19 June 2001
Insects. Termites are the most destructive wood-destroying insects
found on waterfront structures. Other insect pests include: wood-boring beetles,
ants, and bees. An insect frequently associated with damage to piers and docks
is the wharf-borer, Nacerda, a beetle about 8 mm long, yellowish-brown to dark
red in color. Some insects, such as termites, require wood for food and shelter;
others, such as carpenter ants, require wood for nesting only. Most wood-
destroying insects thrive under damp conditions.
3-22.214.171.124 Fungi. Three categories of wood-decay fungi are: white rot, which
tends to bleach the affected wood; brown rot, often termed "dry rot," which
produces a brown, crumbling type of decay; and soft rot, which softens the wood.
Slight strength reduction of infected wood can be caused by stain fungi, which
produce bluish black to steel gray or brownish discoloration of the wood. Molds
also produce a discoloration of the wood surface and are regarded as merely a
blemish, but their presence indicates that conditions may be favorable for decay
organisms. Most wood-destroying fungi require damp conditions for growth.
3-2.2.2 Physical Deterioration. Physical deterioration of timber piles and
other wood structures is generally due to the following causes:
3-126.96.36.199 Abrasion. Abrasion of timber piles occurs principally in the intertidal
zone. The rate at which piles are destroyed by abrasion depends on the amount
of floating debris in the harbor, the velocity of water moving past the piles, ice in
the harbor, and the action of marine borers. Fender piles are also abraded by
camels and ships.
3-188.8.131.52 Overload. Overloading of piles may result from a continuous heavy
load or infrequent, severe loads. Overloading may be caused by vertical and
horizontal loads. Failure of one pile requires the adjacent piling to carry the extra
load. Continual overloading can lead to collapse of the entire structure.
3-184.108.40.206 Connection Failure. When a timber pile connection fails, the structure
is free to move and will eventually fail. If untreated wood is exposed, connection
failure may first allow the entry of marine borers if below the waterline, or insects
and fungi if above the waterline.
3-220.127.116.11 Timber Wall Movement. Outward wall movement can result from hori-
zontal loading of the backfill material caused by excessive loading behind the
structure or failure of tie-backs. Loss of backfill material can result in movement
in the opposite direction. If either condition continues, the structure will fail.
3-18.104.22.168 Single Timber Piles. Single timber piles or those used in light
structures may be lifted by ice freezing to the pile and pulling it as the ice moves
with the tide.
Preventive Maintenance for Wood and Timber. The primary
preventive maintenance (PM) measure at the waterfront is to select the type of
wood best suited for the particular use and to purchase wood products and