Reappraisal of vertical motion effects on soil liquefaction

摘要: INTRODUCTION Ground motion induced by an earthquake is in general characterised a vector with its components along the vertical and two horizontal directions. In current practice research, effect of ground often disregarded while attention focused mainly on motion. Two primary reasons have been accepted for neglect seismic First, engineering structures are considered to adequate resistance dynamic forces motion, which generally much smaller than counterparts. If explicitly included design, it typically assumed that ratio (V/H) response spectra will not exceed two-thirds (International Code Council, 1996). Second, negligible influence soil liquefaction because induces almost purely compressive stresses, cannot cause changes effective stress subsoil (Ishihara, However, there repeated observations from recent earthquakes, such as those Northridge, California, 1994 Kobe, Japan, 1995 (Bardet et al., 1997; NCEER, 1997), rule-of-thumb poor descriptor motions. The spectral ratios may substantially near field moderate large earthquakes at short periods. A typical case comes three-dimensional borehole array recordings obtained Port Island, during Kobe (Yang & Sato, 2000), indicated peak acceleration was twice high surface (Fig. 1). An integrated study this history 2000; Yang 2000) has revealed both motions were closely related liquefied layers and, particularly, condition partial saturation near-surface soils played crucial role amplification Partial conditions occur certain situations result fluctuating groundwater tables associated natural or man-made processes. They also exist offshore sites marine sediments. Thus considerable interest arises reappraising especially, clarifying whether dependent condition. Aimed goal, analyses conducted means verified, fully coupled numerical procedure model deposit subjected variety combinations loading conditions. significant finding understanding always hold true; rather, This paper presents main results mechanisms. Implications testing geotechnical laboratory addressed briefly.