Breaking up a large rock

[dillo99]

I was helping a neighbor dig a drive out entrance for his basement when we encountered a large rock. The thing is about 6ft in diameter and maybe up to 4 ft deep. There is no way we can move this with our equipment so we are wondering how we might break it up. I am assuming some type of jack hammer from a rental store would tackle this beast but I have never used one. Does anyone have experience with these? It would have to be something we could likely rent.

Any ideas would be appreciated - except dynamite (the rock is about 4 feet from the house!).

Thanks,

Mike

 

[Paddy]

If it is granite, your in for a work out!

 

[john_bud]

Well, I havn't had the "pleasure" of dealing with a rock of this size, but you will need to buy (rent) a hammer drill and some long bits. 3/8" to 1/2" size. Drill a series of holes in as deep as you can with the holes 2" apart or so. You can try the holes farther apart and see if it works, can't hurt. Each rock is an individual...

Then drive in some small wedges and tap them down gently from one edge working across then back. You want to maximize the forces equally across. Wear safety glasses. If there is a grain to the rock, try and follow it.

Now if you were doing this in the winter, you could just drill the holes and fill them with water. It would freeze and crack the rock - done. I'm guessing you don't want to wait that long (lol).

jb

 

[kmdigital]

If it is what is called igneous or native rock, such as granite, etc, it is virtually impossible to break a rock of that size with a jackhammer. Now if it is sedimentary rock, such as sandstone, which is highly unlikely unless someone buried it there, you can probably break it with a jackhammer. Otherwize, do what john_bud said, or hire someone with a heavy equipment to come in and remove it for you. Might be the cheapest way in the long run.

 

[dillo99]

It is not granite and is in part sedimentary rock. Our native rock around here has some hard spots but those are interspersed with sedimentary stuff that is not too bad.

Waiting til winter is probably not in my neighbors plan so I guess we will have to try the hammer drill/wedge approach.

Thanks.

 

[SPYDERLK]

I was helping a neighbor dig a drive out entrance for his basement when we encountered a large rock. The thing is about 6ft in diameter and maybe up to 4 ft deep. There is no way we can move this with our equipment so we are wondering how we might break it up. I am assuming some type of jack hammer from a rental store would tackle this beast but I have never used one. Does anyone have experience with these? It would have to be something we could likely rent.

Any ideas would be appreciated - except dynamite (the rock is about 4 feet from the house!).

Thanks,

Mike

What is the shape of the rock? -A potato, a ball, a slab? Dimensions~? Orientation of shape wrt vertical and wrt house. Depth @ bottom/top?? 4ft? Can you dig out side or ends? We need to know as close as possible what you are dealing with.
Larry

 

[gordon21]

Less than $100 worth of Dexpan will take care of your problem. No need for a jackhammer, which probably wouldn't work anyway.

Dexpan is a controlled explosive. It works on the same principle as freezing water. it expands and cracks the rock in half or thirds or whatever you want. It does NOT explode. It works in a couple hours. No licenses or permits necessary. It is typically available at welding supply places.

Do a google search and you can find a local supplier in your area. Your existing equipment can then take out the smaller pieces.

 

[3RRL]

You could try what John Bud said but instead of using wedges, where you apply pressure only one that specific wedge point (one at a time) you could try this....
Get those expandable big lag bolts that expand inside the holes. Put the female into the holes and run the boltT in with an impact wrench. That will put even stress at each hole trying to force the rock apart..split along the line of the holes. Then whack it a sledge to create a "stress fracture" along the holes....retighten the bolts and it might pop off?

I have insert them into rocks and accidentally split them before when I didn't want to.

 

[dillo99]

What is the shape of the rock? -A potato, a ball, a slab? Dimensions~? Orientation of shape wrt vertical and wrt house. Depth @ bottom/top?? 4ft? Can you dig out side or ends? We need to know as close as possible what you are dealing with.
Larry

The rock is basically a slab - looks like it is about 2 ft in depth, but difficult to tell - it could be deeper in the center. The slab is then basically kinda round - about 6 ft across. We were able to dig around it some, but it is in a difficult spot as it is about 5ft below grade in what was basically to be a driveway into the basement. My neighbor was going to put some kind of retaining wall on each side so we did not knock the side walls down much - so there is only a few feet of working room on each side. We were able to expose some of the edges of the rock with the backhoe. The rock sits about 4 ft from his basement wall.

Thank you all for the ideas.

 

[SPYDERLK]

Mike, heres a few brainstorm ideas. The xpandable things, incl "explosive" sound good. In addition to/instead of these you could cut/scribe a line using an abrasive masonry blade on a circular saw and then fire a bunch of masonry spikes into it. Alternately, you may be able to roll it out whole if you can dig around it and then pass a couple of strong web straps around it. One end of each would be immobilized. The top ends would be pulled on. This favors rolling and can give a 2 to 1 mechanical advantage. Also, when in the open I have had good luck breaking across the small cross section by dropping other big rocks on them from 10' high.
Luck.
Larry