Timber and Rock
Wave Height Range: Below five feet.
Many structural forms are possible for timber and rock groins. Figure 81 shows a timber crib structure
that retains a stone f ill. Care must be taken to insure that the rock is larger than the gaps between the
timbers. Rock has escaped from the offshore compartment of the groin in the figure for that reason.
Treated timbers should be used; and to insure structural stability, they should be securely fastened
together with long wrought iron or coated steel rods, threaded at the ends to accommodate washers and
nuts.
Alternate arrangements for timber groins are possible. Two rows of round structural piles can be
driven or augured deep into the beach, with timber planking spiked to the piles. The piles can be placed
close together with the planking set in the space between (Figure 82), or the piles can be more widely
separated to form a crib-type structure (Figure 83).
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