The method of Andrus e Stokoe is based on measurements from seismic refraction tests, (Vs).
The velocity of the shear waves is corrected by the overpressure, using the equation (Robertson et al., 1992):
where
VS1 shear waves velocity corrected by the overpressure
VS shear waves velocity measured in situ
Pa atmospheric pressure (about 100 kPa)
σ’vo effective initial pressure in the same units of measure as Pa
For the calculation of the resistance to liquefaction, Andrus and Stokoe have proposed the following relationship:
Where the presence of fine content FC (%) intervenes in the calculation model by the following specifications:
CSR is calculated using the formula mentioned in the Introduction chapter of this Guide, for different magnitude must be inserted the corrective factor MSF (Magnitude Scaling Factor) as recommended by NCEER (see Table 1 - Seed Idriss method).
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