I've got a situation similar to this one (slab finishing/patching around roughed-in plumbing remodel), but in my situation the finishing job poses a couple extra problems:
1) The trench routes under a floor-to-ceiling, built-in wall cabinet, so there is about 1.5 to 2 feet of trench I can't access vertically.
I'm worried about getting a good meld between the concrete I fill underneath the built-in and the bit of slab that remains below it. Obviously there is a reasonable pocket I need to fill, and I can't think of a great way to get the concrete under it so that it's well-packed.
2) The area (small laundry/utility room) is carpeted, and currently there's a surgically-cut area of carpet pulled away from the trench.
I've read concrete "bleeds" out some water before its ready to be finished/smoothed. How long should I let it sweat before I smooth it, and is it worth my while to attempt protecting the carpet beyond the trench? The carpet should ultimately be replaced, so my biggest concern is getting a level patch, but I'm wondering where will the bleeding water go?
Am I over-thinking this, or is it as simple as mix some 'crete, dump it in the trench, and smooth with a short length of 2x4?!?
The trench going under the built-in. There are at most, 2 or 2.5 inches between the slab and the pea gravel there.
Top-down view of the trench showing the carpet. I'm worried, what happens to the water the concrete will bleed out?