Compaction and separation work are popular countermeasures to prevent floating of underground structure due to liquefaction of sandy soil. However, it is difficult to decide the extent of densification, the width of area to be compacted and the rigidity of sheet pile wall rationally. In this study, a series of 1g shaking table tests on a underground structure surrounded by loose sand were carried out with compaction around thestructure, separation by sheet pile wall and both of them to investigate its effect on the dynamic stability of underground structure. No serious damages were observed when the ratio of the width of compaction area to the thickness of liquefied layer is greater than 1.0 in a series of tests. The greater the rigidity of sheet pile wall, the less floating of the underground structure was observed due to shaking. The increment of the restraint of floating to the rigidity of sheet pile wall gradually tends to decrease as the value of its rigidity increases.
