A friend and I spent the last 2 days putting in railroad ties for a 16x20 shop we're building on my property in Petersvile. The plan was to put in 9 posts and we managed to get 8 put in but we ran into a huge rock right where the 9th post was supposed to go. It's roughly 6'x6'x2' so we can't move it and blasting it is out of the question.

Does anyone have any ideas on how to get that post put in? We're thinking about drilling a hole into it, putting a piece of rebar in with an epoxy, drilling the rr tie and putting them together then cross bracing it with some of the other posts. Thoughts?

Drill several holes in the rock, drop rebar in each, put a sonatube around them and fill the tube with concrete... set an anchor in the top.

If the rock is deep enough, it might make a good foundation. Do like you said with the rebar and pour concrete around it.

Or, jack hammer the bitch out of there.

AkMtnHntr:

You could drill the hole with a rock chisel and hammer. You might use up a few chisels in the process and it would be difficult to get the hole wide enough to accept a 6x6 post.

Or you could rent an electric jack hammer and use it to drill the hole in the rock. It will take a while since electric jack hammers are kind of whimpy, but you're only doing a small job and that is the tool for the job.

KC

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Or drill the rebar in a pattern that the tie can fit in between, frame up around the whole thing and concrete it.

More info, this rock is only about 8" below the surface so not sure if the soba tube would work but that's a good idea. There's no way we can drill a hole big enough to set the post in (using railroad ties) either. We thought about trying to bust it with a jack hammer but I don't have the power source handy, my property is about a mile off the road and getting equipment in there during the summer is damn near impossible because of all the muskeg/swamps.

sonatube would be my choice, with enough and large enoguh bar..

I wouldn't 'attach' anything to a rock that might potentially shift as the frost wills. A single, simple hole and rod (rebar) to locate and hold a block or other supporting post is all I'd do in your circumstances.

When we put up our cabin on the windy west coast of the state a dozen years ago...it's all permafrost here.... I intentionally tried to locate it on the biggest rocks I could find and just built on pads sitting on those rocks.



So far it has worked perfectly with no corrections needed after the first year or two.

I still have a lot to learn.. permafrost and all.

But how is putting a tie on top of a rock that will move, better than a concrete tube on top of a rock that will move?

Ability to cut or shim the RR tie is all I've come up with so far?

Which brings up movement... if on "piers" and due to permafrost and geo issues, would you figure a way to float the building on the piers instead of "bolt" down?

pier block with adjustable bracket.

I like Arts idea, but you could also consider a post and pad setup. Pad sets on the rock with foam under it or sandwiched in with the post on top. That's done in the bush a lot. Probably a 3'X3' pad. Good luck, that rock would have to be where the LAST post was going.

I can tell you that there is no permafrost on our property, we've already put in 8 rail road ties and we hand dug them all in about 3 hours. If the rock was a bit more flat on top I'd just do the pier block as Dan suggested but I don't know if they make them big enough for a rail road tie.

Have your own welded up. No big deal

And surprisingly cheap from most decent welders.

With that extra info it makes it more obvious to KISS it.

I would be just as concerned, if not more so, with what the annual frost might do to that rock in terms of shifting. (And the same is true of the posts you've set.) But as long as the foundation can shift without tearing the building apart, you should be good. A lot (most) of the homes built on the permafrost out our way have very heavy beams set of pads. The floor joists are build on these main beams. The beams are stout enough: laminated 2x6 or 2x8 d-fir lumber sandwiched to a thickness of 16 - 24 inches, that they don't flex a lot if one of the pads rises or falls with the seasons and cause great damage to the building. (Doors might not latch properly during some months of the year without shimming.) Too light a 'foundation' beneath the floor might allow a single post or pad to affect the building significantly.

Get it built the way you want it. Get your own pier block and have the saddle and post welded up. Use all thread for the bottom with washers and nuts so you can adjust as needed. You can have the saddle made any size you want.

There won't be any shifting of the post we already put in the ground, the soil at the bottom of the holes was a gray heavy Sandy/gravel type. I talked to a guy that's lived out there for over 35 years and he said the ground in these ridges froze maybe a foot and a half. We put about 20lbs or so of 3/4" rock in the bottom of the holes and put a foot at the bottom of each tie so I don't believe there will be any movement of the posts.

I may go the saddle route as that seems like the best option.

Is the 9th post a corner or middle post??

Middle post, front of the shop.

middle post, front.... put whatever, carry the load with an engineered lam beam from post one, through the middle to post 3 or whatever the number....

I suspect the ties are more for decay-proofing the foundation than for structural... and a torsion box floor or similar will sit on the ties... direct contact or even damp crawlspaces would eat an engineered beam before they got it built.

Wel I think I'm going to try and remove that rock using some Ecobust to break up that rock. That seems like the best way to deal with this damned thing and make me feel good about that post being secure.

If it's in the middle it's only breaking a 16' span into two 8's right.?

It seems like you could pour some concrete over the top of the rock leaving a flat surface and just use a block to support the floor beam there since it's only a mid span. Leave enough room to use some wood shims that you can add to or knock out later if it heaves or settles. Just throwing out ideas....

The rock would be a better footer than anything you would do... and it is likely deep enough to not matter on heaving.

I am not in favor of making extra work for myself. Sounds like you are!

^^^^^^^^^^^THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^ What is the span for your posts?

Yep. If the frost isn't very deep there, and it sounds like it isn't, that big old rock will probably be the best footer you've got. Then again, it would sure suck to have to jack and shim 8 posts because the big old rock is so stable and steady that it doesn't sink like the rest.

For a single story cabin that is not subject to cold regions design requirements, you may find that doweling into a good sized rock and casting a short concrete pier or pad to support an adjustable "Simpson EPB" bracket (if available in your AO) 6" to a foot above grade will adequately support your 4x floor girder. If you're using RR ties for floor framing, shim using a treated 4x4 (flat) in the EPB. If you keep the exposed threaded base short, they are good for around 3,000 pounds. For the stubby pier, you can use a precast pier block with a center hole set on a pad of concrete above the rock in various fashions.

Insert standard engineering design liability boilerplate here for the above limited suggestions based upon very limited information....

hmm... not familiar at all with torsion box. I've read it before in the code books but never seen it. Will have to read back up on it again

Just chopper-in a backhoe and dig the rock out.

I'll vote Sitka's idea, especially since you've already sunk 7 of 8.

But ain't it just the way for rocktop #8 to be middle front??

Torsion boxes make a TON of sense in remote locations because they use a lot less material to build a really stiff floor. Slick way to go but they need sound deadening insulation of some kind to prevent a drum effect...

`Much ado about not much..

If it were me, I'd dig down around the rockto good base (you mentioned it wasn't deep ) about 14-16 inches deep , or to a 3X3 foot square at least 6 inches deep (reinforce if you feel like it), whichever came first and pour a concrete slab to grade level or slightly above and either put in a - as mentioned before- custom built to tie adjustable device, or block to specs.

That rock seems golden to me.

And that's overbuilding I think. The best way to do things. It is after all a mid- support. The screw up or down devise would be more in favor with me than blocking. Simpler down the road. If ever needed.

Fixt