Last edited 08 Oct 2020

Socket piles

Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.

Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils. Deep foundations are necessary where the bearing capacity of the surface soils is insufficient to support loads imposed and so they are transferred to deeper layers with higher bearing capacity.

Pile foundations are a type of deep foundation. They are formed by long, slender, columnar elements, typically made from steel or reinforced concrete, or sometimes timber. A foundation is described as 'piled' when its depth is more than three times its breadth.

Pile foundations are principally used to transfer loads from superstructures, through weak, compressible strata or water onto stronger, more compact, less compressible and stiffer soil or rock at depth. They are typically used for large structures, and in situations where soil is not suitable to prevent excessive settlement.

The term ‘socket piles’ (or rock sockets), refers to a technique that is used to embed a pile into solid rock. This can be necessary to utilise the full structural capacity of the piles for both compressive and tensile forces. It is a technique that is typically used for offshore applications, such as drilling into a rocky seabed, where the depth is shallow or there is sloping solid rock.

The technique involves drilling into the rock layer to create a socket which is slightly larger than the pile. This creates a void around the outer edge of the pile which is filled with grout, usually Portland cement or an ultra-high strength grout depending on the structural requirements. This 'socket' in the rock provides the pile with stability by providing to resistance against lateral loads and uplift forces.

The safe load-carrying capacity of the socket piles will depend on a number of factors in relation to the behaviour of the rock mass:

  • The properties of the rock.
  • The presence of fractures in the rock.
  • The size and spacing of any fractures.
  • The degree of weathering of fractures.
  • The presence of any soil within fractures.

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