Ineffective soil at the top of piles 1

[KootK]

I need to settle a little debate with my boss. Here's the situation:

Normally, the soils reports that we get from our geotechs instructs us to ignore the top 2 meters or so of the pile length when calculating skin friction and lateral load resistance.

By boss says that that the 2 meters is from the top of the pile cap, not the top of the pile itself. He is assuming that the issue is frost disturbance to the soil. Therefore the two meters is measured from the soil surface surrounding the pile/cap assembly.

I was under the impression that the two meters should be taken from the top of the pile which, in this case, is the bottom of the pile cap. I thought that it was all about the soil near the top of the pile being disturbed by construction activities associated with constructing the piles.

So, who's right here? For what it's worth, these are cast in place concrete piles.

 

[ishvaaag]

The particular interpretation should be asked to those making the recommendations, for it might mean either.

Anyway, any of you, if you don't see mandatory clause and clear one in the applicable code, and not precision is coming from the geotechs, you are left with the technical books recommendations, that may also vary given the different backgrounds, what is sound because there are different situations and what is good somewhere is not at another place, and helps to understand what when.

I could look at some of these books and would be such thing, just a particular case advice even from one accepted source.

 

[jgailla]

Kootenay, I agree with you.
When I did soil capacity calculations for piles, I was taught to ignore the top 5 feet of soil to account for construction disturbance, future excavations, etc.
It shouldn't affect your calculations much. If your pile is failing without the extra soil and passing with it, I think you're cutting it too close anyway.
It's dirt, which is a pretty variable material even in the best conditions.

 

[jdonville]

KK,

See the FHWA references for the rationale for drilled shafts. Usually, I don't see this applied to driven piles unless the soil conditions near surface are obviously bad...

Jeff

 

[KootK]

Jeff,

Could you point me to a specific FHWA reference? I mulled around their website but didn't get too far.

KK

 

[jdonville]

http://isddc.dot.gov/OLPFiles/FHWA/009752.pdf

See page 275 and surrounding pages for discussion.

Jeff