2012 Volume 7 Issue 1 Pages 175-184
The iron sand ore deposits had been excavated and the discarded sand from iron ore production had been backfilled at many mining areas in Asahi City, Chiba Prefecture until the end of 1960s. The backfilled sands were liquefied at various backfilled basins due to the main and/or the maximum after shock of the 2011 off the Pacific coast of Tohoku Earthquake. The behaviors of the liquefied soil at the brinks of the backfill basins were new and classified into three types, such as heave, cave-in and landslide based on victim interviews, visual inspections, topographical surveys and soil investigations. The mechanism of these behaviors was attributed to the relationship between the direction of predominant displacement of liquefied soil and the location of the excavation boundary. Based on the time histories of the pore water pressure buildup obtained from a numerical analysis, the backfilled sand liquefied during the main event at several places and it liquefied during the maximum after shock at the other places, which coincides with the testimonies stated by the victims.
