Hardening Soil Model - Typicial relationships between E50, Eur, and Eoed

Dear Alexandra, 

I believe that you have been assisted in a service request, but here is the information for the general knowledge of the forum:

During the validation of the material set, when you try to save (by clicking OK), an iterative algorithm is used to check if all parameters fit within the Hardening Soil formulation by trying to fit the parameters M and alpha (see section On the cap yield surface in the Hardening Soil Model, Material Models manual). There are some basic criteria that must be met even before the iteration-test is performed:

• E_50,ref < E_ur,ref / 2
• E_ur,ref > E_oed,ref
• E_ur,ref < 20 * E_50,ref
• E_oed,ref > 0.1 * E_50,ref

Based on the validation check of the parameters (the basic checks and the iterative validation), a restriction will be given for why the parameters do not fit within the model. These parameters can include any of the stiffness and strength parameters. If this given restriction is met by changing the mentioned parameter, the validation may continue and check other parameters, until all criteria are met. This could mean that you (or the program) needs to update the parameters more than one time. Therefore, it is not so easy to say why a parameter it not correct for the Hardening Soil model. E.g. based on the other parameters, some standard correlations may not work, like K0NC = 1 - sin(phi).

Dear Alexandra, 

I believe that you have been assisted in a service request, but here is the information for the general knowledge of the forum:

During the validation of the material set, when you try to save (by clicking OK), an iterative algorithm is used to check if all parameters fit within the Hardening Soil formulation by trying to fit the parameters M and alpha (see section On the cap yield surface in the Hardening Soil Model, Material Models manual). There are some basic criteria that must be met even before the iteration-test is performed:

• E_50,ref < E_ur,ref / 2
• E_ur,ref > E_oed,ref
• E_ur,ref < 20 * E_50,ref
• E_oed,ref > 0.1 * E_50,ref

Based on the validation check of the parameters (the basic checks and the iterative validation), a restriction will be given for why the parameters do not fit within the model. These parameters can include any of the stiffness and strength parameters. If this given restriction is met by changing the mentioned parameter, the validation may continue and check other parameters, until all criteria are met. This could mean that you (or the program) needs to update the parameters more than one time. Therefore, it is not so easy to say why a parameter it not correct for the Hardening Soil model. E.g. based on the other parameters, some standard correlations may not work, like K0NC = 1 - sin(phi).

Dear Stefanos,

Thank you very much for this information.

Dear Plaxis-support

I would like to model a material which exposes small but distinct difference in the elasticity modulus between first loading and unloading/reloading. However I wonder about the basic criteria that must be met for the Hardening Soil model. Is there no way to have a material behavior with E_50,ref > E_ur,ref / 2 (e.g. E_50,ref = E_ur,ref / 1.5)?

Looking forward to your response. Thanks in a advance and kind regards

Roman

Dear Roman,

As indicated by Stefanos, these are the criteria that are already applied to the input values. So no, there is no possibility in the HS model to use E50 > Eur/2.  You may be able to do that in other models, but not in the HS-model.

With kind regards,

Dennis Waterman