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?