BIM360 Design Collaboration for Civil 3D Getting Started 03 XREFs 

Note: When you save a file to BIM360 it will automatically copy the xrefs to BIM360 BUT it will place in a default folder structure that does not match your CAD Standards. Make sure you move the Xrefs to the location/folders you want them in.
Updates to XREFs while a file is open are not automatic and you will not get a notification a change has been made by another user. You must Check Reference Status button on the Collaborate tab/ribbon.