A simplified coupled soil-pore water pressure generation for use in site response analysis

Site response and liquefaction analysis have traditionally been decoupled in engineering practice. Simplified total stress nonlinear effective stress constitutive models are available for use in one-dimensional (1D) site response analysis, while several advanced soil constitutive models have been developed for use in dynamic finite difference and finite element analyses. In this study, we describe a new simplified coupled hyperbolic constitutive model with an energy-based excess porewater pressure generation capability (MRDF-u: modulus reduction and damping curves fit using a reduction factor and including porewater pressure generation, u). We then validate this model using sets of cyclic triaxial compression and cyclic direct simple shear tests. Comparisons of stress-strain, excess porewater pressure, modulus reduction, and damping illustrate that the proposed MRDF-u constitutive model reasonably captures relevant elements of the cyclic behavior of sands, but does not simulate dilation. In particular, the MRDF-u captures excess porewater pressure generation during cyclic loading and can be employed in a coupled 1D nonlinear, effective stress site response analysis to evaluate the occurrence of liquefaction in sands.