Seismic corrections to the angle of friction of layer bearing the foundations, are only relevant in well compacted, cohesionless soils. It is incorrect to apply them in loose or averagely compacted soils, as in these, seismic vibrations produce an effect opposite to expansion causing increase in compaction and angle of friction.
Correction factor applicable in computation of bearing capacity in seismic conditions, that account for the phenomenon of expansion may be Menu data between the authors below:
Vesic
According to this author it is sufficient to reduce the angle of friction in the foundation layers, by 2º. The problem with this proposal is that it takes no account of the intensity of the specific seismic stress (see max. seismic acceleration parameter). On the other hand this correction seems to be confirmed by actual observations in a number of seismic events.
Sano
The author proposes a reduction in the angle of friction in the bearing layers according to the following:
where Amax is the maximum seismic acceleration.
This method in contrast to Vesic does take account of the intensity of seismic stress. Experience however seems to demonstrate that an uncritical application of the method leads to excessively conservative values of Qlim
Okamoto
The author proposes a reduction in the angle of friction in the bearing layers according to the following:
where Amax is the maximum seismic acceleration.
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