Best pile type for very soft soils with little resistance to concrete flow In very soft soils that offer little lateral resistance to the flow of fresh concrete, which pile type is particularly suitable because it forms and compacts an enlarged base by ramming a concrete plug?

Introduction / Context:
Soil conditions control the choice of pile system. In very soft clays or silts, fluid concrete may not displace soil well and can contaminate or wash out. A system that confines, compacts, and forms an enlarged base improves capacity and mitigates defects in such soils.

Given Data / Assumptions:

• Soil is very soft with minimal resistance to flowing concrete.
• Objective: reliable toe formation and higher end bearing.
• Cast-in-situ options considered.

Concept / Approach:

The Franki pile uses a dry concrete plug at the base of a casing. Heavy ramming compacts soil and forms an enlarged base (bulb) before concreting the shaft. This controlled formation is advantageous in soft soils because it limits uncontrolled flow and provides a dense base with increased bearing area and skin friction development along the compacted zone.

Step-by-Step Solution:

Verification / Alternative check:

Textbook case histories show Franki piles performing well in soft strata due to the enlarged, compacted base and controlled concreting sequence.

Why Other Options Are Wrong:

Simplex and vibro piles do not necessarily create a rammed bulb; Raymond piles are thin-shell precast shells; under-reamed piles are suited to expansive clays with bulbs formed by under-reaming tools, not by ramming plug.

Common Pitfalls:

Confusing under-reamed with Franki bulbs; ignoring the need for controlled compaction in very soft soils.

Final Answer:

Franki pile