• State Verified Answer
  • +1 person also asked this people also asked this
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 20 subscribers
  • Views 358 views
  • Users 0 members are here

Modified Cam Clay and Soft Soil Material Parameter Determination

Nataly Filipouskaya
Offline

Hi all,

I am using the Modified Cam Clay in my model, and while trying to calibrate the model to the lab test curves, I noticed a possible inconsistency in the definition of the stiffness parameters lambda and kappa.

In the material manual of Plaxis 2D, and according to the general parameter definition, the Modified Cam Clay requires an input of lambda and kappa (not the modified version of lambda* and kappa*). In comparison, the soft soil model, uses the modified values.

However, when I run a soil test, the result did not match the lab curves at all. 

I tried to input the modified parameters (divided by (1+e)) - and the curves matched!

Which made me study the manual and the forum. The material manual refers to the soft soil for parameter derivation, while there it mentions the original Cam Clay, but not the modified Cam Clay parameter...

So unfortunately, I couldn't find a clear statement, whether modified or non modified parameters should be used as input for the modified cam clay.

From my calibration attempt, it seems that the modified parameters are required, which is controversial to the parameter naming (no * in lambda and kappa) and the text of the manual.

Could you please clarify.

Thank you! 

Nataly

Parents
  • 0 Offline

    Dear Nataly,

    Note that the use of the * is not model-specific.  Lambda and kappa are the compression and swelling index in stress-void ratio space whereas lambda* en kappa* are the compression and swelling index in stress-volume strain space. 
    In PLAXIS the Modified Cam-Clay model is in stress-void ratio space, hence the parameters are lambda and kappa. The Soft Soil and  Soft Soil Creep models are in stress-volume strain space, hence the parameters are lambda* and kappa*.
    One can also see that when using the MCC model, the results depend on the initial void ratio e_init whereas for the Soft Soil model this is not the case - this already clearly indicates the models use different parameters.
    Have you checked if you used the correct e_init for your simulation? This may be the reason why your curves didn't match.

    With kind regards,

    Dennis Waterman

Reply
  • 0 Offline

    Dear Nataly,

    Note that the use of the * is not model-specific.  Lambda and kappa are the compression and swelling index in stress-void ratio space whereas lambda* en kappa* are the compression and swelling index in stress-volume strain space. 
    In PLAXIS the Modified Cam-Clay model is in stress-void ratio space, hence the parameters are lambda and kappa. The Soft Soil and  Soft Soil Creep models are in stress-volume strain space, hence the parameters are lambda* and kappa*.
    One can also see that when using the MCC model, the results depend on the initial void ratio e_init whereas for the Soft Soil model this is not the case - this already clearly indicates the models use different parameters.
    Have you checked if you used the correct e_init for your simulation? This may be the reason why your curves didn't match.

    With kind regards,

    Dennis Waterman

Children
Communities
Support and Services
Training and Learning
Social Media