For rationalizing the earthquake-proof design procedure of harbour structures, experimental studies were performed on lateral earthpressure and dynamic pore water pressure of water saturated sand during vibraion.
　Water saturated sand was filled in thickness of 70cm into a vibrtation box and vibrated. The inner size of the vibration box is 262cm (length)×50cm(width)×100cm(height). It has a movable wall which is one side wall of the vibration box and supported by a hinge at its lower end and by springs at its upper part. For some experiments, the movable wall was fixed to the vibration box and used as a fixed wall. Three kinds of sand with different permeabilities, each other, were used. Lateral earthpressure and dynamic pore water pressure acting on the movable wall and on the fixed wall, were measured during vibration.
　Followings are main findings from the studies:
　(1) Water saturated sand was liquified by vibration in low acceleration, compared with dry sand. During the liquifaction, the pore water pressure was higher than the hydro-static water pressure.
　(2) A linear relation was found between the lateral earthpressure acting on the fixed wall after the vibration and the maximum acceleation of the table motion.
　(3) The amplitude of lateral earthpressure of water saturated sand was almost same with that of dry sand in the experiments with the fixed wall.
　(4) The amplitude of lateral earthpressure acting on the movable wall was very small compared with that acting on the fixed wall.
　(5) For the sand whose coefficient of permeability was larger than 1cm/sec, the dynamic pore water pressure was near with the dynamic water pressure calculated by Westergaard's formula.