The seismic earth pressure acting on the rigid caisson foundation was studied by the model vibration tests. In order to account for the characteristics of the seismic earth pressure influenced by the backfill ground vibration, frequency of an input sinusoidal wave was chosen from 1Hz to 50Hz. The authors separated the seismic earth pressure into the static component and the dynamic one.
　The fundamental information of the dynamic earth pressure with frequency, the effect of the caisson mass on the dynamic earth pressure, its phase difference from the inertia force of the caisson and its distribution, were given in this experiment. The applicability of and problem of Mononobe-Okabe formula was studied by comparing with the experiment. The authors also analyzed the experimental results using the numerical model called rigid body-ground spring model. It was found reasonable that the seismic earth pressure was separated into two parts, the dynamic component and the static one.