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I was planning to install some low voltage landscaping lights and I needed to go under a 10 foot wide concrete driveway. Can I use a flexible drill bit to dig a 1/2 wide hole and fish some 1/2 pex piping as a conduit? What are the pros and cons compared to digging out a 10 foot long trench and hammering a pvc pipe in?

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    That's a rather vague question. Can you? Sure! Pros and cons of pex vs. PVC? Of a drill bit vs. a dug trench? What are you asking? It mostly depends on your skill set and available tools.
    – isherwood
    Commented Jun 14, 2023 at 20:57
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    I'd probably connect a garden hose to your pex and water-bore through.
    – isherwood
    Commented Jun 14, 2023 at 20:58
  • Fully agree with @isherwood, although it is soil dependent. I have used water drilling to get a ~10 foot piece of 1" PVC under a concrete driveway. Very quick and easy.
    – Jon Custer
    Commented Jun 14, 2023 at 21:25
  • Hopefully you have some leeway on the other end as far as the terminal location of the conduit, because it's kinda hard to bore dead straight. IDK that you're gonna have any luck with fishing 1/2 PEX though. Consider a larger pipe, like 1" or 1.5" PVC, and cutting it into sections that you can connect with couplers. Otherwise your bore pit may need to be 12' long.
    – Huesmann
    Commented Jun 15, 2023 at 15:57
  • @Huesmann - 1" PVC is pretty flexible - you will need 4 feet or so of a trench, but not the full length.
    – Jon Custer
    Commented Jun 15, 2023 at 16:51

4 Answers 4

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Others make a point of what's under the driveway being unknown. You want something that isn't so noticeable.

Try this:

Circular saw with a concrete cutting blade.

Straight edge across the driveway as a guide.

Cut across the driveway just about 1/2 inches deep.

Move the straight edge over just about the width of the blade, to make another pass. You now have a trough cut about 1/4 wide by 1/2 deep.

Tuck your cable in the trough. ( adjust the width or depth if needed)

Fill the trough with concrete filler caulk.

After the trough is caulked sweep with an old broom or stiff bristle brush to mimic the brushed texture of the driveway.

After a few weeks of weather and dirt from use the line is about invisible.

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Consider the challenges ahead.

Driveway concrete is usually laid on top of crushed compressed stones. Sometimes but rarely (the cheap method) just on top of dirt.

So you will probably facing/drilling into crushed stones.

Water drilling will not work here.

Since you plan to use a flexible drill extension you will have no control where the drill goes.

Before you give up on this method, excavate near concrete and inspect what are you facing.

If rocks, then plan using diamond saw to cut a trench. Consider the driveway concrete is usually 6 inch thick, so you need a saw that can cut that depth. Once you are through the concrete excavate a trench for your pipe.

THE EASY WAY

Since as you say it is low voltage cable, it does not need to go underground.

Choose a driveway cable protector and be done with it.

driweway

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If I understand you correctly, I think you will wreck your drill, its not designed for lateral forces.

I would hire a concrete cutter to cut two 10ft lengths and then cold chisel out the groove. Then place the conduit in the channel.

Or, if possible, take it into the garage up the wall and across the ceiling and down the wall again.

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Using a drill isn't likely to work because the hole will certainly crumble and cave in over a 10 foot tunnel. Depending on the soil conditions, it will collapse entirely at least in several spots.

The benefit of the flexibility of 1/2" PVC will also be your downfall: Hammering or pushing on the end of a 10' long piece of 1/2" PVC will look a lot like trying to push a piece of cooked spaghetti. A larger diameter pipe would be more rigid, but as you mention, may need a longer trench. What about driving in a 1" or 2" EMT instead? The thinner walls may help and, obviously, the softer the soil the easier the tunneling will go.

Last time I drove a PVC pipe under cement, it was a 3" schedule 40 PVC drain line for my downspouts. It took 2-3 hours because of not only the gravel that was under the slab, but because it was close to the house and that's where all the rock from excavating the foundation ends up. I ended up splitting the end of pipe several times and destroying several wood blocks with the sledgehammer I was driving it with. That was only a 36" wide sidewalk. The time before that I spent only an hour getting a 1.5" line under a sidewalk because I had the luxury of being able to go under most of the gravel.

Depending on what fill is under your driveway, going deeper (18"-24") may be worth it to get underneath most of the rock. Plan on sacrificing some of the pipe in the process so you can cut a clean end on both ends after it's in place.

Also, maybe come back and post an update after the job is done so others with similar projects can learn from your adventure? Good luck!

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