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. These are the default locations for the PLAXIS CONNECT Edition. Example for PLAXIS CONNECT Edition Version 21:
Note: replace "V21" with "V20" when using that PLAXIS CONNECT Edition V20
PLAXIS Legacy versions (PLAXIS 2D AE - PLAXIS 2D 2019, PLAXIS 3D 2013 - PLAXIS 3D 2018), these user-defined soil model's DLL files should be placed in a subfolder called udsm:
All dongle/hardware lock (HWL) based versions of PLAXIS 2D/3D are treated as "V8i SELECTseries 10" according to Bentley's Support Policy. This means that Bentley will discontinue support for hardware lock based versions of PLAXIS after December 31, 2021. This includes PLAXIS 2D 2019 and older, and PLAXIS 3D 2018 and older.
To see the benefits of the latest versions and how to get the latest version, please see PLAXIS CONNECT Edition: upgrade from Hardware lock to Flexible licensing
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.
Disclaimer: the Bentley Systems, Inc and PLAXIS organisation cannot be held responsible for any malfunctioning or wrong results due to the implementation and/or use of user-defined soil models.
UDSM - Anisotropic Clay Models: S-CLAY1 and S-CLAY1S [Models]
UDSM - Barcelona Basic Model [Models]
UDSM - CLoE Hypoplastic Model [Models]
UDSM - Generalized Hardening Soil Model [Models]
UDSM - Hypoplastic model with inter-granular strain [Models]
UDSM - Isotropic Jointed Rock with Mohr-Coulomb Failure Criterion [Models]
UDSM - MIT S1 Model [Models]
UDSM - Mixed Isotropic-kinematic Hardening Elastoplastic Models for Structured Clay [Models]
UDSM - SHANSEP MC model [Models]
Concrete model [Models]
UDSM - Swelling Rock Model [Models]
UBCSAND3D Model [Models]
UDSM - Visco-elastic perfectly plastic model [Models]
64 bit User Defined Soil model [Tips and Tricks]
How to use a user defined soil model in PLAXIS [Videos]