The bearing capacity of a driven pile is the maximum vertical load the pile can safely support, made up of the point resistance on the load-bearing soil layer plus the shaft friction along the sides of the pile. Calculating this capacity is essential to determine how many piles are needed under a building.
Two components
The bearing capacity has two contributions:
- Point resistance (end bearing) — the resistance the pile tip experiences on the load-bearing layer (often Pleistocene sand in the Netherlands)
- Shaft friction — the friction between the pile shaft and surrounding soil along the full pile length
For long, slender piles, shaft friction can be nearly equal to point resistance. For short piles, the point resistance dominates.
How is it determined?
Cone Penetration Testing (CPT) is the standard method. The cone resistance (qc) measurement maps the soil profile. Using the appropriate codes (Eurocode 7 / NEN 9997-1) the design capacity is calculated:
- Characteristic capacity (Rk) — derived directly from qc values
- Design value (Rd) — Rk divided by the partial safety factor
- Allowable load — the value used in structural calculations
Applications
The bearing capacity is used for:
- Pile layout — the number and distribution of piles under the foundation
- Pile type selection — choice between precast concrete, cast-in-place, steel or timber
- Pile diameter and length — matched to the desired load per pile
- Driving records — during piling, the driving log is compared with the calculated length
- Test loading — on critical projects, the bearing capacity is measured on site
Negative skin friction
When fill or settling clay and peat layers compress, the soil pulls down on the pile instead of supporting it. This negative skin friction reduces the net bearing capacity and must be subtracted from the calculated value.
Related terms
- Pile
- Pile foundation
- Cone penetration test
- Negative skin friction
- Soil investigation
- Foundation
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