At Arizona State we had a concrete pier in the basement of the Physical  
Sciences building that apparently reached ten feet depth beneath the  
foundation...quite expensive I imagine. The pier was about 6 foot  
square  and was raised two feet above the floor and had a 4 inch gap  
around the edge that was filled with a very rubbery type of substance.  
The filling was important for keeping water from inundating the  
building, since this was a basement. The building was on top of  
alluvial fan and river bed deposits, so very coarse grained material.  
This did a pretty good job for long period recordings, but was not  
ideal since it did not touch bed rock. A few faculty petitioned the  
maintainers of Sun Devil stadium some years ago to see if they could  
put one there since it was on a bedrock outcrop ("A" mountain), however  
the stadium was being prepared to host Super Bowl XXX at the time, and  
they didn't like the idea of putting holes in their foundation.

I would recommend that you check out the type of clay to make sure it  
doesn't swell a great deal when saturated with water...

Cheers!
John

On Tuesday, November 5, 2002, at 04:19  AM, ian@........... wrote:

>
> 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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