Foundations

Axial Pile Capacity Calculator

Combine project-specific average shaft and toe resistances to estimate ultimate and allowable compression capacity for one circular pile.

Engineering schematic

Single-pile axial resistance

Static symbolic figure. Enter project values in the calculator fields below.

Circular pile section showing compression load, diameter, embedded length, upward average shaft resistance, toe resistance, and shaft and toe capacity equations. — Symbols
D, L
pile diameter and embedded length
fs,avg
project-specific average unit shaft resistance
qb
project-specific unit toe resistance
Qs, Qb
ultimate shaft and toe resistance components

Result

Allowable axial geotechnical capacity: 893.47 kN

Pile perimeter

1.885 m

Shaft surface area

33.93 m²

Toe area

0.283 m²

Ultimate shaft resistance

1526.81 kN

Ultimate toe resistance

706.86 kN

Ultimate axial capacity

2233.67 kN

Allowable axial capacity

893.47 kN

Step-by-step calculation

Pile resistance areas
$A_s=\pi DL=33.93\ \mathrm{m^2},\qquad A_b=\frac{\pi D^2}{4}=0.283\ \mathrm{m^2}$
Shaft and toe resistance
$Q_s=f_{s,\mathrm{avg}}A_s=1526.81\ \mathrm{kN},\qquad Q_b=q_bA_b=706.86\ \mathrm{kN}$
Ultimate capacity
$Q_{\mathrm{ult}}=Q_s+Q_b=2233.67\ \mathrm{kN}$
Allowable capacity
$Q_{\mathrm{allow}}=\frac{Q_{\mathrm{ult}}}{FS}=\frac{2233.67}{2.5}=893.47\ \mathrm{kN}$

What this means

The result combines the entered average shaft and toe resistances for one circular pile. Confirm settlement, structural capacity, downdrag, lateral behavior, group effects, and load-test requirements separately.

Important limitations

Unit shaft and toe resistances must come from a project-specific geotechnical method or recommendation; this calculator does not derive them from soil descriptions.

Assumptions

Single vertical circular pile
Uniform average unit shaft resistance over the embedded length
Toe resistance acts over the full gross base area
Compression loading without scour or downdrag

Formula Used

Q_{\mathrm{ult}}=f_{s,\mathrm{avg}}\pi DL+q_b\frac{\pi D^2}{4},\qquad Q_{\mathrm{allow}}=\frac{Q_{\mathrm{ult}}}{FS}

Step-by-Step Example

A 0.6 m diameter pile embedded 18 m with average shaft resistance 45 kPa and toe resistance 2,500 kPa has approximately 2,234 kN ultimate and 894 kN allowable capacity at FS = 2.5.

Engineering Notes

Derive unit shaft and toe resistances from a project-specific static method, in-situ testing correlation, load testing, or geotechnical recommendation.
Layered profiles should normally be summed by layer rather than represented by one unweighted average shaft resistance.
Check settlement or load-transfer response; geotechnical serviceability may control before the calculated allowable capacity is reached.
Evaluate pile structural capacity, group efficiency, block failure, downdrag, uplift, lateral response, scour, constructability, and load-test criteria separately.

FAQ

Does this calculator determine unit shaft and toe resistance?

No. Those inputs must come from an appropriate project-specific geotechnical method or recommendation.

Can I model layered soil?

Use a separate shaft area and unit resistance for each layer, sum those contributions, and then add toe resistance. This initial tool accepts one average shaft value.

Is allowable capacity the same as design capacity?

Not necessarily. The required resistance factors, safety factors, load combinations, testing, and settlement criteria depend on the governing design framework and project requirements.

Related Engineering Guides

Axial Pile Capacity ExampleCombine shaft and toe resistance and interpret what the result does not cover.Driven Piles vs. Drilled ShaftsCompare construction effects, verification, and applications.Foundation Inspection and Quality ControlConnect design resistance with installation records, testing, and acceptance.