For water contents of medium and fine-textured soil materials at suctions less than about 200 kPa, the reference laboratory water retention is for the natural soil fabric. Class limits are expressed both in terms of suction and water content. In order to make field and field office evaluation more practicable, water content pertains to gravimetric quantities and not to volumetric. The classes are applicable to organic as well as to mineral soil material. If the soil is frozen, the water content or suction pertains to what it would be if not frozen.
Criteria use both suction and gravimetric water contents as defined by suction.
MWR is the midpoint water retention. It is halfway between the upper water retention and the retention at 1500 kPa. Three classes and eight subclasses are defined. Classes and subclasses may be combined as desired. Symbols for the combinations currently defined are in table 3-2.