In relation to sand in a metal pier, here is a quote from an archived thread here at IIS:
"Adding the sand adds mass which lowers the natural frequency of your pier.
For a given vibration energy, a high frequency vibration has a smaller amplitude than a low frequency vibration. Adding the sand gives a larger amplitude of vibration than without it.
There may be anecdotal evidence that sand filling helps to dampen the vibration more quickly, but that's of little value if the first movement is enough to blur your image anyway.".
See the original thread here:
http://www.iceinspace.com.au/forum/a.../t-146710.html
Check Sheeny's post in that thread.