In this report, we review the liquefaction prediction/judgment method based on particle size and N value (called the particle size/N value method) as follows. Applicability to sand containing a lot of fine grains, applicability to sand containing a lot of sediments, and applicability to large seismic ground motions were discussed in the 1993 Hokkaido Nansei-oki Earthquake and the 1995 Hyogo-ken Nanbu Earthquake.・We used a non-liquefaction case. From the case analysis, it was found that there are cases where the prediction/judgment results are on the dangerous side. In addition, the particle size and N-value methods were modified using case analysis and repeated triaxial test results using undisturbed samples. The conclusions obtained are as follows.
(1) The critical N value applied to sand whose particle size distribution is included in Bf may give a risky judgment.
(2) A correction method of N-value for sand from which the plasticity index can be obtained was proposed using the plasticity index.
(3) The critical N value applied to sand with a grain size distribution in Bc may give a risky judgment.
(4) The coefficient of permeability is used as a guideline for judging when sand containing a large amount of sediment crosses the grain size range considered to be ``possible to liquefy''.
(5) The maximum equivalent N value that can be judged not to cause liquefaction even with a huge ground motion with an equivalent acceleration of about 500Gal is 25, not 20.
(6) Incorporating the above (1) to (5), the existing granularity/N-value method was modified.