During the 1995 Hyogo-Ken Nanbu Earthquake, many quay walls were damaged and most of these quay walls were caisson type. These caisson type quay walls moved toward seaside and suffered tilting and settlements. To investigate the reason of these damages, we should consider the effect of big acceleration induced by shallow interplate earthquake, the effect of liquefaction in replaced soil behavior beneath the caisson, because extensive liquefaction phenomena were observed in Port Island and Rokko Island. A series of underwater shaking table tests with a scale of 1 to 17 model quay wall were performed. The reproductive shaking teble test results using real seismic records at Kobe Port Island were consistent with observed displacement of the caisson and observed settlement of the soils behind the caisson. The results show that the overall deformation of quay wall was consist of the relative displacement between the caisson and foundation rubble mound and foundation rubble mound moved toward seaside and sank into replaced soil. Therefore, the increase of excess pore water pressure in replaced soil induced the decrease of shear resistance of soil and it caused the horizontal displacement towards sea and settlement.
　The shaking table tests using another input motion were also perfermed. The input motion was recorded in Hachinohe port during 1968 Tokachi-Oki earthquake and converted to the base acceleration time history. The obtained displacement of caisson was small during the input motion with a probability of return period of adout 75 years. The results show that the reduction of earth pressure in back fill by means of inprovement of soil was ensure against the failure of quay wall.