G&G genius ideas squad needed

Something to bear in mind is that it will take almost 380 litres of compost to fill a single tube (not cut in half).

I would try to figure out a way to turn them into water reservoirs which pots can sit in or on top of, like a very long, cylindrical Quadgrow. That would really cut down on the compost needed.

A big hydro growing system type thing, might be possible.

IF you were thinking of staggering them in height, I'd put one on top of the other alongside the tunnel with a path between........
Like this............PT,/2 pipes/path/2 pipes/PT.
Not sure that would work with the cradles though??

I’ve just had a Play with this . PT /2 pipes /path /1 pipe /PT.
That works.
not quite enough space for 2 pipes either side. 

I could cut the other half pipe into 1m lengths and probably do a teared stand.

Have you worked out how you're going to block the open ends of the pipes to stop everything running/falling out?

Have you worked out how you're going to block the open ends of the pipes to stop everything running/falling out?

Plastic weld some end plates on.  Apparently (according to Bob) as long as the plastic you’re using to weld is the same as the stuff you’re welding to. It’ll work.

On a much smaller scale, I used pieces of polystyrene sheet to block the ends of the guttering I grow salad in, in the GH. That's what made me think about your massive pipes!