To use the xMat from Plaxis, it has to be compiled as a dynamic-link library xmat64.dll first, e.g. with the Intel compiler like

ifort /free /fpp /DPLAXIS_DLL /dll xmat.f /recursive /MT /exe:xmat64.dll

Then the library xmat64.dll has to be moved or copied into the udsm directory in the Plaxis installation path.

Please note, that for compilation the macro PLAXIS_DLL has to be defined next to the flags for free format, preprocessing and dynamic library (as shown).

Afterwards, the xMat should be available as user defined material in Plaxis and all constitutive models from the xMat can be selected. Please note, that for some models it might be important to initialize some state variables or they will fail to run. State variables for the xMat can be defined in Plaxis below the specification of the material parameters.