AWH,
Detailed discussion on the EWSL and the CBR cover curve can be found in suitable great detail with worked examples in the (older) textbooks.
The ICAO pavements manual (1983 is the latest version: ICAO Aerodrome Design. Manual, Part 3, Pavements, 2nd Edition, 1983) has this, as does the pavement engineer's bible - Yodar & Witczak [Yoder & Witczak; Principles of Pavement Design 2nd Ed. Wiley 1975].
The older version of the FAA pavement design manual (up to and included AC150/5320-6D) also has some discussion but does not explain EWSL or CBR cover curve very well.
ICAO/Yodar are very much pre-computer, and thus not available electronically. There might (?) be a link to the ICAO manual in the "useful website and document references" thread on Tech Log.
This is opening the door to fall very deep into the arcane and unintelligible aspects of the topic. Be sure your water wings are well pumped up
