[Marcello]

The first, the turret bunker, was an one of a kind affair built after 2003 for the new iraqi army.
The second and the third were the typical bunkers built to defend the beaches of kuwait from an american amphibious assault.
From what I read and I have been told these were meant to house nothing bigger than machine guns and soldiers (no antitank guns or such). Construction was generally very light, with thin walls made out of precast concrete, concrete blocks and perhaps even concrete filled cinderblocks. Nothing strong enough to withstand direct hit with modern artillery.
As a general rule the iraqis relied, in practice and by doctrine, on earthworks rather than reinforced concrete structures. Probably because the latter were faster and cheaper to build and to repair (and if you had to advance, abandoning them would be no big deal). Given the power of modern weapons a bunker capable of withstanding direct hits would require a significant expenditure of resources, so that approach was not senseless.
The near totality of the bunkers were simple dug shelter like the one in the last picture. Meant to house a squad, they were built by digging an hole and putting in place a steel support structure which was then covered with a thickness of sandabags/gravel and such. If built to paper specs it was supposed to protect against some mortar bombs.