Tunneling - Part Two

[Bill Stock]

OK, so I've started my tunneling project (3" * 12', 5' below grade) mentioned a few weeks back. The pipe is not comng for a week or so, but I thought I would start to see what I was getting in to.

I cored drilled the block (2 x 4" holes) last week in 'anticipation' of the chunnel. I assembled a few tools based on your comments last time, garden auger, pressure washer, telescoping wand. I decided to start the hole using my 5' installer's bit to try and get a straight line and see if there were any obstacles 'out there'? The bit stopped at about 2'+. Damn. Next I got out the garden auger (3"x3') to see it it was a small object I could grind out. Nope. So I put the pressure washer to use to see what was impeding my process? I was hoping it was a soft brick, but it appears to be part of a concrete block at an angle to the hole.

I've tried cracking the block with a piece of rebar and a 3lb hammer, but it just breaks little chucks off. I don't have a lot of room to swin, so it's difficult to use a sledge hammer. Also if I just lay the rebar in the hole it will skip over the top of the block due to the angle it's positioned. I don't know if I can dig it out or sink it, as I'm not sure how big it is. I guess I need a better chisel so I can really smack it. Perhaps some kind of air chisel for my compressor.

All useful suggestions on a better approach for breaking up the obstruction would be appreciated.

[Dan Espen]

Start making the hole wider.

Make sure you're not breaking into some utility line.

[Bill Stock]

Yeah, except my exit hole is only 4". So even if I can free 'the object' it may not come out of the hole. I don't want to make too big a cavern in any event, as I don't want to sink the paving stones above.

I can tell you that it's some kind of concrete and it's HARD. Likely an old piece of wall or foundation. If it were block or brick I would have smashed it by now. I bought a long 60" hard, heavy, pointy thing to hit it with, but it won't budge. I think the pointy thing is a digging/rock bar. I think if I could really swing at it, might make some progress.

My next step is to drill it and then hit it with the pointy thing again.

[Dan Espen]

Mainly I think you want to figure out what it is.

Rock bar would have been my next suggestion. I wasn't sure you had room to use it. They're much easier to use vertically of course.

An electric hammer (like a jack hammer) is another possibility. Rental places have them.

[hallerb]

core drill the obstruction...........

use extensions

[Bill Stock]

Yeah, I think that's my conclusion now too, but it's a $100 a shot to rent.

I discovered tonight that my 18" masonry bit would reach the obstruction, since the nose of my hammer drill will squeeze through the hole in the block. I managed to drill about 4 3/4" holes through it, but still can't crack it with the rock digger. If I pound it four about ten minutes I get to break off a small chunk. Woohoo! :-) Not to mention, the bit is now dull, the chuck is slipping and I smacked my head on the block wall when the bit skittered. It's OK though, both my head and the block are hollow.

On the bright side I discovered the enemy is about 4" thick and made of fairly dense concrete, 30+ years old.

[Bill Stock]

I wondered about an air chisel, but I did not see any bits long enough. I guess an electric hammer is the next step up. I'll have to price them versus a core drill (again).

[Don Young]

I guess abandoning that hole and starting another nearby is not an option? You should be able to fill up the original hole okay.

Don Young

[Bill Stock]

Not really, since I expect to find more. I feel somewhat fortunate that this one is within hitting distance. So I'd like to at least get past this one before I give up.

Even though the one tunnel needs to be 12', once I get past 6'+ I can dig from the other side. This will not be pleasant either but should progress faster.

[Jim Elbrecht]

-snip-

Old concrete should yield fairly easily. Any chance of welding up some long bits for your air chisel from rebar and some sacrificial chisels? [you mentioned you had a compressor earlier- and if you don't have an air chisel, Harbor freight sells them for less than $20 with a 1/2 dozen chisels]

Jim

[Bill Stock]

Thanks, hadn't thought of using rebar in an Air Chisel.

I took Hallerb's advice and bought a shiny new Rotary Hammer. The old hammer drill wasn't holding up to the abuse too well anyway. I just wish I hadn't spent the $100 on the rental two weeks ago.

[Pat]

Only being somewhat sarcastic, and depending on what state you live in, have you tried a large-ish firecracker to push it to the side? Pack in a couple of m-80s or something and BAM.

[Bill Stock]

Yeah, did cross my mind, especially with the 3/4" holes I have drilled in it now. I thought a small "cherry bomb" might crack it. But from what I remember as a kid (lifting garbage cans) it might do quite a bit more.

I'm in Canada anyway, so they can't legally be bought as far as I know.

[sylvan butler]

Yeah, that's just the ticket... Pack some explosive powder deep into the bottom of a horizontal, mostly cylindrical hole about 4" in diameter and set it off. Does that sound like anything familar to you?

Like maybe a cannon?

sdb

[Wile E Coyote]

good thing you're not claiming to be a weapons expert

[Nick Hull]

The trick is to use a high brissance explosive, like a #6 cap, that produces little gas but a sharp shock wave.