the method of slices approach by Bishop or Fellenius will be detailed in most undergraduate oil mechanics text books. In your search the term "Soil Mechanics" will lead you to what you require. There will be numerous authors on this subject. Andy Machon
Depending on your reasons for wanting to see a hand calc, interest, desire to learn, checking someone else's work, I would recommend going right to the source. Bishops and Janbu both did their doctorate work on slope stability. A copy of their papers should be part of any engineering university library.
