In order to make clear the occurrence mechanism of earthquake damage to some kinds of objects, to develop earthquake-proof countermeasures for them, to work out rules for identifying the sites liable to be damaged by earthquakes and so on, the structures of grounds have been investigated with many examples of earthquake damages. Objects include embankments, buildings, bridges, tanks, quays, power substations etc. Their damage includes liquefaction and others that have ocurred in sandy ground. In this paper the occurrence mechanism of earthquake damage to objects on sandy ground is studied referring to deformed states of ground and objects, and structures of the ground.
The results are summarized as follows:(1) When the ground under objects is made of sand only, the earthquake damage occurs very rarely;(2) in the ground under earthquake-damaged objects are encountered many upside-down types of ground in which soft clayey soil layers underlie sandy ones. But when they are horizontallystratified, the earthquake damage occurs very rarely;(3) objects are lible to be deformed, when they straddle thick and thin parts of soft clayey soil layers under sandy ground, when they cross buried valleys with upsidedown type grounds, or when comparatively thin soft clayey layers between sandy ground and their underlying hard soil layer tilt;(4) above-mentioned soft clayey layers consist of soils like peat or clay; and (5) the deformation due to earthquakes reflects the structure of the ground.
Also, it is estimated that most of these damages were caused by large differential displacements of nonuniform ground in which the thicknesses of soft clayey layers are non-uniform, or extraordinary vibrations of soft clayey soil layers in buried valley type grounds under earthquakes, just like those in other seismic damages.
