2026 Volume 21 Issue 3 Pages 309-323
Damage factors to pile foundations during earthquakes can be broadly classified into inertial forces from the superstructure and ground displacement of the surrounding ground, and many studies have been conducted so far. The soils covered in previous studies have tended to be either “loose-filled” or “dense-filled” soils, either “completely dry” or “completely saturated”. But in fact, there are also grounds where unsaturated and saturated layers are formed above and below the groundwater level, as well as medium-dense grounds. In this study, 1G-field shaking table tests were conducted to understand the vibration characteristics of saturated / unsaturated medium-dense sandy ground and seismic mechanical behavior of group-pile foundations in saturated / unsaturated medium-dense sandy ground, for different unsaturated layer thicknesses. As a result, the maximum bending moment was observed near the mid-depth of the soil layer, rather than at the pile head where the inertial force is dominant, in saturated / unsaturated mediumdense sandy ground. When the unsaturated layer thickness accounts for 60% of the total layer thickness, the degree of dependence of the bending moment of the group-pile foundation on the ground displacement is more than twice as large as that on the inertial force.
