There is a U.K. book that has many examples of inverted domes
, triangular pyramid shells etc used in Sewage farms ,constructed with the
apex below grade in and out of the water table, it is called 'Reinforced
Concrete design' by Charles Reynolds.
In the U.K , Australia, and Europe this book is known as the'Bible' of r.c.
this will help you without getting you envolved in other peoples codes.