Abstract
It is indispensable to understand the phenomena and to store the fundamental data for establishing a highly reliable criterion to judge the possibility of seepage flow failure. Experiments on upward seepage flow failure were conducted using a parallelepiped container with glass beads. It was observed that small size particles jump up and down at the surface of the specimen before the failure and then the specimen starts to shrink or swell depending on the initial void ratio while the coefficient of permeability also begins to re-enlarge. It means that local piping necessarily occurs as the sign of failure due to boiling or global piping except the case with a uniformity coefficient of nearly 1.0.
