Driving open ended plastic piles through granular soil.

[scottmnj]

I have a contract to drive 80' x 12"d open fiberglass pipe piles to a theorhetical elevation of -66ft. Avg. Mudline is at -40ft. First 20ft of driving is through a M.Dense Silty Sand N = 20. Last 6 ft is through a V. Dense Silty Sand N=40. My contract prohibits jetting. We are using an air hammer to drive these. Piles are fetching up to the point where significant damage is being done to the piles somewhere between 13 - 20 feet embedment. I believe these piles never had a chance to be driven to the theorhetical depth in these soil conditions without jetting them. The nature of the pile material will not stand up to the required heavy driving. Also, I believe that there is a significant loss of energy during the driving as a result of flexiblility of the pile. It should be mentioned that these piles are being used to construct 3 pile dolphin clusters, not a foundation. I would appreciate any comments.

 

[BigH]

I'd tend to agree that it is the wrong pile for the job - especially driving through a compact (medium dense) silty sand. Did you consider putting on a driving shoe? How about using a vibratory hammer?

 

[scottmnj]

Thanks BigH. The piles came with a steel driving shoe attached. This shoe is basically a steel ring around the toe of the pile with a cutting edge. As far as a Vibratory hammer goes; the spec states that if a vibratory hammer is used the last 5 feet must be driven with an air hammer. I think the designer is trying to have his cake and eat it too.

 

[Qshake]

Any way to vibrate and then proof with a hammer? That might avoid the 5 feet of driving. Any dynamic testing?

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[dicksewerrat]

Can you drill out 10 inches inside the pile as you sink these? Are these end bearing or friction? And are you held to this material?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[wiktor]

I agree that the fiberglass pile could not be driven to specified depth. Vibrating could help a little, but the last 6' will be problematic, as driving >60'of fiberglass pipe thru 6' of N40 dense sand is next to imposible.
If you can not change the driving technique to waterjetting with may be last 3-4' hammered, consider using 10" steel pipe as a driving guide, with enlarged shoe. The shoe should be solid, not just a ring. After driving to the specified depth, just withdraw the steel pipe.