When users want to import a network from Land XML to Autodesk Civil 3D, they need to specify the import settings.
Use the Civil 3D LandXML command from the ribbon Insert:
Browse for the XML file and once you select the file, a window with import settings will open. Click on the button Edit Import Settings:
Set the Pipe Network Import Settings (most of the time the correct part list, circular pipe type and circular structure type is sufficient however, some network types might require other settings as well):