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I think a well designed pier will not benefit from sand - it will already be extremely rigid and this usually means it will also be strong and heavy - since they are most often made from steel or cement.
If its rigid and resists bending (the primary purposes) and if vibration is damped to earth (a secondary purpose and usually by product of the first), then any resonances or intermittent vibrations (caused by movement of other gear, wind, cable movement, fans, stop start slews, gear rotation etc) will be transferred to the ground in a very short period of time.
This will provide a vibration free platform.
Ringing vibrations tend to be dampened by adding sand - that is both a function of adding mass, changing the resonant frequency and some absorbtion. The ringing sound means that the frequency is quite high and therefore the amplitude very small - this isnt generally likely to affect imaging. ie there are plenty of other problems (seeing, tracking, polar alignment, optical aberrations, poor focus) adding to your imaging noise than this !
Greater mass usually means a higher resonant frequency
Will adding sand improve a poorly designed pier's performance ? - If its not adequately attached to the ground - the extra weight will provide a better mechanical transfer of vibration energy.
It will not add anything to the rigidity or strength of the pier.
But if you start with a well designed pier in the first place - and that usualy means simply going to a larger diameter and greater wall thickness steel pipe, you won't need to add anything.
Scrap steel pipe is dirt cheap - I have never understood why anyone would skimp on the part of an imaging system that only costs around $120 in the first place !
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