Plaxis User Defined Soil Models

01 October 2012
Note: with the release of PLAXIS 3D 2016 and PLAXIS 2D 2017, Plaxis will only support 64-bit user defined DLL files. 32-bit DLL files will not be loaded by the Plaxis programs with these versions.

PLAXIS has a facility for user-defined (UD) soil models. This facility allows users to implement a wide range of constitutive soil models (stress-strain-time relationship) in PLAXIS. Such models must be programmed in FORTRAN or another programming language, then compiled as a Dynamic Link Library (DLL). Finally, you need to add this DLL to the PLAXIS program directory.

In principle, the user provides information about the current stresses and state variables and PLAXIS provides information about the previous ones and also the strain and time increments. In the material database of the PLAXIS input program, the required model parameters can be entered in the material data sets.

For more details, please read the attached document and example code.


These user-defined soil model's DLL files should be placed in a subfolder called udsm:

  • PLAXIS 2D: C:\Program Files\Plaxis\Plaxis 2D\udsm
  • PLAXIS 3D: C:\Program Files\Plaxis\Plaxis 3D\udsm

For older versions (PLAXIS 2D 2012, PLAXIS 2D Classic and earlier and in PLAXIS 3D 2012 and earlier) the user-defined soil model's DLL files should be placed in the program's installation folder, e.g.

  • PLAXIS 2D: C:\Program Files\Plaxis\Plaxis 2D
  • PLAXIS 3D: C:\Program Files\Plaxis\Plaxis 3D


Disclaimer: the PLAXIS organisation cannot be held responsible for any malfunctioning or wrong results due to the implementation and/or use of user-defined soil models.


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