Sinking enclosed patio

I have a house that was build really well in the 50's, but everything done after that, including an added enclosed patio was done poorly. The patio is about 10 feet deep and 20 feet wide. I just finished replacing the windows and siding for the house and patio. Now I pulled up the floor in the patio and found that the floor is cracked from sinking. One small section is still in good shape because it was poured over the old concrete stoop leading from the back door. The rest has sank about 4 or 5 inches.

I had an animal digging under the patio a few years ago and have since then covered up the hole and not had any more animal problems. But I believe there is no footing or at least not a good one. I also think a portion of the patio is just floating now.

I thought about pouring a concrete mixture over the top to level everything off, but I know it will continue to sink and crack. A contractor suggesting cutting out the floor as close to the walls as possible and pouring a new floor. I'm still worried that the old concrete will continue to sink and crack the new concrete or separate from the new concrete.

Is there anything that can be done shy of tearing down and pouring a new foundation? If I jack up the structure to pour a new foundation, I am affraid the new windows (which are now level) will crack. Can I add pilings to support the walls? Or can I use rebar to structurely connect the old to new concrete? Any help is appreciated.

You definitely do not want to pour on top of a sinking slab. That will just add weight making the problem worse.

You can't remove the floor w/o taking down the structure? What about cutting around the perimeter or is the structure on the move as well?

I think it is very possible to cut around the perimeter and pour a new floor. But I'm concerned that the remaining concrete around the perimeter (which has all of the load on it) will continue sinking and either separate from the new concrete or at least crack at the joint between new and old. I am a mechanical engineer, so this is what makes sense in my head, but I do not have any experience with concrete at all. I only know what I can find online.

Should I not worry about the perimeter of old concrete sagging after the new floor is poured? Or is there a good way to support the perimeter of old concrete so it doesn't continue to sag?

So the foundation holding up the structure is also shifting? If yes, you have bigger problems than just a sinking floor. You likely want to consult a structural engineer to determine if the structure be saved. There are ways to reinforce an existing foundation but it may not make good economic sense if all we are talking about is a stand alone porch.

The slab was poured up to the house foundation and the covered porch is integrated into the house structure. So I do not want to tear down the existing porch structure except as a last resort.

Someone suggested mud jacking the floor to level it off, then I would have to use a self leveling compound to smooth out the floor over the cracks. Does anyone know if mud jacking will work for my situation? The slab is cracked into 3 different pieces. The low sections are where the walls sit on the slab. Will mud jacking raise the concrete with the weight of the walls sitting on them? Or will the center of the room raise up only?

itsreallyconc, I do not think there is a footer at all. I think it is just a slab poured on the ground. The frame is sitting on the slab. The cracks in the slab run from the center of the slab out to the perimeter. If mudjacking would work to raise the slab which is in 3 pieces and make it relatively level, I was planning to support the slab with concrete piers dug down below the frost line and set along the perimeter every so many feet (still need to figure that distance out). But if mudjacking is only going to lift the concrete from the center because there is more weight on the perimeter, then it won't be helpful. That is where my question came from.

Also, can you please explain the screw anchor system w/ foundation clips? I am not familiar with that.

Finally, I added some pictures that will hopefully help.

Thanks for the help and quick reply. I will check with the local mud jackers to see what they will be capable of.

Have you got this fixed up yet. Do want to save the money and do the hard work your self?

I have not fixed this yet. I am waiting for the spring time when I have some more money saved up and the weather is better. I do hope to find a way to save money by doing the work myself.

Usually 3" of settlement would be all you would have but you don't have a footing or foundation and with soil under the slab you will always have chance frost heaving the floor up. My answer is to do it once do it right and it is a lot of work.
1 cut the floor 24" from the outside walls with diamond saw
2 28" from the back wall build a temp wall and lift the whole structure to leval
3 Jack hammer the 24" perimiter out
4 dig a ditch under the wall to frost depth in your area witch I don't know
5 poor a footing 18" wide use 2x6 to form hammer stakes in and lift to level and nail to stakes and you will have a/ 7" deep add 2 evanly spaced 5/8 rebar
6 build or rent forms for 8" foundation the outside of the foundation should be plumb with the outside of the walls. set the level poor strip 1 1/2" below the wall.
It will be a treat to get the concrete in there and thats why you go a little low and the full 8' wide. when its done you can put a treated 2x in to bring it to height
7 If your house has a perimiter drain, continue it around the outside of your room
8 add 4" sheet foam white to the inside of the foundation from the footing to 3" below the finnished slab height.
9 slide in the treated 2x4 and set the building down and drill and bolt down.
10 back fill the inside with sand and wet it down with the hose so it settles
11.remove the rest of the floor and compact the dirt with a plate compacter
12. level with sand at leaving about 31/2" for the slab.
13 cover the area with 6mill poly and a 3 1/2" sill foam around the outside to keep the slab away from the foundation. This will allow future movement.
14 Hire a placer to poor the slab while you drink the beer.

This system is called slab on grade and its really common out here, we do the whole house like this.

I suspect this is a lot and anyone would be looking for the shortcuts but I thought you should have all the goods so you could make an informed decision
Keep me posted Neal