In this paper, a new constitutive model is proposed to describe the mechanical behaviors of soils under diŠerent loading conditions. New evolution equations for the development of stress-induced anisotropy and the change of overconsolidation of soils are proposed. By combining systematically the above two evolution equations with the evolution equation for the structure of soil proposed by Asaoka et al. (2002), the newly proposed model is able to describe not only the mechanical behavior of soils under monotonic loading, but also the behavior of soils under cyclic loading with diŠerent drained condition. Special attention is paid to the behavior of sand subjected to cyclic loading under undrained condition. That is, for given sand with diŠerent densities, very loose sand may liquefy without cyclic mobility, medium dense sand will liquefy with cyclic mobility while dense sand will not liquefy, which is just controlled by the density, the structure and the anisotropy of the sand. A suitable model should uniquely describe this behavior without changing its parameters. Present research will show the possibility of the proposed model.

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Earthquake motions include waves of various frequency bands ranging from low to high frequency. Notably, the dominant frequency affects the seismic stability of fill slopes. Hence, to analyze the deformation–failure mechanism during an earthquake, 1g shaking-table tests were conducted in this study on saturated fill slopes considering the resonance phenomenon. Results show that the deformation–failure mechanism of a fill slope cannot be defined by only one sliding surface. Multiple sliding surfaces are formed progressively depending on the ground and external conditions. Moreover, evaluating the seismic stability of fill slopes depends not only on the magnitude of the acceleration, but also on the relationship between the natural frequency of the fill slope and the input frequency. These phenomena cannot be considered in the seismic-intensity method nor in the Newmark’s method used in conventional design. When implementing seismic countermeasures, it is important to determine the frequency characteristics of fill slopes and design the countermeasures considering the predominant frequency of the seismic wave anticipated at the site.

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One of the important characteristic of the liquefaction damage observed at Urayasu city during the Great East Japan Earthquake is that liquefied and non-liquefied site was inhomogeneously distributed. The difference in damage levels has often been explained by the presence/absence of past ground improvement and by the difference in the dates of reclamation work. Such causes of extensive damage are, no doubt, correct. However, sufficient explanations have not been provided yet concerning the mechanism of liquefaction occurrence in ground with large fine fraction content and the reason why the liquefaction damage was non-uniform. In this study, seismic response analysis with multi layered system was employed paying special attention to the stratum organization at the deeper part of the subsurface liquefiable layer. Analysis result showed that, in addition to characteristic of the earthquake motion and inhomogeneity of the ground itself, irregularly shaped stratum organization of Urayasu city was one of the important factor for extensive and non-uniform liquefaction damage.