SuperPile 2017 Online Proceedings, (DFI)
Bonner Bridge Replacement: Innovative Method to Field Verify Post-Scour Axial Resistance of Jetted and Driven Pile Foundations under Significant Scour Conditions in Outer Banks of NC
Beth Howey, LG, P.E. and Michael Batten, P.E.
PCL Constructors and HDR, Inc. won the bid to design and build the 2.7 mile replacement bridge for the Herbert C Bonner bridge along the Outer Banks of North Carolina. The current bridge is over 50 years old and connects two sandbars over a dynamic and constantly shifting inlet, with continual scour issues since it opened to traffic. Numerous retrofits have been added to try to maintain adequate pile penetration; the bridge has closed in the past due to excessive scour and significant loss of pile support. HDRís task was to design foundations that could withstand the significant potential scour (to elevation -84 feet!) and be installed in the harsh ocean environment. Further, HDR had to devise a method to field verify that the prestressed concrete piles would maintain adequate axial resistance during the design scour event when they were installed in the non-scour condition to significant depths into a dense sand layer. Jetting was required to reach the required tip elevations, yet there is very little research on the effects of jetting on pile resistance. HDR utilized Pile Dynamic Analyzerģ (PDA) data to measure the effects of jetting on the side resistance and then used this data to predict the long term performance of the piles under the design scour elevations utilizing the effective stress analysis (or Beta Method) for determining the long term side resistance. We will provide a summary of this procedure and discuss its implementation during construction with lessons learned.
|article #2693; publication #1031 (SP-2017)|