[Feetsdr]

On a concrete front walk that's probably 30 years old, 1 panel has sunk a little (3/4" of an inch?) and water would pool there for a bunch of years now.

I (foolishly??) got the bug in me to fix it.

I dug under the low corner and Using a car jack (1 1/2 ton cap) I lifted it almost level with the panel next to it. (wasn't able to get higher than that - the jack was straining / really hard to pump it up more / afraid I might bend the lever on the jack.

I started realizing - even if I get it level / higher (to allow for settling).... then what? What do I do to keep the panel up / allow for settling. And there;s a gap now between the bottom of the concrete and undisturbed dirt... (yeah, it's just dirt under it? I thought there'd be an inch or 2 of gravel?)

Oh, and how to get the jack out THEN fill the area (taking the jack out = the corner will sink?

Any thoughts on the panel weighing more than 1 1/2 tons? Or is it likely binding against the next panel?

YES, I did look around a while ago for a company that does this work, but no one I found was interested in a small homeowner job like this.

THANKS!

 

[SPS-1]

I am thinking that when you first started lifting the corner, the pivot point was close to where you were lifting, so it went up easy. When you got it level, the pivot point is now the far side of the slab, and its a lot harder to lift.

Best I can think of is put wood board at the bottom of the hole. Then wedge a 2x4 in there to (hopefully) support the slab. Then pull out the jack and pack dirt in there.

You will need to get that corner higher than level, because I expect that packed dirt will settle somewhat.

 

[stadry]

don't worry about it re-sinking as it will if you only use soil/dirt for supporting fill,,, rough terrain jacks are far better for this purpose - 1 on either side

 

[ktownskier]

Get some rubble to fill it in. at least for the most part.

or, get a sonotube or a bucket or some container and fill it with concrete so it is solid and place it on a concrete paver that has a couple inches of sand under it. Or two inches of gravel, then 2" of sand.

Measure the height with the paver(s) so that you can get a correct sized container. Fill it with concrete, let it set and then force it under the sidewalk section. You can use a 2x6 to help lift it a bit.

Like others have said, make it slightly proud as it will settle.

If you want to fill in around the concrete tube, to prevent more washout, you can fill it in with fence post foam:

I set a couple of replacement posts with this stuff and it was amazing. It is not a replacement for concrete, but, it is damn strong. And it will EXPAND!! So, try and squeeze it as far in as you can and STAND BACK!! Put some loose sand on the concrete surfaces surrounding it, so that it won't stick as easily. put a tarp down on the grass or plastic drop clothe. It cuts easily when dried.

 

[dj3]

I have just the plan for you, but you will have to try to get the slab higher than the adjacent slab.
Place a couple of blocks on either side of the jack, so that they reach the slab - you may have to pack some gravel under them to make them reach the bottom of the slab. Then lower the jack and let the slab rest on those blocks, the slab may sink a bit, but you can allow for that.
Then lower the jack and pull it out. If the thing stands, back fill with gravel and stones.
This is the same rational with jacking a car and placing jack stands under it to allow for the jack to be pulled out.

 

[HotRodx10]

Depending on how long of "a while" it's been, you might try checking around again for a company that does slab lifting. It's become much more common for small residential work in just the last year or so.


You might also ask a local concrete supplier about "flowable fill" or "slurry", which are low strength (still plenty strong enough to support the slab), very runny, sand-cement mixtures that will flow under the slab and fill the voids. You just need to block the slab up with something you don't mind leaving there. You may have to build a dike up about 6" or so around where you want to pour it in, so you can overfill it a little to get it to fill all the voids. Once it's stiff, but not hard (about like ice cream), cut off the excess that's not under the slab, and backfill the hole.

 

[SeniorSitizen]

Block it up with a brick with the brick holes horizontal, pull the jack then pour the cavity full of Rockite.


EDIT: EDIT:

 

[huesmann]

Looks like you have a little room for a 2x4 on the left side of the jack. Cut a piece of PT 2x4, jack the slab a little higher than you want it, slip the 2x4 under, remove the jack, and see if it's at the elevation you want it. Get some flowable fill (grout) and fill the hole. You could use some concrete bricks to fill up some of the space.

 

[Feetsdr]

WOW!!! Thanks for all the great ideas!

That sika stuff is interesting! I use their leveling cauilk product between the panels.

I found this video:

AS a way to lift without the jack in the hole.

What do you think of that? What type of C clamp can you use? Just a harbor freight cast iron one? Their page doesn;t talk about strength. I think I'd put 1 end of green bar on a cinder block and the clamp on the low end and jack near that end / just lifts the clamp end?

And for blocks underneath... cinderblock? red brick?

rockite? Is that better than the urethane? Was trying to see how much load the urethane could handle but didn't.

Would you use dirt or the gravels to fill in most of the hole? Gravel can shift? can't tamp it down? Dirt woudl be less pourous? (soak with water as I go along?

 

[stadry]

wonder what the truck's minimum quantity is for flowable fill ? here's its 5cy - same as conc,,, that's REALLY a wallet-buster,,, skyhook ? bodacious big crowbar ?
already gave you the easiest & safest method,,, typically we're in & out of the same task in 45min for a $350 charge,,, if you ARE a podiatrist, what's YOUR time worth ?

 

[HotRodx10]

wonder what the truck's minimum quantity is for flowable fill ? here's its 5cy - same as conc

Here, from most of the ready-mix places, there's a short load charge (around $50) for orders less than 4 CY, so a 1 CY load would be about $170. However, we have one supplier with a 1 CY trailer mounted mixer, who charges about $150 for that 1 CY load. You can also get bag mix flowable grout, as huesmann suggested, depending on how big the void ends up being after digging under, etc. and what the OP is willing to spend in DIY labor vs. $$.



Most likely, 2 or 3 bags of a flowable grout mix from a big box store would probably be adequate, but then you have to have something like a big wheelbarrow to mix it in, etc. Depending on what the OP has or doesn't have, what his time is worth, what his physical capabilities are (some of us are getting to the point where slinging around 60 or 80 lb bags could cost more in chiropractor bills than the delivery fee would have), paying $50 or $100 more to have someone else do the heavy lifting, where all he has to do is point and say "dump it in that hole there", could be the more attractive option.

 

[Nealtw]

We just blocked up the concrete and made balls of stiff concrete mix and packed them in the cavity until it was full.

 

[HotRodx10]

We just blocked up the concrete and made balls of stiff concrete mix and packed them in the cavity until it was full.

That's an alternative, too. Seems like a labor intensive one for a void of any significant size, though.

 

[Nealtw]

That's an alternative, too. Seems like a labor intensive one for a void of any significant size, though.

Have you ever seen where they tunnel under a slab house for plumbing repairs. That is how they back fill with just a mud balls

 

[HotRodx10]

That is how they back fill with just a mud balls

Not saying it won't work, but after watching the video, it still looks more labor intensive than pouring in a wheelbarrow load of runny grout.

 

[huesmann]

Also, like I said, you can use small concrete bricks/blocks or pieces of them to pack most of the hole, to minimize your flowable grout requirement—you could probably get away with a single bag/mix.

 

[ktownskier]

As for lifting the slab,https://www.homedepot.com/p/Husky-69-in-Post-Hole-Digger-and-Tamping-Bar-34219/204168182. It works pretty well and I used it for a lot of other things.

 

[jcpost62]

WOW!!! Thanks for all the great ideas!

That sika stuff is interesting! I use their leveling cauilk product between the panels.

I found this video:

https://www.youtube.com/watch?v=p5tIUz82rRI

AS a way to lift without the jack in the hole.

What do you think of that? What type of C clamp can you use? Just a harbor freight cast iron one? Their page doesn;t talk about strength. I think I'd put 1 end of green bar on a cinder block and the clamp on the low end and jack near that end / just lifts the clamp end?

And for blocks underneath... cinderblock? red brick?

rockite? Is that better than the urethane? Was trying to see how much load the urethane could handle but didn't.

Would you use dirt or the gravels to fill in most of the hole? Gravel can shift? can't tamp it down? Dirt woudl be less pourous? (soak with water as I go along?

Really good video! Only comment I would make is using the "couple of blocks" underneath the slab. These will tend to create discrete pressure points around which the slab will try to bend. The bending could cause the slab to crack. Although the slab looks really thick. So this is much less a possibility. My overall suggestion would be to use gravel under the slab to get a uniform distribution of stress on the underside. Think about how they originally poured this slab. Typically, a contractor will create a 2-3 inch thick gravel base that is tamped down tightly (compacted). Then they pour the concrete on top of the firm base. In my experience with concrete, the better the base, the less like the slab will crack -- the better the job outcome. In your case, it seems the best you could do is fill under the slab with gravel as uniformly and best you can. You don't have the room to tamp it down. It also depends on the soil underneath. If it were mostly clay, you would be better off. But, it look like it is mostly dirt (similar to top soil) and that is probably why it sunk in the first place. Hope this helps.