Duplicate Site Collection

Steps to Duplicate Site Collection in Backup in Same Web Application
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Step1:
Create Empty Site Collection

Step2:
Create Empty Database

Step3:
Add Database as Content DB

Step4:
Mount Database to Created Site Collection

Add Content Database
stsadm -o addcontentdb -url http://server:port/ -databasename WSS_Content_New -assignnewdatabaseid  -databaseserver  yourdatabaseserver

Step5:
Restore the Backup File to newly created Site Collection
Backup-SPSite -Identity http://server:port/ -path D:\Portal_05May2013.bak
Restore-SPSite -Identity http://server:port/ -path D:\Portal_10Jun2014.bak -force


Mount-SPContentDatabase "<ContentDb>" -DatabaseServer "<DbServer>" -WebApplication http://SiteName