stick a drill rig over it and go to town coring. i don't know what you're looking for but i'd try to use ndt methods to check it out first then fall back on coring.
Coring is about the "only" method of cutting down a shaft. Be careful on setting up - I've cored some shafts way too many years ago - slight deviations of the drill and you'll end up drilling down a rebar - we even got a core barrel stuck once - drillers spent 2 days and a crane to try to recover - their prob! I'd at least double tube core.
OK, we managed to miss the rebar.
We collected 4, 5-ft long cores using a 2-inch id double wall core barrel.
The resulting cores look just awful. Numerous horizontal separations, discoloration, and I can abrade the surface with my fingernail.
Makes me think 'bad tremie job.'
Any thoughts?
Well before we throw the baby out with the bath water......check the compressive strength of the cores to confirm. If bad, then we have a problem......were they all bad....or just a few......so do we core them all or is it just a select few........if it is just a few, possibly installing a couple of piles with a pile cap may solve the problem (talk to structural) If they are all bad....well it just sucks to be a contractor some days.
By the way.......who was in charge of the pile supervision during the project........was a geotech firm hired to perform pile monitoring......if not........hmmmm....now there was a bad move......and if there was.....well the supervising firm better had tonnes of paperwork covering themselves.
Remember......engineers do on a dime.......what fools do on a dollar.
Seems you had some inexperienced drillers doing the coring? Can't believe that you couldn't get better results (on recovery of pieces with L/D>2) using double tube core barrel - even a single tube. . . . Just a thought....