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Ambiguities in seismic site classification?

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Mccoy

Geotechnical
Nov 9, 2000
907
I'm consulting table 20.3.1 Site Classification in ASCE 07-10.
Do you guys ever come up with some ambiguity basing the classification on the vs,100(feet) or vs,30(meters) method?
From what I see the vs,100 governs upon the qualitative denomimation of the rock-soil so I would expect no ambiguities.
I'm asking this because a main problem in the European regulation is that there are lots of ambiguities, stemming from too many litological and thickness decriptions, which more often than not would lead to classify the site in a special class where site response analyses are required.
I hope this is not the case in the ASCE code.

For example, applying the code algorithm (equation 20.4-1, an harmonic weighted mean) you happen to obtain a 700 ft/s vs,100 in an area where a layer of soft clay soil is underlain by stiffer soil. So the underground is not all stiff soil but soft soil and stiff soil,
You still have a stiff soil class D? That is, vs,100 governs regardless of the soil qualities and coexistence of stiff and soft soil?
 
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