4.3. Performance of the hard structure
Since crest lowering could affect the overall function of
a breakwater, possible changes in the crest elevation should be
predicted and its actual changes should be monitored to avoid extra
maintenance costs. Structure monitoring was conducted during the
monitoring schedule, including crest elevation measurement and
cross-section survey. 4 cross-sectional profiles were considered on
each segment of the breakwater; 2 profiles on the trunk section and
2 on the roundheads of the breakwater were surveyed by a total
station.
The rubble mound’s cross-section can be reshaped by bothwave
action and settlement which results in breakwater crest lowering. It
is very common to dump quarry rocks on the sea bed to make
a mound structure. The dumped stones produce a weak initial
profile which is likely to reshape after completion of the
construction. But in this project it was possible for the contractor to
carry and place the stones on the structure by hand during low
tides. This method of construction led to a more integrated structure
where small changes were allowed to take place in the original
cross-section.
While the breakwater’s cross-section did not show substantial
changes and reduction of the crest level was much lower than
expected, monitoring results indicate that the foundation settlement
is limited to about 10 cm by using the bamboo mats. The
effective function of bamboo mats in this project recommends
using this natural material on mud beaches as foundation mats.