Hitting Major Rocks

bradjacob

I'm building a shed on a pretty nice slope. So we're doing piers 3 feet down. Of course we got 2 holes without an issue, then BAM - the rear holes! We hit what seemed like a rock ledge on both rear pier holes. We even dug around and kept hitting more rock. These are the two rear holes that will hold the the longest posts - so we gotta get down deep.

What is best approach? Will renting a jack-hammer chip away at Eastern Pennsylvania rock? (sorry if that's vague).

Or do I need to get in an excavation company?

Or should I just hire some day-laborers and give it hell?

Just looking for some insight on what others have done when faced with this...

denick

Brad, Is it ledge? Or a large rock? or a few large rocks?

If its ledge you should be able to pin the footing to the ledge.
If the rocks are large but moveable you may need to excavate.
In the past if the rocks were large (that they extend below frost lavel we would just pour a spread footing over them.

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john1066

you might be better off getting an excavation company to dig out for the piers unless it is ledge you may want to investigate it more but one trick is try a jack hammer if you feel the ground around you moving its a boulder if its not moving ledge

are we talking about rock this serious

bradjacob

Wow! Yeah, after looking at the picture, I can say for certain that it's not ledge. These are home just finished being built about 2 or 3 years ago. All the grading was done by the home builder, so what's down there is just boulders.

And yeah, when I stab at the rock with my wrecking bar, the ground does shake. Has the hollow vibration. We're gonna try the jackhammer. But if we need an excavator, I guessing this can get pretty expensive? I have no idea what to expect in terms of price. But it looks like two holes need to be done. And these are the rear-most holes, which is where I need to bury my posts the deepest.

john1066

thats usually the best test but it works well. for an excavator you could just go rent one for the couple hours its going to take for you to do the job. depending on how deep your going komatsu makes a small excavator that won't tear the yard up too bad and works pretty good. its a pc09 ive used one before to help my buddy with some roof drains some rental places have them around

rino1494

It is probably where the excavator dug a pit and buried all of his excess rocks.

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bradjacob

You are right on the money. The first 6" is a breeze, then we hit all the backfill. I'm just hoping the jackhammer works.

Morning Wood

In the long run it is actually a good thing to have rocks down there. Makes for good drainage. If you have a hammer drill you can drill holes and use feathers and wedges to split the rock apart into smaller pieces. It would be quicker to just get a small machine in there and dig it out though.

bradjacob

What does one of those machines cost to rent (per day) - and what would I need to remove a rock with (let's say) a 3-4 diameter?