Commercial Building Inspector B2Structural SystemsMedium
A structural engineer is reviewing the foundation plans for a new commercial building on a site with highly expansive clay soils. To mitigate the effects of soil movement, the design includes a deep foundation system. Which of the following deep foundation elements is typically installed by drilling a shaft and then filling it with concrete, often with reinforcement?
- AMicro Pile
- BHelical Pile
- CDrilled Shaft (Caisson)
- DDriven Pile
Show answer & explanationAnswer & explanation
Correct answer: C. Drilled Shaft (Caisson)
Drilled shafts, also known as caissons or bored piles, are constructed by drilling a cylindrical hole into the ground and then filling it with concrete, typically with a reinforcing steel cage. This method is effective in various soil conditions, including expansive clays, to transfer loads to deeper, more stable strata.
Why the other options are wrong
- A. Micro piles are small diameter (less than 12 inches) drilled and grouted piles, often used for underpinning or limited access sites.
- B. Helical piles are screw-in foundation elements, installed by rotating them into the ground.
- D. Driven piles are pre-manufactured and hammered or vibrated into the ground.
Drilled Shaft (Caisson)
A deep foundation element constructed by excavating a cylindrical shaft into the ground and filling it with fluid concrete, often incorporating a steel reinforcing cage.
- Also known as bored piles or caissons.
- Suitable for various soil types, including expansive clays.
- Load transfer through end bearing and/or skin friction.
Memory trick: Deep foundations: some driven, some screwed, some drilled.