The reversible lanes viaduct project on the Tampa Crosstown Expressway,was planned to allow heavy, rush hour traffic to more efficiently move within the busy east-west corridor of Tampa.  The elegant design of this 5-mile long elevated structure called for concrete box segmental structural units supported on relatively slim mono-piers.  Each of the piers was supported on single drilled shaft foundations.  The entire project included 218 piers (up to 60 feet high), each supported on 6-foot to 8-foot diameter drilled shafts installed as deep as 105 feet below ground.

 On April 13, 2004, during construction, one of the piers (No. 97) plunged 11 feet causing a collapse of the two sections of the structure.  Measurements taken shortly after the collapse indicated that at least one additional pier had experienced settlement (although much less than Pier No. 97).  Ardaman & Associates, Inc. was brought onto the project by the owner to evaluate the potential causes of the collapse and to determine whether the remaining drilled shaft foundations on the project (over 200 piers) were capable of supporting the design loads.  Ardaman’s engineers oversaw an extensive exploration of the highly variable subsurface conditions, employing numerous data gathering devices such as Standard Penetration tests, Cone Penetrometer Tests and cross-hole seismic testing. The analysis of the data included detailed and advanced statistical methods and recommendations for modifying those foundations determined to be insufficient for the anticipated loads. The modifications included construction of “sister” shafts adjacent to previously constructed shafts or construction of a series of “mini-piles” around existing shafts to provide additional carrying capacity.

 Ardaman’s report for this project was reviewed by a panel of nationally recognized university researchers and the Florida Department of Transportation, and they agreed with Ardaman’s evaluation and recommendations.  Ardaman’s response to this high profile project clearly exhibits a high level of technical capability along with an innovative approach, and represents a clear advancement of the state-of-the-art of drilled shaft design in Florida.  The project was opened to the public in September 2006.