The Gates of Justice are MASSIVE, it would take hundreds of Giganto Gatlings to budge it even an inch
Look at it http://www.onemanga.com/One_Piece/548/06/
once Luffy gets to Marine HQ, he will have laid waste to two of the main 3 places Marine's control….EL was demolished by the buster call, ID is in pieces with hundreds of prisoners escaping, and now he's heading to marine HQ....the trend continues and Marine HQ will be in ruins
And with WB and crew heading there as well, it's pretty much certain that it will.