Local site Effects of Transient Dynamic Characteristics of Irregularly Layered Grounds

To explain the heavily damaged area for Kobe earthquake in 1995, nonlinear response characteristics of 2D irregularly reclaimed soil layers of saturated and unsaturated soil are investigated by using the existing FE program for effective stress analysis. For numerical computations, a typical Kobe ground model and a reference ground model with the absorbing boundary conditions are used. In order to understand the local transient characteristics of grounds due to liquefaction, the time-dependent fundamental natural period are investigated as a key parameter. Main conclusions are that liquefaction changes the dynamic characteristics of the sites into the transient high-cut filters and also slightly affects the dynamics of adjacent sites. Combination of irregular layering and rapid change of the dynamic characteristics of grounds due to liquefaction induces dominant shock of acceleration and shear strain at the specific sites, that is, at the central area of the alluvial layer and at the coastal area of the reclaimed layer, respectively