Dear Prof. Masin and Soil Model Community,
I am using HP clay subroutine in Plaxis 3D to simulate soil structure interaction problem. I want void ratio and OCR variation along the depth to back analyse centrifuge test. In Plaxis, either or OCR remains constant depending on input. Moreover, I found HP subroutine in plaxis calculate void ratio without considering kheppa line. Please see details and explanations in the attached images. My objective is to obtained initial void ratio and OCR variation along the model depth. Also, I want to confirm the position of e input in parameters in ln(1+e) – lnp space. Thanks

Void-ratio-as-input-1.PNG OCR-as-input-0.PNG

  1. David Mašín
    David Mašín 4 years ago

    Dear Muhammad,
    Actually, there are these two options only, initialise through constant void ratio or constant OCR. By the way, these only work with “K0 initilisation procedure”. With gravity loading procedure, void ratio will redictribute during gravity loading. If you need more complex distribution of void ratio with depth, you will have to approximate it through using many soil layers which will have the same parameters, just different initial void ratio.
    Regards David

  2. Muhammad Shakeel Author
    Muhammad Shakeel 4 years ago

    Dear Prof. Masin,
    Thanks for your reply.
    May I know how the model calculate undrained shear strength (cu)? Is it based on initial void ratio like critical state frame work or some other way? My concern is, if void ratio is constant along the model depth how can we obtained increasing cu along the depth with increasing effective stresses having constant void ratio?

    Thanks for your help.


    • David Mašín
      David Mašín 4 years ago

      Hi Muhammad,
      Yes, HP model calculates cu based on the critical state soil mechanics framework. If you set constant void ratio with depth, you get constant undrained shear strength with depth. You can either initialise OCR, than cu will be distributed over depth based on that OCR. Or, you need to define layers with different void ratios.

  3. Hashmi Sohawon
    Hashmi Sohawon 4 years ago

    Hi both,

    Does this mean that the undrained shear strength can therefore be calculated for the hypoplastic model using the same formula for the MCC model:

    Su=M/2 exp^(((Γ-1-e)/λ))


    • David Mašín
      David Mašín 4 years ago

      Just with a difference that in the oridnary Modified Cam clay normal compression lines are considered as linear in p vs 1+e plane, whereas hypoplastic model adopts Butterfield’s formulation with normal compression line linear in ln(1+e) vs ln p plane, so the equation needs to be updated accordingly. David

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