Longitudinal cracks have often been observed around the shoulder of seismically damaged embankments when the liquefaction takes place at a shallow part in their foundation ground. The reason why the cracks tend to appear around the shoulder of embankment is discussed considering the stress redistribution in the embankment. When the foundation ground beneath an embankment is fully liquefied, the vertical stress near the bottom boundary of embankment should become a principal stress because of the loss of the tangential stress at the bottom boundary due to the high excess pore water pressure of the liquefied layer. This change of the boundary condition of the embankment causes the redistribution of stresses in it. To examine the effect of the stress change inside the embankment, a finite element analysis was conducted. Results indicate that the position of the first crack is independent on the cohesion of the embankment material and when the crack appears, it moves to the shoulder of the embankment with an increase of the internal fiction angle of the embankment material and with a decrease of the slope angle of the embankment.
River dikes in Japan have often suffered damage from past earthquakes. Most of them are considered to be triggered by the occurrence of soil liquefaction beneath the embankments. It is desired to establish a rational method to evaluate the safety of existing dikes, degree of possible failure, and also the effectiveness of remedial measures to reduce the deformation of river dikes. For this purpose, it is necessary to clarify the failure mechanism of dikes when their foundation ground is liquefied. When the past damaged dikes are examined, it is known that almost always the resulting settlement of them appeared along with longitudinal cracks at the crest or on their slopes.
