The 2011 off the pacific coast of Tohoku earthquake (Mw=9.0) caused great damage of geotechnical structures in the vicinity of the eastern coasts. In contrast, many of reinforced soil walls constructed along the coast were less damaged by the tsunami. In this study, a model test using water tank is conducted to evaluate the behavior of a reinforced soil wall under strong water flow and water pressure like tsunami as an experimental prototype. The scale of model is 1/40, the height of wall is 25cm and the water level is 20cm, supposing that a tsunami hit the wall whose height is 10m in a full-scale without overflowing. Water flow hit the wall keeping its velocity and level. When the water penetrates into the backfill soil until ground water level is same as the level of water flow, the water was stopped and drained out of the tank.
In this study, 2 test cases were conducted. One is a sound wall, and the other is a wall with some opening of the front panels which simulates the gap of the wall due to residual settlement after an earthquake.
The sound wall has no deformation during and after the tsunami action. In the wall with some opening, around 30 minutes after the start of the tsunami action, the wall panel showed gradual deviations such as slippage. In all cases, the pore water pressure in the backfill soil rises with seepage of the water, but the soil was not completely saturated.
It was found that a reinforced soil wall does not have large deformation unless there are some opening of the front panels and the backfill soil flow out of the wall. This result shows that reinforced soil wall does not collapse by seepage to the backfill soil or wave force of tsunami, but collapses by backfill soil flowing out from wall surface. Our results support that a reinforced soil wall has high tsunami-resistance. Given this information, it is necessary to prevent the wall from making some opening and prevent the backfill soil from flowing out.