Instead of drilling, first, try jetting around existing timber piles. Maintain upward force on the piling as jetting is performed. The existing timber piles are probably "like-new" below the mudline.
Is this a 7-pile dolphin?

I'm unfamiliar with "jetting". Does this disturb the stream bed?

Proposed dolphin cluster is 7 piles at 24" diameter. Existing timber are 12 - 14" diameter piles.

High pressure water jetted into the ground next to the piles with a small metal pipe shoved into the ground as far as you can.

Sort of liquidises the soil for a short period of time so there may be a bit of sediment but then your pile comes out of the ground.

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Also: If you get a response it's polite to respond to it.

bridgeengineer2007 - Jetting 12"+ timber piling is performed more or less as described by LittleInch... just on a larger scale, using heavy equipment instead of manpower, and underwater:



Jetting will significantly disturb the stream bed.

Typically, pile extraction is considered part of a qualified Contractor's "means & methods". The Engineer does not specify how to perform the work. If the Engineer gets into the construction details, and the prescribed method does not work correctly... the Engineer, not the Contractor, has a big problem (what to do next).

There are several ways for a Contractor to extract piling.

Please don't double post again.

It's against the rules and one or both posts may just vanish....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.