Hello Everyone,
I have been trying to simulate the cyclic triaxial test using the SANISAND04 subroutine. When I plotting the stress path (p-q plot), I am getting only the positive value of q. Maybe because the definition of q i.e; sqrt(J2) always gives a positive value. How to get the negative values of q?. Am I missing something in modeling in Abaqus?. Please help me to figure things out. I have attached the exact figure in which I am getting the values below the p axis.

Thanking you


  1. Arie Koot
    Arie Koot 4 years ago

    According to the code qq =statev(31) is always possitive


    if you want negative q as well then take q=S11-S33
    S11 and S33 is abaqus output include waterpressure assume S33 is vertical
    because waterpressure in 1 and 3 is the same it is not in q.

  2. MOHD SAQIB Author
    MOHD SAQIB 4 years ago

    @Arie, Thanks, if we add water pressure it will cancel automatically right ?. i.e: q=(S11-u)-(S33-u). I did the way you suggest but there is not much variation inS11 and S33 which leads to the very small value of q=(S11-S33).

    • Dimitrios Konstantinidis

      Hello Saqib,

      I am also facing the same problem with the negative values of q in the Plaxis Soil Test platform.

      Did you manage to solve this issue ?

      Looking forward to your response.


  3. MOHD SAQIB Author
    MOHD SAQIB 2 years ago

    Hello Dimitrios.
    For getting the negative values of the deviatoric stresses, just product it with the lode angle. You will get the desired results.

    • Dimitrios Konstantinidis

      Hello again Saqib,

      Sorry for the late response. I don’t get notifications from the replies.

      So in order to better understand what you say, you are suggesting to:

      -Run the cyclic test that i want with the PLAXIS Soil Test platform using the SANISAND dll.
      -Get the q-p output from the Soil Test output table.
      -Use a routine of my own (Matlab or even excel) to calculate the lode angle for each increment and multiply that to the output q that PLAXIS gave me?

      Thanks for your help.


Leave a reply

©2024 SoilModels

Log in with your credentials

Forgot your details?