Driven timber piles and bored concrete piles are deep foundations which differ from materials and construction methodologies.
1. Driven Timber Piles
Driven timber piles can provide a very economical foundation system for light timber framed dwellings with timber floor provided the site is reasonably flat and floor level is not too far above ground.
Timber piles are available in sizes from 150mm to 350mm diameter and upward on specific requirement and in length well up to 12m, for longer lengths the poles can be spliced. Timber piles can be treated to H4, H5 or H6 grade for protection.
Driven timber piles are easy to install, can be cut with a saw. However, timber piles will rot above the ground water level. Have a limited bearing capacity. It can easily be damaged during driving by stones and boulders. The piles are difficult to splice and are attacked by marine borers in salt water.
Bored reinforced concrete piles are typically required for heavily loaded foundation systems, such as is found in high rise construction, commercial and industrial applications. Although less common in domestic construction they are often specified on "Geotechnically challenged" sites especially the steeper grounds. The piles take foundation loads down to more solid ground, where they are less likely to exacerbate slope instability.
They can be constructed in a wide choice of diameters, typically ranging from 300mm to 1800mm, and to depths of up to 70m at rakes of up to 1:4. They can thus be tailored precisely to the particular requirements of the building or excavation. This flexibility means that bored piles can provide solid foundation elements suitable for almost all site conditions.
Bored concrete piles can be inspected before casting can easily be cut or extended to the desired length. An enlarged base can be formed which can increase the relative density of a granular founding stratum leading to much higher end bearing capacity. Reinforcement is not determined by the effects of handling or driving stresses.
However, tensile can damage to unreinforced piles or piles consisting of green concrete, where forces at the toe have been sufficient to resist upward movements. It has limitation in length owing to lifting forces required withdrawing casing. The construction is time consuming. They cannot be used immediately after the installation.
3. Other factor s influencing the choice
There are many other factors that can affect the choice of foundation. All factors need to be considered and their relative importance taken into account before reaching a final decision: Location and type of structure, ground conditions, durability, and cost.