What Are The Different Types of Foundation Piles?

It used to be possible to categorize the various types of pile and their method of installation, using a simple division into ‘driven’ or ‘bored’ piles. This is adequate in many situations, but does not satisfactorily cope with the many different forms of pile now in use.

A more rigorous division into ‘displacement’ or ‘non-displacement’ piles overcomes this difficulty to some extent, but some piles are installed by a combination of these methods and their description may require qualification.

In the displacement (generally driven) pile, soil is displaced radially as the pile shaft penetrates the ground. There may also be a component of movement of the soil in the vertical direction.

Granular soils tend to become compacted by the displacement process, and clay soils may heave, with little immediate volume change as the clay is displaced.

Piles of relatively small cross-sectional area, such as steel ‘H’ section piles or open pipe piles, are termed ‘low displacement piles’, and the effects of compaction or soil heave are reduced. This can be advantageous if long lengths of pile are to be driven through granular deposits, if the piles are at close centres, or if clay heave is a problem.

In the non-displacement (generally bored) pile, lateral stresses in the ground are reduced during excavation and only partly reinstated by concreting. Problems resulting from soil displacement are therefore eliminated, but the benefit of compaction in granular soils is lost and in all soils spoil is produced which may be costly to remove from a site, especially if it is contaminated.

The displacement of the soil by a pile during installation is therefore a fundamental property, and its recognition in any classification of pile type is clearly advantageous. Little-used types such as pre-formed screw piles can also be covered by the (low) displacement classification, whereas they could not be correctly termed ‘driven piles’.

In a further development of the screw pile that is becoming more frequently employed, especially on contaminated sites where it reduces or eliminates the production of spoil, a hollow screw-form auger is rotated into the ground and the bore filled with concrete as it is back-rotated out or retracted without rotation.

The two main categories of pile types may be classified further according to whether pre-formed units are used, and whether the pre-formed unit is used as temporary support for the ground and withdrawn during concreting or left in place.

For nondisplacement piles, factors such as pile diameter and underreaming are introduced to the classification, as they have a bearing on the method of installation, and particularly

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