# Desai Yield Surface, Parameters

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1. Dec 11, 2016

### sandon

Hey guys,

Desai Yield Surface:

I have a hard time understanding the parameters of the model for soils. If I have three principle stresses, σ1, σ2, σ3. And R is defined as the Tri-axial strength in tension, how would I define R.

Lastly can I just say that
I1 = σ123
J2= 1/6 * ((σ12)2 +(σ23)2+(σ31)2)