here are a couple ways that might work:

one way would be to select the base circle and then use the move tool + Ctrl Key (PC or Option Key (MAC) to copy the circle up along the Blue axis a distance of 10'.

then type '18x', and then press Enter for the other 18 copies that you're looking for.

or another way, would be to approaching this task from the perspective of building 20, 10' cylinders on top of each other. To do it this way:

create your base circle, then use push pull to pul the circle up to a height of 10'.

Then use Push Pull + the Ctrl Key (PC) or Option Key (MAC) to pull up a second cylinder an additional 10'.

Then double-click with Push Pull + Ctrl or Option to repeat the 10' distance as many times as you want.

-mike