Trenching in brownstone

[kaiser715]

I gotta get power and water 400' to my new shop. Power line by code needs to get 18" below grade, so I need to dig out to 22" or thereabouts.

Problem I've found thru a couple of test digs with the backhoe is a layer of brownstone, mostly about 16-18" down (below mixed clay), but in at least one place, just a few inches below the surface.

Backhoe will just scrape/skitter across the surface of this. Pretty much the same as the excavator and dozer ripper that the grading contractor had on site for other work. BUT...being brownstone, it is soft enough that you can scrape/cut it with a utility blade on a knife.

I was thinking maybe to rent a hydraulic breaker on a mini-excavator.

Then I thought (after pricing out the mini-ex)...I mostly need to go about 4 inches down once I hit the brownstone...why not an electric demolition hammer (and a couple of younger folks to run it)? I think the brownstone is soft enough for it to go quickly, and basically would be cutting a channel 5" x 16" (width of bucket) by 400'. Thats less than about 200 cu ft of breaking/cutting.

Opinions/ideas/comments???

 

[PCustoms]

Can you go to 12" and dump some concrete on top of the condiut? Pretty sure this would meet code.

Seems cheaper/easier then busting up all the rock.

 

[macdabs]

I dig utility lines often on average 100' -350' for primary at 48" depth. All in rock mountain tops in the north east. Sandstone and limestone is the norm with clay. Your best bet with out ripping up the yard and making a mess is a mini excavator with a 12'' bucket with new teeth . You may also want to rent a single 18'' ripper for the machine with the bucket. Ripper would just look like a single tooth on a box blade. 400' is a long dig and the mini should have a front blade to make backfilling the ditch easy when your done. You will also need a tri axle of cracker dust if your backfill material is junk to protect the conduit.

Mac

 

[chaosracing]

Maybe try a ditch witch attachment on a skid steer. They can rip thru lots of stuff.

 

[Stuart in MN]

I don't know what brownstone is, and you didn't mention what state or country you're in, but assuming this is for the service entrance conductors from the electric utility you should call them to discuss. They probably have similar experience with this brownstone stuff. Maybe they'll allow the conductors to be a bit shallower than they otherwise require, or maybe you can install them using conduit or with some concrete poured over the top.

 

[kaiser715]

This is run from service entrance to my shop. Power company says best way is to either go under it, or around it. On the power feed to the house, said they'll start with a backhoe, if that doesn't work, then directional drill. I have gotten quotes of 12-15 bucks a foot for drilling. Double that # if I want to run water, too.

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[kaiser715]

This is in Lee County, NC.

Brownstone is a soft sedimentary rock/hardened clay.

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[ard]

Rotary trencher w rock teeth. Vermeer, etc.

 

[Fixin'Stuff]

The Austin, Texas area is mostly limestone, just a few inches below the topsoil. I've seen a trencher in use there that is similar to what's shown in the picture being used to trench lawns to lay in sprinkler systems. The difference was that they used a smaller, self-contained rig. No tractor required and the blade appeared to be about 3 feet in diameter. Can't find a pic of the smaller one.

There are replaceable carbide points on the blade. Looks like they'll cut through just about anything. Found this pic using "wheel trencher" to search.

 

[kaiser715]

Can't find anyone with a rock wheel around here. Did see an old one on CL about 3 hours away, but somebody beat me to it.

Seem to be more popular out west

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[kspwski]

If you can't find a rockwheel, look for a chain trencher with rock teeth on it, especially if you don't have to go too deep. Rental yards might have em.