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maxpatch67 04-30-2009 03:23 PM

digging trench through solid rock
We're digging a french drain system and hit solid rock for about 10 feet in length. We need to get about 1 foot deep through that length of rock and then its dirt again. What is the best option? Paying for a rock saw rental(really expensive) or jackhammering it? What's best. Please help. We have to get through it and there is no where else to put the drain.

Grampa Bud 04-30-2009 03:34 PM

Rent yourself a Stihl Partner saw if you want to cut the outline and crosshatches about every 6". Or just rent a Bosch electric jack hammer with a straight breaker bit and a spade bit. It's 120 VAC and you will probably need a bottle of Jack after the job is over, but it will do the job.

Daniel Holzman 04-30-2009 04:43 PM

The best tool depends on how strong and hard the rock is. I had a similar situation where I had to install approximately 25 feet of 4 inch diameter drain line through granite, which is very hard and very strong. The method I used to chip the stone was to use an electric hammer with a pointed bit to "soften" up the rock along a line, then a flat "spade" bit to remove the rock. Very hard work, took a long time, but it worked.

If you have unlimited funds, an air trac is the best, but you will need to hire that out, can't rent that tool so far as I know. If you had a really large project, you would use explosives, but for your job that would not be cost effective.

If the rock is soft, such as shale, soft limestone, or siltstone, you could do the work with a star drill by hand.

There are unusual techniques that sometimes work, such as drilling small, closely spaced holes into the rock using a hammer drill, then filling the holes with expansive cement (Google expansive rock breaking). This works fine with certain types of rock, and is relatively easy, assuming you rent an adequately sized hammer drill.

jayharold 05-02-2009 10:46 AM

If you can rent a compresser and air hammer I think they hit better than a electric hammer.

bjbatlanta 05-02-2009 01:24 PM

Go to and check out DEXPAN. Don't know if it's available in your area or how much it costs, but it looks interesting....

Aggie67 05-02-2009 02:03 PM

This thread reminded me of my fishing jaunt Friday morning. I went to a local reservoir I hadn't fished at before. It was a private reservoir for decades, then finally opened as a state park a few years ago, and this was my first time fishing it.

So I'm there for a few hours, and it rolls around to 10:00 am, and I'm casting, all of a sudden I hear a steam whistle. Whoooot! Whoooot! Whoooot! I'm thinking, well it's not time for lunch anywhere around h.... "WhaaAHBOOOOOOMMMM" Ground shakes under my feet and my heart skipped a few beats.

The reservoir was on the other side of a mountain from a gravel quarry. Must be solid rock, because I felt it good in my ankles.

Max, what type of rock is in your way? Shale, schist, basalt? Makes a difference in the cutting tool. I had to trench through basalt once. We perforated the surface with hammer drills, and then broke it up with a point bit mounted to a skid steer.

Also, wear some chaps and goggles. The stuff broke up like hand grenades going off.

maxpatch67 05-10-2009 01:26 AM its raining a BUNCH here in Tennessee. It won't stop!!!

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