Caissons v/s Piles

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Sayali Pawar

February 28, 2023 16:56

Hi @Michael Ermann I came across this question below. Would really appreciate it if you can help me understand the logic behind the answer

Q . You are required to build a small house on a silty clay soil type where bedrock is 30’ below the surface of soil. Which of the below foundations would you choose?

1. Socketed Caisson
2. Belled Caisson
3. End Bearing Pile
4. Frictional Pile

The answer provided was Frictional Pile and the justification was that for a small house you do not require to go all the way down to bedrock.

I’m assuming that silty clay is a cohesive soil

Based on Amber book video I understand that Caisson foundations can only be used in Cohesive soils only. Caissons cannot be used for non-cohesive soils.  

Can you confirm whether Pile foundations can be used in both Cohesive and Non-Cohesive soils? Is Frictional Pile the correct choice here?

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  Rebekka O'Melia March 01, 2023 15:33

  Hi Sayali,

  Yes, a frictional pile is the correct answer here. 

  All the other choices are essentially the same - a socketed caisson, belled caisson, and end bearing pile all have to bear directly on the bedrock (or bearing soil).  The silty/clay wouldn't support them.  This link has a good diagram if you scroll down the page a bit:  https://civillearners.com/2021/09/22/deep-foundations/

  Hope this helps!

  Rebekka O'Melia, R.A., NCARB, B. Arch, M. Ed, NOMA, Step UP ARE 5.0 Courses

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  Sayali Pawar March 11, 2023 23:07

  This helps a lot. Thank you!

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