Is this possible to do with concrete?

So I just bought a house with a 2 car garage. The garage floor on one side has sunken a fair amount- there is a crack form the middle of the garage at the wall extending diagonally to the corner of the opposite wall (near the garage door). The triangle of concree this created has sunken about 8" at it's deepest and the deepest corner has been broken out so there is no concrete in that corner, just dirt (I was told a sewer pipe broke and washed out under the slab)

The end result I am looking for is an epoxy floor coating and possibly a 4 post lift (years down the road).

I want to try and jack the cracked and sunken part with a few car hydraulic jacks (2 2-1/2ton) and try to backfill under the slab, then lower it. Do you think it would work? What should I use to backfill under it?

Thanks in advance for suggestions.

I don't think so. How can you compact the material you replace if there is a slab over it? If it can't be compacted it will again settle and cause more issues. I know they can drill holes and fill the void with expanding foam, but if you want a lift installed, I don't think it would be stable without cutting out sections to put good footings for the lift. If it were my garage I would remove the damaged section, fill and compact the soil, and then repour. The bigger issue I see is you don't know how big the actual void is until you remove some of the concrete... you might have a much bigger problem than you think.

google the term "mud jacking" - from your description, this sounds like the solution you may need.

here's the description from the first link that popped up:

Concrete mudjacking is a process in which a concrete grout is injected below sunken concrete slabs in order to raise them back to their original height. It is a very cost effective, and efficient way to fix sunken sidewalks, driveways, patios, basement floors, and even foundation walls. If you're experiencing sunken concrete slabs on your property, mudjacking is a quick and easy way to get things back to their original state.

What is Concrete Mudjacking?
Mudjacking, also referred to as concrete raising, concrete lifting, and slabjacking, is actually more straightforward than you might think. A concrete repair contractor will come to your home, drill a hole in the concrete slab that is causing you trouble, and then inject a mixture of pond sand and concrete (commonly referred to as "grout") beneath the slab in order to raise it up. The grout fills the void beneath the slab that is causing it to sink, then pressurizes and hydraulically lifts the slab up to its original position. The process takes a few hours to complete, and your concrete slab should be ready for regular use again within a day after the work is finished.

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Thanks for the thoughts.

I actually got the idea from looking at mudjacking websites.

As for compacting whatever I put under the slab, I figured I would raise the slab a bit higher than necessary and do my best to compact it using stone and then sand to fill the voids, hoping that the eventual level is adequate until I have the funds to do it correctly to support a lift.

i may try it just as a first step because it costs me nothing to try out. If it doesn't work, I'd have to fill the space anyway, right? No loss in trying it.

Ditto on the repouring of the section that is bad. And on the other hand, if that section is bad, who's to say that the fill underneath other places hasn't settled but the concrete hasn't cracked yet. If you take a spud bar or something similiar, you can go around and "thump" the floor. Listen to it, and when you hit a spot that has sunkem fill, you can hear it. It makes a definate hollow sound. For putting in a lift, I would want a known solid area to set the lift. An example is my nephew. He had a four post (still does) that you could have wheels or remove them. In his garage, the previous owner had patched the floor where concrete had sunk with asphalt. One leg of his lift set on this area (maybe 1 1/2 foot square) He had a car on it and the one leg sank a little more toppling the car. What had happened wehen the leg sank a little, it let the other legs splay (?) out somewhat, throwing everything off balance. After getting things back in order, lift out of the way, he found out the asphalt was only about an inch thick just to fill a hole and level the floor but the concrete under it was broken in pieces where it had sunk due to bad fill.