Abstract
The mechanism of the damage to a gravity type quay wall caused by liquefaction of the backfill ground during an earthquake is made clear through a shaking table test and theoretical examination. A series of model shaking table tests was conducted focusing on the occurrence of liquefaction in the backfill ground. The movement of the caisson is found to be quite different depending on whether liquefaction occurred in the backfill ground or not. The fluctuating earth pressure on the caisson suppresses the movement of the caisson when liquefaction does not occur. On the other hand, sliding of the caisson is enhanced since the fluctuating component of earth pressure and the inertial force coincide in phase angle when liquefaction occurs in the backfill ground. When liquefaction occurs, observed earth pressure agrees with that evaluated by Westergaard's formula originally derived for the water pressure on the dam. The fluctuating earth pressure acting on the back wall of the caisson in the process to liquefaction was carefully observed in the model shaking tests. It was found that the amplitude of the earth pressure first decreased to a very small value because of the reduction of the stiffness of the backfill due to the excess pore water pressure generation, and then increased because the phase angle of the earth pressure changed 180 degrees. This indicates that stability criteria of the caisson should be developed not by the onset of the liquefaction but by the sudden phase change. This feature is demonstrated by the simplified mass-spring-dashpot model proposed by the authors.
