Rule of Thumb = Friction Angle - 30 _xp8*2~-
QS&B"7;g
For more details, please read Nhjq.&
WK>|IgK
Bolton, M.D. (1986) The strength and dilatancy of sands 0+* NHiH
^!&6=rb
Vermeer & DeBorst (1984) Non-associated plasticity for soils, concrete and rock