Cutting a trench through rock

Long story: I'm an electrician more than an excavator. Most of our projects there is an excavator already involved so I step back, let them dig the ditch. I dig when nobody else wants to. It's common to encounter ledge. There are solutions. NEC says covering with 2" concrete is acceptable if a proper depth ditch can't be dug. We have a project where it gets complicated, therefore expensive to use other ways. we need about ?100? feet of 12" deep trench through dolomite ledge. I imagined a diamond saw 3' diameter mounted on excavator or CTL. It appears there is no such thing. I've talked with a few professionals, they agree it is a hydraulic hammer job, might take a week. Another wants to blast. I don't think the owner, or neighbors will go for that. Any suggestions? Ditch I need will be 12" deep, at least 6" wide, I'll say 100' long.

Dolomite is some hard ****, it doesn’t shear all that great unless there’s some sort of relief created. In my experience it does hammer decent. We did some 108” piers 20’ deep in dolostone/dolomite. We perforated with 24” down hole hammer in a pattern then used a 108” core barrel with C4 teeth to create the 108” shaft then came back with various augers to fracture the perforated material and remove it. Based on your explanation I would say hammer it. Sometimes it takes what it takes. I have seen blasting used quite accurately. Years ago we’d use det cord to break cores loose. Thing is, to blast you have to drill and a good bit of the time doing that could be used hammering it anyway.

They make rock saws for skids/CTL's and big trenchers. I've seen attachments that fit on larger excavators as well. Now finding one to rent will probably be an issue. Heavy-Duty Rock Saw Cut through asphalt and concrete with greater efficiency with the Heavy-Duty Rock Saw. erskineattachments.com Do you have a Ditch Witch dealer close? The DW dealer is next to my closest Cat branch and I've seen trenchers there with pretty good sized rock saws. Ditch Witch® acquires HydraWheel™ line of rock saws - Ditch Witch Ditch Witch announced today that it has acquired specific assets from River City Manufacturing, Inc., including the HydraWheel design of rock saws. www.ditchwitch.com If you go the hammer route rent a 20-30K excavator with a hammer on it and clean the ditch with your backhoe or mini. I have a hammer for our 305's that is very useful on a lot of things but it's not going to get the production needed on what you are doing.

Primacord......

DDoug said: Primacord...... Click to expand... 100' long, 1' deep, 6" wide? Nah hammer it out. Once the pre-blast survey and seismographs are placed on the adjoining properties one can rent a 20K machine with a hammer for $6-7K a week and be done with the job before the "you cracked my house" lawsuits showing up.

CM1995 said: 100' long, 1' deep, 6" wide? Nah hammer it out. Once the pre-blast survey and seismographs are placed on the adjoining properties one can rent a 20K machine with a hammer for $6-7K a week and be done with the job before the "you cracked my house" lawsuits showing up. Click to expand... July 4th after dark.....no problem-o.....

I'm thinking CM1995 might be the best option I've heard. Blasting isn't going to be a good choice, too many whiney people to appease, likely needs permits on a higher level than excavation. I had envisioned a rock saw on a heavy machine would work. It seems nothing like that exists locally. I've been on the dumb end of a diamond chainsaw hand held, by the end of the first day not much to show for my efforts. With a 14" blade, I might go 5" deep, then jack hammer to clear that first 5". Next day less is accomplished. Third day may or may not accomplish my goal.

There is a used skid steer 12“ planer on CL right now for 2500 that would do that job. Be even better with some water.

Also hammer. Skid steers need great conditions to cut rock. Good traction, smooth. Just get whatever hoe you can rent with a hammer. It may not be as big as you want but just do it. For a foot deep I would just march into it and lay waste plenty deep, then return with a bucket and clean it out. Little bit of bedding to smooth for the conduit as needed. Then pour it in.

I was on a job once where the rock was so hard they had a blaster come in and drill it in a 12" grid pattern to give the hammer some relief and a place for the rock to fracture. It was slow but blasting was not a option in downtown Greenwich CT

In India the answer would be hire a couple of hundred guys with lump hammers and cold chisels..... Seen it done more than once.

Nige said: In India the answer would be hire a couple of hundred guys with lump hammers and cold chisels..... Seen it done more than once. Click to expand... I've seen similar in Africa as well.

Dolomite is a Limestone that commands respect as hard as Granite. Acid Resistant, extremely Dense and usually a Really DARK Gray Color. Can be Chipped or shattered yet requires MASSIVE Pressure as in ANFO. JY is Correct, saw the Hammer set up they ended up using on Dolomitic Limestone, Cut multiple holes, break out between the holes. Planers and Carbide bits just Smoke and Spray Sparks as they erode. Several quarries here mine it, one was aptly Nicknamed Hell Hole, by the Nuke, supplied 98% of ALL the rock in the Plant's Concrete. Blast Drillers hated making the Bore Holes for the Charges, drills took a shellacking.

DDoug said: Primacord...... Click to expand... AKA DetCord.

Well there is always Dexpan. Dexpan Up to 30% Off Wholesale Discounts! Dexpan Non-Explosive Expansive Demolition Grout for sale. Easy concrete removal, rock breaking, cracking and splitting. www.dexpan.com

Nige said: In India the answer would be hire a couple of hundred guys with lump hammers and cold chisels..... Seen it done more than once. Click to expand... Rutland VT might find 500 men on the sidewalks on any warm day. Most live in run down motels paid for by the State. None want to work.

DMiller said: Dolomite is a Limestone that commands respect as hard as Granite. Acid Resistant, extremely Dense and usually a Really DARK Gray Color. Can be Chipped or shattered yet requires MASSIVE Pressure as in ANFO. JY is Correct, saw the Hammer set up they ended up using on Dolomitic Limestone, Cut multiple holes, break out between the holes. Planers and Carbide bits just Smoke and Spray Sparks as they erode. Several quarries here mine it, one was aptly Nicknamed Hell Hole, by the Nuke, supplied 98% of ALL the rock in the Plant's Concrete. Blast Drillers hated making the Bore Holes for the Charges, drills took a shellacking. Click to expand... Danby VT is home of the world's largest underground marble quarry. in the 1980s they wanted to avoid damage to marble by blasting. The overlying ledge is Dolomite. They contracted to have three tunnels each 500 feet deep through the low value rock above the softer marble. It was a ten month contract. At two years the contractor gave up.

Rockwheels: Rock Grinder & Excavation Attachment | Drum Cutter Explore RockZone's Rockwheels for efficient rock excavation, grinding, and trenching. Find high-quality attachments designed to tackle tough rock-cutting tasks. rockzoneamericas.com

materthegreater said: Rockwheels: Rock Grinder & Excavation Attachment | Drum Cutter Explore RockZone's Rockwheels for efficient rock excavation, grinding, and trenching. Find high-quality attachments designed to tackle tough rock-cutting tasks. rockzoneamericas.com Click to expand... I looked in to a drum cutter for a 1800' water line project. A lot of them are only good up to 30 MPa rock. Dolomite normally ranges 30-60 MPa. Weathered rock can be easier to fracture and the really hard stuff is up around 90 MPa.

CM1995 said: Well there is always Dexpan. Dexpan Up to 30% Off Wholesale Discounts! Dexpan Non-Explosive Expansive Demolition Grout for sale. Easy concrete removal, rock breaking, cracking and splitting. www.dexpan.com Click to expand... I've seen it work. My neighbor as many, had a 7' boulder in his cellar. It took up a lot of space. He felt blasting wasn't an option. I don't remember the cost. Our boulders are extremely hard, probably some variety of granite. He hired someone to drill several holes. It broke it up to pieces he could cary up the stairs.