Best way to compact soil under a slab overhang


I have redone plumbing under the concrete slab and in some cases I had to dig up soil (sand mostly) under the slab as the plumbing went under it. I had hollowed out a cavity three feet deep and about 18" under the slab (the overhang is 18" in addition to the actual trench which is 24").
When I put sand back in to backfill I can compact the sand in the open trench by jumping up and down on it. However on the overhang area I can step on it until the soil is built up till about 8" below the slab. Any tricks in getting the soil compacted sideways into this overhang to get it as tight as possible?
Thanks in advance,
MC
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In other apps I'll often toss some in then soak with water. When it goes down, add more and repeat. Bit late now for that for you and probably not practical in your case.
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On Mon, 28 Dec 2009 22:17:12 -0500, "MiamiCuse"

Water. Wet the sand and tamp it in. flow more sand in and wet it. Pack it and let it dry. If it settles, put some more "slurry" in and let it settle. Then pour your concrete over it. The watering will wash sand down into the gravel below too, so it won't sift down later.
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Use a low strength concrete wet mix - about a third to a quarter as much cement powder as when you want a proper strong mix. Pour it or shovel it in. It won't shrink at all but it can settle if you don't work it a bit into the cracks and crevices or prevent it from sloughing out the front opening.
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Concrete yards know this as a "six sack mix". You can get it with sand or fine gravel aggregate. I've used it often to fill undermined slabs even in structural settings (even driveway ramps in gas stations).
-Zz
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