Liquefaction of an Artificial Island in Kobe, Japan
Ahmed-W. Elgamal*, Member, ASCE,
Mourad Zeghal*, Associate Member, ASCE,
and Ender Parra*, Student Member, ASCE
Abstract:
Widespread liquefaction occurred during the recent Hyogoken Nanbu
1995 earthquake, in Japan. At the reclaimed artificial Port Island in
Kobe, the observed large-scale liquefaction was documented by
acceleration records from a downhole seismic array. In this array,
four accelerometers recorded the soil stratum response, from the
ground surface down to a depth of 83 m. These recorded accelerations
are used herein to obtain direct estimates of the corresponding
seismic shear stress and strain histories within the soil layers,
which shed light on: (1) the site seismic response during liquefaction
and associated loss of soil stiffness at shallow depths near the
ground surface, and (2) the virtually linear site response at deeper
elevations. Response of the liquefied upper layer is characterized by
cycles of large shear strain and very small shear stress. Conversely,
the lower strata exhibited no sign of stiffness degradation throughout
the earthquake. A computational simulation of this case history is
performed in order to assess the mechanisms of site amplification and
excess pore-pressure buildup. The results of this study demonstrate
that acceleration histories recorded by downhole arrays represent a
valuable direct source of information on site response during seismic
excitation.
