Eur 2*E50 in HSM model

Question

Dear all, 
 Is there an explanation for the limitation Eur > 2*E50 in HSM model ? 
 I would like to model satured sand with Eur = E50. 
 Thank you a lot, 
 Best regards.

Dennis Waterman · Answer

Dear Pauline, 
 The explanation is that even for sands Eur > E50 because primary loading is more elasto-plastic than unloading/reloading, hence the stiffness in primary loading is always lower than in unloading/reloading. For numerical reasons Eur = 2*E50 is the lower limit, but since generally Eur > 3*E50 this is not a practical limitation. Eur = E50 means the soil behaviour is purely elastic. I won't say that is never true (never say never when it comes to soil), but as Berk already mentioned, in that case you can just use the Mohr-Coulomb model. 
 With kind regards, 
 Dennis Waterman