I am converting my music studio, with no utilities, to a studio apartment. With that said I am having to cut the slab to install the sewer. I am in Los Angeles and am wondering what is the correct procedure to backfill the trench to avoid settling in the long run.

Thanks for your help!!

Best, Matt

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  • Your last image is the same as the 2nd, did you intend to put up a 4th image? If so, just edit it in.
    – FreeMan
    Nov 29, 2020 at 19:53
  • 1
    Out of sheer curiosity - it seems perplexing to me that you've managed to get this far into the project without knowing what to do next. The work actually looks decent. Did you hire out this part and are trying to DIY the rest of the way?
    – J...
    Nov 30, 2020 at 13:30

2 Answers 2


You need to use a tamper and tamp each 6"-12" of fill as you go:

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It is also important that you have a plan to tie the new concrete to the existing slab, to help prevent independent movement. For mine we drilled horizontally into the edges of the existing slab and used epoxy to set bent rebar rods into it, then tied those to the rebar grid for the new concrete.


Use non-compressible fill - road base - on the inside.

On the outside I'd probably use road base and put some of the broken concrete in the hole avoiding voids.

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