Seismically Induced Flow Slide on Centrifuge

Some initial results of centrifuge model tests to examine the mechanism causing flow failure of a less permeable layer resting on a more permeable layer, subjected to seismic loading conditions, is presented. The centrifuge model that was subjected to a base motion using a servohydraulic shaker, consisted of a clay layer overlying a sand embankment submerged in water. During shaking the clay layer almost completely flowed off the sand and collected at the toes of the embankment. Settlement of the sand was also observed during shaking. As the soil overlying the sand is relatively impervious before flow failure, sand particles rearrange without any global change in volume. Locally, however, it is possible that loosening of sand close to the interface between sand and clay did occur due to the densification of the sand beneath it. This may leave a liquid film or a layer of very loose sand at the interface thus creating an unstable situation which will result in the creation of a flow slide of the impermeable material overlying the sand.