Driven Cast-in-Situ Piles – Which keep a cast iron shoe after casing removal? Among the following cast-in-situ pile types that use a hollow cylindrical steel casing during driving, which retain a cast iron shoe at the toe even after the casing is withdrawn?

Introduction / Context:
Several cast-in-situ pile systems use a temporary steel casing driven with a shoe to form a hole and support surrounding soil. Understanding which systems retain the toe shoe helps in identifying construction sequences and toe bearing characteristics.

Given Data / Assumptions:

• Hollow steel casing driven with a cast iron shoe.
• Concrete placed after forming the hole.
• Question concerns which systems leave the shoe in place after casing withdrawal.

Concept / Approach:

In the Simplex system, a cast iron shoe is driven with the casing; after forming the bore and placing concrete, the casing is withdrawn but the shoe is left at the toe, providing a form and seating for the cast-in-situ pile. Vibro piles (of the driven-vibration casing type) also employ a shoe that remains to form the base while the casing is extracted. Franki piles use a dry concrete plug and can form an enlarged base by ramming; they do not rely on leaving a cast iron shoe in the ground. A pedestal pile develops an enlarged footing formed by forcibly pushing concrete into the soil, without the same shoe retention scenario.

Step-by-Step Solution:

Verification / Alternative check:

Standard piling references illustrate Simplex and vibro casing methods with shoes left at toe upon casing withdrawal.

Why Other Options Are Wrong:

Single selections omit the other valid system; Franki and pedestal operate differently regarding toe formation.

Common Pitfalls:

Confusing vibro-replacement stone columns with vibro concrete piles; assuming all cased systems retrieve the shoe.

Final Answer:

Both Simplex and Vibro piles