SEISMIC RESPONSES OF SHORT GROUPED-PILES EMBEDDED IN LIQUEFIABLE SANDY SOILS DURING EARTHQUAKES

Abstract

A series of centrifuge shaking table tests was conducted to simulate the seismic responses of
grouped-piles that was embedded in liquefiable sandy soils and subjected to earthquake loading. The groupedpiles connected with a pile cap were used to support 4 sets of model dry storage spent fuel casks. Different test
conditions including the elevations of pile cap, and the grouped-piles embedded in the dry and saturated sand
beds with the different levels of groundwater table are reported. Using pre-shaking the profile of shear wave
velocity in the tested sand bed and the natural frequencies of both the sand bed and the grouped-piles were
determined. The lower shear wave velocities and the lower natural frequencies were measured for the saturated
sand bed, but no obvious difference in the natural frequency of the grouped-piles system with the pile cap
embedded in the sand deposit were observed. The grouped-piles with the pile cap exposed to the ground surface
and embedded in the saturated sand bed have the lowest natural frequency. The magnitudes of bending moment
along pile depths would increase with the increases of base shaking. The lowest bending moment were
measured for the grouped–piles with the pile cap embedded in the dry sand bed while the largest bending
moments were observed for the grouped–piles with the pile cap embedded in the saturated sand bed and the
groundwater table at the surface.