Yogurt wrapper under the slab?

[Jeff Handy]

You should force concrete way back into that void, and fill it up.

 

[Brandon1023]

You should force concrete way back into that void, and fill it up.

Good idea thanks. I'll try my best to pack it in there.

On a side question, the way I compact the trench backfill is by dampening it with a hose and walking on it for a while, one thin layer at a time. I once read on another Forum that if you break the concrete with a jackhammer and there's plenty of jagged edges, the new patch won't settle because it will bind in a sense to the rough part. If there's a better option I'd love to hear it. Obviously gravel might be best but this is the fill they built the house with.

 

[Jeff Handy]

I have a hand tamper.
I have also used a five foot piece of 4 x 4 in tighter spaces.
And a digging bar with a tamping head is good for very tight spots.
But not good for low ceilings.
Pros will have better advice.