Define and classify pile foundations

Pile foundation: a pile is a long, slender structural member of timber, concrete or steel, driven into or formed in the ground to transfer the structure's load to a deeper, stronger stratum or to the surrounding soil by end bearing and/or shaft friction. A pile foundation is a group of piles connected by a pile cap.

(i) Based on material

• Timber piles: economical and light, used for light loads and temporary works; need protection from rot and borers above the water table.
• Concrete piles: precast (reinforced or prestressed) or cast-in-situ.
• Steel piles: H-piles, pipe piles (open or closed end); high load capacity and easy to splice; prone to corrosion.
• Composite piles: two materials, e.g. timber below the water table with concrete above.

(ii) Based on method of installation

• Driven piles: installed by hammering or vibration (precast concrete, steel, timber); displace soil.
• Bored (drilled) piles: a hole is bored, then filled with concrete (bored cast-in-situ).
• Driven cast-in-situ piles: a casing or shell driven, and then filled with concrete (e.g. Franki, Raymond).
• Jacked and screw piles: pressed or screwed into ground where vibration must be avoided.

(iii) Based on load transfer

• End-bearing (point-bearing) piles: pass through weak soil and rest on rock or dense soil; load is carried mainly by the tip.
• Friction (floating) piles: carry load by skin friction along the shaft in deep soft soil.
• Combined (friction and end bearing): most piles in practice.