# Big rock in a hole. How to remove?



## begreen (Sep 9, 2012)

They augered the big holes for the garage posts last week. Lots of rocks. They manage to get all drilled except for one that has a big rock 3 ft down. It's about 30" long, 18" wide and we're not sure how deep. Try as they could it wouldn't budge.

What are the options here? Any suggestions besides dynamite?


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## BravoWhiskey (Sep 9, 2012)

First post! Had pretty much the same situation with a big rock about two feet down. Before getting a backhoe we asked the building inspector if it would be OK pour a little concrete to square things up and go from there, and fortunately he didn't have a problem with it.


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## Beetle-Kill (Sep 9, 2012)

www.micro-blaster.com- or a bigger hole?


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## begreen (Sep 9, 2012)

BravoWhiskey said:


> First post! Had pretty much the same situation with a big rock about two feet down. Before getting a backhoe we asked the building inspector if it would be OK pour a little concrete to square things up and go from there, and fortunately he didn't have a problem with it.


 
That thought crossed my mind, but we only get an inspection once a week and this project has been delayed too long already. If he says no, we're out another week at least before they can start putting up the poles. But thanks for the suggestion, it's worth asking about.

I like the microblaster idea, but can't locate one so far. The nearest dealer appears to be a few hours away.


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## Highbeam (Sep 9, 2012)

Keep making the hole bigger until the rock can be removed. Some of my holes were very oversized, that's okay. The only thing you have to worry about is if the rock is a boulder, like a VW bug. I was setting poles at about this time last year. The frame of a pole building goes up really fast.


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## onion (Sep 9, 2012)

Do you know what kind of rock it is?  If it is limestone some acid will weaken it maybe to the point you can bust it up.  Hannibal cut a path through a rock slide in the Alps by heating rocks REALLY hot then quenching them quickly.  The rapid cooling cracked it.  Might be fun to try anyway...


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## Jack Straw (Sep 9, 2012)

Jack hammer?


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## ScotO (Sep 9, 2012)

Do you have a local tool rental place?  If so, give a gas-powered jackhammer a try.  I used one last year when I took my old porch steps out (they were solid poured concrete with HUGE sandstones thrown in the mix).  Worked like a charm.  Those two-cycle jackhammers are pretty slick.


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## Ehouse (Sep 9, 2012)

Don't wait for the inspection, call him on the phone.  Ask if you can drill 4 holes and tie into the rock with rebar.

Ehouse


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## Frozen Canuck (Sep 9, 2012)

Ehouse said:


> Don't wait for the inspection, call him on the phone. Ask if you can drill 4 holes and tie into the rock with rebar.
> 
> Ehouse


 
Bingo.
Use the rock as an anchor/base for a foundation.
The only time we have had this refused is when the rock is above the frost line.
With your location I am guessing you are already below that elevation.
Side note; if you are in an earthquake area code may have alot to say about how you anchor to the rock.


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## Frozen Canuck (Sep 9, 2012)

& yes call the inspector tomorrow AM. Be prepared to email photos.


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## Jags (Sep 10, 2012)

Heat the sucker up as hot as you can and then quick drench the rock with a bunch of water.  It is possible to crack rocks this way.


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## begreen (Sep 10, 2012)

Burn ban going on right now after 49 days with no rain. That can't happen. I'm thinking jackhammer or backhoe.


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## semipro (Sep 10, 2012)

Check out Dexpan® Non-Explosive Controlled Demolition Agent by Silent Cracking.  

You drill some holes, mix this stuff up and put it in holes.  It expands as it sets.


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## Highbeam (Sep 10, 2012)

This is a pole building. The poles must be a certain depth and the hole a certain width to provide vertical strength (pole sinking) and to restrain lateral loads like the wind. Imagine a fence post. You wouldn't want a shallow fence post because a rock was in the way, it would just blow over and you wouldn't want to attach the fence post to a rock of unknown size even if you could. You need to get the bottom of the hole to full depth. Get that rock out of there.

BG lives in the puget sound. These big rocks were deposited when the glaciers dug it out. The rocks are smooth on the outside and can be very large. They are not limestone and are generally cemented in place with hardpan clay type soil. Most of the rocks are basalt.


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## Jags (Sep 10, 2012)

Rotohammer a few holes and then use a tapered punch (big sucker) and sledge to split the rock.  I have done cement the same way.


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## begreen (Sep 10, 2012)

I just told the company building the problem to solve the problem. The office didn't even know about it. Told them inspection is on Thursday and I am not accepting excuses.


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## Highbeam (Sep 10, 2012)

Is the inspector coming out to see the empty holes to measure depth, diameter, and location? That was my only inspection prior to final approval. They wanted to be sure I put the building where I said I would.


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## pen (Sep 10, 2012)

Sounds like you charged them for making it happen regardless, let us know what they wind up doing as I'm curious.

Around here, it's 42 inches down for posts with a concrete base to meet requirements. However, for the jobs I've been on, I've seen us hit solid rock at a little over 2 feet down and each time the inspectors told us to build from there. In some cases, we drilled a hole in the rock, and stuck rebar down into it, then a hole up through the bottom of the post so that it would accept the rebar.  Other times I've seen folks use a hilti nail gun and secure a post anchor plate to the rock.  Either case, it needs to be truly solid. 

pen


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## Highbeam (Sep 10, 2012)

pen said:


> Either case, it needs to be truly solid.
> 
> pen


 
And the pole has a HUGE amount of leverage on any mickey mouse attachment method. I was required to go 48" to bottom of pole. Pole on top of 8" thick footing and hole backfilled with concrete and two bars of rebar tying the backfill to the slab.

My kids could hide in the holes.


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## begreen (Sep 10, 2012)

Highbeam said:


> Is the inspector coming out to see the empty holes to measure depth, diameter, and location? That was my only inspection prior to final approval. They wanted to be sure I put the building where I said I would.


 
Yes, that appears to be the gist of it. My understanding is that the depth on this one hole is inadequate due to the rock. It's not bedrock that you can anchor too, just a large stone.


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## pen (Sep 11, 2012)

Highbeam said:


> And the pole has a HUGE amount of leverage on any mickey mouse attachment method. I was required to go 48" to bottom of pole. Pole on top of 8" thick footing and hole backfilled with concrete and two bars of rebar tying the backfill to the slab.
> 
> My kids could hide in the holes.


 
They made you backfill the hole with concrete?  As in surround the pressure treated post with concrete?  If so, around here encasing pressure treated in concrete would be a big no go. 

pen


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## Highbeam (Sep 11, 2012)

pen said:


> They made you backfill the hole with concrete? As in surround the pressure treated post with concrete? If so, around here encasing pressure treated in concrete would be a big no go.
> 
> pen


 
Yes sir. Apparently very common in this area as the concrete supplier had done many this way. The engineering required it.


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## Seasoned Oak (Sep 11, 2012)

You might try a boring drill. My son has a set that goes up to 5" diameter .diamond edge bores thru just about any kind of rock. I have an electric jackhammer but some rocks are just too hard for it. YOu could rent those boring drills at a tool rental center.


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## pen (Sep 11, 2012)

Highbeam said:


> Yes sir. Apparently very common in this area as the concrete supplier had done many this way. The engineering required it.


 
Wow, we are told that will rot the pressure treated off. Funny how things vary from region to region.

In the case you mention, if they want to be pricks, they'll have us pour a sonotube full of concrete with a galvanized post holder at the top, and mount to that.


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## Highbeam (Sep 12, 2012)

pen said:


> Wow, we are told that will rot the pressure treated off. Funny how things vary from region to region.
> 
> In the case you mention, if they want to be pricks, they'll have us pour a sonotube full of concrete with a galvanized post holder at the top, and mount to that.


 
That connection then, the post holder to the post, will provide nearly zero strength against the post falling over. Unless there is a very long sleeve that runs over the post, like several feet, the lateral strength of the system is ruined abd all you get is vertical strength.

I didn't plan on concrete backfill, just the footing cookie under the pole but the engineering was very certain that it was required. More than one structural engineer since I got three bids. To be fair, my location must design for 115 mph wind loads and the building is 30x60 so a lot of exposure on the big side with not much width.


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## basod (Sep 12, 2012)

I'm guessing the narrow nature of the hole may exclude a feather/wedge from being used.
I'd try a rotary/hammer drill and see how far an 18" bit will go.  You may go through the stone and see soil tailings - if not than time to call in the backhoe


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## SmokeyTheBear (Sep 12, 2012)

pen said:


> They made you backfill the hole with concrete? As in surround the pressure treated post with concrete? If so, around here encasing pressure treated in concrete would be a big no go.
> 
> pen


 

Pen,

There are multiple pressure treatments and any ground contact rated can be set in concrete.

The normal PT stuff is for above ground only, no ground contact allowed.


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## Jags (Sep 12, 2012)

SmokeyTheBear said:


> Pen,
> 
> There are multiple pressure treatments and any ground contact rated can be set in concrete.
> 
> The normal PT stuff is for above ground only, no ground contact allowed.


 
Yep - generally 3 ratings. Above ground, ground contact/underground and submersible (water, think piers, docks, etc.).


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## Seasoned Oak (Sep 12, 2012)

Lowes sells 2 types the higher rated wood is more expensive.


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## Jags (Sep 12, 2012)

Seasoned Oak said:


> Lowes sells 2 types the higher rated wood is more expensive.


 
And I believe they can special order the third (at least around here they can), but they don't stock it.


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## MasterMech (Sep 14, 2012)

begreen said:


> Burn ban going on right now after 49 days with no rain. That can't happen. I'm thinking jackhammer or backhoe.


 
Think both.  Where's that excavator that tore down the old garage?  Many mini's are able to take a hammer attachment.  Or you/the company could rent one and pound through.


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## begreen (Sep 14, 2012)

I called the guy with the excavator. He was bummed out and chagrined to tell me his young apprentice had flipped it. Not sure when it will be back online.

After spending most of a day flaking granite with a jackhammer it was decided that this rock is staying. The engineers are penciling out a rebar and cement overshoe solution. And our project slips another week.


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## Highbeam (Sep 14, 2012)

begreen said:


> I called the guy with the excavator. He was bummed out and chagrined to tell me his young apprentice had flipped it. Not sure when it will be back online.
> 
> After spending most of a day flaking granite with a jackhammer it was decided that this rock is staying. The engineers are penciling out a rebar and cement overshoe solution. And our project slips another week.


 
Cool, you found one of those huge granite boulders. They are so rare that there are specail names for them, like irregulars or oddballs, or something. We have to write contract provisions for just in case one is encountered while putting in a water main or something.


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## begreen (Sep 14, 2012)

I have a property full of them. We have 2 large ones that we discovered when landscaping for the greenhouse. They are like 60" x 40" x 24". I was amazed that the guy was able to move them with his excavator. And many more 1-3 man granite rocks were discovered and used for garden walls and features. The local gravel yard is also full of them. I think they grow here.


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## Highbeam (Sep 14, 2012)

We affectionately call them "donikers". I hope it is not some sort of racial slur or anything it is just what the construction guys have always called them and the name sticks. A big old donicker fell into the trench from the sidewall.


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