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The purpose of this paper is to clarify the meaning of the values of standard penetration resistance used in correlations of field observations of soil liquefaction with values of N1 measured in SPT tests. The field data are reinterpreted and plotted in terms of a newly recommended standard, (N1)60, determined in SPT tests where the driving energy in the drill rods is 60% of the theoretical free‐fall energy. Energies associated with different methods of performing SPT tests in different countries and with different equipment are summarized and can readily be used to convert any measured N‐value to the standard (N1)60 value. Liquefaction resistance curves for sands with different (N1)60 values and with different fines contents are proposed. It is believed that these curves are more reliable than previous curves expressed in terms of mean grain size. The results presented are in good accord with recommended practice in Japan and China and should, thus, provide a useful basis for liquefaction evaluations in other parts of the world. Finally, suggestions are made concerning the significance of the term “liquefaction” as it is often used in conjunction with field evidence of this phenomenon.
Seed et al. (Sun,) studied this question.