You can use commands to quickly access the functionality for exchanging files between Autodesk Civil 3D and Autodesk InfraWorks.
Command
Description
IMX_IMPORT
Imports an IMX file that was exported from InfraWorks and creates Autodesk Civil 3D data
IMX_EXPORT
Exports Autodesk Civil 3D data to an IMX file that can be imported into InfraWorks