In the place commands for each type of singularities, the user has the option to select what type of definition to place i.e. template or cell. For more complex or custom solids that defines singularities object, one can create the geometry in external files, that can be stored in the Auxiliaries catalog and then place those objects in the design file.

The default path for storing the external files is C:\ProgramData\Bentley\OpenTunnel Designer CONNECT Edition\Configuration\Organization-Civil\_Tunnel Default Standards - Metric (Imperial)\OpenTunnel Designer\Cell\Auxiliaries