The behavior of seepage flow developed in an embankment due to rainfall and its associated features of expansion of the saturated wet zone, which promotes instability of slopes, are studied in this paper. Centrifuge seepage tests are conducted on sand model fills by use of a newly developed device, which can supply a uniform and constant strength of rainfall over the slope surface. Finite element unsteady saturatedunsaturated seepage analyses are made on the prototype of the model fill for the same rainfall conditions as adopted in the tests. A fairly good correspondence is attained in these comparisons, giving conclusions that the centrifuge seepage test using the new device is more reliable in reproducing uniform rainfall, and that it can serve much effective data to examine the accuracy of FE seepage analysis.
In such earth structures as road embankments and earth fill dams, seepage flow appears to develop in the embankment during rainfall by the percolating water through the slope surface. The flow forms a fully saturated zone in the initially unsaturated field of the embankment and it enlarges and extends to the interior as the time elapses. The resultant increase in the weight of wet soil and that in the pore water pressure developed within the medium can be the principal causes to promote instability of slopes. Although the centrifuge model test can give a definite solution on them, it has another problems in realizing a uniform and constant strength of rainfall due to the action of the Corioli''s force and collision of raindrops (Okumura et al., 1985). Finite element analysis has therefore been used as the most powerful and practical procedure in understanding the behavior, though reliability of the solution still should be verified in all respects through laboratory and field investigations.