Stuck core Bit in concrete 3

[BECT]

Hello,

We were in the process of coring 64mm dia. hole for Williams anchors. Our core bit stuck when it was 57" into the concrete. I am planning to do additional 75mm hole on top of it and take this core bit out and then grout it back . Once the grout is set , I will drill hole again 64mm hole. Has anybody encountered similar problem.

Another idea is to put pipe in the bit and weld all around and then pull it with jack.

see attached picture. Let me know your thoughts

Thanks

 

[jayrod12]

is that supposed to be 5 to 7" into the concrete, or did you really mean 57"?

I don't mind either option, although I wonder if a pipe wrench turning it counterclockwise might not free it up a bit to back it out.

 

[r13]

Seems there is widened gap between the drill bit and the concrete, have you tried to pour lubricant to loosen the bit? Or just core another hole nearby, if precision is not a issue.

 

[phamENG]

Can't say I like the idea of filling with grout and then setting the anchor in the grout. Seems like the anchor tension capacity will be reduced to the friction at the interface of the grout to concrete, which probably won't be much.

If jayrod's idea doesn't work, I have a really outside of the box (and probably impractical) idea - drop some dry ice in the hole and let the bit contract, then pull it out. Then you can just let the dry ice sublimate and move on with the anchor installation.

 

[bones206]

I think overdrilling with a larger diameter bit is a safer way to go. Yanking it out with a jack could damage the surrounding concrete (analogous to a concrete anchor breakout cone).

 

[Celt83]

you could try filling the bit with some ice to force some thermal contraction and see if that free's it up.

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[Ingenuity]

I have had this happen numerous times. It really really sucks when it is a large 12" dia core bit...and you hit prestressing strand...and the diamond teeth shear-off. Bad days!

First question I usually ask of myself (or the driller/operator) is why did it happen? Often it is that you hit a rebar on the outside edge and the small crescent-shaped segment that resulted has displaced into the the space between the core bit teeth - wham, wedged tight.

Your photo looks like a barrel bit, with segments that flush-screw attach to each other, to achieve greater core depths. Barrels have a rather thin wall thickness, and my experience has been that about 50% of the time it is tough to remove successfully (hydraulically with an attachment) without breaking the core.

I assume abandoning the core and re-locating is not an option.

I would proceed as follows:

1. Try to remove the stuck core segments using an attachment of some sort and a hydraulic jack - what do you have to loose. To avoid concrete breakout cone, use an annular steel plate around the top of concrete bearing surface and the jack (preferably a center-hole ram) should load this plate such that you are doing a CONFINED pull test. If you don't confine in this area then you do risk a possible breakout;

2. If the hydraulic removal works, then do a visual on the hole and check for an obstruction, then proceed with coring (new core bit/s?) to required depth;

3. If the jacking operation was not successful, then plan B of oversize 75mm core hole. Using the 75mm core, I would drill to the depth of the stuck core, stop, remove the stuck bit, then switch back to 64 mm bit and drill to required depth. Clean out hole and presumably grout in the bar. If you are using Wil-X cement grout with the Williams bar the additional annular space at the top of the core should not be a problem. If it is a epoxy-based grout then you may need to add a filler to the larger annular but I doubt you will (unless you bar is small dia) because the surrounding concrete will be a large heat-sink and take care of the exothermic reaction and avoid cracking to your epoxy.​

If the core hole is too smooth for sufficient bonding, I have acid-etched the core wall and flushed with copious amounts of water to neutralize. Works well in removing cement paste and 'opening' the pores of the concrete.

 

[dhengr]

BECT:
You might have some luck if you where pulling up on the core pipe with a hydraulic jack, and at the same time imparting some axial impact loading on the core pipe; like that induced by an impact drill or hammer, axially, not torsionally.

 

[Ron]

Expanding on dhengr's concept...

A couple of inches of the barrel is sticking above the surface. Drill a hole in each side and run a dowel through it. Try first to turn the bit by hand (and an hefty pipe wrench), then pull with a hydraulic jack as dhengr suggests. Might try both at same time.

 

[Ingenuity]

I wonder if a pipe wrench turning it counterclockwise might not free it up a bit to back it out.

Do NOT turn the bit counterclockwise. These appear to barrel bits and turning counterclockwise will then unscrew the segments - then you have a bigger problem - barrel segments down the hole!

 

[IRstuff]

Seems like some lubricant might help in removal.

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[jayrod12]

Do NOT turn the bit counterclockwise. These appear to barrel bits and turning counterclockwise will then unscrew the segments - then you have a bigger problem - barrel segments down the hole!

Learned something new today.

 

[BJI]

I would avoid any lubricant, it could lead to bonding issues for any subsequent grouting. Adequately de-greasing and cleaning down hole seems impractical. I think jacking is the way to go, cycling the pressure until it comes loose. Use a maximum ceiling pressure on the jacking operation based on a cone break-out calculation.

 

[Ingenuity]

Yanking it out with a jack could damage the surrounding concrete (analogous to a concrete anchor breakout cone).

...cone break-out calculation

If the hydraulic jack loads the concrete around the perimeter of the core hole (see photo below) the concrete will be 'confined' and there will be NO cone break-out.

 

[BJI]

Assuming you have a hollow jack, and in that size, and compact enough, then it would be confined. If you use a welded beam with compact jacks under each end then it might not be.

 

[Ingenuity]

What I have done in the past is to fabricate a custom steel stool/chair with annular bearing plate (slightly larger than the hole OD), and welded a threaded rod to the stuck bit, and a 5-ton center hole ram to pull the bit out. Concrete is confined, no cone failure.

 

[Rabbit12]

The OP just disappeared. Would be nice if they could come back and tell us the outcome.

 

[BECT]

hello all,

My apologies getting back so late. Thanks to all for the brilliant ideas and special thanks to Ingenuity for penning down all the scenarios. We put extension above the drill bit and tried to pull out with overhead crane but all it did was pull the top extension off of the bit and hence not successful. As we were running out of time we decide to drill additional 3.5" core on top of it and went down 57" where it was stuck. We discuss this with William anchors and they said step drilling is ok as I am installing my anchor 144" deep into the concrete where I need to expand my shell in a hole dia. of 64mm(2.5"). We did make sure that shell expand in 65mm hole dia. and we have 2-3ft of 64mm dia. above the shell. All went well.

Root cause: The crew after having lunch forget to use water while coring and it gets hot and expand and finally stuck. This is what I learned.Some are also saying it its piece of rebar/metal but from historical drawings I couldn't find any rebar or metal.

Ingenuity , I gave them the option of welding also and pull with hydraulic jack. But time was kind playing major role and we end up doing additional coring as stated above.

Regards

 

[Ingenuity]

BECT:

Pleased to read that it all worked out in the end. Hardened slurry, lack of water lubrication...and a work crew returning from lunch...something was going to go wrong.

12' coring is a decent drill depth!

I assume you are using Williams Spin-Lock anchors. I am curious, what are you holding down?

 

[dik]

I just had a project where 'refusal' was about 20' down... and I wanted the soldier piles to be embedded into 6' of bedrock... the foundation contractor broke a $37,000 24" dia drill bit... refusal, as we learned, was a layer of glacial 'boulder' moraine.

Dik