Method of Iwasaki et al (1978; 1984)

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Method of Iwasaki et al (1978; 1984)

This method was developed based on the observation that the severity of the damage produced by liquefaction on structures is related to the volume of soil liquefied inside the deposit.

The method is based on the estimation of two quantities: the factor of safety (FS) and the liquefaction potential index (LPI). The liquefaction potential index LPI, indicative of the extension that the phenomenon of liquefaction can have within the stratum, is derived from the expression:







CSR for earthquakes with a magnitude greater than 7.5 is calculated using the method proposed by Seed and Idriss (1982).


For the computation of the Cyclic Resistance Ratio CRR are proposed the following expressions obtained from numerous tests of undrained cyclic strength:


for soils with 0,04 mm D50 0,6:




for soils with 0,6 mm D50 1,5:




D50 is the diameter of granules to 50% (in mm) and Nm is the average number of blows in the standard penetration test SPT.

The classification of the liquefaction risk through the method of Iwasaki et al. is shown in Table 2.


Table 2 - Risk classes


Liquefaction risk

LPI = 0

Very low

0 < LPI  ≤ 5


5 < LPI  ≤ 15


15 < LPI  

    Very high        




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