Background
Carolina Beach State Park is one of the busiest units in the state park system. The marina is the focal point of this park which also includes camping facilities and miles of hiking trails. It is located along the Cape Fear River near Wilmington, NC.
Project Scope
The existing wood bulkhead in the marina was less than15 years old, yet it had sustained major damage due to rot and marine borer/shipworm infestation. The water conditions in the area were brackish to salty. Due to environmental regulations over the past several decades, water in the area has become much cleaner. This clean salt water provides the ideal conditions for marine borers that literally eat wooden sheet piling and poles. The depth of the marina in some areas required a seawall with 10-15 foot exposures. These wall heights led to substantial loading requirements which normally require a steel wall. Andrew Consulting Engineers considered steel sheet piling, wood, and heavy UltraCompositeTM FRP. After careful analysis, UltraComposite FRP was specified for the seawall primarily for its strength characteristics, long life cycle, low maintenance, and low cost. The project would include over 2,500 linear foot of seawall utilizing both UC-30 and UC-50 UltraCompositeTM FRP sheets. Both of the sheet profiles are manufactured in a facility that meets the latest ISO 9001:2008 certification standards.
Performance
In the high load areas of the marina bulkhead, UC-50 was used taking advantage of its loading capacity of over 17,000 ft/lbs-ft. The UC-50 is also 3' wide which provided for very efficient installation while minimizing driving episodes. The use of a lightweight UltraCompositeTM (~30% the weight of steel) provided a huge reduction in freight and handling costs to the project. In addition, the lightweight nature of the UC-50 and UC-30 also reduced the safety risks and liability at the job site.
Construction
The UltraCompositeTM sheets were driven with a vibratory hammer similar to the same units that install steel sheet piling. In this case, a MKT V-2C/HP-85 driver was utilized. This unit possesses a driving force of 25 tons, a frequency of 1,800 CPM, and an eccentric moment of 550 in-lbs. Contractor Intercostal Diving, Inc. had success installing the sheets with over 120 feet installed per day. There were various soil conditions encountered ranging from silty sand, moist medium firm to dense clays with some gravels to dense medium sands.