Thanks to Mark/Cookiemonster from homeone.com.au forum, there's this article from VIC government web site with some detail information about easements.
It talks about "what is an easement?", "what can I put over an easement?" (diagram shown below, thanks to Matt/mattwalker), and some other stuffs.
This article should give you a better idea about what easement is and provide some knowledge about things can/can't be done on easements.
Please also note that the regulations between different states/councils might be different and they might change as well. Always consult your local council for latest information.