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mart v · Sep 3, 2008, 01:17 PM

How do I go about tunneling under a slab or whom do I contact to do the job if you feel I could not do the job myself? I need to reroute a kitchen sewer line and have determined I need to tunnel under the slab approx. 15 feet. I will cut the old line, cap it, and run a new line to tie into an existing sewer line that was added during a remodel a number of years ago(black ABS). We will be cutting a large piece of the kitchen slab because of a crack in the slab, approx. 3 feet by 6 feet so there will be no constraints working in the kitchen. Outside I plan to dig the trench to the old sewer line.

albinfla · Sep 3, 2008, 03:31 PM

To tunnel under a slab..

Dig a deep enough and wide enough hole to work in at both ends.
Start with a 16' piece of pipe... it sounds like you're probably using 1-1/2" for kitchen drain.
Glue a cap on one end of the pipe. Drill a hole right in the center of the cap.
Glue a female adapter on the other end of the pipe.
Make a hose adapter with a 1-1/2" male adapter, and a 1-1/2 slip x 3/4 female reducing bushing.
And, get a 3/4 pipe x 3/4 female hose fitting so you can thread your hose end into the adapter.
Turn on hose, and push it under to connect the two holes- the hole outside and the hole in the kitchen.
You may run into some road-blocks. If you do, pull back a couple of feet and try to redirect your pipe. You can also ram it a little. But, don't get carried away ramming it. It is plastic pipe.

You could also use a slip coupling instead of a male and female adapter tied together. I always use a male adapter in case I need to add length to the pipe.
Good Luck,
Al

speedball1 · Sep 3, 2008, 04:04 PM

The problem with tunneling under the slab is that you can never replace the fill dirt back under the slab firm enough to support it properly. This can end up cracking the slab over time. Years ago I repaired a copper water line by tunneling under the slab for about 10feet. I had to set a vacume cleaner up to blow air under there because the air was so bad that my torch wouldn't stay lite. I hate to think about what the air would be like under there, full of ABS cement fumes, when you're gluing up pipe fittings. Snort a open can to get a idea. And I haven't even mentioned a cave in.
If there's another way to do this job I would look around and find it.
Good luck, Tom

albinfla · Sep 3, 2008, 04:45 PM

Tom,
I agree that if there is another way to do it, I would find it.

You are correct if you are talking about digging under a slab. However, if you are jetting as I suggested, it only displaces a small amount of dirt. I feel a little uncomfortable about going under the house slab, but I have done it under patios, sidewalks, and streets. They do it under streets all of the time. Under streets they use water and high pressure compressed air. I've never had that luxury, only water pressure!

Since you are standing in open holes on the ends, fumes are not an issue. I would dig the hole a few feet away from the slab so they don't cave in the footer.

What other suggestions would you have Tom?
Al
No suggestions Al. Just a comment on tunneling. This was directed at Mart since he was the one that mentioned tunneling under the slab. Jetting the pipe in is a much better and safer solution then tunneling

ballengerb1 · Sep 3, 2008, 05:08 PM

I think your best bet will be to rent a jack hammer or concrete saw and cut yourself a trench through the floor.

truck 41 · Sep 3, 2008, 10:28 PM

Hello, your are already cutting a section of floor out, you may as will cut a trench for your drainline and save yourself a lot of fustrations trying to bore a hole across from one point to another. Goodluck ----Zeke---