/diy/ - Do It Yourself

>>369280
Seconding this. There are also corrugated metal culverts this can be done with that are pretty swank. They can be built on any scale and can hold a lot of soil on top.

Here's a pic of a really big one.

This link will give you a ton of info on the subject,

http://www.radshelters4u.com/index3.htm

Anyone else that frequents these types of threads, copy that link above so you can paste it later if another thread crops up.