tunneling under concrete - Contractor Talk - Professional Construction and Remodeling Forum

wireless · 01-13-2009, 10:12 AM

Will digging under a concrete walkway weaken the walkway? A customer wants to install a intercom on a concrete column in middle of a concrete yard. Someone proposed drilling down through the concrete and then dig over from the side to meet up with the hole to pull the wires/conduit through. I was wondering if the area above the cavity would start to crack?

MBS · 01-13-2009, 11:13 AM

Quote:

Originally Posted by wireless

Will digging under a concrete walkway weaken the walkway? A customer wants to install a intercom on a concrete column in middle of a concrete yard. Someone proposed drilling down through the concrete and then dig over from the side to meet up with the hole to pull the wires/conduit through. I was wondering if the area above the cavity would start to crack?

How far from the edge of the concrete to the post? What type of soil is it? Is it on a sand base? How thick is the concrete? All these things are factors.

If your slab is at least 4 inches thick, and poured over sand, you can easily jet PVC conduit under the slab with a garden hose with minimal earth removal, and in that case there should not be any problems.

wireless · 01-13-2009, 12:51 PM

Quote:

Originally Posted by MBS

How far from the edge of the concrete to the post? What type of soil is it? Is it on a sand base? How thick is the concrete? All these things are factors.

If your slab is at least 4 inches thick, and poured over sand, you can easily jet PVC conduit under the slab with a garden hose with minimal earth removal, and in that case there should not be any problems.

The column is about three feet off the edge. The soil in the area is generally clay. I am not going to be the one to actually to the "tunneling". The HO's handyman came up with the idea, I just want to know if long term it is a good idea.

Martin Co · 01-13-2009, 02:29 PM

A simple way to tunnel under a concrete walkway or drive way that is stable, is use a good shop-vac.

When using a good shop-vac, duct tape the end of a hose to the pvc piping that your going to use. And watch it bore the hole for you!

Then, once you have the hole bored out, get a long string that will make it through the hole length wise. Make a duct tape ball that will clear the hole and tape it to the string. Once the ball gets to the other side, you can pull your wiring through! Use the shop-vac to pull the ball from the other side..

An old "Italian builder" taught me that trick! Very intelligent builder.. Reminded me of the guy on the tv show house! So I called him house..lol... He always gave me the "tough-love" treatment!

I always get that puzzled look when I do it and contractors are amazed!

-Mike...

Your place for custom siding & decks.

platinumLLC · 01-13-2009, 02:32 PM

If you go down about 12" you should be fine. You are only running a small intercom cable so you won't need a big hole. For installing post lamps my electrician will dig a hole at the edge of the concrete and then pound a piece of EMT under the sidewalk where there is another hole and then tape uf wire to it and pull it back threw. I have used my pressure washer to tunnel bigger holes under ground.

MBS · 01-13-2009, 06:45 PM

Remember, safety first. Whenever working in a tunnel, wear a hard hat! and keep a good flash light with you at all times.