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Liquefaction hazard analysis


(La Lettre Terrasol, December 2017)
Terrasol is frequently called on for liquefaction hazard analysis (by SNCF, EDF, CEA, etc.). Nowadays, these are systematically conducted using the semi-empirical procedure known as «NCEER», formalized by Youd and Idriss (2001) after the NCEER / NSF workshops in 1996/1998: this procedure consists in the
introduction of safety factors by comparing the project earthquake-induced shear stress (CSR) with the cyclic shear resistance of the site materials (CRR), based on in-situ testing results.

This is an opportunity for us to identify the ambiguities, and/or inadequacies, of the specific recommendation guides and the existing normative  frameworks.
Regarding this matter, Terrasol is conducting a review about the main sticking points of the NCEER procedure implementation in the normative framework applicable to the various categories of structures, and in connection with the initial assumptions of the validity domain defined by its authors. These considerations have resulted in the ongoing development of a dedicated software.

This tool will incorporate additional indicators existing in the scientific literature: spatial arrangement of cumulative liquefiable thicknesses, liquefaction potential index, severity index with respect to liquefaction.
Together with the evaluation of seismic-induced settlements, they will allow to provide spatial perspective to the analysis which is limited to safety factors, offering the prospect of multi-criteria hazard mapping.

M. Hocdé and F. Cuira