**6. Discussions**

Many Earth dams had the cracks in the direction of dam axis at the crest when a big earthquake happened. In this study, to examine the mechanism of the cracks along the dam axis, the centrifugal loading tests are conducted. Moreover, numerical analyses are used to examine the mechanism theoretically.

It was found from experimental examination that the cracks in dam-axis direction shown as the earthquake damage were caused by the extension strain. Therefore, the extension stress was caused by the parts of the crest. However, the large extension strain at the upper part could not be realized by numerical analyses. This means that the cracks in the dam-axis direction cannot be explained theoretically at present.

While the extension failure is not examined in the design process, the counterplan for the cracks is necessary as the earthquake resistance. It is, however, difficult to examine the efficiency because it is impossible that the extension stress at the upper part of the dam body cannot be evaluated properly at present.

The shear strain at the cross section is developed to the slope direction in the experiment. While the shear strain distribution coincided with the sliding failure of the slope, the failure form by sliding was not observed. On the other hand, the distribution of the shear strain by numerical analysis was quite different from the observed one. Although the earthquakeresistance is examined for shear failure by Newmark's method [10] or the method by Watanabe and Baba [11] in Japan, the discussion about the critical situation of the seismic behavior of the fill dam would be needed.
