**1. Introduction**

In Japan, there are approximately two hundred 10,000 small-Earth dams, which have significant reservoirs for irrigation. Such kinds of dams whose heights are smaller than 15 m are called irrigation dams. Many irrigation dams were constructed by experience over 100 years ago. It is reported that about 20,000 irrigation dams were damaged during the long-term use, which need repairing and strengthening [1].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Many irrigation dams were not designed for earthquake resistance, and the cracks at the crest in the direction of the dam axis are remarkable. **Figure 1** shows the example of the crack at the crest of the Earth-fill dam. The relatively big open crack occurred. This type of open crack can be seen in the damaged Earth-fill dam so often. Not only the old Earth-fill dam but also the recent rock-fill dam has a crack in the dam-axis direction when the big earthquake hit. **Figure 2** shows the crack situation at the crest of the rock-fill dam constructed in 1988. This dam was designed for earthquake resistance. Although the acceleration was not measured, it was inferred that relatively big acceleration occurred because the earthquake inducing the crack was in 2011 off the Pacific coast of Tohoku. The open crack was propagated at a 3 m depth from the crest. The cracks shown in the figures cannot be seen to be induced by shear failure. The earthquake resistance is examined for shear failure with the slip-circle method according to the standard. It is difficult to repair the damaged dam effectively when the mechanism of the crack on the crest is not clarified. On the contrary, if the mechanism becomes clear, an effective counterplan may be considered. In this chapter, the centrifuge loading test is carried out to confirm the mechanism of the crack at the crest. Although the authors already carried out the 1-G shaking test and inferred that the tensile stress is the reason for the crack by observing the behavior of the cross section [3], this study aims to confirm more concretely the reason. Therefore, the centrifuge loading test of 50 G was planned to simulate the more realistic situation and the observation from the vertical direction also tried to observe the crack situation. Moreover, the simple numerical

Seismic Crack Investigation in an Earth Dam by Centrifugal Loading Test

http://dx.doi.org/10.5772/intechopen.78788

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The 1-G shaking table tests were carried out to investigate the dam and embankment behavior, and it was found that the acceleration response at the upper part of the embankment has a large effect on the behavior of the slope [3]. The crack in the dam-axis direction was also examined and the crack was considered to be caused by tensile stress. The tensile stress was affected by the vertical vibration as well as horizontal one [4]. Like others, the relation between the natural period and failure feature was investigated [5]. The effect of the aspect

For the centrifugal loading tests, the acceleration response and residual deformation were investigated for the Earth-core rock-fill dam and concrete-faced rock-fill dam [7]. The effect of the liquefaction of foundation on the deformation of the dam was examined [8]. Moreover, the seismic response and liquefaction of loose embankments were also investigated [9].

As mentioned earlier, the previous studies focused on the seismic response, slope sliding and deformation and so the situation of the surface of the dam was focused. On the other hand, the authors investigated the behavior of the cross section by 1-G shaking table test [2] as mentioned earlier. **Figure 3** is the strain distribution of the model used for 1-G shaking table test. By using

simulation has tried to reproduce the experimental results.

ratio of the dam on the vibration mode was also examined [6].

**Figure 3.** Strain distribution by 1-G shaking test [2]: (a) shear strain and (b) volumetric strain.

**2. Previous studies**

**Figure 1.** Crack at the Earth-fill dam.

**Figure 2.** Crack at the rock-fill dam.

repair the damaged dam effectively when the mechanism of the crack on the crest is not clarified. On the contrary, if the mechanism becomes clear, an effective counterplan may be considered.

In this chapter, the centrifuge loading test is carried out to confirm the mechanism of the crack at the crest. Although the authors already carried out the 1-G shaking test and inferred that the tensile stress is the reason for the crack by observing the behavior of the cross section [3], this study aims to confirm more concretely the reason. Therefore, the centrifuge loading test of 50 G was planned to simulate the more realistic situation and the observation from the vertical direction also tried to observe the crack situation. Moreover, the simple numerical simulation has tried to reproduce the experimental results.
