Pile capacity terminology: Which statements are correct regarding bearing capacity and safety factors for piles?

Introduction / Context:
Pile foundations are designed using ultimate capacity, settlement criteria, and appropriate factors of safety. It is important to distinguish definitions of working (safe) load, ultimate load, and the factor of safety typically adopted in practice.

Given Data / Assumptions:

• (a) Bearing capacity of a pile: load sustainable without excessive settlement.
• (b) Ultimate bearing capacity: maximum load beyond which the pile continues to sink without additional load increase.
• (c) Safe bearing capacity: ultimate capacity divided by factor of safety.
• (d) Factor of safety taken as 6 (claim to be evaluated).

Concept / Approach:
Statements (a), (b), and (c) reflect standard definitions recognized in geotechnical engineering. The factor of safety for piles is generally not as high as 6; typical values range around 2 to 3 (varying with design code, test data, and variability). Therefore, statement (d) is incorrect, making “All of these” wrong. The correct selection is the set containing (a), (b), and (c) only.

Step-by-Step Solution:
Verify (a): aligns with settlement-based working load definition → correct.Verify (b): describes ultimate behavior (continued sinking at essentially constant maximum load) → correct.Verify (c): safe capacity = ultimate / FOS → correct.Assess (d): FOS = 6 is excessive for piles; typical practice adopts 2–3 (sometimes different for tension or lateral) → incorrect.Therefore choose “(a), (b), and (c) are correct.”

Verification / Alternative check:
Pile load test interpretations and code guidance consistently use moderate safety factors, refined when static load test data are available.

Why Other Options Are Wrong:
Only (a) and (b): ignores correct statement (c).Only (d): statement (d) is incorrect.All/None: do not match the truth set.

Common Pitfalls:
Confusing geotechnical factor of safety with structural load factors; assuming a universal FOS irrespective of site data quality.

Final Answer:
(a), (b), and (c) are correct.