Hello Everyone,

I am using the UMAT code for clay hypoplasticity provided by Prof. Masin — https://soilmodels.com/download/plaxis-umat-hypoplas-zip/

I made a oedometeric test model in Abaqus2018 and applied the umat code (umat_hcea.for), the parameters I used are listed in the Fig.1. However, the result show the void ratio of whole model was 0 when the simulation started. In my understanding the initial void ratio doesn’t necessarily to be determined by users and can be calculated by other parameters. Am I right? And if I want to specify a void ratio, where can I input the value?

Thank you very much!


Fig2-1.PNG Fig1-0.PNG

  1. Manuel Bode
    Manuel Bode 3 years ago

    Hello Shen,

    the model is able to calculate the inital void ratio depending on the material parameters and a given overconsolidation (OCR).
    As user you either have to define an initial overconsolidation or an initial void ratio. Both can be done by initializing the value of the State Variable 7 in ABAQUS.
    If SDV 7 10, you initialize an overconsolidation with OCR = SDV 7 – 10.
    E.g. A value of 12 means OCR = 2.
    I hope i could help.

    Best Regards,

    • Shen Wang Author
      Shen Wang 3 years ago

      Hello Manuel,

      Thank you for your help! I used another umat without anisotropy (https://soilmodels.com/download/hypoplasticitygeoslope-zip/) and found how to define initial void ratio/consolidation, it is the same as in your comments.

      I have another question however — why is the OCR value is recognized as input-10? Do I miss some background of soil mechanics?

      Thank you!

      Best regards,

  2. Manuel Bode
    Manuel Bode 3 years ago

    Hello Shen,
    it doesn’t have a mechanical reason. It is only for the subroutine to distinguish between initial void ratio input and initial OCR input. Every input value that is > 10 is interpreted as initial OCR by the subroutine.

    Otherwise the for exaple the value 1 could be an OCR as well as an initial void ratio.

    Best Regards

  3. Ashesh Choudhury
    Ashesh Choudhury 10 months ago

    Whenever I am running the UMAT for clay hypo in ABAQUS, it is getting exited by failing the test – “strain rate from the ABAQUS is not NAN” i.e. testnan =1. How to solve this issue?

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