19 June 2001
Improper handling of treated wood.
A design that promotes retention of water.
A design that unnecessarily places wood timbers below water.
Major design deficiencies, which promote physical deterioration,
Insufficient strength of piles resulting in overloading (loss of
strength and embrittlement caused by treatment with salts and
Improper connection hardware or pile connections that restrict load
transfer to other parts of the structure.
Inability of sheet pile walls to retain backfill or insufficient strength in
the soil foundation that results in sheet pile movement.
3-2.2.1 Biological Deterioration. Wood-destroying organisms infest wood
structures both above and below the waterline. Marine borers are the principle
cause of deterioration in the immersed zones and are found in harbors and
estuaries worldwide. Marine fouling organisms found on the wood surface do not
cause wood deterioration and may even serve to retard marine borer damage.
Insects and fungi are the main wood-destroying organisms above the waterline.
3-184.108.40.206 Marine Borers. There are two general types of marine borers that
attack marine timbers: crustaceans and mollusks. The major wood-boring crus-
taceans are the Limnorians; the principle wood-destroying mollusks are the
Teredines (Teredo and Bankia) and the Pholads (Martesia). See Figure 3-1.
Crustaceans. Of the three common crustacean wood borers -
Limnoria, Sphaeroma, and Chelura - Limnoria is considered to be
the most economically important. These borers burrow just below
the wood surface forming a network of interlacing tunnels. The
weakened wood is easily eroded by wave action often resulting in a
characteristic "hourglass" shape. Limnoria tripunctata is of
particular importance because it can attack creosoted wood.
Teredines. The Teredines are commonly referred to as
"shipworms" because of their wormlike appearance. Penetration of
the wood occurs during the microscopic larval stage. As the
shipworms grow, their tunnels increase in diameter and length
while the entrance holes remain about the same size. Attacked
piles may appear sound on the surface, yet be completely riddled.