The aim of this study is to clarify the mechanism of the damage to quay walls during earthquakes. The dynamic behavior of quay wall during earthquake was observed in model shaking table tests, with the effect of liquefaction on the damage. The transient nature of the dynamic earth pressure on caisson was observed and analyzed with a mass-spring-dashpot model. From some series of model shaking table tests on the caisson type model quay walls with different vibration properties, it was clarified that the liquefaction of backfill soil enhances the damage to quay walls. In the case of no-liquefaction of backfill the fluctuating earth pressure acts in the opposite direction to the inertia force on quay wall. On the other hand, in the case of liquefaction of backfill the direction of fluctuating earth pressure is same as that of inertia force; resultant thrusting force becomes much larger than that in the case of no-liquefaction. This transient behavior of earth pressure in the process of liquefaction is explained regarding the interaction between caisson and backfill ground; the stiffness of backfill ground reduces due to the generation of pore water induced by the liquefaction. A simple mass-spring-dashpot model was derived taking account of the vibration properties of caisson-backfill ground system.
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