As a first step, read Article 19 of Terzaghi, Peck and Mesri; see Figure 19.4. See also Section 2.3.2 of M.J. Tomlinson's Foundation Design and Construction (6th Ed.). Further, check out Conduto's Geotechnical Engineering Principals and Practice , Section 13.4 (specifically Figure 13.11 derived from NAFVACS). Hope this helps (I stayed away from Bowles, for obvious reasons!).