The main thing with a pier is to have no resonances that can be driven by your mounts motors.
The only thing sensible in the video is the taper of the ribs as this will make the the whole assembly have a low Q. In laymans terms it means that all frequencies will have an equal and low chance of exciting the pier to any sort of resonance.
It is not about absolute rigidity! It is about damping resonances.
As for the concrete into the ground you only need to go as deep as any earth movement will make your polar alignment change.
My concrete pier base is about 400mm square and goes down nearly two meters to bedrock.
See here
http://www.iceinspace.com.au/forum/s...et+pier&page=3
These blokes have the correct ideas for the wrong reasons.
My pier cost me $160 made by a local metal fabrication shop.
Bert