My question is on the necessary soil depth in order to maintain a
near-steady temperature year-round for a wine cellar.  Most wine
experts agree that a less than 10 degree Fahrenheit change over a 12
month period is best for long-term storate of wine.  For simplicity,
assume that the cellar will be 10? wide by 10? long and have a 6?
ceiling.  Assuming the cellar is not attached to another structure and
is sunk in the ground by itself (and presumably access is by stairway
from the surface), how many inches (or feet) of soil must be on top of
the ceiling the of the cellar in order to achieve a near-steady
temperature year-round without mechanical temperature control?  Assume
as well that the ground surface above the cellar does not have any
shade and gets direct sunlight year round.  The goal is to create
something as close to a ?wine cave? as possible in an area where there
are no hills or caves.

Maybe one of the sites linked to the answer to this question could help:
http://answers.google.com/answers/threadview?id=701561