Okay so if I need to install a 3” pvc branch under my basement floor, how wide should I break thru the concrete? Of course I want to minimize this, as it’s less to carry up in buckets, and also less concrete to repour for the patch...

Max depth will be approx 20” below the floor. (First 4” is the concrete)

Is 12” wide trench appropriate or what do you suggest?

my code says plastic pipe underground must have fine sand 6 inches in all directions.
so a 12 inch trench should get you close enough to keeping any sharp rocks from damaging the pipe.

How important is this sand around the pipe? Will #57 stone (the 3/4” gravel) really hurt a pipe bedded in it?

Wondering if anyone’s actually ever seen pipe damaged by gravel?

Nope......You can be the first to see it, if you want.

the strange thing is that my plumbing code calls for fine sand BUT once the pipe is 10 feet beyond the foundation wall then another set of regs kicks in. those are sewer layers regs and they call for gravel around the pipe. (go figure????)

Thanks for the input. That is extremely interesting about the sand vs the gravel.

It’s hard for me to imagine enough movement underground to drive a rock thru a pipe. Seems anything that moves that much, will have the force to break the pipe anyway...

I think the movement they refer to is expansion from running hot water thru the system.

will you be cutting the concrete with a wet saw for a clean edge or breaking the slab with a jackhammer resulting in a rough edge and possibly cracks?

For sand vs gravel, I have always used gravel below the pipe till about 4 inches or so below the pipe and compact the heck out of it, then switch to sand all the way to the top. I use sand because they are much easier to compact by hand and by watering down without affecting the pipes. Gravel leaves too much voids and there is a possibility the new concrete weight may settle on it and cause the gravels and voids to redistribute and shift the pipes. I tend to dig several inches lower than the bottom of the pipe, then compact the bottom of the trench, then lay the pipes down by sliding bricks under each fitting to attain the slope I need. Once I got everything in place then sand backfill half way up the sides of the pipes, hose it down to make sure the sand runs down and fill up the bottom of the pipes, add more sand, hand compact, water, sand, hand compact, rinse and repeat. About 4" below concrete I do a subterranean termicide treatment.

As for the trench widtjh I have always cut more than what I think I need and bite the bullet on more debris and more backfilling effort and concrete patching. I would rather cut wider and have more flexibility then risk having to do another cut 4 to 6 inches wider for whatever reasons you may or may not know now. The governing factors may not show up until you actually do it. I would run through the entire execution step by step in your mind to visualize where you may run into issues. Some of the things that I ran into in the past such as having to install a pipe at 24" deep and with me laying on my belly on the ground I can get a handle on the pipe but it's a challenge to apply primer and cement all the way around the PVC, and also a challenge to push a longer 3" or 4" pipe fully into a fitting and rotate it with hands fully stretched. Would have been easier if I can get into the trench instead of being on top of it. Also where you tie into the existing pipe where you may need to make cuts I found how you do the cutting may make a difference. Once I made a 12" trench and used a corded sawzall that's almost 20" long I found it exceedingly hard to make the cut through the cast iron pipe holding the saw vertically with me lying on my belly, and the sawzall has a vent at the tail of it so as it cut sand was being blown onto my face, that was not fun at all.