What is piling?

Piles are columnar foundation elements which are used to transfer loads from buildings down through unsuitable bearing soil onto a bearing surface. The piles can gain their capacity from the friction around its circumference or as end bearing (from the base of the pile).

Piles can also be used to carry tension forces to stop a structure pulling out of the ground; this is common for skyscrapers or tower cranes. They are also used to transfer lateral loads into the ground or retain soil (for example in a retaining wall).

In the domestic realm piles are typically employed for foundations where the soil available at the formation level is not adequate.

Piles will typically be installed at construction stage but it is often quite common to install piles to provide additional support to existing structures (for example when they have encountered subsidence issues).

At the start of a new build the foundations represent a significant risk because the ground conditions may not be known and predictions may not be accurate. Piling is generally quite expensive compared with other foundation solutions such as trench footings or a ground bearing slab (raft foundation).

Materials

Piles are typically made of reinforced concrete (concrete with steel reinforcing bar embedded into it), timber or steel depending on its application.

Installation methods

Rotatory bored pile

A rotary pile is installed by drilling a hole inst the ground down to a level predetermined by the design. A reinforcing steel cage is then placed into the bore and then the bore is filled with concrete .

Continuous flight auger pile

Similar to rotary bored but the concrete is injected down the stem of the auger on the drilling rig as the auger is retracted from the bore. This is a very quick and efficient method in soil which would otherwise require a casing to support the bore.

Driven piles

Specialist rigs ill drive a material (e.g. a steel casing, a timber pile or precast concrete pile) into the ground. This has the advantage of compressing the soil at the base of the pile therefore improving the end bearing capacity. This benefit can be considered by the design engineer which will usually have the effect of reducing the depth piles are driven to.