They are driven by percussion means similar to precast concrete piles, have good ﬂexibility and resistance to shock and, if kept permanently wet or permanently dry, they can have a very long life.
There is some danger from attack by marine organisms below water, and from micro-fungal attack and wood-destroying insects when kept dry. However, careful selection of the species of timber and the use of preservatives can overcome most of the problems. In Victorian piles charred faces were used to prevent surface deterioration. To assist in the driving of the pile, steel hoops are often used around the head of the pile and steel shoes on the toe to prevent damage from impact forces in these locations and to ease the driving. There is some danger of undetected damage below ground level in a similar manner to that of the precast concrete pile. However jetting or pre-boring in difﬁcult conditions can help in overcoming this problem. The pile can be in the form of trimmed tree trunks or shaped timber cross-sections (see Fig. 9.38).
Timber piles are usually in a range of 5–12 m long and if lengths in excess of this are required they can be spliced using specially designed steel connections.
Fig. 9.38 Typical timber pile cross-sections.