embedment depth of pier design - 2007CBC/IBC2006

[fbmok]

I'm a little bit confused that why the eq.18-1 (for nonconstrainted case) limits the embedment depth of 12'? Does that mean the max. embedment depth is only 12'?
If look further in the notes area of 1805.7.2.2, there is no limit for the embedment depth d for constrained case, why is that? Thanks for answering...

 

[cntw1953]

I don't have the code. Can you explain "constrained case vs nonconstrained case", and what is to be "embedded" (depth of pier below grade)?

 

[jenofstructures]

based on what i understand, "non constrained" means it does not have pavement as a part of supporting system when its "constrained" floor pavement is provided

i believe constrained non-constrained is for piles or in poles

 

[fbmok]

Nobody answered my question. Why the depth limits at 12', what's the phylosiphy implied by the depth limitation? Is it possible that in the reality, the embedment depth will be needed much larger than 12'?

 

[JAE]

Does the definition of "d" apply to both equations?

If so, you don't have an problem.

 

[tictock]

"research shows that soil strength does not increase consistently with great depths"

 

[WHEngineer]

The code does not restrict the maximum embedment depth to 12 feet for the non-constrained case, only the lateral load calcs are limited to 12 feet. For an axial loaded pier, the depths can be greater. In addition, effective lateral resistance will decrease with depth, so 12 feet is likely an arbitrary number that represents the diminishing lateral resistance at greater depths for small diameter piers or piles.

 

[WHEngineer]

To add to my previous post, a small diameter pier or pile, especially of wood, will not provide significant bending resistance at depths over 12 feet, likely resulting in unacceptable lateral deflections.