A liquefaction test method is developed to evaluate liquefaction resistances under a partial drainage condition. The dynamic triaxial test can be performed under different conditions of drainage, with open and closed drainage system as well as retarded drainage.
　A series of liquefaction tests both under a perfectly undrained condition and under partially drained conditions were conducted on Bandaijima sand taken from Niigata, where severe disasters were caused by the liquefaction of saturated sands in Niigata earthquake in 1964. Effects of drainage conditions and frequencies of loading on liquefaction resistances are evaluated. It is found that the strength ratio, SR(Nl) defined by the ratio of liquefaction resistances under a partial drainage condition to that under a perfectly undrained condition can be well represented by the relative density and the non-dimensional parameter defined by α=k/fL, where k is the coefficient of permeability, L is the drainage distnace and f is the frequency.
　The prediction method of liquefaction is proposed on the basis of the results describved above. The liquefaction phenomena which occurred in the past earthquake are analyzed using the proposed method.Analytical results show that the thin silty layer located at the subsurface deposits may play an important role for causing the liquefaction of the deposits according to the drainage condition.