Series of undrained torsional shear tests were conducted to investigate the local deformations directly and indirectly on homogeneous and heterogeneous sand specimen by image analysis.

Colored Silica sand specimen (homogeneous)

The dots pasted on membrane were used for the indirect evaluation of local deformation, while sand particles for the direct evaluation. Since the digital image was distorted largely after twice refractions, Suitable coordinate correction was developed in the undrained torsional shear test when the vertical displacement was prohibited during shearing. Based on the obtained results, vertical slippage between the membrane and specimen was observed when there was no effective stress. In addition, the leap of vertical slippage only occurred during liquefaction status.




Segregated sand specimen

(Katori sand, from Katori city in Chiba prefecture)

Water sediment method was developed to simulate the formation of layered deposit of reclaimed land, which was constructed by dredging and pumping. The sand layer was intercepted by low permeable fine layer after construction. During earthquake, the upward seepage may concentrate underneath the fine layer. The water film beneath fine layer will induce lateral flow. Based on the local strain distribution after initial liquefaction, negative vertical strain was found at the fine layer. Shear strain localization was also observed at the fine layer. Accompanied with pore water and sand particle migrations, local water film was observed at the fine layer.




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