28. Damage process of an embankment during an earthquake
For the seismic performance assessment of an embankment, the sliding displacement is calculated assuming that a circular sliding failure occurs. However, this method cannot often explain the actual damage to an embankment subject to an earthquake.
Therefore, shaking table tests were performed using centrifuge model test apparatus to understand damage process during an earthquake in detail.
The results showed that displacement accumulated gradually due to vibration and increased rapidly from a given displacement level as shown in Fig. 1.
After that, a sliding line was generated to end up with a brittle fracture (Fig. 2). The shear strain distributions inside the embankment were observed by using PIV image analysis (Fig. 2), and it was also found that the strain accumulated from the vicinity of the toe of the slope and gradually expanded to inside the embankment. The maximum value of shear strain inside the embankment when the displacement increased rapidly was 9.6% around the toe of slope (Fig. 2 (3)).
This value agreed with the value immediately before reaching Damage Level 3 of embankment material at which point the strain in the embankment material increased rapidly (Fig. 3 (3)), when the damage level of the embankment was defined using the deformation characteristics of embankment material (as shown in Fig. 3),.
From the above, it was found that when the shear strain in the vicinity of the toe of the slope, which was the origin of the sliding line, reached Damage Level 3 for the embankment material, the displacement started to increase rapidly, and when it reached Damage Level 4--which corresponded to the peak strength for embankment material--a sliding line was generated to occasion a brittle fracture.
In this manner, the damage process of an embankment makes it possible to explain the actual damage sustained under an earthquake.
This finding can be utilized for detailed seismic performance evaluations for embankments, and investigations to determine the cause after an earthquake.