ERDC/CHL CHETN-III-66
June 2003
OFU HARBOR BREAKWATER, AMERICA SAMOA: The island of Ofu is one of a group of
seven islands in American Samoa located in the South Pacific Ocean. Ofu Harbor is situated on a
reef platform off the northwest coast of the island. The harbor was originally constructed in 1975,
but sustained severe damage over the years by tropical storms, hurricanes, and typhoons.
Construction of the current harbor configuration was completed in 1994. It is protected by a
185.93-m- (610-ft-) long breakwater. Base conditions were established for the breakwater in 1996
(Bottin and Boc 1997) under the "Periodic Inspections" work unit of the MCNP Program. The
structure was revisited in 2002 (Bottin and Meyers 2003) to determine if changes had occurred.
The breakwater (Figure 1) is armored with a
single layer of uniformly-placed 4,082.33-kg
(4.5-ton) concrete tribar units. It has a concrete
rib cap system on the crest to stabilize and
buttress tribars at the upper sea- and harbor-side
slopes. The structure has a crest elevation (el) of
+4.57 m (+15 ft), and side slopes of 1V:1.5H.
Due to the nonavailability of local stone, the
structure was built utilizing a unique concrete
design for the underlayer units. Basically the
design entailed using various sized concrete units
for breakwater construction as opposed to stone.
Most of the underlayer consisted of 1,632.93-kg
(1.8-ton) concrete units approximately 1.22 1.22
0.61-m (4 4 2 ft) with 5.08-cm (16-in.)
holes in their centers and 22.86-cm (9-in.)
semicircular holes on each side. When placed on
the breakwater slope, the underlayer units, with
the holes, resemble a slice of Swiss cheese and
have been labeled Swiss cheese blocks. In
addition, both 2,267.96-kg (2.5-ton) and
510.29-kg (1,125-lb) concrete units were formed Figure 1. Ofu Harbor breakwater
by pumping high-strength, fine aggregate concrete
into geotextile bags. The 2,267.96-kg (2.5-ton) units were used as a rib cap underlayer and placed
along the harbor side of the structure near its origin. The 510.29-kg (1,125-lb) units were used as an
underlayer for the tribars around the breakwater head since the Swiss cheese blocks could not be
placed in this area due to the tight radius.
During the initial photogrammetric survey of October 1996, selected tribars were targeted (three
targets each) and precise positions of these units were obtained as well as centroid data and
orientations of the targeted armor units. A walking survey of the structure revealed no broken armor
units, however, one sea-side tribar was slightly separated from the rib cap. In addition, it was noted
that some of the Swiss cheese block underlayer units along the slope had slightly separated in a
vertical direction. The maximum separation was about 20.32 cm (8 in.) The geotextile bags had
deteriorated and some spalling along the edges of the 510.29-kg (1,125-lb) high-strength concrete
underlayer units was also noted around the head of the structure. In general, the breakwater
appeared to be in excellent condition.
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