Seabrook Sector Gate Complex – Geotechnical Considerations and Issues

The Seabrook complex features a 95-foot opening sector gate flanked by two 50-foot opening vertical lift gates and tie-in T walls that connect to the existing hurricane protection to the east and west. The project is located at the northern terminus of the Inner Harbor Navigation Canal (IHNC), near Lake Pontchartrain, in New Orleans, Louisiana. The project is being constructed for the U.S. Army Corps of Engineers (USACE) under the Early Contractor Involvement (ECI) contracting method.
Several geotechnical issues had to be addressed during design. For starters, key components of the project were located over a deep scour hole in the canal. The scour hole was as deep as 85 feet below the water surface. The scour hole had to be filled to foundation grade. Filling with clean sand was the method selected. Vibro-compaction was selected to densify the material in-situ. Filling the scour hole with clean sand resulted in a pervious foundation. Seepage had to be addressed for both the permanent structures as well as the cofferdam.
All structures for the Seabrook complex are pile supported. Pile design had to consider vertical and lateral loading. A test pile program was conducted but it was performed on the canal bank and could not duplicate all foundation conditions, thus requiring some interpolation to model some pile sections or design with a higher factor of safety.
The north wall of the cofferdam was designed to provide the interior storm protection required for the June 2011 hurricane season. Construction completion is scheduled for June 2012.