Question 1

What are the two components of pile axial capacity?

Accepted Answer

Pile capacity Q = Qs + Qp, where Qs is shaft friction resistance (side shear) and Qp is end bearing resistance at the pile tip. Both depend on soil type, pile geometry, and construction method.

Question 2

What is the factor of safety used for pile design?

Accepted Answer

The allowable pile load is typically Qa = Qu / FS, where FS = 2.5 to 3.0 for static analysis methods without load testing, and FS = 2.0 when load tests are performed.

Question 3

How does the Meyerhof SPT method estimate pile capacity?

Accepted Answer

For driven piles: Qs = K Pa N̄ As and Qp = 40 N Ap (kN), where N̄ is the average SPT blow count along the shaft, N is SPT at the tip, As is shaft area, and Ap is tip area.

Question 4

What is the difference between driven and bored piles for capacity?

Accepted Answer

Driven piles densify the surrounding soil (higher β values), while bored piles can disturb and weaken it. As a result, bored piles typically have 50–70% of the shaft friction of driven piles in similar soil conditions.

Question 5

When should pile groups be used instead of single piles?

Accepted Answer

Pile groups are used when the column load exceeds the capacity of a single pile, or when differential settlement must be minimized. Group efficiency η accounts for overlap of stress zones; η = 1.0 for well-spaced piles (≥ 3d center-to-center).

Step	Formula	Substitution	Result
D	D	600	600 mm
L	L	15	15 m
Pu	Pu	300	300 kN

Step	Formula	Substitution	Result
Qu	Qp+Qs	303.1+706.9	1010 kN
Qa	Qu/FS	1010/2.5	404 kN	✓

Step	Formula	Substitution	Result
D	D	600	600 mm
L	L	15	15 m
Pu	Pu	300	300 kN

Step	Formula	Substitution	Result
Qu	Qp+Qs	303.1+706.9	1010 kN
Qa	Qu/FS	1010/2.5	404 kN	✓

Pile Capacity

Pile Capacity (SPT)

Load

Geometry

SPT Data

Pile Capacity

Given:

Geometry

Tip Resistance

Shaft Resistance

Capacity

DCR

Pile Capacity

Pile Capacity (SPT)

Load

Geometry

SPT Data

Pile Capacity

Given:

Geometry

Tip Resistance

Shaft Resistance

Capacity

DCR