Where the main water supply pipe passes through a foundation a sleeve is required that is two sizes bigger than the pipe.
I always thought it was to reduce or prevent corrosion, but the moisture content of the soil is likely to be similar to that of the concrete, so the pipe would be exposed to moisture anyway. It seems like some years back I read a different explanation but can’t remember what it was. I don’t think it’s to accommodate settling, because the sleeve is not meant to be sacrificial. Anybody?
Movement of the soil relative to the foundation (which would include settling) but also things like frost heaves, shrink-swell soil, settlement of the excavated trench, etc.
Can also be accomplished with a “relieving arch” where the pipe passes through the foundation, and is a little more descriptive of what it is for.
The biggest reasons for sleeves through a foundation is to facilate the installation of your concrete forms. No one wants to cut around pipes.
The other reason is to provide some protection to the pipe from heaving, settling, removing, replacing, allowing insulation if required, expansion, contraction, and weight of the concrete itself. Also a specified item in any Spec job. Even under footings, pipes should be sleeved.