All of that work is already done for you.
Mike Oehler paid a structural engineer to design the modular tables in the back of his book, "The $50 and Up
Underground House".
There is no other book that I know of that will give you that information and how to do it safely for low cost. Try it any other way and be prepared to pay into the mid hundreds of thousands.
Mike's engineer designed the roof to hold 2 feet of earth and a foot of
water, however Mike recommends reducing loading to 18".
His info is at www.undergroundhousing.com.