The aim of this study is to reveal the mechanism of damage to gravity type quay walls during an earthquake. The dynamic behavior of the quay wall was observed in model shaking table tests on various types of model caissons, with liquefaction of backfill. The transient feature of the earth pressure on quay walls from backfill during shaking was observed and analyzed. A series of model shaking table tests on gravity type model quay walls with different vibration properties showed that liquefaction of the backfill soil increases the damage to quay walls. The transient behavior of earth pressure in the course of liquefaction is analyzed. 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 static earth pressure increases and the direction of dynamic fluctuating earth pressure is same as that of inertial force; the resultant thrusting force on the caisson becomes large compared with the case of no-liquefaction.
Many port and harbor facilities in Japan have been severely damaged in recently large earthquakes; in particular quay walls suffered heavy damage due to the liquefaction of reclaimed lands. Foundations of structures and underground structures were damaged also due to lateral flow deformation of the backfill, which was triggered by the displacement of quay walls (Inagaki et al., 1996; Kamon et al., 1996). From close examination of the damages to quay walls in Hokkaido Island, Japan, during three recent large earthquakes, i.e., 1993 Kushiro-oki, 1993 Hokkaido Nansei-oki and 1994 Hokkaido Toho-oki earthquakes, it is clear that the occurrence of liquefaction in the backfill increases the degree of the damage to quay wall (Japanese Geotechnical Society, 1994; Hokkaido Development Bureau, 1996).