H-Piles: Minimum Embedment?
H-Piles: Minimum Embedment?
(OP)
For H-piles bearing on bedrock, is there a minimum length which should be provided between the bottom of footing and top of rock, other than for cost considerations? The overburden for this particular project is mostly clay material.





RE: H-Piles: Minimum Embedment?
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RE: H-Piles: Minimum Embedment?
RE: H-Piles: Minimum Embedment?
Additionally some DOTs require that pile groups are designed such that under no load condition does a pile experience uplift. I'm sure others allow some uplift.
Most geotechs will recommend that the upper 5 feet of disturbed soil be disregarded anyway which doesn't leave a lot of resistance.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: H-Piles: Minimum Embedment?
I am embarrassed. I misread your question and answered wrong.
The 10 foot requirement between the rock and the bottom of footing has a lot to do with how the pile behaves under load. Much less than 10 feet and the element does not behave as a column. Different methods of analysis come into play. The same situation can exist with cast-in-place concrete piers.
RE: H-Piles: Minimum Embedment?
Based on emmgjld's statement that the 10 foot minimum is to allow the pile to behave as a column, this seems to be reasonable.
Would shorter piles change the distribution of load from the footing to the piles?
RE: H-Piles: Minimum Embedment?
I have always recommended to make the foundation a pile foundation or a footing/pad foundation. The in between state does not lend itself to straight forward computations and it is not desirable to mix foundation types. I try to avoid the 'neither fish nor fowl' condition.
RE: H-Piles: Minimum Embedment?
When you anticipate them, it is most often dealt with by pre-boring the pile in place.
Regards,

Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
RE: H-Piles: Minimum Embedment?
RE: H-Piles: Minimum Embedment?
Your question/analysis is very similar to my reasoning when I have anticipated very short piling. As I generally have very large pile capacity (90+ tons S.F.>2.5) for fairly small loads (<40 tons) I usually disregarded the so called problem unless I had a concern with subsurface topography (similar as you mentioned) or geology.
Qshake,
The few cases where I had to really think about the problem were when I was surprised by the short depth and either loads (V & H) were high or the short pile was caused by unanticipated subsurface topography.