[dgarud]

Couple of comments:

1) What is the size of the pipes you are considering? Will it be big enough for humans to get into for maintenance - I was thinking what would happen if a delivery vehicle breaks down or a small animal gets into a tunnel.

2) Have you considered small blimps as delivery vehicles? The technology has got considerably better and should be less noisy than drones.

[tuberelay]

1) 700mm diameter - broken down vehicles should be shuntable, but a person could get in there reasonably easily.

2) helium blimps lift 1 gram per litre of helium, so to lift 10kg of groceries they would need a 10 cubic meter blimp or a 2.7 meter diameter sphere - seems big and difficult to control especially in winds.

[S4M]

A person could get in a pipe of 700mm diameter? I seriously doubt it.

[lgregg]

It's a tight fit but works. I would have to put one arm forward and one arm back to shift my shoulders for a torpedo tube (approx 21in or 533mm depending on nation). 700mm is another 6 inches. The average male's shoulder width is about 18 and go wide as 24 inches (often hard core weight lifters).

https://www.google.com/search?q=person+in+a+torpedo+tube&tbm...