Timber friction pile - top 6ft excavated

[BurgoEng]

I have been asked by a co-worker to find out if excavating around the top 6ft of a 45ft friction timber pile (to remove contaminated soil) would impact the capacity of the pile. The piles currently are not supporting any load. They were only driven and are awaiting pouring of pile caps.

The thought is to excavate the top 6ft, and backfill with crushed stone. Intuitively, I would think this should not effect the capacity of the piles, with the thought that most of the strength of the pile is gained deeper down their length and the top 6ft or so is not a factor.

Thoughts?

 

[eric1037]

I usually ignore the top 5 feet of the pile when I calculate capacity. I would contact the geotech who provided the capacities and ask them their assumptions.

Off the cuff, I think it should be OK since you are putting good, compacted soil back in before applying load to the piles.

If the piles are laterally loaded (probably not with wood piles, but it happens) then you may have to take a different material into account.

 

[BigH]

I see no problems with this.

 

[TDAA]

I guess the question I have is: Why the excavation?

 

[BurgoEng]

In response to TDAA...

There is contaminated soil on site (or, there was) and it was supposedly cleaned up and then the piles were driven. Another sample was taken after driving, and the contamination is just barealy (~5%) over the limit. They are oging to test again, but if need be, they will need to take out the soil and replace with clean.

 

[TDAA]

OK, thankn you. At least you have a good reason to do the excavation. I also belive this should be OK.

I would be cautios of creating a bathtub effect when backfilling withh the granular material, if you are removing cohesive materials. I would recommend a below fill drain in that case.

 

[DRC1]

If these are new piles I agree there should not be a problem. Someone should look to check if capacities were field measured and what the actual vs. required is.
If these are existing timber piles, you may have a concern. exposing timber piles that have been submerged can start te piles to decay. Iftat is the case the piles must be consently wetted down.