14 
sea side of the structure it also was noted that some of the “swiss cheese block” 
underlayer units had separated along the slope (approximately sta 4+50). One 
separation was about 20 cm (8 in.) as shown in Figure 12, with a few others 
about 10 cm (4 in.). It appeared that the separations were caused due to the 
lower underlayer units subsiding on their bottom ends. The geotextile bags had 
deteriorated and some spalling along the edges of the 510-kg (1,125-Ib) high- 
strength concrete underlayer units was also noted around the head of the struc- 
ture (Figure 13). In general, the breakwater appeared to be in excellent 
condition. 
Figure 12. Separation between “swiss cheese block” underlayer units 
Targeting and Ground Surveys 
Points were required to serve as control (both horizontal and vertical refer- 
ence) for the ground-based survey work as well as the photogrammetric work on 
the breakwater. Ground surveys were initiated from known Corps of Engineers 
monuments, which included stations CBM3, X, RAMP, and CAMBRA. An 
additional monument (brass disk) designated “TOM” was cemented into the con- 
crete cap of the breakwater. Also, 16 additional control points (designated 2 
through 17) were established on the cap of the breakwater. These were estab- 
lished by painting a black target. A 0.64-cm (1/4-in.) hole was drilled at the 
center of each target for identification in subsequent surveys. The additional 
monument and control points were established using global positioning system 
control surveying and electronic land surveying techniques. Positions and eleva- 
tions of the monuments and control points established on the structure are 
presented below. Their approximate locations are shown in Figure 14. 
Chapter 2 Monitoring Plan and Data 
