In August 1994, a 150 foot section of a bulkhead at a port in Florida failed. The arrow in Fig. 1 indicates where the top concrete cap of the bulkhead rotated outward approximately seven feet due to the failure. Summit Engineering was asked to assist in determining what caused the bulkhead to fail. Potential causes included a possible fractured water line behind the bulkhead, the impact from a cruise ship which had docked 8 hours prior to the bulkhead failure or a design or construction defect.
The 700 foot long bulkhead system was constructed to create a 44 foot deep channel for large sea going vessels to dock. The bulkhead is supported on the land side by a series of soil anchors 75 feet long which were augured into the ground and grout filled. Since the concrete cap had rotated outward seven feet, it was believed that the soil anchors had failed.
During the repair activities in late 1995, several of the soil anchors were removed and examined, Fig. 2. Although still covered in water, the bottom of the concrete cap was also examined. It was determined that there were several soil anchors whose tops were not fully encased in concrete as designed. These soil anchors were exposed to the splash zone from the changing tides. This expose created a very corrosive environment for the soil anchors.
The arrow in Fig. 2 shows a soil anchor which has experienced a loss of cross-sectional area due to long-term corrosion. The soil anchors were designed to be loaded to nearly 70% of their tensile strength. The corrosion of the improperly encased soil anchors resulted in surface cracks and a reduction in cross-sectional area. The combination of a reduction in cross-sectional area and stress raisers from the surface cracks caused the soil anchors to be overloaded and fracture. As the corroded soil anchors failed over time, other soil anchors had an increased load applied to them. Finally, the loads increased until the soil anchors for a 150 foot long section of the bulkhead shown in Fig. 1 failed and allowed the concrete cap to rotate outward into the harbor.
It was concluded that the failure of the 150 foot section of the bulkhead was due to improper construction and long term corrosion of several soil anchors.