On the crew dying inside an submarine if breached,

 

it's different in the pillars.

 

 

 

First, the water is drained.

 

That is when the crew goes in.

 

 

It means there is no pressure while they're in there.

 

 

Second, if breached, it'd be a small breach.

 

It can't suddenly break apart.

 

Water would be seeping in.

 

 

If then, the height is too high to predict this.

 

Like the space escalator,

 

'sides' can be added.

 

 

If so, instead a cylindrical pillar, as mentioned before,

 

a cube. Dropped and closed as a valve.

 

 

Inside it could be a pillar construction with cement and iron support

or whatever people may choose it to be.

 

But... it would be a monumental task. To stack these and build something in it.