PDMY - Query on hyperbolic/backbone curve

[cycaucklanduni]

Query on Automatic Surface Generation of the Tau - Gamma hyperbolic/backbone curve

Note 2 of the PressureDependMultiYield (PDMY) Wiki states that the following relationship is used to automatically generate the backbone curve:-

http://opensees.berkeley.edu/wiki/images/d/dd/PreDep_Tau.png

Could someone help me understand what the "G" term refers to ?

Does this refer to

(1) Gmax - Maximum shear modulus; or

(2) Gr - the reference shear modulus ($refShearModul) which is defined as a "reference low-strain shear modulus, specified at a reference mean effective confining pressure of 80kPa as given in the Wiki? This seems to tie in with Yang (2000) PhD Thesis "Numerical modelling of earthquake site response including dilation and liquefaction", Equation 2.11 on Page 54 - where G refers to the "low-strain elastic shear modulus"; though it is not clear if this is necessarily associated with a confining pressure of 80kPa?; or

(3) Some other definition?

Your comments would be much appreciated!

Thanks.