If you have the foundation texts by Bowles, Teng, Tscheb0tarriof, Das, they all have a unique method of doing cantilever and anchored sheetpile designs. It may take you few days to do a spreadsheet and you know what all the numbers are. Besides, the software firms have access to these same sources.
Each of the above texts have other papers of interest that will lead you to more case studies. For example, Tschebotarriof, in the late 1940's, did some model studies of sheetpiles and then recommended an earth pressure envelope for cantilever system and one for one level anchor. Blum, in the early 193o's and later in the 1950's did a free cantilever method and also his famous equivalent beam method. Spend some time gathering the above references and you will see it is as simple as analyzing a cantilever beam and a beam with an overhanging support- nothing harder than a Mechanics of Materials class.