How are cracked footings repaired?

[db4570]

Hi, Everyone.

I started this in another thread a long time ago:

http://countryplans.com/smf/index.php?topic=7676.msg101114#msg101114

The bullet points: cabin in the woods, way up north, really cold in winter, concrete block wall of walk-out basement cracked and shifted out with gap of an inch or two, been like that for some years. Pictures in other thread.

Had home inspector/contractor inspect the place. He's convinced the wall didn't just crack on its own, but that the footings cracked and heaved. Talking with the family member who built the place, he believes a big rock next to the wall got frost-heaved into the wall, cracking and moving it. But my last conversation with him, when I quizzed him thoroughly on the footing construction, he disclosed the footing is only about two feet deep back there. Should be four. I think I discovered what caused the problem with the wall above.

So the footing on this side of the cabin almost definitely is cracked and needs replaced. I intend to shore up the cabin, knock down the wall, and then what? Do I then hire a backhoe to dig out the old footings, and how do they do it? Do they bust it up first? Do they have to dig down along side the footing to the bottom and then pull it out sideways? That's a lot of dirt that needs to be excavated, and it's really rocky. Like boulders. I can't imagine any way to get the old footing out other than pulling it out sideways. I really wish there was a way to preserve some basic trench shape to act as forms so I don't have to build them. But it seems like it's just going to be a giant excavated hole.

Any input, suggestions, ideas, or experiences appreciated. Or alternative methods, even if unorthodox.

Thanks!

David

[diyfrank]

You will have to dig like the footing was never there. Just dig down till you have the shallow footing exposed. jack and support the building from the inside if possible. Saw cut and remove the damaged area. Use a jack hammer if necessary. once the new grade is prepped and the the remaining section is undermined to a point you can over lapped the two, you drill and place rebar in the old section to be saved and form up the new section to be pored. lay your steel and tie it together with the steel you placed in the existing wall/ footing. Order you mix.
http://countryplans.com/smf/index.php?topic=7389.0

[db4570]

Hi, Frank. Thanks for the help.

So would I definitely need to tie the old footing to the new? Or if they are both stable, do they need to be physically connected? How would the rebar be attached to the old footing? Is it somehow cemented in, or just pressed in the hole? How far in does it go?

I'm also hoping to do this with a minimum amount of form work. Is the form work pretty straightforward? I have some old 2x6s and OSB laying around, so I am guessing I could use that.

Thanks!

David

[diyfrank]

I would connect the two but I would image it could be done with separation.
I wouldn't go through the trouble of repairing it without connecting them myself.
I would drill with a roto hammer into the existing footing at the point you saw cut and epoxy the rebar into the holes.
Tie your steel from the new footing to the epoxied steel in the existing foundation.
Forms are pretty straight forward. You want around 8" deep and maybe 20" or so wide footing.
Re stacking the blocks may be a trick, I'm not sure it would worth trying. It might be less trouble to pore a concrete wall all the way up to replace the damaged area.
They have clips for holding the form boards together but as long as its straight and your form board are braced well you should be able to make something work.

[diyfrank]

Do you have any more pictures that show more of the building? inside ?

[db4570]

Here is the only picture I have of the inside:



You can see where I temporarily put the window back in with bent nails after it popped out.

Is there any reason why when I re-pour the deeper footings I can't go all the way to ground level or even a few inches above, and start laying block from there? Would save me having to work down in the ditch, and I'm hoping it might be a lot quicker, if I can keep my form simple.

Also, I assume the footing is overlapped by the floor slab a couple inches. Is that going to be a challenge to pour?

[diyfrank]

The picture isn't really much help, sorry. It's hard to tell the size, shape and load. Judging by the picture it looks tiny.

What I would be interested in seeing is, 1 of each side of the cabin  that shows the entire side + the land around it and 1 or more of the inside that shows all the room inside as to see what bracing could be done.

Sure you could fill the entire trench with concrete but that would be a lot more concrete. If you're deeper then a couple feet you should excavate in such a way you have room and easy access for the repair.
You have the potential to have things go very badly if you don't shore it correctly and excavate with plenty of room for a safe working area.

There are a couple different ways to fix this but there is no quick easy fix here. 
The way the blocks stack, to try and weave them back together would require you to take more apart and re stack. It wouldn't be easy but it's not impossible either.