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Ventilation shaft and Head House

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I would suggest that the Geotechnical Engineer would be the one to define
the seismic induced forces on the underground portion of the shaft since
they are not covered by any code. 

Seismic induced forces on your shaft will be the result of the varation in
soil pressures from ground motion and from the deformation of the ground.

It is my understanding that a number of Geotechnical Engineers do not
provide earthquake induced soil pressures unless they are requested.  There
is some debate that given the normal factors of safety that are used there
is little need to consider these additional soil pressures.

If your structure is stiffer than the ground through which it passes then
you will have to perform a soil structure interaction type of analysis to
establish the design forces.  On the other hand if the shaft is more
flexible than the ground, which might be the case if the shaft is in hard
rock, your shaft should go along for the ride with little problem.

For the portion above ground you would treat it as any other building.

Mark Gilligan


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>I am working on a preliminary design of the above metioned and am asking
if anyone knows of a good reference for a 22 foot inside diameter
vetilation shaft drilled 200 feet into the ground in a Zone 3 region.  I
mostly interested in force distribution from soil pressures amd seismic
loads.
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