5.2. RUBBLE-MOUND STRUCTURES
195
strength of the model armor units is much greater than what would be
required for similitude (see the next section for modeling techniques to reproduce armor unit structural strength). Funke and Haines (1976) and
Hudson, et al. (1979) described effective mixtures for use in manufacturing artificial armor units. Other laboratories also have developed effective
molding compounds. The report by Funke and Haines (1976) gave detailed
information on armor unit manufacturing techniques.
Preparation of rubble-mound structure model materials is expensive,
tedious, and time consuming. For this reason, model materials are sorted
into sizes and saved in bins for re-use in future models (Hudson, et al.
1979).
Construction of rubble-mound structures at the Waterways Experiment
Station (Hudson, et al. 1979) is done in a dewatered wave facility. First,
the core material is placed dry to the correct dimensions, then saturated
with low-velocity spray and compacted with trowels to simulate compacting
by waves. Underlayers are placed dry with a shovel and smoothed to the
correct slope and dimensions by hand without compacting or rearranging
of individual stones.
Although special placement of armor units can produce increased stability, this type of placement is difficult to achieve in the prototype, especially
for the underwater portions. Consequently, prototype armor layer construction tends to be more of a random placement. During model construction,
great care is taken while hand-placing armor units to replicate the random
placement method that typifies the prototype structure. The model builder
must conscientiously avoid the natural temptation to “key in” the armor
units. While building a model structure, it may help to have a minimum
number of stones to chose from at any given time. This better simulates the
usual prototype situation, and it may help suppress the natural tendency to
select units that best fit holes in the armor layer. Figure 5.5 shows a rubblemound structure model under construction at the Waterways Experiment
Station.
Tprum, et al. (1979) described model construction using a pair of tongs
to place individual armor units similar to crane placement in the prototype.
During the process, the wave flume was filled with water. The total number
of units to be placed on the structure was estimated from the prototype
structure cross-section. T0rum, et al. did not mention if the water was
darkened to simulate the experience by crane operators who must place
armor stone “blindly” beneath the water surface.
Raichlen5 suggested that perhaps the most realistic construction method
would be to build the structure in darkened water using a miniature crane
5 Personal communication. Dr. Fredric Raichlen, California Institute of Technology.
195
strength of the model armor units is much greater than what would be
required for similitude (see the next section for modeling techniques to reproduce armor unit structural strength). Funke and Haines (1976) and
Hudson, et al. (1979) described effective mixtures for use in manufacturing artificial armor units. Other laboratories also have developed effective
molding compounds. The report by Funke and Haines (1976) gave detailed
information on armor unit manufacturing techniques.
Preparation of rubble-mound structure model materials is expensive,
tedious, and time consuming. For this reason, model materials are sorted
into sizes and saved in bins for re-use in future models (Hudson, et al.
1979).
Construction of rubble-mound structures at the Waterways Experiment
Station (Hudson, et al. 1979) is done in a dewatered wave facility. First,
the core material is placed dry to the correct dimensions, then saturated
with low-velocity spray and compacted with trowels to simulate compacting
by waves. Underlayers are placed dry with a shovel and smoothed to the
correct slope and dimensions by hand without compacting or rearranging
of individual stones.
Although special placement of armor units can produce increased stability, this type of placement is difficult to achieve in the prototype, especially
for the underwater portions. Consequently, prototype armor layer construction tends to be more of a random placement. During model construction,
great care is taken while hand-placing armor units to replicate the random
placement method that typifies the prototype structure. The model builder
must conscientiously avoid the natural temptation to “key in” the armor
units. While building a model structure, it may help to have a minimum
number of stones to chose from at any given time. This better simulates the
usual prototype situation, and it may help suppress the natural tendency to
select units that best fit holes in the armor layer. Figure 5.5 shows a rubblemound structure model under construction at the Waterways Experiment
Station.
Tprum, et al. (1979) described model construction using a pair of tongs
to place individual armor units similar to crane placement in the prototype.
During the process, the wave flume was filled with water. The total number
of units to be placed on the structure was estimated from the prototype
structure cross-section. T0rum, et al. did not mention if the water was
darkened to simulate the experience by crane operators who must place
armor stone “blindly” beneath the water surface.
Raichlen5 suggested that perhaps the most realistic construction method
would be to build the structure in darkened water using a miniature crane
5 Personal communication. Dr. Fredric Raichlen, California Institute of Technology.