With the Tunnel designer, among other features, it is possible to define the material of a volume, e.g. when simulating the installation of the shotcrete or the final lining. This is performed in Sequencing mode, in which the tunnel phase steps are defined.
When a project that contains such a definition is being opened in Input program in PLAXIS 3D 2018 any material assignments set in Sequencing mode are lost:
This means that if a new phase is added in Staged construction mode when using the Advance to next tunnel step, it will result in having no material assigned as defined in tunnel designer:
Note that no material assigned means that the default soil material will be kept for the specific slice.
This issue is now solved in PLAXIS 3D CONNECT Edition V20
The suggested workaround for the issue with the Tunnel designer in PLAXIS 3D 2018 is only applicable if the project is not reloaded during the process since this is when the issue occurs.
Be aware that the above steps are required every time you reload the project when it is needed to add new phases in Staged construction or edit the current tunnel definitions.