The effect of stratum organization on the occurrence of liquefaction in subsurface silty sand

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Firstly, elasto-plastic modelling of Urayasu soils based on the boring survey and laboratory testing was conducted. After then, its seismic response analysis was conducted for the purpose of understanding why extensive and non-uniform liquefaction damage was occurred at Urayasu city during 2011 Great East Japan Earthquake. The main conclusions are as follows, 1) existence of the clay layer caused amplification of the seismic wave in the somewhat long-period ranges, leading to large plastic strains sufficient to cause liquefaction even in intermediate soils, 2) existence of the sloped irregularly-shaped boundary generates surface waves which causes localized amplification of the acceleration, continuous oscillation at the ground surface and expansion of the liquefaction, 3) complicated interposition of the surface waves and body waves result in non-uniform ground deformation even for homogeneous ground conditions.