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!

Shen

1. Manuel Bode 2 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,
Manuel

• Shen Wang 2 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 2 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
Manuel

• Shen Wang 2 years ago

I see. Thank you so much!