LIQUEFACTION AND SETTLEMENT OF RECLAIMED GROUND WITH GRAVELLY DECOMPOSED GRANITE SOIL

Abstract

Liquefaction and settlement of reclaimed ground with gravelly decomposed granite soil, which had liquefied during the 1995 Hyogo-ken Nambu earthquake, was studied by a centrifuge model test using in situ soil material and the earthquake record. Three ground models used for the centrifuge test were made with different particle size ranges : 1) under 30 mm, 2) under 2 mm, and 3) 2-30 mm water-washed. A reclaimed layer of about 16 m thickness was modeled in 1/40 scale. The following results were obtained from this study : 1) Inferring from maximum acceleration response, independent of the above three grain size distributions, it was considered that shear failure occurred at a depth between K.P. -8 m to -12 m due to strong motion. 2) The liquefaction degree was not uniform in the depth direction. In grounds consisting of particles smaller than 2 mm, destructive liquefaction occurred at a lower depth ; also, volume compression at a corresponding depth was larger than that at the upper portion. 3) In the case of only-gravel content, no cumulative excess pore water pressure was generated because of high permeability. Settlement after vibration was also smaller compared with two other cases. 4) Permeability during the pore pressure dissipation process, which was identified from back analysis, was higher than the value obtained from the laboratory permeability test ; it also gradually approached laboratory test values during dissipation.