having read the article on installing seismometers, 
http://www.seismo.berkeley.edu/seismo/bdsn/instrumentation/guidelines.html ,
I'm a little unclear on one aspect and would appreciate some advice.

The article states that a 4 inch gap should be left around the base of the 
pier.  What about the rest of the pier?

Also, the 4 inch gap seems to be filled with insulation.  Won't this cause the 
pier to move with the insulation/surrounding ground?

I'll be building on clay soil.  How deep should I go (within reason!) and are 
there any other tips for clay?

TIA

Ian Smith
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