How can I copy a Site Collection to the same Web Application?
I have got Public Site, so I can't save this as a template, or can I?
In order to copy to site in same site collection you need to add a new content Database in that web application, otheirwise it will throw the error. here are the steps:
Restore-SPSite http://server_name/sites/site_name -Path C:\Backup\site_name.bak -Force -DatabaseServer SQLBE1 -DatabaseName SQLDB1