Here is a link to download a pdf copy of slides from the lecture "Critical State Soil Mechanics for Dummies" from Professor Paul Mayne from Georgia Tech University (...given in 2006). Thanks for the great information, Dr. Mayne!
https://www.dropbox.com/s/hd1bf0de319d9bi/CSSM%20for%20Dummies_P%20Mayne.pdf?dl=0

In this lesson, I introduce the basic concepts related to critical state soil mechanics (CSSM). I discuss the relationship between consolidation behavior and shear strength behavior of soil. The critical state line (CSL) is introduced, and its relationship with the normal consolidation line (NCL) and the unload/reload line (URL) is discussed. The idea of yield surfaces is introduced.