Pile End-Bearing Capacity
Pile End-Bearing Capacity
Alongside shaft friction, a pile's tip transmits load directly into the soil or rock it rests on, much like a small, deep footing. In stiff clays, dense sands, or when a pile is driven to refusal on bedrock, end bearing can dominate the total pile capacity even when shaft friction is modest. The unit end-bearing value used here is itself derived from soil strength parameters or in-situ test correlations (SPT, CPT), and errors in that value are magnified across the full base area, so end bearing calculations are often cross-checked against a static or dynamic pile load test.
End-bearing capacity is Qp = qp*Ap, unit end-bearing resistance times the pile base area, with Ap = pi*d^2/4. where q_p is the unit end-bearing resistance and d_pile2 is the pile shaft (tip) diameter.
Inputs
q_p := 3000 kPa=3 MPa
d_pile2 := 0.4 m=400 mm
The base area is the circular cross-section at the pile tip.
A_p := pi·d_pile2^2/4=0.13 m^2
Multiplying unit end-bearing by the tip area gives the total load the soil beneath the pile can carry.
Q_p := q_p·A_p=376991.12 N
Results
For a 0.4 m diameter pile bearing on soil rated at 3,000 kPa, the resulting end-bearing capacity is on the order of a few hundred kilonewtons — comparable in magnitude to the shaft friction capacity of a similar pile, which is typical for piles bearing in dense sand. Because base area grows with the square of diameter, increasing pile diameter is a much more effective way to add end-bearing capacity than adding length.
Assumptions & limitations
- Unit end-bearing resistance assumed uniform across the base area.
- Neglects shaft friction contribution (computed separately).
- No safety factor applied — this is the ultimate (not allowable) capacity.
- Assumes a clean, undisturbed pile base with full soil contact.