Variation of Liquefaction Strength Induced by Monotonic and Cyclic Loading Histories

Once loose sand has liquefied, it becomes denser along with water drainage after liquefaction. Therefore, liquefied sand is regarded as more robust against liquefaction. Such sand after liquefaction is expected to liquefy again only slightly. Nevertheless, examples of repeated ground liquefaction have been reported during some earthquake events. Reliquefaction characteristics of saturated sandy ground must be estimated accurately with consideration of the liquefaction history related to past earthquakes. Moreover, the stress history affecting liquefaction strength must be considered. Cyclic triaxial tests were conducted to estimate the liquefaction strength ratio during and after liquefaction using specimens with a history of overconsolidation. The shear wave velocity, which is related strongly to the soil physical properties, was also measured in the same specimen. Results show that the stress history does not affect the specimen shear wave velocity despite increased liquefaction strength. The increased liquefaction strength induced by the stress history is eliminated by the liquefaction history.