A series of experiments were conducted to examine wave-induced liquefaction in a loosely packed sandbed, which was specifically used to ensure the presence of residual excess pore pressure.Also observed was the compaction of a liquefied sandbed in response to cyclic wave loading.
　In Port of Kushiro, an artificial reef behind a breakwater is now being constructed. This reef is filled with dredging sand and is possibly suffered from the liquefaction with residual excess pore pressure. Experiments were also conducted to simulate the liquefaction and to find the countermeasure.
　In order to clarify the liquefaction in a loosely packed sandbed, a series of numerical simulation were conducted using FEM. To find the strength of sandbed in which the liquefaction does not occure, the relationship between shear modulus and shear strain of sandbed is included in the FEM.VOF-FEM is also used to simulate the liquefaction caused by overtopping wave behind a breakwater.