5.2. RUBBLE-MOUND STRUCTURES
197
ter 7 should provide waves reasonably close to the target wave condition.
However, in most cases generated waves must first undergo shoaling (and
possibly refraction and diffraction in 3-d models) before reaching the coastal
structure. This transforms the waves generated at the wave board into a
different wave condition in shallower water.
A good practice is to “calibrate” the design waves by running each wave
condition in the wave facility without the structure in place and measuring
the waves near where the toe of the structure will be during testing. The
absence of the reflective coastal structure will provide a better estimate of
incident waves at the structure. Model observations with the structure in
place can then be related to the incident wave conditions, which are easier
for coastal engineers to estimate. The calibration step is not essential, but
it does allow adjustment of test wave parameters to provide even coverage
over the range of test wave conditions or to assure that specific incident
wave conditions are included in the test program.
After the model has been constructed, it should be exposed to lower
energy waves to “shakedown” the structure and allow the armor units to
“nest” into a more compact mound. Hudson and Davidson (1975) suggested
using waves having a height of about 50% of the intended test conditions.
This exposure to small waves could be thought of as simulating lower energy
waves at the beginning of a storm. Hudson and Davidson’s recommendation
is similar to structure compacting described by Tprum, et al. (1979). Their
model structure was compacted by subjecting it to approximately 1000
waves having the same wave period as the target test condition, but with
only 60% of the wave height.
Jensen (1984) listed seven types of test procedures that could be used in
testing rubble-mound structures. A model test program could consist of one
or more of these procedures depending on the objectives of the particular
model study. Jensen’s list is summarized below.
1. Tests with Increasing Wave Impacts. Structure stability testing starts out with mild wave conditions, and
each subsequent test is conducted with incrementally increased wave heights. Owen and Allsop (1983) recommended that testing continue until damage occurs or the
wave height reaches 120% of the design wave height. Incremental testing is the traditional testing method, and
in the case of a structure in shallow water, the engineer
can determine what offshore wave condition produces the
depth-limited breaking wave height, which is usually the
most damaging (Hudson and Davidson 1975). Testing is
performed for a range of wave periods and water depths.
197
ter 7 should provide waves reasonably close to the target wave condition.
However, in most cases generated waves must first undergo shoaling (and
possibly refraction and diffraction in 3-d models) before reaching the coastal
structure. This transforms the waves generated at the wave board into a
different wave condition in shallower water.
A good practice is to “calibrate” the design waves by running each wave
condition in the wave facility without the structure in place and measuring
the waves near where the toe of the structure will be during testing. The
absence of the reflective coastal structure will provide a better estimate of
incident waves at the structure. Model observations with the structure in
place can then be related to the incident wave conditions, which are easier
for coastal engineers to estimate. The calibration step is not essential, but
it does allow adjustment of test wave parameters to provide even coverage
over the range of test wave conditions or to assure that specific incident
wave conditions are included in the test program.
After the model has been constructed, it should be exposed to lower
energy waves to “shakedown” the structure and allow the armor units to
“nest” into a more compact mound. Hudson and Davidson (1975) suggested
using waves having a height of about 50% of the intended test conditions.
This exposure to small waves could be thought of as simulating lower energy
waves at the beginning of a storm. Hudson and Davidson’s recommendation
is similar to structure compacting described by Tprum, et al. (1979). Their
model structure was compacted by subjecting it to approximately 1000
waves having the same wave period as the target test condition, but with
only 60% of the wave height.
Jensen (1984) listed seven types of test procedures that could be used in
testing rubble-mound structures. A model test program could consist of one
or more of these procedures depending on the objectives of the particular
model study. Jensen’s list is summarized below.
1. Tests with Increasing Wave Impacts. Structure stability testing starts out with mild wave conditions, and
each subsequent test is conducted with incrementally increased wave heights. Owen and Allsop (1983) recommended that testing continue until damage occurs or the
wave height reaches 120% of the design wave height. Incremental testing is the traditional testing method, and
in the case of a structure in shallow water, the engineer
can determine what offshore wave condition produces the
depth-limited breaking wave height, which is usually the
most damaging (Hudson and Davidson 1975). Testing is
performed for a range of wave periods and water depths.