Full list of all 30 Fortified achievements worth 1,000 gamerscore. It takes around 50-60 hours to unlock all of the achievements on Xbox One.
Reached level 20 with all player characters
Destroyed 20 enemies within 1 second
Survived to wave 20 in Invasion mode on hard
Survived 10 waves of Invasion Mode
Completed all maps on insane
Reached level 20
Completed every map on hard
Sold 1000 structures
Placed 1000 structures
Destroyed 10 enemies with the Rifle in 5 seconds
Completed any map on hard, other than Easy Street without taking damage
Destroyed 10,000 enemies
Completed any map other than Easy Street using only infantry
Completed any map other than Easy Street without any structure kills
Set fire to 10 enemies simultaneously
Threw 10 enemies at once with the Cryo Blaster secondary attack
Destroyed 50 enemies using Tesla Coils in any single map other than Easy Street
Froze 10 enemies within 1 second
Destroyed 5 flying enemies in 5 seconds with the shotgun
Spent more than $7,500 in any map other than Easy Street
Failed a map more than 5 times
Unlocked every structure and weapon
Completed every map on normal difficulty
Defeated the Stalker
Destroyed 200 flying enemies
Destroyed 1,000 enemies
Defeated the Juggernaut
Completed 5 maps in multiplayer
Destroyed an Annihilator before it deployed
Completed a map other than Easy Street without the base taking damage