Creep calculation in SSC model

Dear Elena,

The parameters of Kappa and Lambda are taken from the primary consolidation curve (mean effective stress vs. volumetric strain). Specifically, the κ* and λ* from the inclination of the settlement curve before and after the preconsolidation stress Pp. See figure 1 below: 

The above is from the following document on Practical application of the Soft Soil Creep model, part III: 
https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46054/practical-application-of-the-soft-soil-creep-model

Here the oedometer test is long-term (not 24 hours), see here from the link [second paragraph]:  

“In principal all four parameters can be derived from a standard oedometer test, provided that the test has been performed for long enough after applying the load step.” 

The creep rate is normalized over a 24-hr period, this covers the change in the rate of secondary consolidation and the Mu* parameter. But Kappa and Lambda do not care about the 24 timeframe.  

The Tau (1day) parameter is not critical here as the equation you list is not the final derivation of the creep rate. When you see the equation develop out in the material models manual you can find that the creep rate collapses into this final form (with the Tau parameter removed): 

The above is from the same link to documents on Practical application of the Soft Soil Creep model, part I.

Dear Elena,

The parameters of Kappa and Lambda are taken from the primary consolidation curve (mean effective stress vs. volumetric strain). Specifically, the κ* and λ* from the inclination of the settlement curve before and after the preconsolidation stress Pp. See figure 1 below: 

The above is from the following document on Practical application of the Soft Soil Creep model, part III: 
https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46054/practical-application-of-the-soft-soil-creep-model

Here the oedometer test is long-term (not 24 hours), see here from the link [second paragraph]:  

“In principal all four parameters can be derived from a standard oedometer test, provided that the test has been performed for long enough after applying the load step.” 

The creep rate is normalized over a 24-hr period, this covers the change in the rate of secondary consolidation and the Mu* parameter. But Kappa and Lambda do not care about the 24 timeframe.  

The Tau (1day) parameter is not critical here as the equation you list is not the final derivation of the creep rate. When you see the equation develop out in the material models manual you can find that the creep rate collapses into this final form (with the Tau parameter removed): 

The above is from the same link to documents on Practical application of the Soft Soil Creep model, part I.

Is there a formula similar to the one you cite to derive the final form of creep rate for the Creep-SCLAY1S model?

By ignoring the anisotropy and debonding in the Creep-SCLAY1S model, is the creep calculated in the same way in the two models?

They are both able to simulate isotache behavior, but what are the differences in the creep formulation?

Does also the SSC model allow for creep within the NCS?

Dear Elena,

To answer your question:

The formula is mentioned in the documentation (equation 2.11 - 2.13) found in the link below (see Downloads):
https://communities.bentley.com/products/geotech-analysis/w/plaxis-soilvision-wiki/46106/udsm---creep-sclay1s

Indeed, you are correct, that if you ignore the anisotropy and bonding, the two models are the same and the equations become the same.

Finally, indeed, the creep is present from the beginning of time, so even within the NCS.