Key words: seepage, seepage failure, rockfill dam, unsaturated soils, wetting front, numerical analysis.

Stratifications in the rockfill, however, cause the seepage water to advance more quickly in the horizontal direction along the interface between the sandwich layer and the rockfill, thus increasing the possibility of seepage failure.

As such, the evolution of the seepage failure in the three-dimensional cases is faster than that in the two-dimensional analyses, and the two-dimensional analyses will underestimate the risk of seepage failure, particularly near the abutment boundary.