Talking of concrete pentration by 155mm dumb rounds, here's a useful example of ww2 era testing. There's an average pentration of 3 feet on concrete reinforced pillboxes. Sometimes much more than 2 metres was achieved.
https://www.alternatewars.com/WW2/Do...5-FEB-1944.htm
Concrete containment shields on nuclear plants seem to be around 2 metres thick.