抄録
The undisturbed sand samples were obtained using both the in-situ freezing method (FS sample) and the rotary-type triple tube sampling method (TS sample) from four sites. The liquefaction strength of these samples was determined by conducting undrained cyclic triaxial tests. The liquefaction strength and the relative density of these samples were compared. Test results were also discussed with other researchers using the data presented from the point of view of sample disturbance during sampling. The following conclusions were made : (1) In the case of natural sand deposits, the liquefaction strength of the TS samples was about the same or lower than that of the FS samples. For artificial fill of loose sand, however, the liquefaction strength of the TS samples was higher than that of the FS samples. (2) In some cases, for the natural medium dense sand, the liquefaction strength of the TS samples was much lower than that of the FS samples even though both samples have almost the same relative density. This result means that, factors other than the relative density, such as changes in the micro-fabric during sampling and/or effects of aging on the extent of sample disturbance should be considered. (3) In the case of natural sand deposits, a strong correlation was seen between the liquefaction strength ratio (ratio of liquefaction strength between FS sample and TS sample) and the SPT N-value normalized by an effective overburden pressure of 98 kPa(=1 kgf/cm2), N1, such that the liquefaction strength ratio increases with increases in N1.
