sm_jamieson coughed up some electrons that declared:

Just putting in the hardcore (MOT 1) for my floor slab. 100mm required
(BCO agreed).
First floor slab I've done.
To what depth should I rake it out before compaction to end up with
100mm ?
In other words, how much should I expect it to compact ?
Thanks,
Simon.

I don't know about MOT 1, but I can tell you for a fact that reclaimed
washed railway ballast compacts from 8" as shovelled and raked out to 6" of
solid mass under several runs with a standard single-person vibroplate
compacting machine. I learnt this little fact after 3 of us busted a gut
moving the damn stuff to help a mate make his new crossover and drive.

Said ballast consisted of rock lumps typically about 1.5" across, no fines
and not much below 1". If that's similar to type 1 MOT, then I would expect
similar compaction ratios.

HTH

Tim