 1,700 micropiles in some very challenging karst ground conditions in an area prone to sink holes.” These micropiles were drilled to depths ranging from 25-ft to over 225-ft and varied in size from 5 ½” to 9 ⅝”. The steel casing was reinforced with a full length #18, #20, or #24 Grade 75 Nucor Skyline threaded bar.

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