One way is to use concrete slabs; put the first on the ground, then subsequent slabs use Z function to raise off ground, then change the Pitch angle (minimum 6 deg).
Best to copy your 1st slab, raise it and change pitch angle, place it, copy that slab, increase height and pitch angle by same amounts as previously.
After you hit 90 degree pitch, rotate slab 90 degrees.
If you get good at it, you can CTRL click a few slabs at a time, and change height and pitch of all together.
Once you have tube made, use ramp object at open ends.
You'll notice at top of loop, that slab size has been made wider - you need to play with X and Y function settings.
Alternately, if you can find a layout that someone's already made with a loop, save the layout, then CTRL Click the structure that's already there and place in your own layout. Although you can only copy 30 objects at a time, nothing to stop you copying part while in one layout, loading your own layout, placing to suit, going back to original layout, copying the rest of the objects, then go back to your layout and placing with previously copied objects.