| Sedimentological analysis was applied to all-core specimen acquired from the sites where liquefaction widely took place or ground failure occurred triggered by the 2011 East Japan Earthquake. Besides the usual core analysis procedure, digital soft X-ray images were taken of a number of 10-mm thick, 60-mm wide by 25-cm long plate samples, retrieved from the cores. Dense and detailed grain size analysis was conducted at 2.5 to 10 cm, and 1/4 φ intervals making use of traditional sieving technique in combination with a laser diffraction particle size analyzer. Accordingly, digital soft X-ray images were of great use for identifying the characteristic textures in liquefied sand layers. Moreover, grain size characteristics of the liquefied sands showed particular features discriminating them from non-liquefied sands. Namely, above analytical procedure is capable to identify liquefied horizon directly from core samples. Conventionally, liquefaction potential was speculated simply from the SPT N-values and fines content (Fc) in FL method. The liquefaction criteria of the FL method were determined based on surface liquefaction evidences, such as sand boils, rupture, and local subsidence not on the direct subsurface evidences. Consequently it has led to overestimation or misjudgment of liquefaction potential when applying the FL method. In contrast, all-core drilling and sedimentological analysis of the cores can only provide the essential information for understanding liquefaction which inherently generates within the subsurface. |
