UDSM for Interfaces

Question

Dear Plaxis/Bentley community, 
 we are working on soil-geogrid interaction and want to apply user-defined properties to the interface via a UDSM. The overall goal is to update the shear stiffness of the interface elements in each calculation step depending on the actual normal and shear stress on the element. 
 We noticed that when assigning a UDSM to an interface, the properties (stiffness, strength) defined in the "Interface-Tabsheet" are used, instead of the values of defined in the "Parameters-Tabsheet. 
 
 Is it possible to assign the parameters of the "Parameters-Tabsheet" to an interface via a UDSM, or are the "Interface-Tabsheet" values used by default? 
 Or alternatively, is it possible to set the interface stiffness to &ldquo;standard&rdquo; and strength to &ldquo;rigid&rdquo;, meaning that the interface takes its parameters from the &ldquo;Parameters-Tabsheet&rdquo;? 
 
 We have also noticed that when using the "InterfaceStiffness" = "Standard" mode instead of the "InterfaceStiffness" = "Kn/Ks" mode, we are able to assign Eoedref in the GUI, but cannot define Eoedref during remote scripting even if we used the proposed formulation in the manual. 
 
 How can we access Eoedref during remote scripting (when using a UDSM for the interface)?&rdquo; 
 
 Thanks for your help! 
 Best regrads Jan Derksen

Jan Derksen · Answer

Update: 
 First of all, I would like to thank the support team for their immediate response and detailed information. Some key points are listed below: 
 
 The only constitutive model that can be used to represent the response of an interface element is elastic isotropic (either linear or non-linear) coupled with Mohr-Coulomb failure criterion. The flow rule can be either associated or non-associated. 
 When using a standard model (e.g. HS, HSsmall, soft soil, etc.) and using &ldquo;standard&rdquo; as stiffness option for the interface tabsheet, the properties defined in the parameters tabsheet are used to define the properties of interface. 
 For a UDSM, the stiffness properties of the interface are computed based on UD-power, UD-Pref and Eoedref defined in the interface tabsheet. This means that the properties of the surrounding soil have no influence on those of the interface. But this interface formulation takes normal stress dependency of the stiffness into account. 
 
 In summary, it is currently not possible to assign the properties of the "parameter tabsheet" to interfaces when using UDSM. Thus, interfaces are limited to the UD- power, UD-Pref and Eoedref formulation in combination with UDSM at the present. 
 Anyway, I would be very thankful if you could provide a workaround or other solution that enables a UDSM to be applied to the interface as well.

UDSM for Interfaces

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