Piles
Timber piles have been used around the world to support heavy loads for centuries, and are still in use today. Longevity is perhaps best emphasised by the fact that piles support the historic city of Venice (circa 1000 A.D.). A more contemporary example is the Empire State Building (New York) (see note 1).

Piles are used in commercial, industrial and domestic buildings. They are also extensively used in marine environments – such as bridges and wharves - due to their durability.

Timber piles are deep footing members driven into the ground to minimise footing movement and transfer structural loads to deep sub-strata. This is necessary because many structures have loads that cannot be supported by surface soils.
Piles obtain their load carrying capacity by one of two means. Either by friction with the earth - which is particularly effective due to the natural tapered shape of the piles; or by end bearing on the soil sub-stratum. Combinations of the two are also possible.

Piling design requires structural engineering assistance. Design issues include: loads, allowable settlement, timber strength and soil conditions. Hardwood piles are installed by pile driving rigs such as drop hammers, hydraulic hammers or diesel hammers. All are commonly mounted on excavation machines with high masts to facilitate the hammer action.

Pile size and taper are determined by the natural features of the tree. The taper results from the natural growth and profile of the tree. On average it is in the order of 8mm per lineal metre, thus a 10m long pile would increase in diameter by approximately 80mm over its length. This taper assists the load carrying capacity of the pile compared to straight sided piles (i.e. extra compaction and friction). Diameter is determined by the narrower end of the pile which is known as the toe. Standard toe diameters are 180, 210, 230, 280 and 300mm, but larger or smaller diameters may also be available. Common lengths are 6.0, 8.0, 9.5, 11.0, 12.5, 14.0, 15.5, 17.0, 18.0, 20.0, 21.5 and 23 metres. Other lengths can be supplied, some up to 30 meters.

Species available for pile usage are Spotted Gum and Blackbutt, but limited quantities of other available species include: Grey Box, Grey Gum, Grey Ironbark, Red Ironbark, Messmate, Tallowwood and Turpentine. (Turpentine is mainly used for marine applications).
 

Special applications for piles include difficult environments such as corrosive soils or where ground water is present. Here timber out- performs equivalent steel or concrete pile options. Timber piles have been successfully used in marine environments for many years – especially in tidal zones where severe corrosive environments exist. Though this a good application for timber, there is still the risk of attack by marine boring animals (e.g. toredo borers) and crustaceans. In addition, in-ground situations are sensitive to fluctuations in the water table which encourages decay. Protection in these situations is achieved by:

• Using timber species that are naturally resistant such as Turpentine which has a high silica content. The retention of the turpentine bark provides additional protection against decay and borer attack.
  
• Using timbers impregnated with preservative treatments. This typically involves one of two vacuum pressure treatments. One uses Copper Chrome Arsenic (CCA), and the other uses Pigmented Emulsified Creosote (PEC). In some marine environments a double treatment is required using both chemicals (Refer to AS1604). Treatments penetrate the sapwood (i.e. the outer part of the log) which is less durable than the heartwood (i.e. the inner part of the log).
  
• Using mechanical barriers e.g. Copper sheathing or concrete collars.