SharePoint doesn’t allow the backup of a site collection and restore it in the same content database. If you backup a site collection and restore it, it will give you the following error.

So you need to make a new content database in the web application (in case the replication of the site collection at the same content database) so that the backed up site collection and the restored one are in different content database, but be careful to put the first database offline before you restore the new site collection.