Microscopic Measurement of Sand Fabric from Cyclic Tests Causing Liquefaction

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Courtesy of ASTM International

An experimental study was made to clarify and confirm: (1) the effects of a specimen preparation method on the fabric of sand; and (2) the change of sand fabric due to cyclic loading leading to liquefaction. Microscopic observations were made on the thin sections produced from sand specimens prepared by dry pluviation, dry vibration, and wet tamping methods. This study showed that dry pluviation tends to produce more “random” particle orientations and larger deviation of local void ratios than wet tamping. On the other hand, the dry vibration method produced intermediate results. This difference in fabric has the key impact on the liquefaction resistance of specimens prepared by different methods. Application of cyclic shear tends to alter the initial fabric of sand. For a “randomly” arranged sand mass, cyclic shear tends to line up the orientations of sand particles, resulting in less random arrangement of sand particles. For a “regularly” arranged sand mass, cyclic shear tends to diverge the orientations of sand particles. These findings help explain various static and cyclic behavior of sand.

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