5.2. RUBBLE-MOUND STRUCTURES
191
Another example of model verification given by Hudson and Davidson
(1975) concerned model tests conducted in 1948 of a proposed construction
technique for a breakwater at Silver Bay, Minnesota. The construction
method called for the breakwater core material to extend above still-water
level so that it could be used as a roadbed for dumping material off the
sides and ends of the yet-to-be-completed structure. During construction
is was expected that storm waves would damage the structure. However,
the tests indicated that, even with damage, this method would result in a
less expensive structure once it was completed and the structure stabilized.
Storm damage that occurred during actual construction in 1953 closely
resembled that predicted by the physical model.
Tprum, et al. (1979) compared damage that occurred on the Bilbao
Oil Harbor breakwater during a heavy storm to damage obtained from
a 1:80 scale model conducted in a 2-d wave flume. Although differences
were noted in the various damage profiles between prototype and model,
the tests reproduced the damage distribution quite well in some profiles.
Tprum, et al. concluded that the model gave “fair agreement with the
prototype damage,” and at no time was the model damage greater than
that observed in the prototype. They concluded that the model did not
necessarily give conservative results.
Perhaps the most rigorous demonstration of rubble-mound physical
modeling validity was provided by Lillevang, et al. (1984). They used
a 3-d fixed-bed hydraulic model to reproduce significant damage to the Diablo Canyon west breakwater that occurred during a January 1981 storm.
Five huge concrete capping blocks, weighing almost 3 000 kN (300 tons)
each, were displaced from the seaward 46 m of the breakwater. After careful assessment of the environmental conditions and introduction of several
novel model construction techniques, the physical model’s capability to reproduce prototype damage was confirmed in five separate tests. Three of
the tests utilized bursts of nine uniform waves of the same height, and two
of the tests were conducted using irregular waves scaled to replicate the
prototype spectrum measured in 33 m depth. Interestingly, all five tests
produced the same damage, demonstrating remarkable consistency. The
tests revealed that damage at Diablo Canyon west breakwater was initiated when a Tribar armor unit at the toe of the structure near the terminal
cone was dislodged, leading to further unraveling of the structure. The final
damage closely matched that of the prototype, and the sequence of damage
in all five tests was reported to be essentially identical. Lillevang, et al.
(1984) then used the verified physical model to design a repair capable of
withstanding the new design condition.
Lillevang, et al. recommended that problems involving wave attack on
the head of a rubble-mound structure should be examined in a correctly
191
Another example of model verification given by Hudson and Davidson
(1975) concerned model tests conducted in 1948 of a proposed construction
technique for a breakwater at Silver Bay, Minnesota. The construction
method called for the breakwater core material to extend above still-water
level so that it could be used as a roadbed for dumping material off the
sides and ends of the yet-to-be-completed structure. During construction
is was expected that storm waves would damage the structure. However,
the tests indicated that, even with damage, this method would result in a
less expensive structure once it was completed and the structure stabilized.
Storm damage that occurred during actual construction in 1953 closely
resembled that predicted by the physical model.
Tprum, et al. (1979) compared damage that occurred on the Bilbao
Oil Harbor breakwater during a heavy storm to damage obtained from
a 1:80 scale model conducted in a 2-d wave flume. Although differences
were noted in the various damage profiles between prototype and model,
the tests reproduced the damage distribution quite well in some profiles.
Tprum, et al. concluded that the model gave “fair agreement with the
prototype damage,” and at no time was the model damage greater than
that observed in the prototype. They concluded that the model did not
necessarily give conservative results.
Perhaps the most rigorous demonstration of rubble-mound physical
modeling validity was provided by Lillevang, et al. (1984). They used
a 3-d fixed-bed hydraulic model to reproduce significant damage to the Diablo Canyon west breakwater that occurred during a January 1981 storm.
Five huge concrete capping blocks, weighing almost 3 000 kN (300 tons)
each, were displaced from the seaward 46 m of the breakwater. After careful assessment of the environmental conditions and introduction of several
novel model construction techniques, the physical model’s capability to reproduce prototype damage was confirmed in five separate tests. Three of
the tests utilized bursts of nine uniform waves of the same height, and two
of the tests were conducted using irregular waves scaled to replicate the
prototype spectrum measured in 33 m depth. Interestingly, all five tests
produced the same damage, demonstrating remarkable consistency. The
tests revealed that damage at Diablo Canyon west breakwater was initiated when a Tribar armor unit at the toe of the structure near the terminal
cone was dislodged, leading to further unraveling of the structure. The final
damage closely matched that of the prototype, and the sequence of damage
in all five tests was reported to be essentially identical. Lillevang, et al.
(1984) then used the verified physical model to design a repair capable of
withstanding the new design condition.
Lillevang, et al. recommended that problems involving wave attack on
the head of a rubble-mound structure should be examined in a correctly