Jeff, I made my concrete pier 450 mm dia and it's 2.2 m high. I've never detected any low-frequency vibration after the pier is struck, so I reckon that it's about the right dia/height. I agree that a 200 mm pier 1800 mm high made from concrete would seem too thin.
To avoid the potential for the pier interfering with equipment on top, and to provide a means of changing the equipment height at some time in the future, I opted for a steel pier on top of the concrete pier.
See
http://www.iceinspace.com.au/forum/s...ad.php?t=36222 for a pier pic (I think at around post #7).
Chris