Extended Iwan-Iai (3DXii) constitutive model for 1-directional 3-component seismic waves in liquefiable soils: application to the Kushiro site (Japan)

The influence of pore water pressure has to be taken into account when the propagation of seismic waves in saturated soils is simulated, because it controls the strength decrease during the dynamic process and can induce phenomena such as cyclic mobility and liquefaction. The decrease of effective stresses leads to permanent deformation in the soil and damages to the surface structures. This research aims at validating a 1-directional propagation model of 3-component seismic waves (1D-3C) in a horizontally layered soil, in the case of saturated soil. A 3-D non-linear elasto-plastic model for soils is used and the variation of the shear modulus reduction curve with the pore water pressure is taken into account during the seismic event. In the case of multiaxial stress states induced by a 3C seismic motion, if no additional information is available, the modulus reduction curves in shear and compression, normalized with respect to the elastic moduli, are assumed identical, since the Poisson's ratio is supposed to be constant during the process. The multiaxial stress state in saturated soils induced by a 3C seismic motion is analysed for various stress paths. The 1D-3C wave propagation model is used to compute the seismic response of the Kushiro soil profile (Japan). The stratigraphy and geotechnical properties are deduced from in situ and laboratory tests provided by the PRENOLIN benchmark. Numerical results are in correct agreement with the records at the surface in terms of acceleration envelope