I have a ground floor apartment that has a floating slab concrete floor that is beginning to settle as much as 3 inches in some areas. The interior partition walls are not tied in to the structure frame but are setting on the slab floor. Some areas under the floor have settled as much as 36 inches due to prior excavation and not properly backfilling the excavation area. There is plumbing under the concrete, water & drain pipes. Is there a method where a loose aggregate could be pumped in through a hole in the slab that would surround the plumbing but not damage the plumbing structurally and then a pressure grout of some kind used to raise the floor to its original level?

Woo the big guy. Lets address the sinking of the floor first before we go throwing anything under there! I'm a builder ans ALL my flags are up here. If this is a true story then I need many things checked and answers here.
1. How do you know there is a 36" sink hole under slab how was that figured out?
2. I'm i correct to assume the poor backfilling was for the reason that your slab and foundation was built on fill and the block/concrete walls aren't effected/ and for that to happen you are one lucky dog or when they built the walls those walls were laid many courses below fill in slab grade and they are setting on virgin ground.
3. Lets check floor waterline leaks. If you are on a well or city water check the gage coming in the house with all fixtures off and see if the usage city meter moves or your well pump line loses pressure slowly. Don't just do a quick stand there for a while or accurately note the pressure and check is again in an hour or so. If the well pump has to start then its a good sign that water is either leaking under slab or a bad check valve on well line but thats shouldn't be the case here.
4. Do you know where the waterlines are in the slab? Or the sewer line?
5. How old is this floor ans structure?
6. Either you have water leak under floor. Or is sitting on a sink hole ( limestone miked with water produces carbonic acid and causes sink hole that show up later)
To do this correctly Drill holes in concrete floor and get a metal rod probe and push it down in many areas of the floor through many drolled holes to get an assessment and topography of the heights and depths of the floor. Once that goofy assessment is done I would just get into it and remove all the crete and back fill and Mechanical tamp it and then start to back fill with 2a modified stone and get that leveled so a 4"2b clean stone under new concrete floor and a 6 mil vapor barriers ( now seams) and pour new crete.

Now that I given all this information and feel like I answered a test question. I need to know about your APT. Why would a person living in an apartment ask this question or want this info when it's the owner of the structure that's should be asking this question??

Signed 21 Boat

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