Evaluation of a simplified soil constitutive model considering implied strength and pore-water pressure generation for one-dimensional (1D) seismic site response

Pore-water pressure (PWP) generation can lead to soil softening and liquefaction of sandy soils during earthquakes, with potential influence on site response and seismic design. The authors evaluated the generalized quadratic/hyperbolic (GQ/H) constitutive model, which captures small-strain stiffness, large-strain shear strength, and is coupled with a widely used cyclic strain-based PWP generation model (termed GQ/H+u). A suite of cyclic direct simple shear tests with a range of relative densities (similar to 30%- 80%) and effective vertical stresses (similar to 25-200 kPa) and dynamic centrifuge tests with liquefiable sands were used to evaluate the ability of the GQ/H+u model to simulate cyclic soil behavior. Results indicate that GQ/H+u provides reasonable estimates of PWP increase during cyclic shear, with differences between measured and computed excess PWP ratios (r(u)) for both element and centrifuge tests generally smaller than 0.1. Computed spectral accelerations are comparable to centrifuge test measurements, with almost no bias at medium to long periods (T > 0.4 s) when the computed maximum shear strain (gamma(max)) was smaller than the limit shear strain (gamma(limit)). When computed r(u) > 0.8 and computed gamma(max) > gamma(limit), spectral accelerations may be underestimated at both short and long periods as dilative behavior is not captured by GQ/H+u.