What is a compression pile?
A compression pile is a foundation pile that is loaded in compression, transferring the building’s vertical load to a deeper, load-bearing soil layer. Compression piles are the counterpart to tension piles and are the most common type of pile foundation.
How does a compression pile work?
A compression pile carries the load through two mechanisms:
- End-bearing capacity — the pile tip rests on a firm layer, usually sand or rock
- Shaft friction — friction between the pile and the surrounding soil
In soft soil conditions (clay or peat), piles are needed to reach the load-bearing layer — typically 8 to 20 metres deep.
Applications
Materials
- Concrete — precast pile or cast-in-situ pile
- Timber — historically common, prone to rot if exposed above the water table
- Steel — tubular or H-profile, especially for heavy industrial loads
- Combination — for example, steel head with concrete shaft
Types of compression piles
- Precast prestressed concrete pile — most common in residential construction
- Cast-in-place pile — bored or grout-injected pile
- Screw pile — screwed into the ground; low vibration
- Vibro-pile — formed by driving a tube and filling it with concrete
Sizing
Capacity is determined based on cone penetration test (CPT) data. From the cone resistance, the design load is calculated.
Compression pile vs. tension pile
A compression pile must resist downward forces from the building. A tension pile is loaded in tension, for example by upward water pressure beneath a basement or in a lightweight hall.
Related terms
- Pile
- Tension pile
- Cone penetration test
- Pile foundation
- Load-bearing capacity
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