Jackhammer rocks in Post holes?

[fidowanttobe]

Gentlemen,
My brother and I are installing 240 of cattle windbreak. 16 post holes for total project. Bing-bang done except 2 holes landed on large granite rocks 10 to 18" down. They are in the straight line so no moving them. Also don't want to dig them out because of the crater that will be left. Anyone here rent a jackhammer to hammer rocks into submission in the bottom of a hole? We haven't and would love to hear from experience. Thanks in advance.

 

[Raspy]

It depends on how big they are. If they are several feet in diameter, you'll just be chipping them away a little at a time and not get anywhere fast. Sounds like a lot of time and effort to rent a jackhammer and try it down in a hole. Do you have a backhoe? Then you could just dig them out with that.

 

[prichard]

What are your posts? What kind of rock?

If small enough diameter you could possibly just drill a hole in the rock with a good size hammer drill?

 

[fidowanttobe]

10" dia 12' long treated round poles. Think it is granite. Not sandrock or anything soft. Beating on them with rock bar only produces chips and sparks. A guesstimation of the rock size is a couple/three feet in dia but we are on the edge of it as hogging the hole out on one side gets us down deeper gradually. Afraid of using the neighborhood excavator as we would then have to tamp in a hole the size of a bedroom.

 

[ArlyA]

I've not used one but people here own or rent gas power jackhammers. They say they work well on fine the hard rocks found here.

 

[Cord]

I've used concrete breakers on rock and it can be really slow going. The key thing to make a breaker work, is the ability to displace the material. This displacement is what forms the crack. When the material is too large or too thick, the hammer can't displace it, thus it never cracks. All you get you get are small rocks coming off the edges. The ability of the breaker to crack your rocks is dependent on the size of the breaker and how big the rock is. Even if you managed to crack the rock, you still will not have a hole you can put the post in.

Couple potential solutions:
1. Core drill a hole in the rock. You can now set the post in the hole and use pea gravel to hold it in place. There are mobile outfits that do this on a per job basis. Figure $1,000 per hole.
2. Set the pole with the minimum embedment and then pour concrete around the base to help lower the center of gravity. This post will require a guy pole to help brace it.
3. Drill and blast (or dexpan) and then dig out the remnants.

 

[KennyG]

I would just move down the line on each side of the rock and put in extra posts. I don't know what your windbreak looks like but I'm assuming it has 16 foot sections. You could just bridge across the extra posts. Disclaimer: I'm kind of lazy and I hate rocks.

 

[Ford850]

2 - 3' in diameter? I think I would dig them out and backfill/tamp.

 

[Snobdds]

Why remove the rocks, let them act as an anchor. Drill a hole in the rock for one large piece of rebar. Epoxy it in. Then put the post in to get an imprint where the rebar is. Then drill a hole the size of the rebar in the wood post. Concrete everything in.

 

[cmyoung2]

Get the jack hammer, use a combination of drill bits and breaker bits, i.e., drill holes, then chip between them. Posts that size shouldn't take very long, just make sure the hole is big enough the first time. had to put in several posts in a slate bed, about the only thing that would work.