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Big rock in a hole. How to remove?

Post in 'DIY and General non-hearth advice' started by begreen, Sep 9, 2012.

  1. begreen

    begreen Mooderator Staff Member

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    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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  2. BravoWhiskey

    BravoWhiskey New Member

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    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.
    firebroad and Adios Pantalones like this.
  3. Beetle-Kill

    Beetle-Kill Minister of Fire

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  4. begreen

    begreen Mooderator Staff Member

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    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.
  5. Highbeam

    Highbeam Minister of Fire

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    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.
  6. onion

    onion Burning Hunk

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    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...
  7. Jack Straw

    Jack Straw Minister of Fire

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    Jack hammer?
  8. ScotO

    ScotO Guest

    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.
  9. Ehouse

    Ehouse Minister of Fire

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    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
    Eatonpcat and DAKSY like this.
  10. Frozen Canuck

    Frozen Canuck Minister of Fire

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    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.
    Eatonpcat likes this.
  11. Frozen Canuck

    Frozen Canuck Minister of Fire

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

    Jags Moderate Moderator Staff Member

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    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.
    firebroad likes this.
  13. begreen

    begreen Mooderator Staff Member

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

    semipro Minister of Fire

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    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.
  15. Highbeam

    Highbeam Minister of Fire

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    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.
  16. Jags

    Jags Moderate Moderator Staff Member

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    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.
    Eatonpcat likes this.
  17. begreen

    begreen Mooderator Staff Member

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    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.
  18. Highbeam

    Highbeam Minister of Fire

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    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.
  19. pen

    pen There are some who call me...mod. Staff Member

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    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
    Eatonpcat likes this.
  20. Highbeam

    Highbeam Minister of Fire

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    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.

    Attached Files:

  21. begreen

    begreen Mooderator Staff Member

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    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.
  22. pen

    pen There are some who call me...mod. Staff Member

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    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
    Eatonpcat likes this.
  23. Highbeam

    Highbeam Minister of Fire

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

    Seasoned Oak Minister of Fire

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    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.
  25. pen

    pen There are some who call me...mod. Staff Member

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    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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