Pile Foundations MCQ with answer and solution

Concept

Continuous Flight Auger (CFA) piles utilize a hollow-stem auger that pumps grout under pressure during extraction, naturally stabilizing the borehole without requiring separate casing.

Step-by-step solution

1. Understand the construction method of auger cast in-situ (CFA) piles. 2. Recognize that the continuous flight auger drills into the soil and grout is pumped through the hollow center during extraction. 3. Identify that the pressure of the injected grout, along with the soil remaining on the auger flights, provides continuous support to the borehole walls. 4. Conclude that this eliminates the requirement for temporary casing for bore hole stabilization.

Explanation

Auger cast piles (also known as Continuous Flight Auger or CFA piles) are constructed by rotating a continuous flight auger into the ground to the desired depth. Concrete or grout is then pumped through the hollow stem of the auger as it is withdrawn, which continuously supports the borehole walls and eliminates the need for temporary casings or drilling mud in most soil conditions.

Why the other options are wrong

B: Quality control depends heavily on operator monitoring and concrete volume records, not inherently superior without proper equipment. C: Pile length is limited by the maximum reach/length of the drilling rig and auger string. D: Pile diameter is restricted by the specific auger size used on the rig.

Shortcut

Remember CFA (Continuous Flight Auger) piles: grout is pumped through the hollow stem during withdrawal, meaning no temporary casing is needed for stability.

Common mistake

Confusing auger cast piles with driven cast-in-situ piles or bored piles that may require heavy steel casings to prevent collapse in loose soils.