The Citadel walls - how do they actually work?

[Para]

Well since we're now kinda finished with the whole City 17 from gameplay view I believe we know everything we are going to know about the walking walls of Citadel. Feel free to speculate about all related things I'm now listing.

What we know is the following:
The walls are used primarly as a way to consume the city around the Citadel. The wall practically walks over the houses and such and then allows Combine to do whatever they want with -to be honest- pile of rubble it leaves behind. The wall itself is kinda dumb, it just keeps doing that one function it is made for with great success rate since it's so massive that stopping just isn't a realistic feat. Apparently the wall is also completely mechanic since having a Synth wall wouldn't make any sense. The wall isn't a warning or defensive system, it's just a wall.

What is unclear to me:
Since the wall walks away from the Citadel, it expands in a ring. This means that the sections between pieces of wall will stretch until new pieces are added to compensate. Where and how those extra pieces are actually added to the wall?

Also since it's clearly a strong infrastructural mechanism it's very likely it has secondary attributes like dividing power and possibly even supplies around the perimeter of the wall. We never see this ingame but I believe that it's almost necessary. This brings up yet another question, how limited such capabilities of the wall are and is there actually crawl spaces/catwalks on the wall itself to make moving along the wall easier? And what about thumpers for that matter, does the wall act as one just in case?

Last but certainly not least, what's under the wall? As we all know, if you can't go through something, you have to go around it. In case of a dark blue metallic ring one would either go over or under it as is done in game but as default I wouldn't leave the wall as is and I believe that mostly because of the chaos caused by Gordon in HL2 caused that the section of the wall I just mentioned was deployed there only lately because of the rising threat of Rebels and Combine just didn't have had time to build underground infrastructure to make sure no one goes under it?

The reason I want to discuss about this is because I believe that from all the wonderous technology in HL2 the walls are the most awesome piece of any equipment Combine has.

 

[Tsoedill]

yeah...

I always wondered about that...

I don't think they only served as protection to the Citadel, but just to pound stuff. But why would the Combine want to pound their future stalkers and soldiers?

 

[ktimekiller]

probably just making synth like infastructures

 

[Solver]

The wall could use advanced nanotechnology. Hypothetically, that would even allow for new segments to be built as the ring expands.

Primarily, I think, though, the walls were immobile for most of the time. As you arrive in City 17, the walls are standing there, allowing the Combine to comfortably control who goes where - and, of course, to prevent anyone getting in the vicinity of the citadel. Their pounding functions were reactivated once full-scale warfare started between the Resistance and the Combine in the city itself. So I guess the walls did some pounding after the initial invasion, and then mostly stayed in place for all those years until HL2.

 

[Operational]

Where and how those extra pieces are actually added to the wall?

I always assumed it somehow consumed parts of the buildings it crushed.

Last but certainly not least, what's under the wall?

I don't think there is anything under it - when you reenter City17 don't you see the wall advancing and the gap that's under it? I could be wrong I really can't remember.