Core Drilling underwater?

[cmeb76]

Hello,
Inland diver with customers wanting our team to core drill an 8" diameter hole horizontaly through 20 feet of solid concrete... no head differential. In all our work we have never core drilled underwater. I have cored hundreds of holes in foundations/floors/walls, but always in the dry. I would be thankfull for any info anyone might have on drilling techniques, drill/bit brands, tips/tricks, rental companies that would have the right equipment. We will be drilling at a depth of 30-40', in crystal clear fresh water, but close to freezing in the midwest this winter.

Thanks...

 

[Wookie]

Use the same concrete drill bits you would use on the surface. The better bit you use, the faster your hole will drill. I use the longest bit I can find, I don't have to clean it as often. I use a Stanley DL-07 drill driven by a 18 hp Briggs and Stratton hydraulic pump at 10 gpm. All of my holes are vertical, so gravity is my friend. I don't know how you will put pressure on your drill to make it advance. Rig something with a ratchet strap, maybe?

 

[MScorpa]

I've done quite a bit of core sampling underwater using a drill like the one shown below. The frame is anchored into the concrete and the core bit is advanced like a drill press. I've only used it to a depth of up to about 18" though, not sure how you would go through a length of 20'? Maybe add extensions but it is going to be a PITA and not very precise.

 

[Dsix36]

I don't have experience doing any of this underwater, so feel free to ignore me.

I have drilled a lot of holes in concrete/rock using a core drill assembly such as MScorpa and without the addition of water, to both flush the hole and cool the bit, the bit will dull much quicker. i am guessing that the very same bits will work equally well underwater (as Wookie stated).

I have worked to core drill several hundred feet in the surface of the earth for blasting purposes and every 20' we would have to add another extension to the bit in order to continue. It was a real PITA and time consuming to bit trip every 20', but I don't see another way.

Enough of my rambling, good luck with your project.

 

[El Buzadero]

I've done many many coring jobs underwater. It is just like doing it in the dry. Make sure you have cooling water flowing throughout the process. It sounds funny, since you're immersed, but the coring blade will heat up in the kerf if you don't have cooling flow.

 

[cmeb76]

Thanks so far for the replys. I have located some bits by CS UNITEC listed as barrel bits... supposed to be able to drill out the entire length as a solid core, then pull the slug out and leave the bit in as a casing. Looks like they come in sections up to 48", which would make for less downtime adding extensions. It would have to be a monster drill though. No question we will have to use a rig like the one MScorpa posted above.
Item # TCB204-48, 48" Core Barrel On CS Unitec, Inc.

 

[DCBC]

...It would have to be a monster drill though. No question we will have to use a rig like the one MScorpa posted above. Item # TCB204-48, 48" Core Barrel On CS Unitec, Inc.

The Dynateck catalog can give you an idea of costs for equipment, should you need to purchase anything. Just go to the downloads section (Dynatek drilling products catalog) at http://www.dynatech.com/). There are a number of other catalogs from their other product lines there as well.

The only advise I would give is to have an appropriately sized drill rig and mast and to use a good quality diamond bit. Good luck!

 

[flots am]

Inland diver with customers wanting our team to core drill an 8" diameter hole horizontaly through 20 feet of solid concrete...

I'll preface this by saying I don't know squat about underwater drilling. However I do know quite a bit about screwing things up.

Anything that's built with 20' of concrete was built that way for a reason. Are you certain the hole isn't going to screw something up and that you're not going to hit any embedded metal, cables, air spaces that shouldn't be flooded, etc.?

flots.

 

[Superlyte27]

I don't know what you know and what you don't know, so here's what we used to do...

the first thing we'd do is drill three 1/2" holes in the concrete in the form of a three points of an equilateral triangle. Then using expansion style redhead bolts we'd screw in 1/2" eyebolts into those three holes. The drill would be placed in the center of this triangle. Using a ratcheting turn buckle cable hooked into the three eyebolts and three points on the drill (to tighten the cables) we'd slowly go around and tighten all three sides of the triangle until the drill was snug. Then we'd start drilling slowly tightening the cables until we had reached our final depth. Don't tighten the cables while the drill is in motion. Stop the drill, tighten each of the cables the same number of turns, then start the drill again. Obviously, the deeper you go, the larger the triangle. Admittedly, I've never had to drill through 20' of concrete, so I'm not sure if this will help your endeavor or not. And even in the clearest water, once you start drilling, the visibility goes away.

 

[MScorpa]

Thanks so far for the replys. I have located some bits by CS UNITEC listed as barrel bits... supposed to be able to drill out the entire length as a solid core, then pull the slug out and leave the bit in as a casing. Looks like they come in sections up to 48", which would make for less downtime adding extensions. It would have to be a monster drill though. No question we will have to use a rig like the one MScorpa posted above.
Item # TCB204-48, 48" Core Barrel On CS Unitec, Inc.

There may be a few potential problems with that approach;

1. The frictional forces associated with rotating a 20' long x 8" diameter drill bit. You'd better have a seriously powerful hydraulic unit and drill to power it.

2. The bit may wear before you reach full-depth, especially if you hit significant steel.

3. A 20' long slug could be difficult to remove from the casing.

What type of structure is this (just curious)? Do you have detailed drawings? Is there any flexibility in the location of the hole?

You'll need a setup more like the one shown below than the previous one I posted: