Two-dimensional and three-dimensional physical model studies were conducted to study repair scenarios for the breakwater at Lajes Air Force Base, Lajes, Azores. In addition, wave transmission into the lee of the breakwater was measured for various breakwater repair scenarios. The intent of the study was to determine the optimum breakwater repair plan.
The Azores islands are located in the mid-Atlantic Ocean. Praia da Vitoria is a bay located on the eastern coast of the island of Terceira in the Azores. The harbor has direct exposure to severe open Atlantic storms from the east. A breakwater was constructed in 1963 on the north side of the bay entrance to provide safe refuge and port for U.S. ships arriving at Lajes Air Force Base. A wharf is located directly in the lee of the breakwater, as shown on the attached photograph. The breakwater was originally armored with 15 t tetrapods. The armor layer has sustained significant damage during initial construction. Repairs to the structure were undertaken in 1963, 1964, 1966, 1970, 1973, 1985, 2002, and 2003. The structure continues to deteriorate. In 2001, the U.S. Air Force employed the U.S. Navy to develop a permanent repair for the structure.
At the request of the U.S. Navy, two 1:56-scale physical hydraulic models were designed and constructed at the U.S. Army Engineer Research and Development Center by the Coastal and Hydraulics Laboratory to study repair scenarios. One model of a breakwater section was built in a 1.5-m wide by 61-m-long flume. A second model, a three-dimensional model of the breakwater and bay covering a region roughly 2 km by 2 km, was constructed in a directional wave basin.
Modifications to the breakwaters were tested that include a CORE-LOC® and antifer cube armor layer with an optional fronting berm of mobile stone. The design CORE-LOC® weight is 31.6 t. The tested options were stable and the best option at study completion was a CORE-LOCÒ-armored superstructure down to the still water level and a fronting berm of stone. Construction of this option began in late 2004.
This study developed a new composite structure type that is a combination of a low maintenance, very stable superstructure coupled with a relatively simple-to-construct underwater semi-mobile rock mound. The composite structure is anticipated to be lower overall cost with much lower construction-related complexity and risk and minimal maintenance over the life cycle. The physical model study resulted in more than $10M of direct savings and considerable reduction in risk.
U.S. Air Force Base, Lajes, Azores, through U.S. Navy NAVFAC.
Point of Contact:
Dr. Jeffrey A. Melby, U.S. Army Engineer Research and Development Center,
ATTN: CEERD-HN-H, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199;
U.S. Air Force Base, Lajes, Azores; U.S. Navy NAVFAC, TranSystems Corp., Baird and Associates.
Location^Azores , Portugal^%Field%|Sponsors^^%Field%|Partners^^%Field%|Owner^^%Field%|Status^^%Field%|Engineers^^%Field%|Contractors^^%Field%|Model Studies^Performed by ERDC-CHL personnel. Length scale 1:56.^%Field%