Multiple-Liquefaction Behavior of Sand in Cyclic Simple Stacked-Ring Shear Tests

Following major earthquakes that occurred in New Zealand (2010–2011) and Japan (2011), soil multiple liquefaction, or reliquefaction, regained major attention in the field of geotechnical earthquake engineering. Not only can liquefaction occur multiple times at the same site, but the devastation caused by reliquefaction is often more severe than that triggered by the first liquefaction. In this study, to address this issue and provide new insights into reliquefaction mechanisms, a series of cyclic simple shear tests was conducted with the use of a newly developed stacked-ring shear apparatus. In the multiliquefaction tests, subsequent liquefaction stages were applied to a single Toyoura sand specimen sheared at different levels of maximum shear strain double amplitude (γDAmax), from 2% to 10%. Tests results showed that: (1) the increase in soil density during the postliquefaction reconsolidation stages had only a minor effect on sand resistance against multiple liquefaction; (2) the extent of γDAmax significantly influenced sand resistance against multiple liquefaction; and (3) the major impact of γDAmax was a change in the soil fabric during multiple liquefaction, as confirmed by image analysis results.