Initial shear stress has effect on soils in side slope

sloping ground and retaining wall

etc. Serious residual strain will occur in soft clay under initial shear stress. But

original Iwan’s model ignored this effect. In this paper

an empirical degradation model of soft clay has been incorporated into Iwan’s series-parallel model to account for cyclic degradation. Simultaneously

an ideal plastic element is paralleled to simulate the development of residual strain. Subsequently

the dynamic stress-strain relationship of each soft clay stratum is described with modified Masing’s rules. In this paper

a modified Iwan’s model is utilized in one-dimensional seismic response analysis. It’s observed that the constitutive model should consider this effect when initial shear stress existed and the earthquake is strong. Otherwise

velocities

accelerations and shear strains may be underestimated.