Piling systems: the pile that develops an enlarged bulb at its lower end by compacting/ramming concrete to form an expanded base is called what?

Introduction / Context:
Different proprietary pile systems were developed to improve load capacity by enlarging the base or improving shaft interaction. Recognizing the system by its construction method is a common exam theme in foundation engineering.

Given Data / Assumptions:

• Pile is provided with a bulb/expanded base at its lower end.
• Bulb is formed by ramming/compacting concrete at the toe.
• Terminology references classic pile types.

Concept / Approach:
The Franki pile (also known as an expanded-base pile) uses a dry concrete plug driven at the toe of a casing; then concrete is rammed to form an enlarged bulb. This increases end-bearing area and mobilizes higher resistance. Other types (Simplex, Mac-Arthur, Raymond) use different erection and concreting methods and typically do not create such a compacted bulb in the same way.

Step-by-Step Solution:
Identify key feature: expanded bulb formed by ramming concrete at the toe.Match with system name: Franki pile.Select “Franki pile (expanded base).”

Verification / Alternative check:
Standard foundation references describe the Franki method with a toe plug and subsequent bulb formation to enhance capacity.

Why Other Options Are Wrong:

• Simplex/Mac-Arthur/Raymond: methods differ (e.g., driven shells, collapsible forms) and are not characterized by a compacted expanded bulb at toe in this manner.
• None of these: incorrect because a named type exists.

Common Pitfalls:
Confusing Raymond's thin-shell process with Franki's expanded-base technique; assuming all cast-in-situ piles form bulbs.

Final Answer:
Franki pile (expanded base)