Drained or partially drained - that is the question

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In model experiments on liquefaction, the boundary condition at the ground surface is in many cases drained because adding an impervious layer is too cumbersome. In reality, however, a liquefied layer is covered by some form of unsaturated/impervious layer. It is hardly seen that the ground water table is located at the ground surface. When focusing on damages caused by liquefaction, duration of liquefaction, which is partly influenced by the drainage condition, is one of the key factors.

This study experimentally demonstrates the difference on soil behavior under drained and partially drained condition. A loose saturated sandy soil whose height is about 95 cm was prepared in an acrylic cylindrical soil tank whose height and inner diameter are, respectively, 140 cm and 15 cm. The soil is liquefied by rotating the soil tank around its central axis with sin wave with amplitude of +/-2 degrees and 50 Hz. Amount of surface settlement and transient behavior of excess porewater pressure are observed and compared by varying the surface drainage condition. To control the surface drainage condition, an aluminum lid, a few millimeters smaller than the inner diameter of the cylinder, was placed on the surface to mimic a partially drained layer. Test results with the lid clearly show the influence of the partially drained layer as manifestation of large surface settlements associated with long duration of liquefaction with large amount of sand ejecta.

4th Asia-Pacific Conference on Physical Modelling in Geotechnics (ACPMG2024)

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