Idriss and Boulanger (2008)

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Idriss and Boulanger (2008)

In the method proposed by Idriss e Boulanger the soil behavior type index IC is calculated using the following formulas:






qc - measured point resistance

Pa - reference stress (1 atmosphere) in same measurement units as σ'v0.

fs - sleeve friction

n exponent depending on the soil type


where n is determined iteratively by the following relation:


The correction to the cone resistance due to the content of fine material is determined by the following procedure:  



Where the fine content FC(%) is calculated with the following expression:


The liquefaction resistance for a magnitude equal to 7,5 (CRR7,5) is calculated from:




For zw > z, with zw groundwater table depth, and for (qc1N)cs ≤ 160 the soil is not liquefiable (NL).

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).

To determine the values of the reduction factor rd are used the following formulas:




The liquefaction factor of safety FS is determined by:


To determine the magnitude scaling factor MSF, the formula of Idriss & Boulanger uses the expression:


The correction factor of the confining pressure Kσ is given by:





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