Not of this size. Certainly single pieces are used in other applications where safety is even more critical such as submersibles. But manufacturing a tube this big would be impossible.

Impossible to manufacture? Or financially impossible to build a factory for the purpose and larger infrastructure to accommodate transportation?

I'm curious if there is something about acrylics which makes it impossible to make very large single pieces.

I guess you could transport it at immense cost. But you'd also need a machine capable of moulding or extruding it this big. Current maximum for plastic pipes is about 3.5m diameter https://www.agru.at/en/applications/agruline/grand-opening-r... so you'd need something which is capable of more than 3 times the diameter.

Could one pour liquid acrylic into a mold (like with a concrete foundation), rather than extruding it?

You're making me think of this industrial scale 3D printer: https://www.youtube.com/watch?v=vL2KoMNzGTo

That's cool but it's all seams with 3d printing, so it seems like that would make the problem worse.

By the way, here's a big cool 3D printer that prints opaque acrylic: https://m.youtube.com/watch?v=b3CY3P28qyQ